Bee Bread Shows Protective Effects in a Streptozotocin-Induced Alzheimer's Disease Rat Model

Bee Bread Shows Protective Effects in a Streptozotocin-Induced Alzheimer's Disease Rat Model | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Bee Bread Shows Protective Effects in a Streptozotocin-Induced Alzheimer's Disease Rat Model Alev Duygu Acun, Ebru Afşar, Deniz Kantar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7268712/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 14 You are reading this latest preprint version Abstract Alzheimer's disease (AD) is currently a global concern, and treating its current symptoms and slowing its progression is an important goal. To this end, identifying biochemical mechanisms that have the potential to prevent and improve the pathology of the disease is a priority. The response of the central nervous system to pathological insults may be neuroinflammation. Kynurenine (KYN) pathway metabolites, which are closely related to neuroinflammation, may have the potential to affect many neural processes such as synaptic plasticity, neurotransmission, antioxidant mechanisms, and neurogenesis. In addition, it has been recently shown that there is a strong correlation between sensory system deterioration and AD progression and that neuropathological changes in sensory regions can be detected before changes in memory-related regions. For this purpose, our study aimed to investigate the effects of changes in the Kynurenine (KYN) pathway on cognitive functions and auditory sensory system functions in an experimental AD model and the effects of bee bread (BB), known to have anti-inflammatory properties, on these parameters. It was shown that BB has the potential to improve memory by exerting a healing effect on neuroinflammation, apoptosis, and the KYN pathway, and also has a therapeutic effect on auditory sensory system functions, reducing sensory system integrity disorders. These results highlight the ability of BB to prevent neurotoxic effects associated with sAD. It may be a potential protector as a food supplement for AD neuropathological health, and further studies are needed for this purpose. Alzheimer’s Disease Kynurenine Pathway Bee Bread Object Location Test Auditory Evoked Potentials Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. INTRODUCTİON Alzheimer's disease (AD), which accounts for 60–70% of cases worldwide, is a progressive neurodegenerative disease that damages nerve cells and ultimately leads to the death of the patient. Brain tissue atrophies due to damage to neural cells, resulting in loss of neurotransmission and synaptic activity between various cortical regions. In the early stages of AD, some researchers accept that there is more widespread atrophy, especially in auditory structures, and auditory dysfunction [ 1 ]. Although it is generally observed that auditory-evoked potentials in the cerebral cortex are reduced in patients with AD or in animal models, there are conflicting results in the literature [ 2 ]. Therefore, the effect of AD on auditory-evoked potentials and their dynamic changes in the development of the disease remain unclear [ 3 ]. Neuropathological changes may begin in sensory areas before AD pathology manifests in memory areas, and neuropathological changes may occur in sensory-related areas before cognitive symptoms become evident [ 4 ]. While AD can cause hearing loss, hearing loss can also accelerate the development of AD [ 5 ]. Auditory evoked potentials (AEPs) are electrical potentials in any part of the auditory system, from the cochlea to the cerebral cortex, evoked by an auditory stimulus. AEPs are a non-invasive method used to obtain information about the function and integrity of the auditory system [ 6 ]. Since AEP does not include cognitive processing and perception patterns, it may be more effective than event-related potentials (ERPs) in evaluating changes in the auditory network. The early components of the AEP are considered suitable for cross-species studies because they represent automatic brain functions that involve auditory discrimination without consciousness [ 7 ]. Rodent AD models are very important because they allow the investigation of the direct relationship between AD neuropathology and its neurophysiological effects on brain neural networks. However, there are few studies in the literature using evoked potentials (EPs)/ERPs paradigms in rodent AD models [ 8 ]. Although changes in AEP responses have been studied in some AD animal models [ 9 , 10 ], the dynamic changes of AEP in the development of AD have still not been fully elucidated. Neuroinflammation is known to play a critical role in the development of AD. The release of proinflammatory cytokines may cause synaptic dysfunction, neuronal death, and inhibition of neurogenesis, and is likely to be linked to AD. Neuroinflammation is closely linked to the kynurenine (KYN) pathway and underlies various neurological conditions. This link is due to the ability of inflammatory factors to affect the activity of enzymes involved in the KYN pathway. The KYN pathway involves the conversion of the essential amino acid tryptophan (Trp) into a series of compounds and is considered an important metabolic pathway as some of the compounds formed are neuroactive [ 11 ]. The KYN pathway and its several metabolites are thought to be altered in AD and to have significant roles in the neuropathogenesis of the disease. Variations in KYN metabolites have an impact on the brain's ability to regulate oxidative stress, cause neuroinflammation, and cause neurotoxicity. Therefore, any imbalance in the metabolism of the KYN pathway may play an important role in AD pathophysiology [ 12 ]. In order to evaluate the systemic and metabolic defects in AD pathophysiology, in-depth study of the KYN pathway is crucial. In the KYN pathway, TRP 2,3-dioxygenase (TDO) and indolamine 2,3-dioxygenase (IDO) are known to be the initial rate-limiting enzymes. Although TDO is the main enzyme under physiological conditions, IDO1 is upregulated in macrophages, microglia, neurons and astrocytes in response to neuroinflammatory stimuli. Proinflammatory cytokines released by microglia activate the IDO enzyme, which raises the neurotoxic quinolinic acid (QA) level. The neuroactive QA metabolite has N-methyl-D-aspartate (NMDA) receptor (NMDAR) agonist characteristics and is a potent producer of free radicals. Additionally, through raising extracellular glutamate levels, it produces excitotoxicity and triggers lipid peroxidation. When anti-inflammatory cytokines are released from astrocytes, the synthesis of kynurenic acid (KYNA), a potent NMDAR antagonist is increased. KYNA exhibits competitive antagonistic activity on NMDA receptors. Overactivation of the KYN pathway may lead to overproduction of QA, and QA has been found to be associated with pathological changes and cognitive functions in AD. QA has been observed to cause learning and memory deficits. A vicious loop may be created whereby overproduction of QA causes greater tau hyperphosphorylation, which in turn triggers activation of microglia in response to Aβ and p-tau. Although it is widely accepted that AD is associated with an elevated KYN pathway, further research is needed to explore the elusive molecular mechanisms behind the relationship between AD and metabolites of the complex KYN pathway and to develop therapeutic strategies for this [ 12 ]. Recently, complementary and herbal medicine has gained popularity and interest. Bee bread (BB) is a natural product formed by anaerobic lactic fermentation of bee pollen. Although BB contains less protein than bee pollen, the digestibility of the protein it contains is higher due to the fermentation of the collected pollen by the bees [ 13 ]. This makes BB a functional food source with higher bioavailability compared to bee pollen [ 14 ]. Properties such as high concentration of simple sugar content, low pH (pH 4), low water activity, high oxidation-reduction potential and the presence of lactic acid bacteria make bee bread a preservative composition [ 15 ]. BB is an important source of antioxidants that can eliminate free oxygen radicals and their harmful effects on cells [ 16 ]. Since TRP is known to be an important compound in the content of BB [ 13 ], it is likely to modulate the KYN pathway. According to a study, propolis extracts suppress IDO activity as part of their immunomodulatory effects [ 17 ]. A high Trp diet has also been previously shown to significantly improve cognitive dysfunction and reduce Aβ deposits [ 18 ]. Therefore, although it seems plausible that BB regulates the KYN pathway and reduces TRP degradation, its therapeutic effects on AD remain unclear. Intracerebroventricular (ICV) administration of streptozotocin (STZ), a glucosamine-nitrosourea molecule derived from soil bacteria, mimics the neuropathological and metabolic changes of sporadic AD (sAD) [ 19 , 20 ]. The ICV-STZ model is widely used to mimic the onset and course of human sAD and to investigate the neuroprotective effects of different drugs [ 21 ]. This study investigated the effects of BB treatment applied to the ICV-STZ sAD model on the level of KYN pathway metabolites and their anti-apoptotic, anti-inflammatory, cognitive functions, changes in sensory brain responses and anti-Alzheimer potential. 2. MATERİALS and METHODS 2.1. Animals and treatment Male albino Wistar rats Forty male albino Wistar rats, 3 months old, weighing 250–300 g, were purchased from Akdeniz University Animal Care Unit (Antalya, Turkey) and housed in groups of 4 in stainless steel cages. Rats were housed under standard conditions (23 ± 1°C and 50 ± 5% humidity) with a 12-h light-dark cycle. Food and water were provided ad libitum. Animals were randomly divided into three groups (n = 6 each group): (1) Sham (SH) group [vehicle (citrate buffer/2 µl/ventricle) plus water gavage treatment]; (2) STZ group [STZ (2mg/kg, 2 µl/ventricle) plus water gavage treatment]; (3) STZB group [STZ (2mg/kg, 2 µl/ventricle) plus BB (200 mg/kg/day) gavage treatment (0,5 g/kg/day) gavage]. Studies have reported that 2 mg/kg is the most effective STZ dose in modeling sporadic AD-like pathology [ 22 , 23 ]. The purity of STZ (Cayman, 13104), whose molecular formula is C8H15N3O7, is over 95%. To prepare an STZ solution corresponding to a dose of 2 mg/kg for a rat weighing 350 grams, 1.05 mg of STZ should be diluted in 6 µl of citrate buffer (0.05M). The 0.05 M citrate buffer solution was prepared according to the procedures given previously [ 22 ]. Since the half-life of the STZ solution is very short (15–30 minutes) and unstable, it was prepared fresh before use. After the surgical procedure, the animals were allowed to recover for seven days and then gavage was applied once a day for 21 days. The nutritional content of BB purchased from Nutral Therapy Company (Erciyes University Technopark, Kayseri) is given in the table (Table 1 ). In previous studies, 200 mg/kg/day bee bread application was preferred because it is known to have positive effects on the number of apoptotic cells, weight control and other parameters [ 24 ]. Table 1 Nutritional contents of BB. Nutritional elements Content Ash 2.31 g / 100 g Protein 22.63g / 100 g (N x 6.25) Carbohydrate 51.91 g / 100 g Dietary fiber 18.18 g / 100 g Fat (acid hydrolyzed) 8.70 g / 100 g Energy 376 kcal / 100 g Gluten (ppm) - Copper (Cu) 12.91 mg / kg Zinc (Zn) 36.67 mg / kg Phosphorus (P) 6665.44 mg / kg İron (Fe) 192 mg / kg Calcium (Ca) 1390 mg / kg Sodium (Na) 78.74 mg / kg Magnesium (Mg) 638 mg / kg Omega-6 0.23 g / 100 g Omega-3 0.55 g / 100 g Humidity 14.45 g / 100 g Total antioxidant activity 447.16 mg TE / 100 g 2.2. Experimental design The ICV-STZ sAD rat model was established as in previous studies [ 22 , 23 ]. A midsagittal incision was made on the scalp of rats placed in a standard stereotaxic apparatus under ketamine (80 mg/kg, i.p.)/xylazine (5 mg/kg, i.p.) anesthesia. To create the experimental groups, the coordinates of the lateral ventricles (AP: -0.8 mm, ML: ± 1.4 mm, DV: -4.0 mm) were drilled bilaterally using a dental drill. To establish the experimental groups, the coordinates of the lateral ventricles were drilled bilaterally using a dental drill, and 0.5 µl/min was injected into the lateral ventricles with a Hamilton syringe and withdrawn after 5 min. After surgery, the incision was sutured, and antibiotic ointment was applied for 7 days to prevent infection. Penicillin (40,000 U) was injected intramuscularly daily for 3 days. After waiting for a 7-day period for AD pathology to occur, gavage was applied for 21 days. Since significant cognitive impairment and neurodegeneration are known to occur approximately 30 days after 2 mg/kg ICV-STZ injection [ 25 – 27 ], the training phase of the behavioral experiment was performed on day 29, and the testing phase on day 30. After electrode placement and recordings for electrophysiological recording on day 31, rats were sacrificed. Perfusion was performed with isotonic heparin via cardiac cannula and then brain tissues were removed and frozen in liquid nitrogen. Brain tissues were stored at -80°C for biochemical analyses (Fig. 1 ). 2.3. AEP Recordings and Analysis To record auditory electrophysiological responses, rats were anesthetized with urethane (1.2 g/kg, i.p. Sigma-Aldrich, St Louis, MO, USA) and fixed in a standard stereotaxic frame. Stainless steel screw electrodes were placed over the auditory cortex of the rats (AP: -4.5 mm, ml: -3.5 and + 3.5 mm) using holes drilled into the cerebellar skull, and reference/ground electrodes were placed bilaterally over the cerebellum region. Before recording, the tympanic membrane and external auditory canal were checked for any damage. Tones of 50 ms duration were delivered to the rat's ear via a loudspeaker 15 cm away. The signal was amplified (Brainamp EEG/EP Amplifier, Brain Products, Munich, Germany), band-pass filtered (0.1–300 Hz, 50 Hz notch filter), and digitized and recorded at a sampling rate of 1000 Hz (Brainvision Recorder, Brain Products, Munich, Germany). Using tones at 2000 Hz that were 85 dB and had a 500 ms short interstimulus interval (ISI), AEPs were recorded. The BrainVision Analyzer (Brain Products, Munich, Germany) was used to average the EEG data. AEPs were divided into 600 ms epochs, 100 ms before and 500 ms after stimulus presentation. The average of 100 AEP waves was used to identify the peaks, and the resulting waveforms were used to calculate the peak-to-peak amplitudes (in microvolts) of the AEP components for each rat. The first large positive wave that appeared approximately 50 ms after the stimulus was defined as P1. Similarly, the large negative wave that appeared approximately 100 ms was determined as N1 and the positive wave that appeared at 200 ms was determined as P2. The peak-to-peak amplitudes of P1N1 and N1P2 were analyzed according to the measurements. 2.4. Behavioral Testing 2.4.1. Object Location Test (OLT) The experiment was carried out in a box system with equal lighting, 40 cm x 40 cm x 40 cm, with a white mat on the bottom and sides. The experiment was conducted in a soundproof room to minimize the effect of any external stimulus on the experimental parameters. The OLT consists of two phases: training and testing. In the training phase, two identical objects, A1 and A2, were selected and placed on opposite sides of the box, and the rat was left in the center of the box and given 5 minutes to explore objects A1 and A2. In the testing phase, 24 hours after the training phase, two identical objects, A1, remained in the same place as in the training phase, while the other identical object, A2, was placed in a new location to test object location memory. The identical objects A1-A2 used in the experiment were fixed to the floor to prevent movement. Before each trial for each rat, the objects and the entire interior surface of the box were wiped with 70% ethanol to prevent the presence of odor cues and air dried. Video recordings were used to determine the time spent by rats with objects, and the rat was considered to have explored the object when its nose was 2 cm away from the object. The discrimination index was calculated using the following formula: Exploration time spent with an object in the new location/Exploration time spent with an object in the new location + Exploration time spent with an object in the old location × 100. 2.4.2. Novel Object Recognition (NOR) Test The novel object recognition test consists of two phases: the training phase and the testing phase. During the training phase, two identical objects (A1-A2) were placed in the experimental system at two opposite positions at the same distance from the nearest corner. The rats were then released from the center to the field and allowed 5 minutes to explore these two identical objects (A1-A2). The rats that completed the training phase were taken to the test phase 24 hours after they were placed back in their cages. To test the novel object recognition memory during the test phase, a copy of the familiar object (A3) and a new object (B1) were placed in the same place as during the training experiment. Each of the objects used in the experiment was fixed to the floor to prevent its movement. The behavior of the rats during the training and testing phases was recorded with a video camera and used to determine the time the rats spent with the objects. To preclude the existence of olfactory cues, the entire box and objects were always thoroughly cleaned with 70% ethanol after each trial. In the novel object recognition test, discrimination index (%) values showing memory strength were analyzed. Discrimination index was calculated using the formula: exploration time spent with novel object/ exploration time spent with novel object + exploration time spent with familiar object × 100. 2.5. Biochemical Experiments Temporal and hippocampal tissue samples homogenized in cold PBS, centrifuged at 2000–3000 r.p.m for 20 min. Supernatants were stored at − 80°C for protein analyses. The sandwich ELISA method is very effective in detecting the target antigen in an unknown sample. Temporal and hippocampal target protein levels in the supernatants of tissue homogenates were measured according to the procedures of a commercially available sandwich ELISA kit. Commercial kits contain 96-well plates coated with rat target protein antibodies, and biotinylated rat target protein antibody is added to these wells and binds to target protein in the sample. These bind to target protein in the sample. A sandwich model is created by adding a horseradish peroxidase (HRP) conjugate polyclonal antibody specific for target protein to obtain immobilized target protein. Then, streptavidin-HRP is added to bind to the biotinylated target protein antibody. After incubation, unbound components are removed by washing 5 times and then substrate solution is added. When the substrate solution is added, HRP reacts with the enzyme to cause color formation, so only the wells containing target protein show a color change proportional to the amount of target protein. Then, an acidic solution is added to terminate the reaction and the optical density (OD) is measured spectrophotometrically at 450 nm. Sample target protein amount was also calculated from the standard curve plot. Target Proteins : Total Aβ1–42 (SunRedBio Rat Aβ1–42 Catalog No: 201-11-0094), Tau protein (SunRedBio Rat Tau Protein Catalog No. SRB-T-86822), glutamate receptor2B (NR2B/NMDAR2B (SunRedBio Rat NR2B Protein Catalog No: 201-11-2688), TRP (SunRedBio Rat TRP Protein Catalog No: 201-11-7308), KYN (SunRedBio Rat KYN Catalog No: 201-11-2152), KYNA (SunRedBio Rat KYNA Catalog No. 201-11-5219), QA (SunRedBio Rat QA Protein Catalog No: 201-11-5093), Caspase-3/CPP32 (SunRedBio Rat Caspase-3 Catalog No: 201-11-0281), interleukin 6 (IL-6) (SunRedBio Rat IL-6 Catalog No: 201-11-0136). 2.6. Statistical analysis Statistical analyses were performed using SPSS 23.0 for Windows (SPSS, Chicago, IL, USA) program. Statistical comparisons of the data obtained from biochemical analyses between groups were performed using one-way ANOVA and post-hoc Tukey test for data conforming to normal distribution. AEP analyses were performed using repeated-measures ANOVA and post-hoc comparisons were made using the Bonferroni test. Results were given as mean ± standard error and p < 0.05 was considered significant. 3. RESULTS 3.1. Treatment with BB Ameliorates Cognitive İmpairment in STZ-induced AD Rats. In the OLT test, the novelty feature is the location, since the objects in the test trial are the same as in the training trial. The OLT is considered a simple and effective test that measures hippocampus-dependent spatial memory. When OLT was examined 24 h after training, it requires de novo transcription and translation [ 28 ]. A statistically significant difference was found between the groups in OLT test [F(2,15) = 46,16, p < 0.001, N = 18] (Fig. 2 A). The OLT discrimination index of the STZ group (45,23 ± 1,5) decreased significantly compared to the SH group (78,68 ± 2,51) (p < 0.001). The OLT discrimination index of the STZB group (76,73 ± 3,78) increased significantly compared to the STZ group (p < 0.001). No significant difference was found between the SH and STZB groups. The major advantage of the NOR over other rodent memory tests is that it relies on rodents' natural tendency to explore novelty. Several different brain regions are critical for the new object recognition memory, including the insular cortex, the perirhinal cortex, and the ventromedial prefrontal cortex [ 29 ]. A statistically significant difference was found between the groups in NOR test [F(2,15) = 39,37, p < 0.001, N = 18] (Fig. 2 B). The NOR discrimination index of the STZ group (49,96 ± 2,2) decreased significantly compared to the SH group (79,13 ± 2,4) (p < 0.001). The NOR discrimination index of the STZB group (74,69 ± 2,8) increased significantly (p < 0.001) compared to the STZ group. No significant difference was found between the SH and STZB groups. Therefore, it was observed that long-term spatial memory of STZ-induced AD group rats was impaired, while BB treatment had an improving effect on memory functions. 3.2. While STZ induction increases Alzheimer-like pathology, BB has an ameliorating effect on this pathology. Data from thousands of studies on the pathophysiology of AD to date identify Aβ and tau protein as key players [ 30 ]. Statistically significant difference was found between the hippocampus Aβ1–42 levels between the groups [F(2,15) = 3,48, p 0.05). Hippocampus Aβ1–42 levels of the STZB group (19,68 ± 1,6 pg/mg) were found to be significantly decreased compared to the STZ group (p < 0.05). There was a statistically significant difference in temporal Aβ1–42 levels between groups [F(2,15) = 30,65, p < 0.001, N = 18] (Fig. 3 B). Temporal Aβ1–42 levels of the STZ group (28,16 ± 1,2 pg/mg) were significantly higher than those of the SH group (16,85 ± 1,4 pg/mg) (p < 0.01). It was observed that temporal Aβ1–42 levels of the STZB group (14,33 ± 1,2 pg/mg) were significantly decreased compared to the STZ group (p < 0.001). No statistically significant difference was found between the hippocampus tau levels between the groups [F(2,15) = 0,56, p < 0.05, N = 18] (Fig. 3 C). Hippocampal Tau levels in the STZ group (2,21 ± 0,33 ng/mg) were significantly higher than in the SH group (1,28 ± 0,16 ng/mg) (p 0.05). There was a statistically significant difference in temporal tau levels between groups [F(2,15) = 11,39, p < 0.01, N = 18 ] (Fig. 3 D). Temporal Tau levels of the STZ group (3,29 ± 0,3 ng/mg) were significantly higher than those of the SH group (1,24 ± 0,2 ng/mg) (p 0.05). In summary, these results indicate that Aβ and Tau pathology occur in the hippocampus and temporal cortex of STZ-induced AD rats and that BB treatment may alleviate the neuronal damage that may arise due to these. 3.3. BB treatment increased Glutamate Receptor-2B/NR2B/NMDAR2B levels in the hippocampal regions of STZ-induced AD rats. NR2B activation may be associated with the pathological progression of AD. Furthermore, the detrimental effects of Aβ prior to neuronal loss appear to be mediated by NMDARs, particularly NR2Bs [ 31 ]. There was a statistically significant difference in hippocampus NR2B levels between groups [F(2,15) = 10,63, p < 0.001, N = 18] (Fig. 3 E). Hippocampus NR2B levels of the STZ group (1,48 ± 0,1 ng/mg) were significantly higher than those of the SH group (2,01 ± 0,06 ng/mg) (p < 0.05). Hippocampus NR2B levels of the STZB group (2,38 ± 0,1 ng/mg) were significantly increased compared to the STZ group (p 0.05). There was a statistically significant difference in temporal NR2B levels between groups [F(2,15) = 13,58, p < 0.001, N = 6] (Fig. 3 F). Temporal NR2B levels of the STZ group (1,91 ± 0,11 ng/mg) were significantly lower than those of the SH group (3,11 ± 0,2 ng/mg) (p < 0.001). Temporal NR2B levels of the STZB group (2,46 ± 0,15 ng/mg) were tented to increase compared to the STZ group (p < 0.05). While increased apoptosis was observed in the STZ-induced rat group, it was significantly decreased especially in the hippocampal regions due to BB treatment. 3.4. Attenuating Effect of BB Treatment on Increased Proinflammatory IL-6 Levels in STZ-induced AD Rats. Chronic neuroinflammation, induced by a series of proinflammatory cytokines such as IL-6, is widely accepted as an early and persistent feature of the AD brain [ 32 , 33 ]. There was a statistically significant difference in hippocampus IL-6 levels between groups [F(2,15) = 11,46, p < 0.01, N = 18] (Fig. 4 A). Hippocampus IL-6 levels of the STZ group (26,42 ± 2,11 pg/mg) were significantly higher than those of the SH group (16,55 ± 1,03 pg/mg) (p < 0.01). Hippocampus IL-6 levels of the STZB group (18,53 ± 2,4 pg/mg) were significantly lower than the STZ group (p < 0.05). There was a statistically significant difference in temporal IL-6 levels between groups [F(2,15) = 5,74, p < 0.01, N = 6] (Fig. 4 B). Temporal IL-6 levels of the STZ group (34,95 ± 6,2 pg/mg) were significantly higher than those of the SH group (14,94 ± 2,95 pg/mg) (p 0.05). Increased IL-6 levels were observed in the temporal cortex and hippocampal brain regions of STZ-induced AD rats, while BB treatment was particularly effective in reducing hippocampal neuroinflammation. 3.5. Apoptotic Marker Caspase-3 Decreased in STZ-Induced AD Rats Due to BB Treatment. There was a statistically significant difference in hippocampus caspase-3 levels between groups [F(2,15) = 11,46, p < 0.001, N = 18] (Fig. 4 C). Hippocampus caspase-3 levels of the STZ group (0,41 ± 0,03 ng/mg) were significantly higher than those of the SH group (0,27 ± 0,01 ng/mg) (p < 0.01). Hippocampus caspase-3 levels of the STZB group (0,27 ± 0.01 ng/mg) were significantly higher than the STZ group (p 0.05). There was a statistically significant difference in temporal caspase-3 levels between groups [F(2,15) = 4,13, p < 0.05, N = 18] (Fig. 4 D). Temporal caspase-3 levels of the STZ group (0,49 ± 0,11 ng/mg) were significantly higher than those of the SH group (0,20 ± 0,04 ng/mg) (p 0.05). No significant difference was found in temporal caspase levels of the STZB group compared to the SH group (p > 0.05). While increased apoptosis was observed in the STZ-induced rat group, it was significantly decreased, especially in the hippocampal regions, due to BB treatment. 3.6. Neuroprotective Effect of BB on the KYN Pathway in STZ-Induced Rats All data of the KYN pathway are presented in Table 2 . Statistically significant difference was found in hippocampus KYN levels between the groups [F(2,15) = 3,98, p < 0.05, N = 18]. Hippocampus KYN levels of the STZ group were higher than those of the SH group (p 0.05). There was a statistically significant difference in temporal KYN levels between groups [F(2,15) = 7,41, p < 0.01, N = 18]. Temporal KYN levels of the STZ group were higher than those of the SH group (p < 0.05). Temporal KYN levels of the STZB group were significantly decreased compared to the STZ group (p 0.05, N = 18]. There was a no statistically significant difference in temporal TRP levels between groups [F(3,20) = 5,35, p > 0.05, N = 18]. There was no statistically significant difference in hippocampus KYN/TRP ratios between groups [F(2,15) = 3,07, p > 0.05, N = 18]. There was no statistically significant difference in temporal KYN/TRP ratios between groups [F(2,15) = 3,34, p > 0.05, N = 18]. The change in the KYN/TRP ratio is a ratio used to determine IDO activity by reflecting the degradation rate of TRP [ 34 ]. There was a statistically significant difference in hippocampus KYNA levels between groups [F(2,15) = 5,82, p < 0.05, N = 18]. Hippocampus KYNA levels of the STZ group were significantly lower than the SH group (p < 0.05). Hippocampus KYNA levels of the STZB group were significantly increased compared to those of the STZ group (p < 0.05). There was a statistically significant difference in temporal KYNA levels between groups [F(2,15) = 9,04, p < 0.01, N = 18]. Temporal KYNA levels of the STZ group were significantly lower than the SH group (p < 0.01). Temporal KYNA levels of the STZB group were significantly higher than the STZ group (p < 0.05). There was a statistically significant difference in hippocampal QA levels between groups [F(2,15) = 9,48, p < 0.01, N = 18]. Hippocampal QA levels of the STZ group were significantly higher than the SH group (p 0.05). No significant difference was found in hippocampal QA levels of the STZB group compared to the SH group (p > 0.05). There was a statistically significant difference in temporal QA levels between groups [F(2,15) = 6,54, p < 0.01, N = 18]. Temporal QA levels of the STZ group were significantly higher than the SH group (p < 0.01). Temporal QA levels of the STZB group were significantly lower than the STZ group (p 0.05). In the STZ-induced AD group, it was found that while excitotoxin KYN pathway metabolites increased, the number of neuroprotective metabolites decreased significantly and the TRP pathway shifted towards QA production. However, BB treatment results were found to reverse these results observed in STZ rats and direct the KYN pathway towards neuroprotective KYNA production. Table 2 Changes in the KYN pathway and its metabolites in the hippocampus and temporal brain regions. Results are presented as mean ± SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p < 0.05; **: p < 0.01; ***: p < 0.001, #: p < 0.05; ##: p < 0.01; ###: p < 0.001) HİPPOCAMPUS TEMPORAL CORTEX KYN (ng/mg protein) SH 1,68 ± 0,26 2,26 ± 0,25 STZ 2,68 ± 0,26 * 3.64 ± 0.45 * STZB 2,06 ± 0,22 2.10 ± 0.13 ## TRP (ng/mg protein) SH 1,64 ± 0,23 2,73 ± 0,23 STZ 1,67 ± 0,23 2,92 ± 0,34 STZB 2,27 ± 0,23 2,59 ± 0,47 KYN/TRP Ratio SH 1,72 ± 0,31 0,85 ± 0,11 STZ 1,75 ± 0,26 1,30 ± 0,16 STZB 0,92 ± 0,009 0,91 ± 0,11 KYNA (nmol/mg protein) SH 1,40 ± 0,22 1,68 ± 0,21 STZ 0,54 ± 0,13 * 0,55 ± 0,16 ** STZB 1.24 ± 0.20 # 1,52 ± 0,22 # QA (ng/mg protein) SH 0,09 ± 0,01 0,13 ± 0,02 STZ 0,16 ± 0,01 ** 0,26 ± 0,04 ** STZB 0,12 ± 0,01 0,14 ± 0,01 # 3.7. Peak-to-peak amplitudes in AEP responses increased due to BB treatment. Recently, sensory system deficits, including auditory systems, have been found to be highly associated with AD progression, and impairments in sensory-related areas may occur before AD pathology becomes evident. Hearing loss due to AD pathology may occur, which may accelerate the development of AD and dementia [ 3 ]. In all experimental groups, peak-to-peak amplitude values of AEP components were measured over one negative (N1) and two positive potentials (P2) seen at the temporal left (T3) electrode region. P1N1 amplitude value was found to differ significantly between the groups [F(2,15) = 7,90, p < 0.01, N = 18]. P1N1 peak-to-peak amplitude value of STZ group (6.49 ± 1.03 µV) was found to decrease significantly compared to SH group (12.40 ± 0.96 µV) (p 0.05) (Fig. 5 A). N1P2 amplitude value was found to differ significantly between the groups [F(2,15) = 23.62, p < 0.001, N = 18]. It was found that the N1P2 peak-to-peak amplitude value of the STZ group (2,40 ± 0,54 µV) was significantly decreased compared to the SH group (11.50 ± 1.35 µV) (p 0.05) (Fig. 5 B). The decreases in peak-to-peak amplitude values ​​of STZ-induced AD rats reflect sensory system integrity (Fig. 5 C). This may occur due to decreased neuronal density or firing desynchronization. It has been observed that BB treatment may have a healing effect on the sensory system, especially by increasing the N1P2 amplitude, which is related to the processing and interpretation of auditory information. 3.8. Correlations of OLT Discrimination Index with Hippocampus IL-6 and NR2B Pearson correlation analysis was used to evaluate the relationship between OLT discrimination index and hippocampus IL-6 levels. As a result of the analysis, a negative relationship was found between OLT discrimination index and changes in hippocampus IL-6 levels (Pearson r= -0.667, p < 0.01, N = 18) (Fig. 6 A). According to the results of the correlation analysis, it can be concluded that there is a significant decrease in OLT discrimination index due to the increase in hippocampus IL-6 levels. Pearson correlation analysis was used to evaluate the relationship between OLT discrimination index and hippocampus NR2B levels. As a result of the analysis, a positive relationship was found between OLT discrimination index and changes in hippocampus NR2B levels (Pearson r = 0,592, p < 0.01, N = 18) (Fig. 6 B). According to the results of the correlation analysis, it can be concluded that there is a significant decrease in OLT discrimination index due to the increase in hippocampus NR2B levels. 4. DİSCUSSİON This study aimed to elucidate the alterations of the KYN molecular pathway, long-term memory, and electrophysiological responses in the ICV-STZ sAD model and to examine the possible neuroprotective effects of BB against ICV-STZ-induced AD. The pathological changes induced by ICV injection of STZ resemble the features of sAD [ 22 ]. Studies have shown that a 2 mg/kg ICV-STZ dose causes significant cognitive impairment and neurodegeneration approximately 30 days after injection [ 22 , 25 – 27 ]. Since our study will evaluate the neurobiological mechanisms underlying long-term memory formation, behavioral tests were performed 30 days after ICV administration of 2 mg/kg STZ. This study also showed that the OLT and NOR discrimination index of the STZ group was significantly decreased compared to the SH group and long-term memory was impaired. The OLT assesses spatial learning that relies mainly on hippocampal activity, whereas the NOR reflects nonspatial learning of object identity that relies on multiple brain regions [ 35 ]. Chronic neuroinflammation induced by a series of proinflammatory cytokines such as IL-6 secreted by activated microglia and astrocytes is widely accepted to be an early and persistent feature of the AD brain [ 32 , 33 ] and is assumed to be responsible for the development of cognitive impairment seen in AD [ 36 ]. In a previous study, AD patients were found to have high IL-6 levels in both brain and plasma, and IL-6 expression was positively associated with AD pathology and declines in cognitive performance [ 37 ]. Our study also showed that IL-6 levels were similarly significantly increased in the examined brain regions in STZ rats compared to the SH group. Furthermore, a significant negative correlation was found between the OLT discrimination index and hippocampal IL-6 levels in the STZ group rats. It is known that the enzymes of the KYN pathway are activated by inflammation. In particular, IL-6 can independently activate IDO and enhance the metabolic pathways from TRP to QA. Therefore, it is thought that neuroinflammation may exert a regulatory effect on AD progression via TRP and TRP metabolites. Indeed, it has been shown that inflammatory cytokines can increase KYN production when they lead to IDO1 activation, which can lead to an increase in the KYN/TRP ratio [ 38 ]. Increased IDO activity increases KYN metabolite production and possible TRP depletion [ 39 ]. The resulting increase in the KYN/TRP ratio indicates the activation and participation of IDO enzyme [ 40 ]. This increase in the KYN/TRP ratio is considered one of the hallmarks of neuroinflammation in AD studies and suggests increased TRP metabolism in AD patients [ 41 ]. The overactivated KYN pathway may lead to overproduction of the excitotoxin QA via microglia activation [ 12 ]. It is known that QA also induces apoptosis in astrocytes and is closely related to the formation of Aβ and p-tau in the brain [ 42 ]. In addition, the excitotoxin QA is known to innervate many NMDARs, including NR2B subunits, which are known to play an important role in learning, memory, synaptic plasticity, and neuronal pattern formation [ 43 ]. NMDARs, mainly located in the postsynaptic region, are glutamate receptors that regulate calcium influx into neurons. NR2Bs are mainly extrasynaptic, and their activation is associated with cell death and neurodegeneration. Aβ has been observed to cause a significant increase in calcium release in NR2B-containing NMDAR in cortical and hippocampal neurons. Furthermore, NMDA receptors containing the NR2B subunit have been shown to be dysregulated by Aβ1-42s, impairing glutamatergic synaptic transmission, which parallels early cognitive deficits. [ 44 ]. NR2B activation may be associated with the pathological progression of AD. Indeed, aberrant and synergistic activation of NMDAR including NR2B at extrasynaptic sites by glutamate and Aβ has been demonstrated in AD [ 45 ]. Therefore, increased QA levels due to inflammation are likely to damage neurons in brain regions through NMDARs, impairing learning and memory, as well as synaptic plasticity KYNA is known as one of the neuroprotective metabolites of the KYN pathway, which can antagonize excitatory neurotoxicity through NMDAR-mediated antagonism and has antioxidant effects [ 46 ]. It has been shown that increasing KYNA levels in AD mouse models can prevent both spatial memory deficits and synaptic loss [ 47 ]. KYNA also has immunomodulatory properties. It exhibits anti-inflammatory effects in inflammatory conditions and plays an important role as an antioxidant and ROS scavenger [ 48 ]. In our study, no significant difference was observed in TRP levels and KYN/TRP ratios in all brain regions examined in the STZ group sAD group rats compared to the SH group, while significant increases were found in KYN, excitotoxin QA, mitochondrial apoptotic marker caspase-3, NR2B and Tau levels, consistent with literature results. Similarly, a significant increase in Aβ1–42 levels was observed in the temporal regions in the STZ group compared to the SH group. Therefore, it can be thought that increased neuroinflammation in AD disease may lead to excessive stimulation of NMDARs and secondary increases in neuronal calcium levels due to excessive production of excitotoxin QA due to excessive activity of the KYN pathway, which may be followed by activation of apoptotic pathways and cell death. Furthermore, in contrast to the observed increase in QA, the neuroprotective KYNA levels in the examined brain regions of the STZ group rats were also found to be significantly reduced compared to the SH group. BB is essential because it is a natural product with high nutritional and medicinal value [ 49 ]. In addition, it is known to be the most powerful antioxidant bee product. Inflammation is a common underlying cause of serious diseases because it initiates a pathogenic cascade such as metabolic pathway failure, tissue damage and even necrosis and apoptosis [ 50 ]. A study comparing the effects of all bee products on chronic inflammation showed that pollen and BB had the highest anti-inflammatory effect and significantly reduced pro-inflammatory IL-6 levels [ 51 ]. In addition, a study conducted in 2025 found that BB application reduced gastric ulcer by reducing IL-6 and caspase-3 levels and had a reducing effect on inflammation and apoptosis [ 52 ]. However, there is a gap in the literature in terms of studies examining the effects of BB on the brain. In our study, it was shown that BB administration significantly decreased hippocampal IL-6 and caspase-3 levels in STZB rats compared to STZ rats and was not different from the SH group. In addition, the OLT discrimination index of the STZB group was significantly higher than that of the STZ group, indicating the potential to improve cognitive functions. As a result, it was concluded that BB treatment could also improve long-term location memory and prevent apoptotic activity. In addition, when the effect of this effect on the KYN pathway and its metabolites was examined, it was found that KYN and QA levels were significantly decreased in the temporal regions of the STZB group rats, while the levels of the neuroprotective metabolite KYNA were significantly increased in both regions. In addition, Aβ and NR2B levels were found to be significantly decreased in both brain regions in STZB rats compared to STZ rats. Mice overexpressing NR2B have been shown to have enhanced facilitated synaptic plasticity and enhanced learning and memory tasks [ 53 ]. NR2B receptors prolong the slow reverberant neural dynamics required for working memory [ 54 ]. In our study, NR2B levels in the hippocampal regions of STZB group rats were found to be positively correlated with the OLT discrimination index reflecting hippocampal learning. Recently, it has been observed that sensory system deteriorations are highly correlated with AD progression. Neuropathological changes in sensory-related areas before AD pathology is observed in memory-related regions [ 4 ] can be seen even before cognitive symptoms. In the APP/PS1 mouse model of AD, decreased auditory brainstem response (ABR) at 3 months of age [ 55 ], and spatial learning deficits occurred at 6–7 months of age [ 56 ]. Therefore, this decline in auditory function that may occur in the early stages of AD may provide important information for the early detection and development of the disease. KYN pathway metabolites affect neural processes including synaptic plasticity, neurotransmission, and neurogenesis. QA toxicity has been identified as one of the critical factors of neuronal damage in AD [ 57 ]. The occurrence of neuropathy with high levels of QA suggests that it may play an important role in the pathogenesis of neurological diseases. Both neuronal and astrocyte cytoskeletons are vulnerable to QA toxicity. QA causes axon-sparing lesions in neurons [ 12 ]. For this purpose, our study also aimed to reveal the changes in auditory sensory networks in sAD and to evaluate the therapeutic effect of BB on AEP responses on the KYN pathway. P1N1 amplitude is associated with early sensory functions and physical properties of the stimulus such as intensity, frequency, spectral and temporal properties. N1P2 amplitude reflects sensory functions related to the processing and interpretation of auditory information [ 58 ]. In our study, it was found that both P1N1 and N1P2 amplitudes were significantly decreased in the STZ group rats compared to the SH group rats. The initial waveforms of AEPs, which reflect neural activity in the auditory cortex and related brain regions, are largely sensory responses to stimuli and activities in the temporal cortex. Therefore, they reflect neural activity in the temporal cortex independent of cognitive activity [ 3 ]. Therefore, it is seen that there are impairments in sensory system integrity in our ICV-STZ rat model reflecting the sAD model. Significant decreases in P1N1 and N1P2 amplitudes in the temporal region, which is sensitive to neurodegeneration in the early stages of AD, may be due to disruptions in synchrony of neuronal firing or decreased neuronal density. When examining whether the learning and changes in the molecular pathway examined due to BB treatment had an effect on AEP responses, it was determined that the N1P2 peak-to-peak amplitude of the STZB group increased significantly compared to the STZ group, and the P1N1 peak-to-peak amplitude tended to increase. Therefore, these decreases in AEP sensory responses indicate that they may have the potential to be a useful biomarker in the detection of early stages of the disease and in the evaluation of the effectiveness of therapeutic agents. Studies have shown that there are gender differences in the AD model induced by ICV-STZ. In general, it has been determined that female rats induced by ICV-STZ are more resistant to ICV-STZ damage and that there are gender differences in brain responses to expected changes. This finding clearly contradicts the knowledge that female rats are prone to AD disease [ 59 ]. However, female rats are generally not preferred in STZ studies because it is thought that they may be resistant to the neurodegenerative effects of STZ due to hormonal oscillations of the estral cycle [ 60 ]. In order to minimize this limitation, we also used male rats in our study. Despite the limitations of this experimental model, the results of our study suggest that the ICV-STZ model may be suitable for examining the contribution of AD pathology and electrophysiological changes. Abbreviations AD Alzheimer's Disease Aβ Amyloid-Beta ICV Intracerebroventricular OD Optical Density AEP Auditory evoked potential ERP Event-Related Potentials EP Evoked Potentials KYN Kynurenine TRP Tryptophan TDO Tryptophan 2,3-dioxygenase IDO Indolamine 2,3-dioxygenase QA Quinolinic acid NMDA N-methyl-D-aspartate NMDAR N-methyl-D-aspartate Receptor KYNA Kynurenic Acid BB Bee Bread STZ Streptozotocin sAD Sporadic Alzheimer’a Disease ISI Interstimulus Interval i.p. Intraperitoneal HRP Horseradish Peroxidase IL-6 Interleukin-6 Declarations Conflict of Interest The authors report no conflicts of interest in this work. Ethics Approval Ethical approval for this work was obtained from Akdeniz University Local Committee on Animal Research Ethics (ethics approval ID: 1656/2023.12.001). Clinical trial number Not applicable Consent to Participate Not applicable. Consent for Publication Not applicable. Funding This study was not supported by any funding. Author Contribution A.D.A. and D.K. generated the rat models. E.A. analyzed ELISA's data. A.D.A. wrote the main manuscript text and prepared figures and table. A.D.A, E.A. and D.K. were involved in data interpretation, critically reviewed and provided their final approval of the manuscript, and agreed to be accountable for the work. Acknowledgments Not applicable. Availability of Data and Materials The data supporting this study's findings are available from the corresponding author, upon reasonable request. References Swords GM, Nguyen LT, Mudar RA, Llano DA: Auditory system dysfunction in Alzheimer disease and its prodromal states: A review. Ageing Res Rev 2018, 44:49–59. Gurevicius K, Lipponen A, Tanila H: Increased cortical and thalamic excitability in freely moving APPswe/PS1dE9 mice modeling epileptic activity associated with Alzheimer's disease. Cereb Cortex 2013, 23(5):1148–1158. Mei L, Liu LM, Chen K, Zhao HB: Early Functional and Cognitive Declines Measured by Auditory-Evoked Cortical Potentials in Mice With Alzheimer's Disease. Front Aging Neurosci 2021, 13:710317. Murphy C: Olfactory and other sensory impairments in Alzheimer disease. Nat Rev Neurol 2019, 15(1):11–24. Morrison C, Rabipour S, Knoefel F, Sheppard C, Taler V: Auditory Event-related Potentials in Mild Cognitive Impairment and Alzheimer's Disease. Curr Alzheimer Res 2018, 15(8):702–715. Ignatious E, Azam S, Jonkman M, De Boer F: Frequency and Time Domain Analysis of EEG Based Auditory Evoked Potentials to Detect Binaural Hearing in Noise. J Clin Med 2023, 12(13). Kim B, Shin J, Kim Y, Choi JH: Destruction of ERP responses to deviance in an auditory oddball paradigm in amyloid infusion mice with memory deficits. PLoS One 2020, 15(3):e0230277. Babiloni C, Blinowska K, Bonanni L, Cichocki A, De Haan W, Del Percio C, Dubois B, Escudero J, Fernandez A, Frisoni G et al : What electrophysiology tells us about Alzheimer's disease: a window into the synchronization and connectivity of brain neurons. Neurobiol Aging 2020, 85:58–73. Wang J, Ikonen S, Gurevicius K, Van Groen T, Tanila H: Altered auditory-evoked potentials in mice carrying mutated human amyloid precursor protein and presenilin-1 transgenes. Neuroscience 2003, 116(2):511–517. Stoiljkovic M, Kelley C, Stutz B, Horvath TL, Hajos M: Altered Cortical and Hippocampal Excitability in TgF344-AD Rats Modeling Alzheimer's Disease Pathology. Cereb Cortex 2019, 29(6):2716–2727. Cortes Malagon EM, Lopez Ornelas A, Olvera Gomez I, Bonilla Delgado J: The Kynurenine Pathway, Aryl Hydrocarbon Receptor, and Alzheimer's Disease. Brain Sci 2024, 14(9). Liang Y, Xie S, He Y, Xu M, Qiao X, Zhu Y, Wu W: Kynurenine Pathway Metabolites as Biomarkers in Alzheimer's Disease. Dis Markers 2022, 2022:9484217. Bakour M, Laaroussi H, Ousaaid D, El Ghouizi A, Es-Safi I, Mechchate H, Lyoussi B: Bee Bread as a Promising Source of Bioactive Molecules and Functional Properties: An Up-To-Date Review. Antibiotics (Basel) 2022, 11(2). Giovanini de Oliveira Sartori A, Martelli Chaib Saliba AS, Seneda Martarello N, Goldoni Lazarini J, Pedroso Gomes do Amaral JE, Fernandes Pinto da Luz C, Alencar SM: Changes in phenolic profile and anti-inflammatory activity of Baccharis beebread during gastrointestinal digestion/intestinal permeability in vitro. Food Chem 2024, 432:137234. Staroň M, Alkassab AT, Sabo R, Demková L, Valenčáková A, Michalko M, Legáth J, Pistorius J, Sabová L: Higher early than late-season residue load of pesticides in honey bee bread in Slovakia. Apidologie 2024, 55(4):41. Clarkson PM, Thompson HS: Antioxidants: what role do they play in physical activity and health? Am J Clin Nutr 2000, 72(2 Suppl):637S-646S. Girgin G, Baydar T, Ledochowski M, Schennach H, Bolukbasi DN, Sorkun K, Salih B, Sahin G, Fuchs D: Immunomodulatory effects of Turkish propolis: changes in neopterin release and tryptophan degradation. Immunobiology 2009, 214(2):129–134. Pan S, Zhang Y, Ye T, Kong Y, Cui X, Yuan S, Liu J, Zhang Y: A High-Tryptophan Diet Alleviated Cognitive Impairment and Neuroinflammation in APP/PS1 Mice through Activating Aryl Hydrocarbon Receptor via the Regulation of Gut Microbiota. Mol Nutr Food Res 2024, 68(2):e2300601. Grieb P: Intracerebroventricular Streptozotocin Injections as a Model of Alzheimer's Disease: in Search of a Relevant Mechanism. Mol Neurobiol 2016, 53(3):1741–1752. Plaschke K, Kopitz J, Siegelin M, Schliebs R, Salkovic-Petrisic M, Riederer P, Hoyer S: Insulin-resistant brain state after intracerebroventricular streptozotocin injection exacerbates Alzheimer-like changes in Tg2576 AbetaPP-overexpressing mice. J Alzheimers Dis 2010, 19(2):691–704. Kraska A, Santin MD, Dorieux O, Joseph-Mathurin N, Bourrin E, Petit F, Jan C, Chaigneau M, Hantraye P, Lestage P et al : In vivo cross-sectional characterization of cerebral alterations induced by intracerebroventricular administration of streptozotocin. PLoS One 2012, 7(9):e46196. Moreira-Silva D, Vizin RCL, Martins TMS, Ferreira TL, Almeida MC, Carrettiero DC: Intracerebral Injection of Streptozotocin to Model Alzheimer Disease in Rats. Bio Protoc 2019, 9(20):e3397. Dehghan-Shasaltaneh M, Naghdi N, Choopani S, Alizadeh L, Bolouri B, Masoudi-Nejad A, Riazi GH: Determination of the Best Concentration of Streptozotocin to Create a Diabetic Brain Using Histological Techniques. J Mol Neurosci 2016, 59(1):24–35. Doganyigit Z, Yakan B, Soylu M, Kaymak E, Okan A, Silici S: Histological, immunohistochemical and biochemical effects of bee bread on stomach tissue of obese rats. Bratisl Lek Listy 2020, 121(7):504–511. Moreira-Silva D, Carrettiero DC, Oliveira ASA, Rodrigues S, Dos Santos-Lopes J, Canas PM, Cunha RA, Almeida MC, Ferreira TL: Anandamide Effects in a Streptozotocin-Induced Alzheimer's Disease-Like Sporadic Dementia in Rats. Front Neurosci 2018, 12:653. Motzko-Soares ACP, Vizin RCL, Martins TMS, Hungaro ARO, Sato JR, Almeida MC, Carrettiero DC: Thermoregulatory profile of neurodegeneration-induced dementia of the Alzheimer's type using intracerebroventricular streptozotocin in rats. Acta Physiol (Oxf) 2018, 224(2):e13084. Vicente MC, Almeida MC, Bicego KC, Carrettiero DC, Gargaglioni LH: Hypercapnic and Hypoxic Respiratory Response During Wakefulness and Sleep in a Streptozotocin Model of Alzheimer's Disease in Rats. J Alzheimers Dis 2018, 65(4):1159–1174. Lima RH, Rossato JI, Furini CR, Bevilaqua LR, Izquierdo I, Cammarota M: Infusion of protein synthesis inhibitors in the entorhinal cortex blocks consolidation but not reconsolidation of object recognition memory. Neurobiol Learn Mem 2009, 91(4):466–472. Acun AD, Kantar D, Er H, Erkan O, Derin N, Yargicoglu P: Investigation of Cyclo-Z Therapeutic Effect on Insulin Pathway in Alzheimer's Rat Model: Biochemical and Electrophysiological Parameters. Mol Neurobiol 2023, 60(7):4030–4048. Gulisano W, Maugeri D, Baltrons MA, Fa M, Amato A, Palmeri A, D'Adamio L, Grassi C, Devanand DP, Honig LS et al : Role of Amyloid-beta and Tau Proteins in Alzheimer's Disease: Confuting the Amyloid Cascade. J Alzheimers Dis 2018, 64(s1):S611-S631. Grochowska KM, Gomes GM, Raman R, Kaushik R, Sosulina L, Kaneko H, Oelschlegel AM, Yuanxiang P, Reyes-Resina I, Bayraktar G et al : Jacob-induced transcriptional inactivation of CREB promotes Aβ-induced synapse loss in Alzheimer's disease. Embo j 2023, 42(4):e112453. Heppner FL, Ransohoff RM, Becher B: Immune attack: the role of inflammation in Alzheimer disease. Nat Rev Neurosci 2015, 16(6):358–372. Wang WY, Tan MS, Yu JT, Tan L: Role of pro-inflammatory cytokines released from microglia in Alzheimer's disease. Ann Transl Med 2015, 3(10):136. Strasser B, Berger K, Fuchs D: Effects of a caloric restriction weight loss diet on tryptophan metabolism and inflammatory biomarkers in overweight adults. Eur J Nutr 2015, 54(1):101–107. Denninger JK, Smith BM, Kirby ED: Novel Object Recognition and Object Location Behavioral Testing in Mice on a Budget. J Vis Exp 2018(141). Souza LC, Filho CB, Goes AT, Fabbro LD, de Gomes MG, Savegnago L, Oliveira MS, Jesse CR: Neuroprotective effect of physical exercise in a mouse model of Alzheimer's disease induced by beta-amyloid(1)(-)(4)(0) peptide. Neurotox Res 2013, 24(2):148–163. Lyra ESNM, Goncalves RA, Pascoal TA, Lima-Filho RAS, Resende EPF, Vieira ELM, Teixeira AL, de Souza LC, Peny JA, Fortuna JTS et al : Pro-inflammatory interleukin-6 signaling links cognitive impairments and peripheral metabolic alterations in Alzheimer's disease. Transl Psychiatry 2021, 11(1):251. Huang YS, Ogbechi J, Clanchy FI, Williams RO, Stone TW: IDO and Kynurenine Metabolites in Peripheral and CNS Disorders. Front Immunol 2020, 11:388. Chiu YC, Yang BH, Yang KC, Liu MN, Hu LY, Liou YJ, Chan LY, Chou YH: A study of tryptophan, kynurenine and serotonin transporter in first-episode drug-naïve major depressive disorder. Psychiatry Res Neuroimaging 2021, 312:111296. Badawy AA, Guillemin G: The Plasma [Kynurenine]/[Tryptophan] Ratio and Indoleamine 2,3-Dioxygenase: Time for Appraisal. Int J Tryptophan Res 2019, 12:1178646919868978. Widner B, Leblhuber F, Walli J, Tilz GP, Demel U, Fuchs D: Tryptophan degradation and immune activation in Alzheimer's disease. J Neural Transm (Vienna) 2000, 107(3):343–353. Rahman A, Rao MS, Khan KM: Intraventricular infusion of quinolinic acid impairs spatial learning and memory in young rats: a novel mechanism of lead-induced neurotoxicity. J Neuroinflammation 2018, 15(1):263. Sharma VK, Singh TG, Prabhakar NK, Mannan A: Kynurenine Metabolism and Alzheimer's Disease: The Potential Targets and Approaches. Neurochem Res 2022, 47(6):1459–1476. Raich I, Lillo J, Rebassa JB, Capo T, Cordomi A, Reyes-Resina I, Pallas M, Navarro G: Dual Role of NMDAR Containing NR2A and NR2B Subunits in Alzheimer's Disease. Int J Mol Sci 2024, 25(9). Bading H: Therapeutic targeting of the pathological triad of extrasynaptic NMDA receptor signaling in neurodegenerations. J Exp Med 2017, 214(3):569–578. Lugo-Huitron R, Blanco-Ayala T, Ugalde-Muniz P, Carrillo-Mora P, Pedraza-Chaverri J, Silva-Adaya D, Maldonado PD, Torres I, Pinzon E, Ortiz-Islas E et al : On the antioxidant properties of kynurenic acid: free radical scavenging activity and inhibition of oxidative stress. Neurotoxicol Teratol 2011, 33(5):538–547. Zwilling D, Huang SY, Sathyasaikumar KV, Notarangelo FM, Guidetti P, Wu HQ, Lee J, Truong J, Andrews-Zwilling Y, Hsieh EW et al : Kynurenine 3-monooxygenase inhibition in blood ameliorates neurodegeneration. Cell 2011, 145(6):863–874. Wirthgen E, Hoeflich A, Rebl A, Gunther J: Kynurenic Acid: The Janus-Faced Role of an Immunomodulatory Tryptophan Metabolite and Its Link to Pathological Conditions. Front Immunol 2017, 8:1957. Dos Santos NCL, Malta SM, Franco RR, Silva HCG, Silva MH, Rodrigues TS, de Oliveira RM, Araujo TN, Augusto SC, Espindola FS et al : Antioxidant and anti-Alzheimer's potential of Tetragonisca angustula (Jatai) stingless bee pollen. Sci Rep 2024, 14(1):308. El-Seedi HR, Eid N, Abd El-Wahed AA, Rateb ME, Afifi HS, Algethami AF, Zhao C, Al Naggar Y, Alsharif SM, Tahir HE et al : Honey Bee Products: Preclinical and Clinical Studies of Their Anti-inflammatory and Immunomodulatory Properties. Front Nutr 2021, 8:761267. Kosedag M, Gulaboglu M: Pollen and bee bread expressed highest anti-inflammatory activities among bee products in chronic inflammation: an experimental study with cotton pellet granuloma in rats. Inflammopharmacology 2023, 31(4):1967–1975. Colak H, Sariyer ET, Yuksel M, Polat IO, Cikler E, Oner N, Karakoyun B: Bee bread shows therapeutic and protective effects by alleviating inflammation, oxidative stress, and apoptosis on acetic acid-induced gastric ulcer in rats. Arch Physiol Biochem 2025:1–11. Tang YP, Shimizu E, Dube GR, Rampon C, Kerchner GA, Zhuo M, Liu G, Tsien JZ: Genetic enhancement of learning and memory in mice. Nature 1999, 401(6748):63–69. Wang M, Yang Y, Wang CJ, Gamo NJ, Jin LE, Mazer JA, Morrison JH, Wang XJ, Arnsten AF: NMDA receptors subserve persistent neuronal firing during working memory in dorsolateral prefrontal cortex. Neuron 2013, 77(4):736–749. Liu Y, Fang S, Liu LM, Zhu Y, Li CR, Chen K, Zhao HB: Hearing loss is an early biomarker in APP/PS1 Alzheimer's disease mice. Neurosci Lett 2020, 717:134705. Ordonez-Gutierrez L, Fernandez-Perez I, Herrera JL, Anton M, Benito-Cuesta I, Wandosell F: AbetaPP/PS1 Transgenic Mice Show Sex Differences in the Cerebellum Associated with Aging. J Alzheimers Dis 2016, 54(2):645–656. Guillemin GJ, Brew BJ: Implications of the kynurenine pathway and quinolinic acid in Alzheimer's disease. Redox Rep 2002, 7(4):199–206. Naatanen R, Paavilainen P, Alho K, Reinikainen K, Sams M: The mismatch negativity to intensity changes in an auditory stimulus sequence. Electroencephalogr Clin Neurophysiol Suppl 1987, 40:125–131. Biasibetti R, Almeida Dos Santos JP, Rodrigues L, Wartchow KM, Suardi LZ, Nardin P, Selistre NG, Vazquez D, Goncalves CA: Hippocampal changes in STZ-model of Alzheimer's disease are dependent on sex. Behav Brain Res 2017, 316:205–214. Bao J, Mahaman YAR, Liu R, Wang JZ, Zhang Z, Zhang B, Wang X: Sex Differences in the Cognitive and Hippocampal Effects of Streptozotocin in an Animal Model of Sporadic AD. Front Aging Neurosci 2017, 9:347. Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.tif Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 27 Aug, 2025 Reviews received at journal 26 Aug, 2025 Reviews received at journal 21 Aug, 2025 Reviewers agreed at journal 13 Aug, 2025 Reviewers agreed at journal 12 Aug, 2025 Reviewers agreed at journal 12 Aug, 2025 Reviewers agreed at journal 07 Aug, 2025 Reviewers agreed at journal 07 Aug, 2025 Reviewers agreed at journal 07 Aug, 2025 Reviewers agreed at journal 07 Aug, 2025 Reviewers invited by journal 07 Aug, 2025 Editor assigned by journal 01 Aug, 2025 Submission checks completed at journal 01 Aug, 2025 First submitted to journal 01 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7268712","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":498587045,"identity":"ddce2481-0506-4bc5-9617-28c910049492","order_by":0,"name":"Alev Duygu Acun","email":"","orcid":"","institution":"Akdeniz University","correspondingAuthor":false,"prefix":"","firstName":"Alev","middleName":"Duygu","lastName":"Acun","suffix":""},{"id":498587046,"identity":"b58f6cd6-8d55-4a7f-960d-e43b58a90a82","order_by":1,"name":"Ebru Afşar","email":"","orcid":"","institution":"Cappadocia University","correspondingAuthor":false,"prefix":"","firstName":"Ebru","middleName":"","lastName":"Afşar","suffix":""},{"id":498587047,"identity":"52046d59-aa65-414e-8791-ac996f776d8d","order_by":2,"name":"Deniz Kantar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA8ElEQVRIie3OsYrCQBCA4QFBm0HbDQfxFUaEWPoqKxZpFAIBsRCxik3Q1tdIY2Wxh2A1Ie1VIgipLBTBRhETrOQ00c5if5adLfaDAdDpvjG+DxMQCNIDIN8gCqD+SNQbpDXC+/98UuZlvN0P1vbUXwZbxxlCpdShwmHxmhih1yC1cruz0HPrMyqC4e8IVPyaUASWUEXZHUVo/SAl6/11EpKxGUWlk1BXaVcjbJyRBDRzSehb4teTMn0UkAhI5BCDuSfCiawFvHKTxSQKjh3FGaTM9lz0T7Jqcjs44mVoVsbtYNPPIP/C9PoE6HQ6ne5JN6GSVRCl4tUwAAAAAElFTkSuQmCC","orcid":"","institution":"Akdeniz University","correspondingAuthor":true,"prefix":"","firstName":"Deniz","middleName":"","lastName":"Kantar","suffix":""}],"badges":[],"createdAt":"2025-08-01 07:53:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7268712/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7268712/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":88896052,"identity":"ea947a59-4ae6-4a02-8d41-3aeb9cd13d8c","added_by":"auto","created_at":"2025-08-12 13:08:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":167255,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic flow chart of the material-method diagram\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/801134f4285a7c2d095b14f0.png"},{"id":88891849,"identity":"ed0d3d0d-6f01-41a1-93ba-56d2767bc2d3","added_by":"auto","created_at":"2025-08-12 12:52:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":12228,"visible":true,"origin":"","legend":"\u003cp\u003eA: The object location memory discrimination index B: The correlations between OLT discrimination index and hippocampus IL-6 levels, C: The correlations between OLT discrimination index and hippocampus NR2B levels. Results are presented as mean ±SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p\u0026lt;0.05; **: p\u0026lt;0.01; ***: p\u0026lt;0.001, #: p\u0026lt;0.05; ##: p\u0026lt;0.01; ###: p\u0026lt;0.001)\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/868120a0fa6064eb51a6649d.png"},{"id":88893846,"identity":"9e9eac2a-5e49-4071-bb71-3531892c1841","added_by":"auto","created_at":"2025-08-12 13:00:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":32799,"visible":true,"origin":"","legend":"\u003cp\u003eA: Hippocampus Aβ levels, B: Temporal Aβ levels, C: Hippocampus Tau levels, D: Temporal Tau levels. N=6 in all experimental groups. E: Hippocampus NR2B levels, F: Temporal NR2B levels. Results are presented as mean ±SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p\u0026lt;0.05; **: p\u0026lt;0.01; ***: p\u0026lt;0.001, #: p\u0026lt;0.05; ##: p\u0026lt;0.01; ###: p\u0026lt;0.001)\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/52612c9c3f3da99d2da1836b.png"},{"id":88891854,"identity":"41fba53a-df6d-4c95-b00e-bbea8b9b5102","added_by":"auto","created_at":"2025-08-12 12:52:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":24679,"visible":true,"origin":"","legend":"\u003cp\u003eA: Hippocampus IL-6 levels, B: Temporal IL-6 levels, C: Hippocampus Caspase-3 levels, D: Temporal Caspase-3 levels. N=6 in all experimental groups. Results are presented as mean ±SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p\u0026lt;0.05; **: p\u0026lt;0.01; ***: p\u0026lt;0.001, #: p\u0026lt;0.05; ##: p\u0026lt;0.01; ###: p\u0026lt;0.001)\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/1376d16268eb3e1b8d8338df.png"},{"id":88893847,"identity":"320a77a0-f299-4787-8693-03d67723b018","added_by":"auto","created_at":"2025-08-12 13:00:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":39916,"visible":true,"origin":"","legend":"\u003cp\u003eA: Averages of peak-to-peak amplitudes of the P1N1 AEP component, B: Averages of peak-to-peak amplitudes of the N1P2 AEP component. C: Representative shape of AEP waveforms evoked by auditory stimuli at the Left Temporal (T3) electrode location. Results are presented as mean ±SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p\u0026lt;0.05; **: p\u0026lt;0.01; ***: p\u0026lt;0.001, #: p\u0026lt;0.05; ##: p\u0026lt;0.01; ###: p\u0026lt;0.001)\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/86d9c8aefa39f92237f8c5db.png"},{"id":88896053,"identity":"183ffcbd-ed18-4634-a83a-596576bdc2b8","added_by":"auto","created_at":"2025-08-12 13:08:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":41355,"visible":true,"origin":"","legend":"\u003cp\u003eA: The object location memory discrimination index B: The correlations between OLT discrimination index and hippocampus IL-6 levels.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/62f2064ee410a21b89a35e1d.png"},{"id":88899042,"identity":"7f7a4c22-3816-45ae-b4d9-9e24ffe7682c","added_by":"auto","created_at":"2025-08-12 13:24:07","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1333634,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/b993316c-d4cf-4a2a-bdcc-d88493a8d94b.pdf"},{"id":88891852,"identity":"9b74c269-f261-4988-9b9a-a2e038ec2287","added_by":"auto","created_at":"2025-08-12 12:52:06","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":134297,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.tif","url":"https://assets-eu.researchsquare.com/files/rs-7268712/v1/38263e8b4e2e3fc015cf7b09.tif"}],"financialInterests":"No competing interests reported.","formattedTitle":"Bee Bread Shows Protective Effects in a Streptozotocin-Induced Alzheimer's Disease Rat Model","fulltext":[{"header":"1. INTRODUCTİON","content":"\u003cp\u003eAlzheimer's disease (AD), which accounts for 60\u0026ndash;70% of cases worldwide, is a progressive neurodegenerative disease that damages nerve cells and ultimately leads to the death of the patient. Brain tissue atrophies due to damage to neural cells, resulting in loss of neurotransmission and synaptic activity between various cortical regions. In the early stages of AD, some researchers accept that there is more widespread atrophy, especially in auditory structures, and auditory dysfunction [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Although it is generally observed that auditory-evoked potentials in the cerebral cortex are reduced in patients with AD or in animal models, there are conflicting results in the literature [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Therefore, the effect of AD on auditory-evoked potentials and their dynamic changes in the development of the disease remain unclear [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Neuropathological changes may begin in sensory areas before AD pathology manifests in memory areas, and neuropathological changes may occur in sensory-related areas before cognitive symptoms become evident [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. While AD can cause hearing loss, hearing loss can also accelerate the development of AD [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Auditory evoked potentials (AEPs) are electrical potentials in any part of the auditory system, from the cochlea to the cerebral cortex, evoked by an auditory stimulus. AEPs are a non-invasive method used to obtain information about the function and integrity of the auditory system [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Since AEP does not include cognitive processing and perception patterns, it may be more effective than event-related potentials (ERPs) in evaluating changes in the auditory network. The early components of the AEP are considered suitable for cross-species studies because they represent automatic brain functions that involve auditory discrimination without consciousness [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Rodent AD models are very important because they allow the investigation of the direct relationship between AD neuropathology and its neurophysiological effects on brain neural networks. However, there are few studies in the literature using evoked potentials (EPs)/ERPs paradigms in rodent AD models [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Although changes in AEP responses have been studied in some AD animal models [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], the dynamic changes of AEP in the development of AD have still not been fully elucidated.\u003c/p\u003e\u003cp\u003eNeuroinflammation is known to play a critical role in the development of AD. The release of proinflammatory cytokines may cause synaptic dysfunction, neuronal death, and inhibition of neurogenesis, and is likely to be linked to AD. Neuroinflammation is closely linked to the kynurenine (KYN) pathway and underlies various neurological conditions. This link is due to the ability of inflammatory factors to affect the activity of enzymes involved in the KYN pathway. The KYN pathway involves the conversion of the essential amino acid tryptophan (Trp) into a series of compounds and is considered an important metabolic pathway as some of the compounds formed are neuroactive [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The KYN pathway and its several metabolites are thought to be altered in AD and to have significant roles in the neuropathogenesis of the disease. Variations in KYN metabolites have an impact on the brain's ability to regulate oxidative stress, cause neuroinflammation, and cause neurotoxicity. Therefore, any imbalance in the metabolism of the KYN pathway may play an important role in AD pathophysiology [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In order to evaluate the systemic and metabolic defects in AD pathophysiology, in-depth study of the KYN pathway is crucial.\u003c/p\u003e\u003cp\u003eIn the KYN pathway, TRP 2,3-dioxygenase (TDO) and indolamine 2,3-dioxygenase (IDO) are known to be the initial rate-limiting enzymes. Although TDO is the main enzyme under physiological conditions, IDO1 is upregulated in macrophages, microglia, neurons and astrocytes in response to neuroinflammatory stimuli. Proinflammatory cytokines released by microglia activate the IDO enzyme, which raises the neurotoxic quinolinic acid (QA) level. The neuroactive QA metabolite has N-methyl-D-aspartate (NMDA) receptor (NMDAR) agonist characteristics and is a potent producer of free radicals. Additionally, through raising extracellular glutamate levels, it produces excitotoxicity and triggers lipid peroxidation. When anti-inflammatory cytokines are released from astrocytes, the synthesis of kynurenic acid (KYNA), a potent NMDAR antagonist is increased. KYNA exhibits competitive antagonistic activity on NMDA receptors. Overactivation of the KYN pathway may lead to overproduction of QA, and QA has been found to be associated with pathological changes and cognitive functions in AD. QA has been observed to cause learning and memory deficits. A vicious loop may be created whereby overproduction of QA causes greater tau hyperphosphorylation, which in turn triggers activation of microglia in response to Aβ and p-tau. Although it is widely accepted that AD is associated with an elevated KYN pathway, further research is needed to explore the elusive molecular mechanisms behind the relationship between AD and metabolites of the complex KYN pathway and to develop therapeutic strategies for this [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRecently, complementary and herbal medicine has gained popularity and interest. Bee bread (BB) is a natural product formed by anaerobic lactic fermentation of bee pollen. Although BB contains less protein than bee pollen, the digestibility of the protein it contains is higher due to the fermentation of the collected pollen by the bees [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This makes BB a functional food source with higher bioavailability compared to bee pollen [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Properties such as high concentration of simple sugar content, low pH (pH 4), low water activity, high oxidation-reduction potential and the presence of lactic acid bacteria make bee bread a preservative composition [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. BB is an important source of antioxidants that can eliminate free oxygen radicals and their harmful effects on cells [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Since TRP is known to be an important compound in the content of BB [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], it is likely to modulate the KYN pathway. According to a study, propolis extracts suppress IDO activity as part of their immunomodulatory effects [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. A high Trp diet has also been previously shown to significantly improve cognitive dysfunction and reduce Aβ deposits [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Therefore, although it seems plausible that BB regulates the KYN pathway and reduces TRP degradation, its therapeutic effects on AD remain unclear.\u003c/p\u003e\u003cp\u003eIntracerebroventricular (ICV) administration of streptozotocin (STZ), a glucosamine-nitrosourea molecule derived from soil bacteria, mimics the neuropathological and metabolic changes of sporadic AD (sAD) [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The ICV-STZ model is widely used to mimic the onset and course of human sAD and to investigate the neuroprotective effects of different drugs [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. This study investigated the effects of BB treatment applied to the ICV-STZ sAD model on the level of KYN pathway metabolites and their anti-apoptotic, anti-inflammatory, cognitive functions, changes in sensory brain responses and anti-Alzheimer potential.\u003c/p\u003e"},{"header":"2. MATERİALS and METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Animals and treatment\u003c/h2\u003e\u003cp\u003e Male albino Wistar rats Forty male albino Wistar rats, 3 months old, weighing 250\u0026ndash;300 g, were purchased from Akdeniz University Animal Care Unit (Antalya, Turkey) and housed in groups of 4 in stainless steel cages. Rats were housed under standard conditions (23\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C and 50\u0026thinsp;\u0026plusmn;\u0026thinsp;5% humidity) with a 12-h light-dark cycle. Food and water were provided ad libitum. Animals were randomly divided into three groups (n\u0026thinsp;=\u0026thinsp;6 each group): (1) \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSham (SH) group\u003c/span\u003e [vehicle (citrate buffer/2 \u0026micro;l/ventricle) plus water gavage treatment]; (2) \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSTZ group\u003c/span\u003e [STZ (2mg/kg, 2 \u0026micro;l/ventricle) plus water gavage treatment]; (3) \u003cspan type=\"Underline\" class=\"Underline\" name=\"Emphasis\"\u003eSTZB group\u003c/span\u003e [STZ (2mg/kg, 2 \u0026micro;l/ventricle) plus BB (200 mg/kg/day) gavage treatment (0,5 g/kg/day) gavage]. Studies have reported that 2 mg/kg is the most effective STZ dose in modeling sporadic AD-like pathology [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The purity of STZ (Cayman, 13104), whose molecular formula is C8H15N3O7, is over 95%. To prepare an STZ solution corresponding to a dose of 2 mg/kg for a rat weighing 350 grams, 1.05 mg of STZ should be diluted in 6 \u0026micro;l of citrate buffer (0.05M). The 0.05 M citrate buffer solution was prepared according to the procedures given previously [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Since the half-life of the STZ solution is very short (15\u0026ndash;30 minutes) and unstable, it was prepared fresh before use. After the surgical procedure, the animals were allowed to recover for seven days and then gavage was applied once a day for 21 days. The nutritional content of BB purchased from Nutral Therapy Company (Erciyes University Technopark, Kayseri) is given in the table (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In previous studies, 200 mg/kg/day bee bread application was preferred because it is known to have positive effects on the number of apoptotic cells, weight control and other parameters [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eNutritional contents of BB.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNutritional elements\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eContent\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAsh\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e2.31 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eProtein\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e22.63g / 100 g (N x 6.25)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCarbohydrate\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e51.91 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDietary fiber\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e18.18 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFat (acid hydrolyzed)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e8.70 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEnergy\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e376 kcal / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGluten (ppm)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCopper (Cu)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e12.91 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZinc (Zn)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e36.67 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePhosphorus (P)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e6665.44 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eİron (Fe)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e192 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCalcium (Ca)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1390 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSodium (Na)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e78.74 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMagnesium (Mg)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e638 mg / kg\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOmega-6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.23 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOmega-3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.55 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHumidity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e14.45 g / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTotal antioxidant activity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e447.16 mg TE / 100 g\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Experimental design\u003c/h2\u003e\u003cp\u003eThe ICV-STZ sAD rat model was established as in previous studies [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. A midsagittal incision was made on the scalp of rats placed in a standard stereotaxic apparatus under ketamine (80 mg/kg, i.p.)/xylazine (5 mg/kg, i.p.) anesthesia. To create the experimental groups, the coordinates of the lateral ventricles (AP: -0.8 mm, ML: \u0026plusmn; 1.4 mm, DV: -4.0 mm) were drilled bilaterally using a dental drill. To establish the experimental groups, the coordinates of the lateral ventricles were drilled bilaterally using a dental drill, and 0.5 \u0026micro;l/min was injected into the lateral ventricles with a Hamilton syringe and withdrawn after 5 min. After surgery, the incision was sutured, and antibiotic ointment was applied for 7 days to prevent infection. Penicillin (40,000 U) was injected intramuscularly daily for 3 days. After waiting for a 7-day period for AD pathology to occur, gavage was applied for 21 days. Since significant cognitive impairment and neurodegeneration are known to occur approximately 30 days after 2 mg/kg ICV-STZ injection [\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e], the training phase of the behavioral experiment was performed on day 29, and the testing phase on day 30. After electrode placement and recordings for electrophysiological recording on day 31, rats were sacrificed. Perfusion was performed with isotonic heparin via cardiac cannula and then brain tissues were removed and frozen in liquid nitrogen. Brain tissues were stored at -80\u0026deg;C for biochemical analyses (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. AEP Recordings and Analysis\u003c/h2\u003e\u003cp\u003eTo record auditory electrophysiological responses, rats were anesthetized with urethane (1.2 g/kg, i.p. Sigma-Aldrich, St Louis, MO, USA) and fixed in a standard stereotaxic frame. Stainless steel screw electrodes were placed over the auditory cortex of the rats (AP: -4.5 mm, ml: -3.5 and +\u0026thinsp;3.5 mm) using holes drilled into the cerebellar skull, and reference/ground electrodes were placed bilaterally over the cerebellum region. Before recording, the tympanic membrane and external auditory canal were checked for any damage. Tones of 50 ms duration were delivered to the rat's ear via a loudspeaker 15 cm away. The signal was amplified (Brainamp EEG/EP Amplifier, Brain Products, Munich, Germany), band-pass filtered (0.1\u0026ndash;300 Hz, 50 Hz notch filter), and digitized and recorded at a sampling rate of 1000 Hz (Brainvision Recorder, Brain Products, Munich, Germany). Using tones at 2000 Hz that were 85 dB and had a 500 ms short interstimulus interval (ISI), AEPs were recorded. The BrainVision Analyzer (Brain Products, Munich, Germany) was used to average the EEG data. AEPs were divided into 600 ms epochs, 100 ms before and 500 ms after stimulus presentation. The average of 100 AEP waves was used to identify the peaks, and the resulting waveforms were used to calculate the peak-to-peak amplitudes (in microvolts) of the AEP components for each rat. The first large positive wave that appeared approximately 50 ms after the stimulus was defined as P1. Similarly, the large negative wave that appeared approximately 100 ms was determined as N1 and the positive wave that appeared at 200 ms was determined as P2. The peak-to-peak amplitudes of P1N1 and N1P2 were analyzed according to the measurements.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Behavioral Testing\u003c/h2\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.4.1. Object Location Test (OLT)\u003c/h2\u003e\u003cp\u003eThe experiment was carried out in a box system with equal lighting, 40 cm x 40 cm x 40 cm, with a white mat on the bottom and sides. The experiment was conducted in a soundproof room to minimize the effect of any external stimulus on the experimental parameters. The OLT consists of two phases: training and testing. In the training phase, two identical objects, A1 and A2, were selected and placed on opposite sides of the box, and the rat was left in the center of the box and given 5 minutes to explore objects A1 and A2. In the testing phase, 24 hours after the training phase, two identical objects, A1, remained in the same place as in the training phase, while the other identical object, A2, was placed in a new location to test object location memory. The identical objects A1-A2 used in the experiment were fixed to the floor to prevent movement. Before each trial for each rat, the objects and the entire interior surface of the box were wiped with 70% ethanol to prevent the presence of odor cues and air dried. Video recordings were used to determine the time spent by rats with objects, and the rat was considered to have explored the object when its nose was 2 cm away from the object. The discrimination index was calculated using the following formula: Exploration time spent with an object in the new location/Exploration time spent with an object in the new location\u0026thinsp;+\u0026thinsp;Exploration time spent with an object in the old location \u0026times; 100.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.4.2. Novel Object Recognition (NOR) Test\u003c/h2\u003e\u003cp\u003eThe novel object recognition test consists of two phases: the training phase and the testing phase. During the training phase, two identical objects (A1-A2) were placed in the experimental system at two opposite positions at the same distance from the nearest corner. The rats were then released from the center to the field and allowed 5 minutes to explore these two identical objects (A1-A2). The rats that completed the training phase were taken to the test phase 24 hours after they were placed back in their cages. To test the novel object recognition memory during the test phase, a copy of the familiar object (A3) and a new object (B1) were placed in the same place as during the training experiment. Each of the objects used in the experiment was fixed to the floor to prevent its movement. The behavior of the rats during the training and testing phases was recorded with a video camera and used to determine the time the rats spent with the objects. To preclude the existence of olfactory cues, the entire box and objects were always thoroughly cleaned with 70% ethanol after each trial. In the novel object recognition test, discrimination index (%) values showing memory strength were analyzed. Discrimination index was calculated using the formula: exploration time spent with novel object/ exploration time spent with novel object\u0026thinsp;+\u0026thinsp;exploration time spent with familiar object \u0026times; 100.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Biochemical Experiments\u003c/h2\u003e\u003cp\u003eTemporal and hippocampal tissue samples homogenized in cold PBS, centrifuged at 2000\u0026ndash;3000 r.p.m for 20 min. Supernatants were stored at \u0026minus;\u0026thinsp;80\u0026deg;C for protein analyses.\u003c/p\u003e\u003cp\u003eThe sandwich ELISA method is very effective in detecting the target antigen in an unknown sample. Temporal and hippocampal target protein levels in the supernatants of tissue homogenates were measured according to the procedures of a commercially available sandwich ELISA kit. Commercial kits contain 96-well plates coated with rat target protein antibodies, and biotinylated rat target protein antibody is added to these wells and binds to target protein in the sample. These bind to target protein in the sample. A sandwich model is created by adding a horseradish peroxidase (HRP) conjugate polyclonal antibody specific for target protein to obtain immobilized target protein. Then, streptavidin-HRP is added to bind to the biotinylated target protein antibody. After incubation, unbound components are removed by washing 5 times and then substrate solution is added. When the substrate solution is added, HRP reacts with the enzyme to cause color formation, so only the wells containing target protein show a color change proportional to the amount of target protein. Then, an acidic solution is added to terminate the reaction and the optical density (OD) is measured spectrophotometrically at 450 nm. Sample target protein amount was also calculated from the standard curve plot.\u003c/p\u003e\u003cp\u003e\u003cspan type=\"BoldItalicUnderline\" class=\"BoldItalicUnderline\" name=\"Emphasis\"\u003eTarget Proteins\u003c/span\u003e: Total Aβ1\u0026ndash;42 (SunRedBio Rat Aβ1\u0026ndash;42 Catalog No: 201-11-0094), Tau protein (SunRedBio Rat Tau Protein Catalog No. SRB-T-86822), glutamate receptor2B (NR2B/NMDAR2B (SunRedBio Rat NR2B Protein Catalog No: 201-11-2688), TRP (SunRedBio Rat TRP Protein Catalog No: 201-11-7308), KYN (SunRedBio Rat KYN Catalog No: 201-11-2152), KYNA (SunRedBio Rat KYNA Catalog No. 201-11-5219), QA (SunRedBio Rat QA Protein Catalog No: 201-11-5093), Caspase-3/CPP32 (SunRedBio Rat Caspase-3 Catalog No: 201-11-0281), interleukin 6 (IL-6) (SunRedBio Rat IL-6 Catalog No: 201-11-0136).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e2.6. Statistical analysis\u003c/h2\u003e\u003cp\u003eStatistical analyses were performed using SPSS 23.0 for Windows (SPSS, Chicago, IL, USA) program. Statistical comparisons of the data obtained from biochemical analyses between groups were performed using one-way ANOVA and post-hoc Tukey test for data conforming to normal distribution. AEP analyses were performed using repeated-measures ANOVA and post-hoc comparisons were made using the Bonferroni test. Results were given as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error and p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered significant.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULTS","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Treatment with BB Ameliorates Cognitive İmpairment in STZ-induced AD Rats.\u003c/h2\u003e\u003cp\u003eIn the OLT test, the novelty feature is the location, since the objects in the test trial are the same as in the training trial. The OLT is considered a simple and effective test that measures hippocampus-dependent spatial memory. When OLT was examined 24 h after training, it requires de novo transcription and translation [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. A statistically significant difference was found between the groups in OLT test [F(2,15)\u0026thinsp;=\u0026thinsp;46,16, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). The OLT discrimination index of the STZ group (45,23\u0026thinsp;\u0026plusmn;\u0026thinsp;1,5) decreased significantly compared to the SH group (78,68\u0026thinsp;\u0026plusmn;\u0026thinsp;2,51) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The OLT discrimination index of the STZB group (76,73\u0026thinsp;\u0026plusmn;\u0026thinsp;3,78) increased significantly compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No significant difference was found between the SH and STZB groups.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe major advantage of the NOR over other rodent memory tests is that it relies on rodents' natural tendency to explore novelty. Several different brain regions are critical for the new object recognition memory, including the insular cortex, the perirhinal cortex, and the ventromedial prefrontal cortex [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. A statistically significant difference was found between the groups in NOR test [F(2,15)\u0026thinsp;=\u0026thinsp;39,37, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). The NOR discrimination index of the STZ group (49,96\u0026thinsp;\u0026plusmn;\u0026thinsp;2,2) decreased significantly compared to the SH group (79,13\u0026thinsp;\u0026plusmn;\u0026thinsp;2,4) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). The NOR discrimination index of the STZB group (74,69\u0026thinsp;\u0026plusmn;\u0026thinsp;2,8) increased significantly (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to the STZ group. No significant difference was found between the SH and STZB groups. Therefore, it was observed that long-term spatial memory of STZ-induced AD group rats was impaired, while BB treatment had an improving effect on memory functions.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.2. While STZ induction increases Alzheimer-like pathology, BB has an ameliorating effect on this pathology.\u003c/h2\u003e\u003cp\u003eData from thousands of studies on the pathophysiology of AD to date identify Aβ and tau protein as key players [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Statistically significant difference was found between the hippocampus Aβ1\u0026ndash;42 levels between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;3,48, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Hippocampal Aβ1\u0026ndash;42 levels of the STZ group (26,32\u0026thinsp;\u0026plusmn;\u0026thinsp;2.27 pg/mg) tended to increase, although not significantly, compared to the SH group (22,35\u0026thinsp;\u0026plusmn;\u0026thinsp;1,3 pg/mg) (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Hippocampus Aβ1\u0026ndash;42 levels of the STZB group (19,68\u0026thinsp;\u0026plusmn;\u0026thinsp;1,6 pg/mg) were found to be significantly decreased compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There was a statistically significant difference in temporal Aβ1\u0026ndash;42 levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;30,65, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). Temporal Aβ1\u0026ndash;42 levels of the STZ group (28,16\u0026thinsp;\u0026plusmn;\u0026thinsp;1,2 pg/mg) were significantly higher than those of the SH group (16,85\u0026thinsp;\u0026plusmn;\u0026thinsp;1,4 pg/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). It was observed that temporal Aβ1\u0026ndash;42 levels of the STZB group (14,33\u0026thinsp;\u0026plusmn;\u0026thinsp;1,2 pg/mg) were significantly decreased compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNo statistically significant difference was found between the hippocampus tau levels between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;0,56, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). Hippocampal Tau levels in the STZ group (2,21\u0026thinsp;\u0026plusmn;\u0026thinsp;0,33 ng/mg) were significantly higher than in the SH group (1,28\u0026thinsp;\u0026plusmn;\u0026thinsp;0,16 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Hippocampal Tau levels of the STZB group (1,84\u0026thinsp;\u0026plusmn;\u0026thinsp;0,22 ng/mg) tended to decrease compared to the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was a statistically significant difference in temporal tau levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;11,39, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18 ] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). Temporal Tau levels of the STZ group (3,29\u0026thinsp;\u0026plusmn;\u0026thinsp;0,3 ng/mg) were significantly higher than those of the SH group (1,24\u0026thinsp;\u0026plusmn;\u0026thinsp;0,2 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Temporal Tau levels of the STZB group (2,21\u0026thinsp;\u0026plusmn;\u0026thinsp;0,3 ng/mg) tended to decrease compared to the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In summary, these results indicate that Aβ and Tau pathology occur in the hippocampus and temporal cortex of STZ-induced AD rats and that BB treatment may alleviate the neuronal damage that may arise due to these.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.3. BB treatment increased Glutamate Receptor-2B/NR2B/NMDAR2B levels in the hippocampal regions of STZ-induced AD rats.\u003c/h2\u003e\u003cp\u003eNR2B activation may be associated with the pathological progression of AD. Furthermore, the detrimental effects of Aβ prior to neuronal loss appear to be mediated by NMDARs, particularly NR2Bs [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. There was a statistically significant difference in hippocampus NR2B levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;10,63, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE). Hippocampus NR2B levels of the STZ group (1,48\u0026thinsp;\u0026plusmn;\u0026thinsp;0,1 ng/mg) were significantly higher than those of the SH group (2,01\u0026thinsp;\u0026plusmn;\u0026thinsp;0,06 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Hippocampus NR2B levels of the STZB group (2,38\u0026thinsp;\u0026plusmn;\u0026thinsp;0,1 ng/mg) were significantly increased compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No significant difference was found in hippocampal NR2B levels of the STZB group compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was a statistically significant difference in temporal NR2B levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;13,58, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;6] (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF). Temporal NR2B levels of the STZ group (1,91\u0026thinsp;\u0026plusmn;\u0026thinsp;0,11 ng/mg) were significantly lower than those of the SH group (3,11\u0026thinsp;\u0026plusmn;\u0026thinsp;0,2 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Temporal NR2B levels of the STZB group (2,46\u0026thinsp;\u0026plusmn;\u0026thinsp;0,15 ng/mg) were tented to increase compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). While increased apoptosis was observed in the STZ-induced rat group, it was significantly decreased especially in the hippocampal regions due to BB treatment.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Attenuating Effect of BB Treatment on Increased Proinflammatory IL-6 Levels in STZ-induced AD Rats.\u003c/h2\u003e\u003cp\u003eChronic neuroinflammation, induced by a series of proinflammatory cytokines such as IL-6, is widely accepted as an early and persistent feature of the AD brain [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. There was a statistically significant difference in hippocampus IL-6 levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;11,46, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Hippocampus IL-6 levels of the STZ group (26,42\u0026thinsp;\u0026plusmn;\u0026thinsp;2,11 pg/mg) were significantly higher than those of the SH group (16,55\u0026thinsp;\u0026plusmn;\u0026thinsp;1,03 pg/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Hippocampus IL-6 levels of the STZB group (18,53\u0026thinsp;\u0026plusmn;\u0026thinsp;2,4 pg/mg) were significantly lower than the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There was a statistically significant difference in temporal IL-6 levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;5,74, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;6] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). Temporal IL-6 levels of the STZ group (34,95\u0026thinsp;\u0026plusmn;\u0026thinsp;6,2 pg/mg) were significantly higher than those of the SH group (14,94\u0026thinsp;\u0026plusmn;\u0026thinsp;2,95 pg/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Temporal IL-6 levels of the STZB group (19,6\u0026thinsp;\u0026plusmn;\u0026thinsp;3,1 pg/mg) were significantly lower than the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Increased IL-6 levels were observed in the temporal cortex and hippocampal brain regions of STZ-induced AD rats, while BB treatment was particularly effective in reducing hippocampal neuroinflammation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Apoptotic Marker Caspase-3 Decreased in STZ-Induced AD Rats Due to BB Treatment.\u003c/h2\u003e\u003cp\u003eThere was a statistically significant difference in hippocampus caspase-3 levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;11,46, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). Hippocampus caspase-3 levels of the STZ group (0,41\u0026thinsp;\u0026plusmn;\u0026thinsp;0,03 ng/mg) were significantly higher than those of the SH group (0,27\u0026thinsp;\u0026plusmn;\u0026thinsp;0,01 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Hippocampus caspase-3 levels of the STZB group (0,27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 ng/mg) were significantly higher than the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). No significant difference was found in temporal caspase levels of the STZB group compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was a statistically significant difference in temporal caspase-3 levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;4,13, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). Temporal caspase-3 levels of the STZ group (0,49\u0026thinsp;\u0026plusmn;\u0026thinsp;0,11 ng/mg) were significantly higher than those of the SH group (0,20\u0026thinsp;\u0026plusmn;\u0026thinsp;0,04 ng/mg) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Temporal caspase levels of the STZB group (0.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 ng/mg) were tented to decrease compared to the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). No significant difference was found in temporal caspase levels of the STZB group compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). While increased apoptosis was observed in the STZ-induced rat group, it was significantly decreased, especially in the hippocampal regions, due to BB treatment.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.6. Neuroprotective Effect of BB on the KYN Pathway in STZ-Induced Rats\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eAll data of the KYN pathway are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Statistically significant difference was found in hippocampus KYN levels between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;3,98, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. Hippocampus KYN levels of the STZ group were higher than those of the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Hippocampus KYN levels of the STZB group tended to decrease compared to the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was a statistically significant difference in temporal KYN levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;7,41, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18]. Temporal KYN levels of the STZ group were higher than those of the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Temporal KYN levels of the STZB group were significantly decreased compared to the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). No statistically significant difference was found in hippocampus TRP levels between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;2,20, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. There was a no statistically significant difference in temporal TRP levels between groups [F(3,20)\u0026thinsp;=\u0026thinsp;5,35, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. There was no statistically significant difference in hippocampus KYN/TRP ratios between groups [F(2,15)\u0026thinsp;=\u0026thinsp;3,07, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. There was no statistically significant difference in temporal KYN/TRP ratios between groups [F(2,15)\u0026thinsp;=\u0026thinsp;3,34, p\u0026thinsp;\u0026gt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. The change in the KYN/TRP ratio is a ratio used to determine IDO activity by reflecting the degradation rate of TRP [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. There was a statistically significant difference in hippocampus KYNA levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;5,82, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, N\u0026thinsp;=\u0026thinsp;18]. Hippocampus KYNA levels of the STZ group were significantly lower than the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Hippocampus KYNA levels of the STZB group were significantly increased compared to those of the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There was a statistically significant difference in temporal KYNA levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;9,04, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18]. Temporal KYNA levels of the STZ group were significantly lower than the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Temporal KYNA levels of the STZB group were significantly higher than the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). There was a statistically significant difference in hippocampal QA levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;9,48, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18]. Hippocampal QA levels of the STZ group were significantly higher than the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Hippocampal QA levels of the STZB group tended to decrease compared to the STZ group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). No significant difference was found in hippocampal QA levels of the STZB group compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). There was a statistically significant difference in temporal QA levels between groups [F(2,15)\u0026thinsp;=\u0026thinsp;6,54, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18]. Temporal QA levels of the STZ group were significantly higher than the SH group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). Temporal QA levels of the STZB group were significantly lower than the STZ group (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). No significant difference was found in temporal QA levels of the STZB group compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). In the STZ-induced AD group, it was found that while excitotoxin KYN pathway metabolites increased, the number of neuroprotective metabolites decreased significantly and the TRP pathway shifted towards QA production. However, BB treatment results were found to reverse these results observed in STZ rats and direct the KYN pathway towards neuroprotective KYNA production.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eChanges in the KYN pathway and its metabolites in the hippocampus and temporal brain regions. Results are presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SEM. (*: Significant vs SH group, #: Significant vs STZ group, *: p\u0026thinsp;\u0026lt;\u0026thinsp;0.05; **: p\u0026thinsp;\u0026lt;\u0026thinsp;0.01; ***: p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, #: p\u0026thinsp;\u0026lt;\u0026thinsp;0.05; ##: p\u0026thinsp;\u0026lt;\u0026thinsp;0.01; ###: p\u0026thinsp;\u0026lt;\u0026thinsp;0.001)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eHİPPOCAMPUS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eTEMPORAL CORTEX\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eKYN (ng/mg protein)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,68\u0026thinsp;\u0026plusmn;\u0026thinsp;0,26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e2,26\u0026thinsp;\u0026plusmn;\u0026thinsp;0,25\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2,68\u0026thinsp;\u0026plusmn;\u0026thinsp;0,26 \u003cb\u003e*\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e3.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45 \u003cb\u003e*\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2,06\u0026thinsp;\u0026plusmn;\u0026thinsp;0,22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e2.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13 \u003cb\u003e##\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eTRP (ng/mg protein)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,64\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e2,73\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,67\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e2,92\u0026thinsp;\u0026plusmn;\u0026thinsp;0,34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2,27\u0026thinsp;\u0026plusmn;\u0026thinsp;0,23\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e2,59\u0026thinsp;\u0026plusmn;\u0026thinsp;0,47\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eKYN/TRP Ratio\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,72\u0026thinsp;\u0026plusmn;\u0026thinsp;0,31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,85\u0026thinsp;\u0026plusmn;\u0026thinsp;0,11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,75\u0026thinsp;\u0026plusmn;\u0026thinsp;0,26\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e1,30\u0026thinsp;\u0026plusmn;\u0026thinsp;0,16\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0,92\u0026thinsp;\u0026plusmn;\u0026thinsp;0,009\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,91\u0026thinsp;\u0026plusmn;\u0026thinsp;0,11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eKYNA (nmol/mg protein)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1,40\u0026thinsp;\u0026plusmn;\u0026thinsp;0,22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e1,68\u0026thinsp;\u0026plusmn;\u0026thinsp;0,21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0,54\u0026thinsp;\u0026plusmn;\u0026thinsp;0,13 \u003cb\u003e*\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,55\u0026thinsp;\u0026plusmn;\u0026thinsp;0,16 \u003cb\u003e**\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20 \u003cb\u003e#\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e1,52\u0026thinsp;\u0026plusmn;\u0026thinsp;0,22 \u003cb\u003e#\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eQA (ng/mg protein)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSH\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0,09\u0026thinsp;\u0026plusmn;\u0026thinsp;0,01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,13\u0026thinsp;\u0026plusmn;\u0026thinsp;0,02\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZ\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0,16\u0026thinsp;\u0026plusmn;\u0026thinsp;0,01 \u003cb\u003e**\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,26\u0026thinsp;\u0026plusmn;\u0026thinsp;0,04 \u003cb\u003e**\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSTZB\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0,12\u0026thinsp;\u0026plusmn;\u0026thinsp;0,01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e\u003cp\u003e0,14\u0026thinsp;\u0026plusmn;\u0026thinsp;0,01 \u003cb\u003e#\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003e3.7. Peak-to-peak amplitudes in AEP responses increased due to BB treatment.\u003c/h2\u003e\u003cp\u003eRecently, sensory system deficits, including auditory systems, have been found to be highly associated with AD progression, and impairments in sensory-related areas may occur before AD pathology becomes evident. Hearing loss due to AD pathology may occur, which may accelerate the development of AD and dementia [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In all experimental groups, peak-to-peak amplitude values of AEP components were measured over one negative (N1) and two positive potentials (P2) seen at the temporal left (T3) electrode region. P1N1 amplitude value was found to differ significantly between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;7,90, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18]. P1N1 peak-to-peak amplitude value of STZ group (6.49\u0026thinsp;\u0026plusmn;\u0026thinsp;1.03 \u0026micro;V) was found to decrease significantly compared to SH group (12.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.96 \u0026micro;V) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.01). N1P1 peak-to-peak amplitude value of STZB group (9.43\u0026thinsp;\u0026plusmn;\u0026thinsp;1.14 \u0026micro;V) tended to increase compared to STZ group, while there was no significant difference with SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA). N1P2 amplitude value was found to differ significantly between the groups [F(2,15)\u0026thinsp;=\u0026thinsp;23.62, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001, N\u0026thinsp;=\u0026thinsp;18]. It was found that the N1P2 peak-to-peak amplitude value of the STZ group (2,40\u0026thinsp;\u0026plusmn;\u0026thinsp;0,54 \u0026micro;V) was significantly decreased compared to the SH group (11.50\u0026thinsp;\u0026plusmn;\u0026thinsp;1.35 \u0026micro;V) (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The N1P2 peak-to-peak amplitude value of the STZB group (2.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54 \u0026micro;V) tended to increase compared to the STZ group, while no significant difference was found compared to the SH group (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). The decreases in peak-to-peak amplitude values ​​of STZ-induced AD rats reflect sensory system integrity (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC). This may occur due to decreased neuronal density or firing desynchronization. It has been observed that BB treatment may have a healing effect on the sensory system, especially by increasing the N1P2 amplitude, which is related to the processing and interpretation of auditory information.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003e3.8. Correlations of OLT Discrimination Index with Hippocampus IL-6 and NR2B\u003c/h2\u003e\u003cp\u003ePearson correlation analysis was used to evaluate the relationship between OLT discrimination index and hippocampus IL-6 levels. As a result of the analysis, a negative relationship was found between OLT discrimination index and changes in hippocampus IL-6 levels (Pearson r= -0.667, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). According to the results of the correlation analysis, it can be concluded that there is a significant decrease in OLT discrimination index due to the increase in hippocampus IL-6 levels. Pearson correlation analysis was used to evaluate the relationship between OLT discrimination index and hippocampus NR2B levels. As a result of the analysis, a positive relationship was found between OLT discrimination index and changes in hippocampus NR2B levels (Pearson r\u0026thinsp;=\u0026thinsp;0,592, p\u0026thinsp;\u0026lt;\u0026thinsp;0.01, N\u0026thinsp;=\u0026thinsp;18) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB). According to the results of the correlation analysis, it can be concluded that there is a significant decrease in OLT discrimination index due to the increase in hippocampus NR2B levels.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. DİSCUSSİON","content":"\u003cp\u003eThis study aimed to elucidate the alterations of the KYN molecular pathway, long-term memory, and electrophysiological responses in the ICV-STZ sAD model and to examine the possible neuroprotective effects of BB against ICV-STZ-induced AD. The pathological changes induced by ICV injection of STZ resemble the features of sAD [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Studies have shown that a 2 mg/kg ICV-STZ dose causes significant cognitive impairment and neurodegeneration approximately 30 days after injection [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Since our study will evaluate the neurobiological mechanisms underlying long-term memory formation, behavioral tests were performed 30 days after ICV administration of 2 mg/kg STZ. This study also showed that the OLT and NOR discrimination index of the STZ group was significantly decreased compared to the SH group and long-term memory was impaired. The OLT assesses spatial learning that relies mainly on hippocampal activity, whereas the NOR reflects nonspatial learning of object identity that relies on multiple brain regions [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eChronic neuroinflammation induced by a series of proinflammatory cytokines such as IL-6 secreted by activated microglia and astrocytes is widely accepted to be an early and persistent feature of the AD brain [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] and is assumed to be responsible for the development of cognitive impairment seen in AD [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. In a previous study, AD patients were found to have high IL-6 levels in both brain and plasma, and IL-6 expression was positively associated with AD pathology and declines in cognitive performance [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Our study also showed that IL-6 levels were similarly significantly increased in the examined brain regions in STZ rats compared to the SH group. Furthermore, a significant negative correlation was found between the OLT discrimination index and hippocampal IL-6 levels in the STZ group rats.\u003c/p\u003e\u003cp\u003eIt is known that the enzymes of the KYN pathway are activated by inflammation. In particular, IL-6 can independently activate IDO and enhance the metabolic pathways from TRP to QA. Therefore, it is thought that neuroinflammation may exert a regulatory effect on AD progression via TRP and TRP metabolites. Indeed, it has been shown that inflammatory cytokines can increase KYN production when they lead to IDO1 activation, which can lead to an increase in the KYN/TRP ratio [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Increased IDO activity increases KYN metabolite production and possible TRP depletion [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The resulting increase in the KYN/TRP ratio indicates the activation and participation of IDO enzyme [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. This increase in the KYN/TRP ratio is considered one of the hallmarks of neuroinflammation in AD studies and suggests increased TRP metabolism in AD patients [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The overactivated KYN pathway may lead to overproduction of the excitotoxin QA via microglia activation [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. It is known that QA also induces apoptosis in astrocytes and is closely related to the formation of Aβ and p-tau in the brain [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. In addition, the excitotoxin QA is known to innervate many NMDARs, including NR2B subunits, which are known to play an important role in learning, memory, synaptic plasticity, and neuronal pattern formation [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. NMDARs, mainly located in the postsynaptic region, are glutamate receptors that regulate calcium influx into neurons. NR2Bs are mainly extrasynaptic, and their activation is associated with cell death and neurodegeneration. Aβ has been observed to cause a significant increase in calcium release in NR2B-containing NMDAR in cortical and hippocampal neurons. Furthermore, NMDA receptors containing the NR2B subunit have been shown to be dysregulated by Aβ1-42s, impairing glutamatergic synaptic transmission, which parallels early cognitive deficits. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. NR2B activation may be associated with the pathological progression of AD. Indeed, aberrant and synergistic activation of NMDAR including NR2B at extrasynaptic sites by glutamate and Aβ has been demonstrated in AD [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Therefore, increased QA levels due to inflammation are likely to damage neurons in brain regions through NMDARs, impairing learning and memory, as well as synaptic plasticity KYNA is known as one of the neuroprotective metabolites of the KYN pathway, which can antagonize excitatory neurotoxicity through NMDAR-mediated antagonism and has antioxidant effects [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. It has been shown that increasing KYNA levels in AD mouse models can prevent both spatial memory deficits and synaptic loss [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. KYNA also has immunomodulatory properties. It exhibits anti-inflammatory effects in inflammatory conditions and plays an important role as an antioxidant and ROS scavenger [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. In our study, no significant difference was observed in TRP levels and KYN/TRP ratios in all brain regions examined in the STZ group sAD group rats compared to the SH group, while significant increases were found in KYN, excitotoxin QA, mitochondrial apoptotic marker caspase-3, NR2B and Tau levels, consistent with literature results. Similarly, a significant increase in Aβ1\u0026ndash;42 levels was observed in the temporal regions in the STZ group compared to the SH group. Therefore, it can be thought that increased neuroinflammation in AD disease may lead to excessive stimulation of NMDARs and secondary increases in neuronal calcium levels due to excessive production of excitotoxin QA due to excessive activity of the KYN pathway, which may be followed by activation of apoptotic pathways and cell death. Furthermore, in contrast to the observed increase in QA, the neuroprotective KYNA levels in the examined brain regions of the STZ group rats were also found to be significantly reduced compared to the SH group.\u003c/p\u003e\u003cp\u003eBB is essential because it is a natural product with high nutritional and medicinal value [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. In addition, it is known to be the most powerful antioxidant bee product. Inflammation is a common underlying cause of serious diseases because it initiates a pathogenic cascade such as metabolic pathway failure, tissue damage and even necrosis and apoptosis [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. A study comparing the effects of all bee products on chronic inflammation showed that pollen and BB had the highest anti-inflammatory effect and significantly reduced pro-inflammatory IL-6 levels [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. In addition, a study conducted in 2025 found that BB application reduced gastric ulcer by reducing IL-6 and caspase-3 levels and had a reducing effect on inflammation and apoptosis [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. However, there is a gap in the literature in terms of studies examining the effects of BB on the brain. In our study, it was shown that BB administration significantly decreased hippocampal IL-6 and caspase-3 levels in STZB rats compared to STZ rats and was not different from the SH group. In addition, the OLT discrimination index of the STZB group was significantly higher than that of the STZ group, indicating the potential to improve cognitive functions. As a result, it was concluded that BB treatment could also improve long-term location memory and prevent apoptotic activity. In addition, when the effect of this effect on the KYN pathway and its metabolites was examined, it was found that KYN and QA levels were significantly decreased in the temporal regions of the STZB group rats, while the levels of the neuroprotective metabolite KYNA were significantly increased in both regions. In addition, Aβ and NR2B levels were found to be significantly decreased in both brain regions in STZB rats compared to STZ rats. Mice overexpressing NR2B have been shown to have enhanced facilitated synaptic plasticity and enhanced learning and memory tasks [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. NR2B receptors prolong the slow reverberant neural dynamics required for working memory [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e]. In our study, NR2B levels in the hippocampal regions of STZB group rats were found to be positively correlated with the OLT discrimination index reflecting hippocampal learning.\u003c/p\u003e\u003cp\u003eRecently, it has been observed that sensory system deteriorations are highly correlated with AD progression. Neuropathological changes in sensory-related areas before AD pathology is observed in memory-related regions [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] can be seen even before cognitive symptoms. In the APP/PS1 mouse model of AD, decreased auditory brainstem response (ABR) at 3 months of age [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], and spatial learning deficits occurred at 6\u0026ndash;7 months of age [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Therefore, this decline in auditory function that may occur in the early stages of AD may provide important information for the early detection and development of the disease. KYN pathway metabolites affect neural processes including synaptic plasticity, neurotransmission, and neurogenesis. QA toxicity has been identified as one of the critical factors of neuronal damage in AD [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. The occurrence of neuropathy with high levels of QA suggests that it may play an important role in the pathogenesis of neurological diseases. Both neuronal and astrocyte cytoskeletons are vulnerable to QA toxicity. QA causes axon-sparing lesions in neurons [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. For this purpose, our study also aimed to reveal the changes in auditory sensory networks in sAD and to evaluate the therapeutic effect of BB on AEP responses on the KYN pathway. P1N1 amplitude is associated with early sensory functions and physical properties of the stimulus such as intensity, frequency, spectral and temporal properties. N1P2 amplitude reflects sensory functions related to the processing and interpretation of auditory information [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. In our study, it was found that both P1N1 and N1P2 amplitudes were significantly decreased in the STZ group rats compared to the SH group rats. The initial waveforms of AEPs, which reflect neural activity in the auditory cortex and related brain regions, are largely sensory responses to stimuli and activities in the temporal cortex. Therefore, they reflect neural activity in the temporal cortex independent of cognitive activity [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Therefore, it is seen that there are impairments in sensory system integrity in our ICV-STZ rat model reflecting the sAD model. Significant decreases in P1N1 and N1P2 amplitudes in the temporal region, which is sensitive to neurodegeneration in the early stages of AD, may be due to disruptions in synchrony of neuronal firing or decreased neuronal density. When examining whether the learning and changes in the molecular pathway examined due to BB treatment had an effect on AEP responses, it was determined that the N1P2 peak-to-peak amplitude of the STZB group increased significantly compared to the STZ group, and the P1N1 peak-to-peak amplitude tended to increase. Therefore, these decreases in AEP sensory responses indicate that they may have the potential to be a useful biomarker in the detection of early stages of the disease and in the evaluation of the effectiveness of therapeutic agents.\u003c/p\u003e\u003cp\u003eStudies have shown that there are gender differences in the AD model induced by ICV-STZ. In general, it has been determined that female rats induced by ICV-STZ are more resistant to ICV-STZ damage and that there are gender differences in brain responses to expected changes. This finding clearly contradicts the knowledge that female rats are prone to AD disease [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. However, female rats are generally not preferred in STZ studies because it is thought that they may be resistant to the neurodegenerative effects of STZ due to hormonal oscillations of the estral cycle [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. In order to minimize this limitation, we also used male rats in our study. Despite the limitations of this experimental model, the results of our study suggest that the ICV-STZ model may be suitable for examining the contribution of AD pathology and electrophysiological changes.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eAD\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAlzheimer's Disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eAβ\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAmyloid-Beta\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eICV\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eIntracerebroventricular\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eOD\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eOptical Density\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eAEP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eAuditory evoked potential\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eERP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eEvent-Related Potentials\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eEP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eEvoked Potentials\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eKYN\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eKynurenine\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eTRP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eTryptophan\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eTDO\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eTryptophan 2,3-dioxygenase\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eIDO\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eIndolamine 2,3-dioxygenase\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eQA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eQuinolinic acid\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eNMDA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eN-methyl-D-aspartate\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eNMDAR\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eN-methyl-D-aspartate Receptor\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eKYNA\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eKynurenic Acid\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eBB\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eBee Bread\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eSTZ\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eStreptozotocin\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003esAD\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eSporadic Alzheimer\u0026rsquo;a Disease\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eISI\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eInterstimulus Interval\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003ei.p.\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eIntraperitoneal\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eHRP\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eHorseradish Peroxidase\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv class=\"DefinitionListEntry\"\u003e\u003cdiv class=\"Term\"\u003e\u003cb\u003eIL-6\u003c/b\u003e\u003c/div\u003e\u003cdiv class=\"Description\"\u003e\u003cp\u003eInterleukin-6\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflict of Interest\u003c/h2\u003e\u003cp\u003eThe authors report no conflicts of interest in this work.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthics Approval\u003c/strong\u003e\u003cp\u003e Ethical approval for this work was obtained from Akdeniz University Local Committee on Animal Research Ethics (ethics approval ID: 1656/2023.12.001).\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eClinical trial number\u003c/h2\u003e\u003cp\u003eNot applicable\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConsent to Participate\u003c/h2\u003e\u003cp\u003eNot applicable.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eConsent for Publication\u003c/strong\u003e\u003cp\u003eNot applicable.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis study was not supported by any funding.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eA.D.A. and D.K. generated the rat models. E.A. analyzed ELISA's data. A.D.A. wrote the main manuscript text and prepared figures and table. A.D.A, E.A. and D.K. were involved in data interpretation, critically reviewed and provided their final approval of the manuscript, and agreed to be accountable for the work.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eNot applicable.\u003c/p\u003e\u003ch2\u003eAvailability of Data and Materials\u003c/h2\u003e\u003cp\u003eThe data supporting this study's findings are available from the corresponding author, upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSwords GM, Nguyen LT, Mudar RA, Llano DA: Auditory system dysfunction in Alzheimer disease and its prodromal states: A review. \u003cem\u003eAgeing Res Rev\u003c/em\u003e 2018, 44:49\u0026ndash;59.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGurevicius K, Lipponen A, Tanila H: Increased cortical and thalamic excitability in freely moving APPswe/PS1dE9 mice modeling epileptic activity associated with Alzheimer's disease. \u003cem\u003eCereb Cortex\u003c/em\u003e 2013, 23(5):1148\u0026ndash;1158.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMei L, Liu LM, Chen K, Zhao HB: Early Functional and Cognitive Declines Measured by Auditory-Evoked Cortical Potentials in Mice With Alzheimer's Disease. \u003cem\u003eFront Aging Neurosci\u003c/em\u003e 2021, 13:710317.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMurphy C: Olfactory and other sensory impairments in Alzheimer disease. \u003cem\u003eNat Rev Neurol\u003c/em\u003e 2019, 15(1):11\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMorrison C, Rabipour S, Knoefel F, Sheppard C, Taler V: Auditory Event-related Potentials in Mild Cognitive Impairment and Alzheimer's Disease. \u003cem\u003eCurr Alzheimer Res\u003c/em\u003e 2018, 15(8):702\u0026ndash;715.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIgnatious E, Azam S, Jonkman M, De Boer F: Frequency and Time Domain Analysis of EEG Based Auditory Evoked Potentials to Detect Binaural Hearing in Noise. \u003cem\u003eJ Clin Med\u003c/em\u003e 2023, 12(13).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKim B, Shin J, Kim Y, Choi JH: Destruction of ERP responses to deviance in an auditory oddball paradigm in amyloid infusion mice with memory deficits. \u003cem\u003ePLoS One\u003c/em\u003e 2020, 15(3):e0230277.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBabiloni C, Blinowska K, Bonanni L, Cichocki A, De Haan W, Del Percio C, Dubois B, Escudero J, Fernandez A, Frisoni G \u003cem\u003eet al\u003c/em\u003e: What electrophysiology tells us about Alzheimer's disease: a window into the synchronization and connectivity of brain neurons. \u003cem\u003eNeurobiol Aging\u003c/em\u003e 2020, 85:58\u0026ndash;73.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang J, Ikonen S, Gurevicius K, Van Groen T, Tanila H: Altered auditory-evoked potentials in mice carrying mutated human amyloid precursor protein and presenilin-1 transgenes. \u003cem\u003eNeuroscience\u003c/em\u003e 2003, 116(2):511\u0026ndash;517.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStoiljkovic M, Kelley C, Stutz B, Horvath TL, Hajos M: Altered Cortical and Hippocampal Excitability in TgF344-AD Rats Modeling Alzheimer's Disease Pathology. \u003cem\u003eCereb Cortex\u003c/em\u003e 2019, 29(6):2716\u0026ndash;2727.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eCortes Malagon EM, Lopez Ornelas A, Olvera Gomez I, Bonilla Delgado J: The Kynurenine Pathway, Aryl Hydrocarbon Receptor, and Alzheimer's Disease. \u003cem\u003eBrain Sci\u003c/em\u003e 2024, 14(9).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiang Y, Xie S, He Y, Xu M, Qiao X, Zhu Y, Wu W: Kynurenine Pathway Metabolites as Biomarkers in Alzheimer's Disease. \u003cem\u003eDis Markers\u003c/em\u003e 2022, 2022:9484217.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBakour M, Laaroussi H, Ousaaid D, El Ghouizi A, Es-Safi I, Mechchate H, Lyoussi B: Bee Bread as a Promising Source of Bioactive Molecules and Functional Properties: An Up-To-Date Review. \u003cem\u003eAntibiotics (Basel)\u003c/em\u003e 2022, 11(2).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGiovanini de Oliveira Sartori A, Martelli Chaib Saliba AS, Seneda Martarello N, Goldoni Lazarini J, Pedroso Gomes do Amaral JE, Fernandes Pinto da Luz C, Alencar SM: Changes in phenolic profile and anti-inflammatory activity of Baccharis beebread during gastrointestinal digestion/intestinal permeability in vitro. \u003cem\u003eFood Chem\u003c/em\u003e 2024, 432:137234.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStaroň M, Alkassab AT, Sabo R, Demkov\u0026aacute; L, Valenč\u0026aacute;kov\u0026aacute; A, Michalko M, Leg\u0026aacute;th J, Pistorius J, Sabov\u0026aacute; L: Higher early than late-season residue load of pesticides in honey bee bread in Slovakia. \u003cem\u003eApidologie\u003c/em\u003e 2024, 55(4):41.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eClarkson PM, Thompson HS: Antioxidants: what role do they play in physical activity and health? \u003cem\u003eAm J Clin Nutr\u003c/em\u003e 2000, 72(2 Suppl):637S-646S.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGirgin G, Baydar T, Ledochowski M, Schennach H, Bolukbasi DN, Sorkun K, Salih B, Sahin G, Fuchs D: Immunomodulatory effects of Turkish propolis: changes in neopterin release and tryptophan degradation. \u003cem\u003eImmunobiology\u003c/em\u003e 2009, 214(2):129\u0026ndash;134.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePan S, Zhang Y, Ye T, Kong Y, Cui X, Yuan S, Liu J, Zhang Y: A High-Tryptophan Diet Alleviated Cognitive Impairment and Neuroinflammation in APP/PS1 Mice through Activating Aryl Hydrocarbon Receptor via the Regulation of Gut Microbiota. \u003cem\u003eMol Nutr Food Res\u003c/em\u003e 2024, 68(2):e2300601.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrieb P: Intracerebroventricular Streptozotocin Injections as a Model of Alzheimer's Disease: in Search of a Relevant Mechanism. \u003cem\u003eMol Neurobiol\u003c/em\u003e 2016, 53(3):1741\u0026ndash;1752.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePlaschke K, Kopitz J, Siegelin M, Schliebs R, Salkovic-Petrisic M, Riederer P, Hoyer S: Insulin-resistant brain state after intracerebroventricular streptozotocin injection exacerbates Alzheimer-like changes in Tg2576 AbetaPP-overexpressing mice. \u003cem\u003eJ Alzheimers Dis\u003c/em\u003e 2010, 19(2):691\u0026ndash;704.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKraska A, Santin MD, Dorieux O, Joseph-Mathurin N, Bourrin E, Petit F, Jan C, Chaigneau M, Hantraye P, Lestage P \u003cem\u003eet al\u003c/em\u003e: In vivo cross-sectional characterization of cerebral alterations induced by intracerebroventricular administration of streptozotocin. \u003cem\u003ePLoS One\u003c/em\u003e 2012, 7(9):e46196.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoreira-Silva D, Vizin RCL, Martins TMS, Ferreira TL, Almeida MC, Carrettiero DC: Intracerebral Injection of Streptozotocin to Model Alzheimer Disease in Rats. \u003cem\u003eBio Protoc\u003c/em\u003e 2019, 9(20):e3397.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDehghan-Shasaltaneh M, Naghdi N, Choopani S, Alizadeh L, Bolouri B, Masoudi-Nejad A, Riazi GH: Determination of the Best Concentration of Streptozotocin to Create a Diabetic Brain Using Histological Techniques. \u003cem\u003eJ Mol Neurosci\u003c/em\u003e 2016, 59(1):24\u0026ndash;35.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDoganyigit Z, Yakan B, Soylu M, Kaymak E, Okan A, Silici S: Histological, immunohistochemical and biochemical effects of bee bread on stomach tissue of obese rats. \u003cem\u003eBratisl Lek Listy\u003c/em\u003e 2020, 121(7):504\u0026ndash;511.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMoreira-Silva D, Carrettiero DC, Oliveira ASA, Rodrigues S, Dos Santos-Lopes J, Canas PM, Cunha RA, Almeida MC, Ferreira TL: Anandamide Effects in a Streptozotocin-Induced Alzheimer's Disease-Like Sporadic Dementia in Rats. \u003cem\u003eFront Neurosci\u003c/em\u003e 2018, 12:653.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMotzko-Soares ACP, Vizin RCL, Martins TMS, Hungaro ARO, Sato JR, Almeida MC, Carrettiero DC: Thermoregulatory profile of neurodegeneration-induced dementia of the Alzheimer's type using intracerebroventricular streptozotocin in rats. \u003cem\u003eActa Physiol (Oxf)\u003c/em\u003e 2018, 224(2):e13084.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVicente MC, Almeida MC, Bicego KC, Carrettiero DC, Gargaglioni LH: Hypercapnic and Hypoxic Respiratory Response During Wakefulness and Sleep in a Streptozotocin Model of Alzheimer's Disease in Rats. \u003cem\u003eJ Alzheimers Dis\u003c/em\u003e 2018, 65(4):1159\u0026ndash;1174.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLima RH, Rossato JI, Furini CR, Bevilaqua LR, Izquierdo I, Cammarota M: Infusion of protein synthesis inhibitors in the entorhinal cortex blocks consolidation but not reconsolidation of object recognition memory. \u003cem\u003eNeurobiol Learn Mem\u003c/em\u003e 2009, 91(4):466\u0026ndash;472.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAcun AD, Kantar D, Er H, Erkan O, Derin N, Yargicoglu P: Investigation of Cyclo-Z Therapeutic Effect on Insulin Pathway in Alzheimer's Rat Model: Biochemical and Electrophysiological Parameters. \u003cem\u003eMol Neurobiol\u003c/em\u003e 2023, 60(7):4030\u0026ndash;4048.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGulisano W, Maugeri D, Baltrons MA, Fa M, Amato A, Palmeri A, D'Adamio L, Grassi C, Devanand DP, Honig LS \u003cem\u003eet al\u003c/em\u003e: Role of Amyloid-beta and Tau Proteins in Alzheimer's Disease: Confuting the Amyloid Cascade. \u003cem\u003eJ Alzheimers Dis\u003c/em\u003e 2018, 64(s1):S611-S631.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGrochowska KM, Gomes GM, Raman R, Kaushik R, Sosulina L, Kaneko H, Oelschlegel AM, Yuanxiang P, Reyes-Resina I, Bayraktar G \u003cem\u003eet al\u003c/em\u003e: Jacob-induced transcriptional inactivation of CREB promotes Aβ-induced synapse loss in Alzheimer's disease. \u003cem\u003eEmbo j\u003c/em\u003e 2023, 42(4):e112453.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHeppner FL, Ransohoff RM, Becher B: Immune attack: the role of inflammation in Alzheimer disease. \u003cem\u003eNat Rev Neurosci\u003c/em\u003e 2015, 16(6):358\u0026ndash;372.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang WY, Tan MS, Yu JT, Tan L: Role of pro-inflammatory cytokines released from microglia in Alzheimer's disease. \u003cem\u003eAnn Transl Med\u003c/em\u003e 2015, 3(10):136.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStrasser B, Berger K, Fuchs D: Effects of a caloric restriction weight loss diet on tryptophan metabolism and inflammatory biomarkers in overweight adults. \u003cem\u003eEur J Nutr\u003c/em\u003e 2015, 54(1):101\u0026ndash;107.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDenninger JK, Smith BM, Kirby ED: Novel Object Recognition and Object Location Behavioral Testing in Mice on a Budget. \u003cem\u003eJ Vis Exp\u003c/em\u003e 2018(141).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSouza LC, Filho CB, Goes AT, Fabbro LD, de Gomes MG, Savegnago L, Oliveira MS, Jesse CR: Neuroprotective effect of physical exercise in a mouse model of Alzheimer's disease induced by beta-amyloid(1)(-)(4)(0) peptide. \u003cem\u003eNeurotox Res\u003c/em\u003e 2013, 24(2):148\u0026ndash;163.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLyra ESNM, Goncalves RA, Pascoal TA, Lima-Filho RAS, Resende EPF, Vieira ELM, Teixeira AL, de Souza LC, Peny JA, Fortuna JTS \u003cem\u003eet al\u003c/em\u003e: Pro-inflammatory interleukin-6 signaling links cognitive impairments and peripheral metabolic alterations in Alzheimer's disease. \u003cem\u003eTransl Psychiatry\u003c/em\u003e 2021, 11(1):251.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHuang YS, Ogbechi J, Clanchy FI, Williams RO, Stone TW: IDO and Kynurenine Metabolites in Peripheral and CNS Disorders. \u003cem\u003eFront Immunol\u003c/em\u003e 2020, 11:388.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChiu YC, Yang BH, Yang KC, Liu MN, Hu LY, Liou YJ, Chan LY, Chou YH: A study of tryptophan, kynurenine and serotonin transporter in first-episode drug-na\u0026iuml;ve major depressive disorder. \u003cem\u003ePsychiatry Res Neuroimaging\u003c/em\u003e 2021, 312:111296.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBadawy AA, Guillemin G: The Plasma [Kynurenine]/[Tryptophan] Ratio and Indoleamine 2,3-Dioxygenase: Time for Appraisal. \u003cem\u003eInt J Tryptophan Res\u003c/em\u003e 2019, 12:1178646919868978.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWidner B, Leblhuber F, Walli J, Tilz GP, Demel U, Fuchs D: Tryptophan degradation and immune activation in Alzheimer's disease. \u003cem\u003eJ Neural Transm (Vienna)\u003c/em\u003e 2000, 107(3):343\u0026ndash;353.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRahman A, Rao MS, Khan KM: Intraventricular infusion of quinolinic acid impairs spatial learning and memory in young rats: a novel mechanism of lead-induced neurotoxicity. \u003cem\u003eJ Neuroinflammation\u003c/em\u003e 2018, 15(1):263.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSharma VK, Singh TG, Prabhakar NK, Mannan A: Kynurenine Metabolism and Alzheimer's Disease: The Potential Targets and Approaches. \u003cem\u003eNeurochem Res\u003c/em\u003e 2022, 47(6):1459\u0026ndash;1476.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaich I, Lillo J, Rebassa JB, Capo T, Cordomi A, Reyes-Resina I, Pallas M, Navarro G: Dual Role of NMDAR Containing NR2A and NR2B Subunits in Alzheimer's Disease. \u003cem\u003eInt J Mol Sci\u003c/em\u003e 2024, 25(9).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBading H: Therapeutic targeting of the pathological triad of extrasynaptic NMDA receptor signaling in neurodegenerations. \u003cem\u003eJ Exp Med\u003c/em\u003e 2017, 214(3):569\u0026ndash;578.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLugo-Huitron R, Blanco-Ayala T, Ugalde-Muniz P, Carrillo-Mora P, Pedraza-Chaverri J, Silva-Adaya D, Maldonado PD, Torres I, Pinzon E, Ortiz-Islas E \u003cem\u003eet al\u003c/em\u003e: On the antioxidant properties of kynurenic acid: free radical scavenging activity and inhibition of oxidative stress. \u003cem\u003eNeurotoxicol Teratol\u003c/em\u003e 2011, 33(5):538\u0026ndash;547.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZwilling D, Huang SY, Sathyasaikumar KV, Notarangelo FM, Guidetti P, Wu HQ, Lee J, Truong J, Andrews-Zwilling Y, Hsieh EW \u003cem\u003eet al\u003c/em\u003e: Kynurenine 3-monooxygenase inhibition in blood ameliorates neurodegeneration. \u003cem\u003eCell\u003c/em\u003e 2011, 145(6):863\u0026ndash;874.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWirthgen E, Hoeflich A, Rebl A, Gunther J: Kynurenic Acid: The Janus-Faced Role of an Immunomodulatory Tryptophan Metabolite and Its Link to Pathological Conditions. \u003cem\u003eFront Immunol\u003c/em\u003e 2017, 8:1957.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDos Santos NCL, Malta SM, Franco RR, Silva HCG, Silva MH, Rodrigues TS, de Oliveira RM, Araujo TN, Augusto SC, Espindola FS \u003cem\u003eet al\u003c/em\u003e: Antioxidant and anti-Alzheimer's potential of Tetragonisca angustula (Jatai) stingless bee pollen. \u003cem\u003eSci Rep\u003c/em\u003e 2024, 14(1):308.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEl-Seedi HR, Eid N, Abd El-Wahed AA, Rateb ME, Afifi HS, Algethami AF, Zhao C, Al Naggar Y, Alsharif SM, Tahir HE \u003cem\u003eet al\u003c/em\u003e: Honey Bee Products: Preclinical and Clinical Studies of Their Anti-inflammatory and Immunomodulatory Properties. \u003cem\u003eFront Nutr\u003c/em\u003e 2021, 8:761267.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKosedag M, Gulaboglu M: Pollen and bee bread expressed highest anti-inflammatory activities among bee products in chronic inflammation: an experimental study with cotton pellet granuloma in rats. \u003cem\u003eInflammopharmacology\u003c/em\u003e 2023, 31(4):1967\u0026ndash;1975.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eColak H, Sariyer ET, Yuksel M, Polat IO, Cikler E, Oner N, Karakoyun B: Bee bread shows therapeutic and protective effects by alleviating inflammation, oxidative stress, and apoptosis on acetic acid-induced gastric ulcer in rats. \u003cem\u003eArch Physiol Biochem\u003c/em\u003e 2025:1\u0026ndash;11.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTang YP, Shimizu E, Dube GR, Rampon C, Kerchner GA, Zhuo M, Liu G, Tsien JZ: Genetic enhancement of learning and memory in mice. \u003cem\u003eNature\u003c/em\u003e 1999, 401(6748):63\u0026ndash;69.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang M, Yang Y, Wang CJ, Gamo NJ, Jin LE, Mazer JA, Morrison JH, Wang XJ, Arnsten AF: NMDA receptors subserve persistent neuronal firing during working memory in dorsolateral prefrontal cortex. \u003cem\u003eNeuron\u003c/em\u003e 2013, 77(4):736\u0026ndash;749.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiu Y, Fang S, Liu LM, Zhu Y, Li CR, Chen K, Zhao HB: Hearing loss is an early biomarker in APP/PS1 Alzheimer's disease mice. \u003cem\u003eNeurosci Lett\u003c/em\u003e 2020, 717:134705.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOrdonez-Gutierrez L, Fernandez-Perez I, Herrera JL, Anton M, Benito-Cuesta I, Wandosell F: AbetaPP/PS1 Transgenic Mice Show Sex Differences in the Cerebellum Associated with Aging. \u003cem\u003eJ Alzheimers Dis\u003c/em\u003e 2016, 54(2):645\u0026ndash;656.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGuillemin GJ, Brew BJ: Implications of the kynurenine pathway and quinolinic acid in Alzheimer's disease. \u003cem\u003eRedox Rep\u003c/em\u003e 2002, 7(4):199\u0026ndash;206.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNaatanen R, Paavilainen P, Alho K, Reinikainen K, Sams M: The mismatch negativity to intensity changes in an auditory stimulus sequence. \u003cem\u003eElectroencephalogr Clin Neurophysiol Suppl\u003c/em\u003e 1987, 40:125\u0026ndash;131.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBiasibetti R, Almeida Dos Santos JP, Rodrigues L, Wartchow KM, Suardi LZ, Nardin P, Selistre NG, Vazquez D, Goncalves CA: Hippocampal changes in STZ-model of Alzheimer's disease are dependent on sex. \u003cem\u003eBehav Brain Res\u003c/em\u003e 2017, 316:205\u0026ndash;214.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBao J, Mahaman YAR, Liu R, Wang JZ, Zhang Z, Zhang B, Wang X: Sex Differences in the Cognitive and Hippocampal Effects of Streptozotocin in an Animal Model of Sporadic AD. \u003cem\u003eFront Aging Neurosci\u003c/em\u003e 2017, 9:347.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bratislava-medical-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Bratislava Medical Journal](https://link.springer.com/journal/44411)","snPcode":"44411","submissionUrl":"https://submission.springernature.com/new-submission/44411/3","title":"Bratislava Medical Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Alzheimer’s Disease, Kynurenine Pathway, Bee Bread, Object Location Test, Auditory Evoked Potentials","lastPublishedDoi":"10.21203/rs.3.rs-7268712/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7268712/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAlzheimer's disease (AD) is currently a global concern, and treating its current symptoms and slowing its progression is an important goal. To this end, identifying biochemical mechanisms that have the potential to prevent and improve the pathology of the disease is a priority. The response of the central nervous system to pathological insults may be neuroinflammation. Kynurenine (KYN) pathway metabolites, which are closely related to neuroinflammation, may have the potential to affect many neural processes such as synaptic plasticity, neurotransmission, antioxidant mechanisms, and neurogenesis. In addition, it has been recently shown that there is a strong correlation between sensory system deterioration and AD progression and that neuropathological changes in sensory regions can be detected before changes in memory-related regions. For this purpose, our study aimed to investigate the effects of changes in the Kynurenine (KYN) pathway on cognitive functions and auditory sensory system functions in an experimental AD model and the effects of bee bread (BB), known to have anti-inflammatory properties, on these parameters. It was shown that BB has the potential to improve memory by exerting a healing effect on neuroinflammation, apoptosis, and the KYN pathway, and also has a therapeutic effect on auditory sensory system functions, reducing sensory system integrity disorders. These results highlight the ability of BB to prevent neurotoxic effects associated with sAD. It may be a potential protector as a food supplement for AD neuropathological health, and further studies are needed for this purpose.\u003c/p\u003e","manuscriptTitle":"Bee Bread Shows Protective Effects in a Streptozotocin-Induced Alzheimer's Disease Rat Model","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-12 12:52:01","doi":"10.21203/rs.3.rs-7268712/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-27T15:00:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-26T17:55:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-21T06:56:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"284371108834319057718812876483196391286","date":"2025-08-14T00:45:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"22803611560579782463529261432510062109","date":"2025-08-12T06:39:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"187211620863606799133198360490506378342","date":"2025-08-12T05:36:58+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"158276344115314953043194014764857410669","date":"2025-08-08T02:45:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"60148001615594331342972661212370754580","date":"2025-08-07T13:06:53+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"72752377436090056148514704087433332751","date":"2025-08-07T13:06:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281353787650683657131359800280737887376","date":"2025-08-07T05:40:04+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-07T05:34:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-01T14:21:36+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-01T14:20:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Bratislava Medical Journal","date":"2025-08-01T07:44:10+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bratislava-medical-journal","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Bratislava Medical Journal](https://link.springer.com/journal/44411)","snPcode":"44411","submissionUrl":"https://submission.springernature.com/new-submission/44411/3","title":"Bratislava Medical Journal","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"c3eaa213-7206-44a6-ae06-60ad9bac1b31","owner":[],"postedDate":"August 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-07T12:09:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-08-12 12:52:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7268712","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7268712","identity":"rs-7268712","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}