Vagus nerve stimulation modulates synaptic plasticity induced by cocaine- seeking in reward-related circuitry

Vagus nerve stimulation modulates synaptic plasticity induced by cocaine- seeking in reward-related circuitry | 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 Article Vagus nerve stimulation modulates synaptic plasticity induced by cocaine- seeking in reward-related circuitry Reza Arezoomandan, Lily Vu, Christopher Driskill, Sven Kroener This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7014180/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 11 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract Cocaine use alters brain networks and connections, impairing inhibitory control over drug-seeking. Cortical-limbic circuits, including the infralimbic (IL), prelimbic (PL) cortices, and basolateral amygdala (BLA), regulate extinction learning and drug-seeking via projections to the nucleus accumbens (NAc). Vagus nerve stimulation (VNS) paired with extinction enhances learning and reduces reinstatement, but its effects on extinction-related networks remain unclear. This study examined how cocaine and VNS affect plasticity in relapse-related pathways. Evoked local field potentials (eLFP) were recorded in the IL, NAc core, and NAc shell following self-administration or reinstatement sessions. In the BLA-IL pathway, cocaine-treated (COC) and sham-VNS (SHAM) groups exhibited the highest baseline eLFP amplitudes and increased long-term potentiation (LTP) induction, which VNS restored to yoked-saline (YS) levels. In the PL-NAc core pathway, high-frequency stimulation (HFS) had no effect on EFPs in VNS-treated animals, significantly differing from the long-term depression (LTD) observed in COC and SHAM groups, which had the highest baseline eLFP amplitudes. In the IL-NAc shell pathway, VNS-treated rats displayed the largest baseline amplitudes, and unlike YS, COC, and SHAM groups, HFS in the IL induced persistent LTP in the NAc shell. These findings suggest cocaine use and craving induce maladaptive neuroplasticity within cortical-limbic circuits, and VNS may modulate these changes, contributing its beneficial effects in preventing reinstatement. Biological sciences/Neuroscience Biological sciences/Physiology Cocaine Vagus nerve stimulation Local field potentials LTP Prefrontal cortex Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Cocaine addiction is a chronic and relapsing disorder characterized by maladaptive neuroplasticity within cortical-limbic circuits. These circuits, which include the prefrontal cortex (PFC), nucleus accumbens (NAc), and amygdala, are critical for regulating reward processing, emotional responses, and decision-making 1 . Chronic cocaine exposure disrupts the balance of synaptic plasticity in these pathways, including impairment in induction of LTP and LTD, resulting in heightened sensitivity to drug-related cues and impaired behavioral control 1 – 3 . These changes underlie the persistent drug-seeking behaviors and high relapse rates observed in cocaine addiction 1 . The infralimbic cortex (IL) and prelimbic cortex (PL), two subregions of the PFC, play largely opposing roles in drug-seeking behavior. The IL inhibits drug-seeking by projecting to the NAc shell or PL, while the PL drives drug-seeking and facilitates reinstatement of drug-seeking through its connections to the NAc core 4 . The basolateral amygdala (BLA) is another key structure in this network, encoding the salience of drug-related cues and influencing the activity of other brain areas involved in drug-seeking including PFC and NAc 5 – 7 . Chronic cocaine use induces significant molecular and cellular changes in reward-related brain regions, leading to disruptions in normal brain function, including impairments in synaptic plasticity 1 . Cocaine induces neuroadaptations within cortical-limbic pathways, which is strongly implicated in the persistence of addictive behaviors. Cocaine induces metaplasticity, a phenomenon linked to increased vulnerability to relapse 2 , 8 . Metaplasticity, defined as a change in threshold or rule for inducing synaptic plasticity, represents a higher-order form of plasticity that is not expressed as a change in synaptic transmission efficacy but rather as a change in the direction or degree of plasticity induced by specific stimulation patterns 9 . This concept is essential for understanding drug addiction mechanisms. Effective treatments for relapse should normalize synaptic transmission and reverse cocaine-induced metaplasticity in reward-related brain areas. Vagus nerve stimulation (VNS) is FDA-approved for use in epilepsy and depression and considered for the treatment of an expanding range of psychiatric diseases including substance use disorders 10 . VNS causes the release of several neuromodulators which modulate cortical plasticity. This plasticity can increase learning and memory in rats 11 , 12 and humans 13 . Recently we showed that VNS facilitates extinction and reduces cue‐induced reinstatement in cocaine self‐administering rats 14 – 16 . Also, we have shown that pairing VNS with extinction of conditioned fear potentiates evoked field responses in the BLA, resulting in LTP in the IL-BLA pathway, suggesting that VNS promotes plasticity in this pathway to facilitate extinction of conditioned fear responses 17 . VNS has been shown to reduce relapse in reinstatement models of drug-seeking as well as modulate synaptic transmission and metaplasticity 14 – 19 . Here we determined how cocaine self-administration and reinstatement induce metaplasticity in key cortical-limbic circuits involved in drug-seeking, including the BLA-IL, IL-NAc shell and PL-NAc core pathways. We also show that extinction training paired with VNS can modulate these changes to reduce reinstatement. Results VNS facilitates extinction and reduces cue-induced reinstatement To examine the effects of cocaine self-administration on neuroplasticity, 30 rats of both sexes (16 males; 14 females) were trained to self-administer either cocaine (COC, n = 16) or which received yoked-saline infusions (YS, n = 14) for at least 10 days. Figure 1 A shows active lever presses in a cohort of COS and YS rats. Cocaine self-administering animals consistently exhibited significantly higher active lever responses compared to yoked-saline animals (F(1, 28) = 46.56, P < 0.0001). To evaluate the impact of VNS on drug-seeking behavior, a separate group of rats underwent cocaine self-administration for a minimum of 10 days, followed by 10 days of extinction training paired with either VNS (n = 18, 10 males and 8 females) or sham stimulation (SHAM; n = 16, 9 males and 7 females). After 10 days of extinction, drug-seeking behavior was assessed in a cued reinstatement session through the presentation of conditioned drug cues (Fig. 1 B). A two-way ANOVA revealed no significant differences between groups in active lever responses during the final 10 days of self-administration (F (1, 33) = 0.013, P = 0.9). During extinction training and the cue-induced reinstatement session, responses at the previously active lever were used as a measure of extinction learning. A repeated-measures two-way ANOVA, with time (sessions) and treatment (SHAM or VNS) as factors, revealed a significant effect of extinction (main effect of time: F (9, 330) = 57.67, P < 0.0001), a significant difference between treatment groups (main effect of treatment: F (1, 330) = 46.59, p < 0.0001), and a significant interaction between these factors (F (9, 330) = 8.52, P < 0.0001; Fig. 1 B). Post hoc analysis showed that rats receiving VNS pressed the active lever significantly less than the sham group on the first two days of extinction (Day 1, P < 0.0001, Fig. 1 B; Day 2, P < 0.0001, Fig. 1 B, C), suggesting that VNS facilitates extinction learning. Twenty-four hours after the final extinction session, drug-seeking was assessed in a cue-induced reinstatement session. An unpaired t-test revealed that VNS animals exhibited significantly fewer responses on the previously active lever during cue-induced reinstatement (t(32) = 7.79, P < 0.0001; Fig. 1 B, D), demonstrating the effectiveness of VNS in inhibiting cue-induced reinstatement. VNS reverses drug-induced LTP in the pathway from the BLA to the IL To determine how cocaine self-administration, reinstatement, and VNS influence synaptic plasticity in the pathway from the BLA to the IL, we performed in vivo recordings in anesthetized rats following the final session of either self-administration or reinstatement in the four treatment groups (YS, n = 6; COC, n = 9; SHAM, n = 6; VNS, n = 9). We placed a stimulation electrode into the BLA and performed recordings of eLFPs in the IL (Fig. 2 A). Single-pulse stimulation in the BLA evoked a characteristic field potential response in the IL which peaked after 10ms (Fig. 2 B). A two-way ANOVA examining the current-voltage relationship of eLFPs revealed a main effect of I–O curves (F (3, 140) = 7.185; P = 0.0002, Fig. 2 C). In the BLA-IL pathway, cocaine self-administration and cue-induced reinstatement significantly altered the current-voltage relationship of eLFPs, resulting in a marked increase in baseline responses relative to eLFPs in YS rats ( P < 0.05). VNS treatment reversed these changes and reduced baseline responses, resulting in no significant difference between the VNS and YS groups (Fig. 2 C). After obtaining stable baseline recordings for a minimum of 10 minutes we used HFS in the BLA to induce LTP to further examine the effect of drug-seeking and VNS treatment on synaptic plasticity in this pathway. Tetanic stimulation delivered to the BLA induced a persistent increase in amplitude of BLA-evoked responses in the IL in all groups (Fig. 2 D- H); however, the magnitude of LTP was significantly greater in COC rats compared to LTP in the other groups F (3, 50) = 6.827; P = 0.0006, Fig. 2 E, H). SHAM animals exhibited smaller LTP compared to rats in the COC group ( P = 0.021; Fig. 2 F, H), but larger amplitudes than rats in the YS group ( P = 0.024; 2H). Pairing extinction training with VNS significantly reversed the drug-seeking-induced LTP, restoring it to YS control levels (Fig. 2 G, H). These results show that drug-seeking behavior strengthens this pathway, and that extinction training by itself can partially reverse these changes. Pairing extinction training with VNS further reduces drug-induced changes resulting in plasticity similar to that observed in YS controls. VNS modulates drug-induced changes in synaptic plasticity in the PL-NAc core pathway The PL can drive reinstatement of drug-seeking via its projection to the NAc core 4 . To determine how cocaine self-administration and cue-induced reinstatement alter synaptic plasticity in the PL-NAc core pathway, and how pairing extinction training with VNS can modulate these changes, we recorded eLFPs in this pathway in our four treatment groups (YS, n = 6; COC, n = 7; SHAM, n = 9; VNS, n = 9) after the last self-administration session or the reinstatement session, respectively (Fig. 1 A, B, 3 A). Stimulation of the PL elicited negative field potentials in the NAc core, which peaked after 20–25ms (Fig. 3 B). The current-voltage relationship between stimulation intensity in the PL and eLFP amplitude in the NAc core were significantly different between the four groups F (3, 135) = 6.509; P = 0.0004; Fig. 3 C). The COC and SHAM groups showed increased baseline eLFP amplitudes compared to the YS group ( P < 0.05). In addition, eLFP amplitudes in the VNS group were significantly reduced compared to those in COC and SHAM rats ( P < 0.05). (Fig. 3 C). To further examine the effect of drug-seeking and VNS treatment on synaptic plasticity we used HFS (50 Hz) of the PL to induce LTP in this pathway. Our results showed a main effect of treatment F (3, 56) = 26.04, P < 0.0001). Consistent with previous reports 2 , this protocol induced synaptic plasticity in YS rats ( P < 0.0001, Fig. 3 D, H). In contrast, in COC and SHAM animals, HFS consistently induced LTD rather than LTP in this pathway ( P = 0.012 and P = 0.0005, respectively, Fig. 3 E, F, H). In VNS rats, HFS did not induce synaptic plasticity (baseline vs. post HFS, P = 0.9), which was significantly different from the LTD induced in COC and SHAM-treated rats ( P = 0.025 and P = 0.001, respectively, Fig. 3 F, H). These results show that VNS can modulate drug-seeking induced changes in metaplasticity in the PL-NAc core pathway. VNS Induces synaptic plasticity in the IL-NAc shell pathway The IL facilitates extinction learning and suppresses cocaine-seeking behavior through its projections to the NAc shell 20 . To determine how cocaine self-administration, reinstatement, and VNS influence synaptic plasticity we recorded eLFPs in this pathway in the four treatment groups after the last self-administration or the reinstatement session (YS, n = 8; COC, n = 9) or reinstatement (SHAM, n = 7; VNS, n = 8) (Fig. 4 A). IL stimulation elicited eLFPs in the NAc shell, characterized by a negative potential peaking at 10ms (Fig. 4 B). The shape, amplitude, and latency of these eLFPs were highly reproducible and remained stable over time. A two-way ANOVA assessing the relationship between stimulation intensity (0.2 mA–2.5 mA) and baseline eLFP amplitude revealed a significant main effect of treatment on I–O curves (F(3,144) = 19.91, P < 0.0001). Specifically, rats in the VNS group exhibited significantly larger baseline responses compared to YS (P < 0.05), as well as COC and SHAM rats (P < 0.01, Fig. 4 C). After obtaining stable baseline recordings, we applied HFS to induce LTP. In YS rats, HFS of the IL failed to induce synaptic plasticity in the NAc shell, showing no significant difference between baseline and post-HFS amplitudes ( P = 0. 0.88, Fig. 2 D, H). In both COC and SHAM rats, post-HFS amplitudes remained consistently lower, indicating that cocaine self-administration and reinstatement facilitated induction of LTD rather than LTP in this pathway ( P = 0.043 and P = 0.042 respectively, Fig. 2 E, F, H). In contrast, pairing extinction training with VNS modified metaplasticity in the NAc shell so that HFS of the IL induced LTP in the NAc shell compared to both the baseline and SHAM group ( P = 0.001 and P < 0.0001 respectively).Taken together, these findings demonstrate that both cocaine-seeking behavior and VNS significantly alter synaptic plasticity in the IL-to-NAc shell pathway (F (3, 56) = 4.475, P = 0.0069). While drug-seeking behavior weakens this pathway, pairing extinction training with VNS strengthens it. Discussion Corticolimbic pathways connecting the PFC, amygdala, and NAc play a crucial role in drug-seeking behavior by integrating emotional cues, reward anticipation, and decision-making 21 . Dysregulation in these pathways reinforces maladaptive behaviors and impairs inhibitory control, perpetuating addiction 1 , 2 . While extinction training can reverse drug-induced changes, it alone is often insufficient to prevent reinstatement. We replicate previous findings showing that pairing extinction training with VNS accelerates extinction learning during the initial session and reduces cue-induced reinstatement, suggesting enhanced consolidation of extinction memories 14 , 16 . We determined changes in synaptic metaplasticity induced by drug-taking and cue-induced reinstatement in key cortical-limbic circuits, including the BLA-IL, IL-NAc shell, and PL-NAc core pathways. We show that drug-seeking behavior disrupts synaptic plasticity in each of these circuits and that pairing extinction with VNS effectively reverses these neuroplastic changes in ways consistent with VNS-induced suppression of drug-seeking. The BLA mediates the consolidation of both cocaine-stimulus association and extinction learning, two processes with opposite effects on subsequent cue-induced cocaine-seeking behavior 5 . The BLA processes the salience of drug-related stimuli within the corticolimbic circuit 6 , contributing to cue-induced reinstatement of cocaine-seeking 22 , 23 . Inactivation of the BLA, along with dorsomedial PFC inactivation, inhibits conditioned cue-induced reinstatement of cocaine-seeking behavior 6 , while cocaine-associated cues trigger c-Fos activation in BLA-to-mPFC pathways 7 . The BLA also plays a crucial role in extinction of drug-seeking through its involvement in extinction memory consolidation and influence on related neural circuits 5 . Extinction of conditioned fear requires neuronal activity in the BLA 24 and IL 25 , as well as functional connectivity between the mPFC and amygdala 26 , 27 . However, how drug-seeking alters synaptic plasticity between the BLA and the IL remains unknown, and our LFP recordings are the first to directly examine synaptic changes in this pathway in-vivo. Our results show that both cocaine self-administration and cue-induced reinstatement paired with SHAM stimulation significantly strengthened baseline synaptic responses (measured as I-O curves) and enhanced LTP induction in the BLA-IL pathway. This suggests cocaine-seeking behavior hyperactivates this pathway to drive maladaptive cue-driven responses. How these changes in synaptic strength relate to the IL's role in extinction learning remains unclear. Extinction paired with SHAM stimulation partially reduced cocaine self-administration effects as the amplitude of LTP in SHAM-stimulated rats following reinstatement was significantly smaller than in the COC group (Fig. 2 H). Importantly, pairing extinction with VNS reversed both the increase in baseline responses in the BLA-IL projection and the amplification of LTP in this pathway that accompanied drug-seeking, resulting in only a small LTP resembling HFS-induced changes in synaptic plasticity seen in YS-control rats (Fig. 2 H). Projections from the BLA to the mPFC contact both pyramidal projection neurons 28 and inhibitory interneurons 29 . In the IL, interneuron activation drives robust feedforward inhibition 29 , so the overall impact of the BLA projection may be predominantly inhibitory. Thus, increased strength and plasticity in the BLA-IL projection induced by cocaine self-administration and reinstatement may lead to IL inhibition and increased drug-seeking behavior 4 . In contrast, extinction (alone or paired with VNS) may reduce this projection's strength, leading to IL disinhibition and improved extinction memory expression. The reduction in synaptic strength in the BLA-IL pathway following VNS is noteworthy for another reason: Several studies show that VNS potentiates synaptic responses relative to control conditions 17 , 30 or enhances LTP 31 . Our study provides the first evidence that pairing behavior with VNS can also lead to synaptic response weakening, even if other pathways' strength was enhanced in the same subject. The mechanisms remain unclear, but they underscore the pathway-specificity of VNS modulation. The NAc core regulates reward evaluation and motor activity. Drug-seeking is associated with increased excitability of PL-NAc core projecting neurons 32 , and drug-induced changes in PL-NAc glutamate transmission drive drug-taking, relapse, and withdrawal. Repeated cocaine exposure strengthens glutamatergic transmission in the PL-NAc pathway 2 , 33 , while PL inhibition can attenuate cue-induced reinstatement of cocaine seeking 34 . Multiple lines of evidence support that chronic cocaine exposure induces LTP-like changes in nucleus accumbens medium spiny neurons 2 , including increased AMPA/NMDA ratios of synaptic currents 35 , 36 , upregulated membrane insertion of AMAP receptors into synaptic membranes 37 , 38 , and heightened behavioral sensitivity to locally administered AMPA 39 , 40 . Consistent with these findings, we show that cocaine self-administration and reinstatement significantly increased baseline eLFP amplitudes relative to YS group levels, suggesting drug-seeking strengthened the PL-NAc core pathway. High frequency stimulation induced persistent LTP in YS control animals, consistent with previous findings 2 . In contrast, cocaine self-administration and reinstatement in SHAM-stimulated rats altered metaplasticity in this pathway, not only reducing LTP induction ability as previously shown 2 , but causing LTD emergence. This suggests LTP induction in this pathway occurs on a sliding scale where prior drug exposure creates a condition where synapses are already potentiated (in an LTP-like state, evidenced by increased baseline responses in I-O curves), making further potentiation difficult due to ceiling effects, while depression remains inducible 9 . Similar drug-induced deficits in LTP or LTD induction in the NAc core have been shown for cocaine 2 , 3 or heroin 41 . These synaptic changes likely underlie heightened sensitivity to drug-associated cues and increased relapse vulnerability 42 . Importantly, we show that VNS modulates drug-induced alterations in synaptic plasticity within the PL to NAc core pathway. Pairing extinction with VNS reduced baseline eLFP amplitudes compared to recordings in COC and SHAM-treated rats, suggesting VNS reversed drug-induced changes in synaptic strength. VNS also partially reversed drug-induced metaplasticity changes seen in SHAM or COC groups, so that in the VNS group, HFS did not result in LTD. Together, these VNS-induced changes may attenuate pathological neuroplasticity associated with addiction, restoring the circuit's capacity for bidirectional plasticity and countering the cocaine-induced "ceiling effect" that favors LTD over LTP. By normalizing exaggerated responsiveness to drug-associated cues, VNS might reduce the conditioned craving that drives relapse. The IL plays a crucial role in the consolidation and expression of extinction memories 43 – 45 , and it inhibits drug-seeking behavior through its projections to the NAc shell and/or the PL 4 , 46 , 47 . Cocaine-seeking induced by IL inactivation is reversed by concurrent inactivation of the PL or BLA, suggesting that during extinction expression, IL actively competes with the cocaine-seeking circuitry 4 . Extinction training induces plasticity in the IL-NAc shell projection 48 , 49 , increasing AMPA receptor expression in the NA shell, with GluA1 levels negatively correlating with reinstatement susceptibility 50 . Conversely, during drug seeking, activity in the IL-NAc shell connection may decrease 32 , 51 , enabling the return of drug-seeking behavior following extinction. Our results provide further support for these ideas as rats in both COC and SHAM groups showed LTD, suggesting that drug-seeking weakened this pathway, consistent with previous studies demonstrating that IL inactivation induces cocaine-seeking 44 . In contrast, VNS strengthened both the baseline response and increased metaplasticity in this pathway so that HFS of the IL caused pronounced LTP in the NAc shell. Together, these findings suggest drug-seeking behavior disrupts connections between the IL and NAc shell, whereas VNS strengthens the connection and enhances synaptic plasticity to aid extinction memory expression. Activation of ascending vagus nerve fibers triggers release of various neuromodulators, including norepinephrine, acetylcholine, and BDNF, within the central nervous system, resulting in widespread cortical and subcortical activation 52 – 57 . This release creates permissive conditions for synaptic plasticity, modulating cognitive and motivational states and influencing both sensory processing and encoding, as well as learning and memory-related processes 17 , 58 . Specifically, long-term VNS increases norepinephrine and dopamine levels in the PFC and NAc, potentially influencing addiction-related neuroplasticity 59 . VNS delivered during extinction from cocaine self-administration also increases BDNF levels in the mPFC, modulating glutamatergic transmission in the IL. Blocking TrkB receptors prevented both VNS' effect on synaptic transmission and its beneficial effects on cue-induced relapse behavior 60 . Consistent with our findings of VNS-induced network reorganization, studies in human patients with major depression indicate that VNS normalizes activity within the ventromedial prefrontal cortex, cingulate cortex, and limbic regions 61 and modulates pathways relevant for reward and motivation, strengthening the functional connectivity between the NAc, mPFC, and ACC 62 , 63 . The VNS-induced changes in metaplasticity in the three pathways examined in our study similarly enhance capacity for adaptive plasticity in the corticolimbic network and contribute to VNS' inhibitory effects on drug-seeking behavior (Fig. 5 ). Conclusion Our study suggests that VNS modulates drug-seeking behavior by modulating drug-induced neuroplasticity within key corticolimbic circuits. VNS effectively enhanced extinction learning and suppressed drug-seeking behavior by reversing maladaptive synaptic changes induced by cocaine use and reinstatement. Specifically, VNS strengthened the IL-NAc shell pathway, crucial for extinction memory expression, and partially reversed synaptic plasticity in the PL-NAc core pathway that drives drug-seeking. These findings support the idea that VNS might serve as an adjunct to addiction treatment, offering a means for targeted synaptic plasticity to reduce relapse vulnerability. Materials and methods Animals and surgical procedures Male and female Sprague Dawley rats (Envigo, ≥ 90 days old) were assigned to four groups: cocaine self-administration (COC, n = 16), yoked-saline control (YS, n = 14), and cocaine self-administration followed by extinction training with either sham-stimulation (SHAM, n = 16) or vagus nerve stimulation (VNS, n = 18). Rats were individually housed on a 12-hour reverse light/dark cycle with ad libitum food and water access. All protocols complied with the NIH Guide for Laboratory Animal Care and were approved by The University of Texas at Dallas IACUC committee and were conducted in accordance with the ARRIVE guidelines for reporting animal research. Rats were anesthetized with ketamine HCl (87.5 mg/kg) and xylazine (5 mg/kg) and implanted with jugular vein catheters and a custom cuff electrode around the left vagus nerve for VNS delivery 14 , 60 . Catheters were flushed daily with gentamicin (2–3 mg/day/animal) and heparin (0.2 ml of 100 units) to prevent infection and maintain catheter patency. Ketoprofen was also administered to reduce pain and discomfort. Drug self-administration, extinction training, and VNS treatment Drug self-administration and extinction training were performed as previously described 14 , 60 . After 7–10 days of recovery, rats learned to self-administer food pellets in a single overnight session before beginning daily cocaine self-administration sessions in operant conditioning chambers (Med Associates). During the 2 hr. self-administration sessions, each active lever press delivered 0.25 mg cocaine (NIDA Drug Supply Program) in 0.05 ml saline over 3 seconds and the presentation of drug-paired cues (illumination of the light over the active lever and the presentation of a 2900 Hz tone), followed by a 20-second timeout. Subjects completed at least 10 days of self-administration with ≥ 20 infusions per session. Rats in the YS groups received saline infusions contingent on lever presses by cocaine-administering rats. Extinction groups underwent 10 days of training where lever presses no longer produced cocaine infusions or presentation of drug-paired cues. During extinction, rats received either sham stimulation or noncontingent VNS (0.4 mA for 30 seconds every 5 minutes). Following 10 days of extinction training, drug-seeking behavior was reinstated in a cue-induced reinstatement session during which presses on the active lever triggered the presentation of the previously drug-paired tone and light but did not result in drug delivery or VNS. In vivo LFP recording Evoked local field potentials (eLFPs) were recorded after either the final self-administration session (COC, YS) or after cue-induced reinstatement (SHAM, VNS). Under urethane anesthesia (1.5 g/kg, i.p.) we recorded eLFPs in three pathways: For recordings of eLFPs in the BLA-IL pathway, a bipolar matrix stimulation electrode (FHC) was placed in the BLA (DV: 7.3, AP: -2.7, ML: 4.9 from bregma) and eLFPs were recorded in the IL (DV: 5, AP: +3, ML: 0.6 from bregma) using a tungsten microelectrode (WPI). For recordings in the IL-NAc shell pathway, the stimulation electrode was placed in the IL (DV: 5, AP: +3, ML: 0.6 from bregma), and eLFPs were recorded in the NAc shell (DV: 7.3, AP: +1.5, ML: 0.8 from bregma). Field potentials in the BLA-IL and IL-NAc shell pathways were recorded in opposing hemispheres in the same rats. We alternated both hemispheres and the order of the recordings across all animals. For recordings of eLFPs in the PL-NAc core pathway, the stimulation electrode was placed in the PL (DV: 3.5, AP: +3, ML: 0.6 from bregma) and recordings were performed in the NAc core (DV: 7, AP: +1.5, ML: 1.4 from bregma). Field responses were evoked every 15 s using a 0.3 ms stimulation pulse, and the basal stimulation intensity corresponded to 40% of the minimum current intensity that evoked a maximum field response, based on an input–output curve determined before collection of baseline data. Signals were amplified using a Model 1600 Neuropore Amplifier (A-M Systems) and a BMA 200 Portable Bioamplifier (CWE, cwe-inc.com). Signals were digitized using a CED 1401 interface (Cambridge Electronic Design, Cambridge, England) and analyzed using Spike-2 (CED). Baseline data were collected for a minimum of 10 min before synaptic plasticity was induced using high-frequency stimulation (HFS) consisting of three bursts of 100 pulses at 50 Hz (2 s), with 20 s inter-burst intervals at the minimum current intensity that evoked the maximum field response. Field potential amplitude was measured as the difference between the mean of a 5 ms window before the stimulation artifact and the negative peak of the field potential after the stimulation artifact. Responses were averaged across 2 min for analysis. Data were normalized to baseline, and the average of a 10 min baseline was set as 100%, and the 10 min period 40–50 min after plasticity induction was used to analyze long-term synaptic changes. Data analysis Statistical analyses used GraphPad Prism 7.0.5. Active lever presses during self-administration and extinction were compared using separate two-way ANOVAs with the factors of treatment and time following with Post hoc analyses. An independent t-test was conducted on the cue-induced reinstatement session to compare reinstatement between VNS and SHAM animals. Changes in eLFP amplitudes following induction of synaptic plasticity were analyzed using repeated-measures ANOVA with a treatment group × time interaction. Input-output curves of eLFPs were analyzed using two-way repeated measures ANOVA with the factors of treatment group × current intensity. P values < 0.05 were considered significant. Declarations Conflict of interest: The authors of this manuscript have no conflicts of interest. Ethical approval: This study has been conducted based on ethical approval from the University of Texas at Dallas. Funding information: This work was supported by a grant from the NIH to SK (Grant number:1R01DA055008). Author Contribution R.A. conceptualization, data acquisition, statistical analysis, writing, reviewing, and editing the manuscript. L.V. and C.D. data acquisition. S.K. funding acquisition, conceptualization, writing, review, and editing of the manuscript. All authors reviewed the manuscript and approved the final version for publication. Acknowledgement The authors are grateful to the following undergraduates in the Kroener lab for their contribution: Mansi Madaik, Zarin Tasnim Hasan, Dravin Raj and Neissa Molin. Cocaine HCl was provided by the NIDA Drug Supply Program. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute on Drug Abuse or the National Institutes of Health. Data Availability The data that support the findings of this study are available from the corresponding author upon reasonable request. References Koob, G. F. & Volkow, N. D. J. T. l. p. Neurobiology of addiction: a neurocircuitry analysis. 3 , 760-773 (2016). Moussawi, K. et al. N-Acetylcysteine reverses cocaine-induced metaplasticity. Nature neuroscience 12 , 182-189 (2009). Knackstedt, L. A. et al. Extinction training after cocaine self-administration induces glutamatergic plasticity to inhibit cocaine seeking. Journal of Neuroscience 30 , 7984-7992 (2010). Peters, J., Kalivas, P. W. & Quirk, G. J. Extinction circuits for fear and addiction overlap in prefrontal cortex. Learning & memory 16 , 279-288 (2009). Fuchs, R. A., Feltenstein, M. W. & See, R. E. The role of the basolateral amygdala in stimulus-reward memory and extinction memory consolidation and in subsequent conditioned cued reinstatement of cocaine seeking. The European journal of neuroscience 23 , 2809-2813, doi:10.1111/j.1460-9568.2006.04806.x (2006). McLaughlin, J. & See, R. E. Selective inactivation of the dorsomedial prefrontal cortex and the basolateral amygdala attenuates conditioned-cued reinstatement of extinguished cocaine-seeking behavior in rats. Psychopharmacology 168 , 57-65 (2003). Miller, C. A. & Marshall, J. F. Altered Fos expression in neural pathways underlying cue‐elicited drug seeking in the rat. European Journal of Neuroscience 21 , 1385-1393 (2005). Smith, A. C. et al. Synaptic plasticity mediating cocaine relapse requires matrix metalloproteinases. Nature neuroscience 17 , 1655-1657 (2014). Abraham, W. C. Metaplasticity: tuning synapses and networks for plasticity. Nat Rev Neurosci 9 , 387, doi:10.1038/nrn2356 (2008). Cimpianu, C.-L., Strube, W., Falkai, P., Palm, U. & Hasan, A. Vagus nerve stimulation in psychiatry: a systematic review of the available evidence. Journal of neural transmission 124 , 145-158 (2017). Clark, K., Krahl, S., Smith, D. & Jensen, R. Post-training unilateral vagal stimulation enhances retention performance in the rat. Neurobiology of learning and memory 63 , 213-216 (1995). Clark, K. et al. Posttraining electrical stimulation of vagal afferents with concomitant vagal efferent inactivation enhances memory storage processes in the rat. Neurobiology of learning and memory 70 , 364-373 (1998). Sun, L. et al. Vagus nerve stimulation improves working memory performance. Journal of Clinical and Experimental Neuropsychology 39 , 954-964 (2017). Childs, J. E., DeLeon, J., Nickel, E. & Kroener, S. Vagus nerve stimulation reduces cocaine seeking and alters plasticity in the extinction network. Learning & Memory 24 , 35-42 (2017). Childs, J. E., Kim, S., Driskill, C. M., Hsiu, E. & Kroener, S. Vagus nerve stimulation during extinction learning reduces conditioned place preference and context-induced reinstatement of cocaine seeking. Brain stimulation 12 , 1448-1455 (2019). Driskill, C. M. et al. Vagus nerve stimulation (VNS) modulates synaptic plasticity in the rat infralimbic cortex via Trk-B receptor activation to reduce drug-seeking. bioRxiv (2024). Peña, D. F. et al. Vagus nerve stimulation enhances extinction of conditioned fear and modulates plasticity in the pathway from the ventromedial prefrontal cortex to the amygdala. Frontiers in behavioral neuroscience 8 , 327 (2014). Keute, M. & Gharabaghi, A. Brain plasticity and vagus nerve stimulation. Autonomic neuroscience : basic & clinical 236 , 102876, doi:10.1016/j.autneu.2021.102876 (2021). Olsen, L. K. et al. Vagus nerve stimulation-induced cognitive enhancement: Hippocampal neuroplasticity in healthy male rats. Brain Stimul 15 , 1101-1110, doi:10.1016/j.brs.2022.08.001 (2022). Peters, J., LaLumiere, R. T. & Kalivas, P. W. Infralimbic prefrontal cortex is responsible for inhibiting cocaine seeking in extinguished rats. The Journal of neuroscience : the official journal of the Society for Neuroscience 28 , 6046-6053, doi:10.1523/JNEUROSCI.1045-08.2008 (2008). Koob, G. F. & Volkow, N. D. Neurobiology of addiction: a neurocircuitry analysis. The Lancet Psychiatry 3 , 760-773 (2016). See, R. E., Kruzich, P. J. & Grimm, J. W. Dopamine, but not glutamate, receptor blockade in the basolateral amygdala attenuates conditioned reward in a rat model of relapse to cocaine-seeking behavior. Psychopharmacology 154 , 301-310 (2001). Ciccocioppo, R., Sanna, P. P. & Weiss, F. Cocaine-predictive stimulus induces drug-seeking behavior and neural activation in limbic brain regions after multiple months of abstinence: reversal by D1 antagonists. Proceedings of the National Academy of Sciences 98 , 1976-1981 (2001). Kim, J. H. & Richardson, R. The effect of temporary amygdala inactivation on extinction and reextinction of fear in the developing rat: unlearning as a potential mechanism for extinction early in development. The Journal of neuroscience : the official journal of the Society for Neuroscience 28 , 1282-1290, doi:10.1523/JNEUROSCI.4736-07.2008 (2008). Laurent, V. & Westbrook, R. F. Inactivation of the infralimbic but not the prelimbic cortex impairs consolidation and retrieval of fear extinction. Learn Mem 16 , 520-529, doi:10.1101/lm.1474609 (2009). Bloodgood, D. W., Sugam, J. A., Holmes, A. & Kash, T. L. Fear extinction requires infralimbic cortex projections to the basolateral amygdala. Transl Psychiatry 8 , 60, doi:10.1038/s41398-018-0106-x (2018). Cho, J. H., Deisseroth, K. & Bolshakov, V. Y. Synaptic encoding of fear extinction in mPFC-amygdala circuits. Neuron 80 , 1491-1507, doi:10.1016/j.neuron.2013.09.025 (2013). Cheriyan, J., Kaushik, M. K., Ferreira, A. N. & Sheets, P. L. Specific Targeting of the Basolateral Amygdala to Projectionally Defined Pyramidal Neurons in Prelimbic and Infralimbic Cortex. eNeuro 3 , doi:10.1523/ENEURO.0002-16.2016 (2016). McGarry, L. M. & Carter, A. G. Inhibitory gating of basolateral amygdala inputs to the prefrontal cortex. Journal of Neuroscience 36 , 9391-9406 (2016). Childs, J. E., DeLeon, J., Nickel, E. & Kroener, S. Vagus nerve stimulation reduces cocaine seeking and alters plasticity in the extinction network. Learning & memory 24 , 35-42, doi:10.1101/lm.043539.116 (2017). Zuo, Y., Smith, D. C. & Jensen, R. A. Vagus nerve stimulation potentiates hippocampal LTP in freely-moving rats. Physiol Behav 90 , 583-589, doi:10.1016/j.physbeh.2006.11.009 (2007). Wayman, W. N. & Woodward, J. J. Chemogenetic excitation of accumbens-projecting infralimbic cortical neurons blocks toluene-induced conditioned place preference. Journal of Neuroscience 38 , 1462-1471 (2018). Gipson, C. D., Kupchik, Y. M. & Kalivas, P. W. Rapid, transient synaptic plasticity in addiction. Neuropharmacology 76 , 276-286 (2014). Stefanik, M. T. et al. Optogenetic inhibition of cocaine seeking in rats. Addiction biology 18 , 50-53 (2013). Kourrich, S., Rothwell, P. E., Klug, J. R. & Thomas, M. J. Cocaine experience controls bidirectional synaptic plasticity in the nucleus accumbens. The Journal of neuroscience : the official journal of the Society for Neuroscience 27 , 7921-7928, doi:10.1523/JNEUROSCI.1859-07.2007 (2007). Gipson, C. D. et al. Relapse induced by cues predicting cocaine depends on rapid, transient synaptic potentiation. Neuron 77 , 867-872, doi:10.1016/j.neuron.2013.01.005 (2013). Conrad, K. L. et al. Formation of accumbens GluR2-lacking AMPA receptors mediates incubation of cocaine craving. Nature 454 , 118-121, doi:10.1038/nature06995 (2008). Loweth, J. A., Tseng, K. Y. & Wolf, M. E. Adaptations in AMPA receptor transmission in the nucleus accumbens contributing to incubation of cocaine craving. Neuropharmacology 76 Pt B , 287-300, doi:10.1016/j.neuropharm.2013.04.061 (2014). Pierce, R. C., Bell, K., Duffy, P. & Kalivas, P. W. Repeated cocaine augments excitatory amino acid transmission in the nucleus accumbens only in rats having developed behavioral sensitization. The Journal of neuroscience : the official journal of the Society for Neuroscience 16 , 1550-1560, doi:10.1523/JNEUROSCI.16-04-01550.1996 (1996). Suto, N. et al. Previous exposure to psychostimulants enhances the reinstatement of cocaine seeking by nucleus accumbens AMPA. Neuropsychopharmacology 29 , 2149-2159, doi:10.1038/sj.npp.1300533 (2004). Shen, H. & Kalivas, P. W. Reduced LTP and LTD in prefrontal cortex synapses in the nucleus accumbens after heroin self-administration. International Journal of Neuropsychopharmacology 16 , 1165-1167 (2013). Kalivas, P. W. The glutamate homeostasis hypothesis of addiction. Nature reviews neuroscience 10 , 561-572 (2009). LaLumiere, R. T., Niehoff, K. E. & Kalivas, P. W. The infralimbic cortex regulates the consolidation of extinction after cocaine self-administration. Learn Mem 17 , 168-175, doi:10.1101/lm.1576810 (2010). LaLumiere, R. T., Smith, K. C. & Kalivas, P. W. Neural circuit competition in cocaine‐seeking: roles of the infralimbic cortex and nucleus accumbens shell. European Journal of Neuroscience 35 , 614-622 (2012). Gutman, A. L. et al. Extinction of Cocaine Seeking Requires a Window of Infralimbic Pyramidal Neuron Activity after Unreinforced Lever Presses. The Journal of neuroscience : the official journal of the Society for Neuroscience 37 , 6075-6086, doi:10.1523/JNEUROSCI.3821-16.2017 (2017). Nett, K. E. et al. Infralimbic Projections to the Nucleus Accumbens Shell and Amygdala Regulate the Encoding of Cocaine Extinction Learning. The Journal of neuroscience : the official journal of the Society for Neuroscience 43 , 1348-1359, doi:10.1523/JNEUROSCI.2023-22.2022 (2023). Fuchs, R. A., Ramirez, D. R. & Bell, G. H. Nucleus accumbens shell and core involvement in drug context-induced reinstatement of cocaine seeking in rats. Psychopharmacology (Berl) 200 , 545-556, doi:10.1007/s00213-008-1234-4 (2008). LaLumiere, R. T., Smith, K. C. & Kalivas, P. W. Neural circuit competition in cocaine-seeking: roles of the infralimbic cortex and nucleus accumbens shell. The European journal of neuroscience 35 , 614-622, doi:10.1111/j.1460-9568.2012.07991.x (2012). Van den Oever, M. C., Spijker, S., Smit, A. B. & De Vries, T. J. Prefrontal cortex plasticity mechanisms in drug seeking and relapse. Neurosci Biobehav Rev 35 , 276-284, doi:10.1016/j.neubiorev.2009.11.016 (2010). Sutton, M. A. et al. Extinction-induced upregulation in AMPA receptors reduces cocaine-seeking behaviour. Nature 421 , 70-75, doi:10.1038/nature01249 (2003). Wu, X., Kobeissi, A. M., Phillips, H. L., Dai, H. & Yao, W. D. A Prefrontal Cortex-Nucleus Accumbens Circuit Attenuates Cocaine-conditioned Place Preference Memories. bioRxiv , doi:10.1101/2025.03.21.644656 (2025). Cao, J., Lu, K.-H., Powley, T. L. & Liu, Z. Vagal nerve stimulation triggers widespread responses and alters large-scale functional connectivity in the rat brain. PloS one 12 , e0189518 (2017). Collins, L., Boddington, L., Steffan, P. J. & McCormick, D. Vagus nerve stimulation induces widespread cortical and behavioral activation. Current Biology 31 , 2088-2098. e2083 (2021). Nichols, J. A. et al. Vagus nerve stimulation modulates cortical synchrony and excitability through the activation of muscarinic receptors. Neuroscience 189 , 207-214, doi:10.1016/j.neuroscience.2011.05.024 (2011). Furmaga, H., Carreno, F. R. & Frazer, A. Vagal nerve stimulation rapidly activates brain-derived neurotrophic factor receptor TrkB in rat brain. PLoS One 7 , e34844, doi:10.1371/journal.pone.0034844 (2012). Follesa, P. et al. Vagus nerve stimulation increases norepinephrine concentration and the gene expression of BDNF and bFGF in the rat brain. Brain Res 1179 , 28-34, doi:10.1016/j.brainres.2007.08.045 (2007). Roosevelt, R. W., Smith, D. C., Clough, R. W., Jensen, R. A. & Browning, R. A. Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat. Brain Res 1119 , 124-132, doi:10.1016/j.brainres.2006.08.048 (2006). Borland, M. S. et al. Pairing vagus nerve stimulation with tones drives plasticity across the auditory pathway. Journal of neurophysiology (2019). Manta, S., El Mansari, M., Debonnel, G. & Blier, P. Electrophysiological and neurochemical effects of long-term vagus nerve stimulation on the rat monoaminergic systems. International Journal of Neuropsychopharmacology 16 , 459-470 (2013). Driskill, C. M. et al. Vagus Nerve Stimulation (VNS) Modulates Synaptic Plasticity in the Infralimbic Cortex via Trk-B Receptor Activation to Reduce Drug-Seeking in Male Rats. The Journal of neuroscience : the official journal of the Society for Neuroscience 44 , doi:10.1523/jneurosci.0107-24.2024 (2024). Pardo, J. V. et al. Chronic vagus nerve stimulation for treatment-resistant depression decreases resting ventromedial prefrontal glucose metabolism. Neuroimage 42 , 879-889 (2008). Wang, Z. et al. Frequency-dependent functional connectivity of the nucleus accumbens during continuous transcutaneous vagus nerve stimulation in major depressive disorder. Journal of psychiatric research 102 , 123-131 (2018). Zhang, S. et al. Prolonged longitudinal transcutaneous auricular vagus nerve stimulation effect on striatal functional connectivity in patients with major depressive disorder. Brain Sciences 12 , 1730 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 11 Dec, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 25 Sep, 2025 Reviews received at journal 07 Aug, 2025 Reviews received at journal 25 Jul, 2025 Reviewers agreed at journal 16 Jul, 2025 Reviewers agreed at journal 14 Jul, 2025 Reviewers invited by journal 14 Jul, 2025 Editor assigned by journal 14 Jul, 2025 Editor invited by journal 09 Jul, 2025 Submission checks completed at journal 03 Jul, 2025 First submitted to journal 03 Jul, 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. 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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-7014180","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":485261559,"identity":"dcee3e27-6280-49ea-8ac3-540cc309dc48","order_by":0,"name":"Reza Arezoomandan","email":"","orcid":"","institution":"The University of Texas at Dallas","correspondingAuthor":false,"prefix":"","firstName":"Reza","middleName":"","lastName":"Arezoomandan","suffix":""},{"id":485261560,"identity":"5b7363a3-d3ad-4e50-ada9-5ccb0e3f1c33","order_by":1,"name":"Lily Vu","email":"","orcid":"","institution":"The University of Texas at Dallas","correspondingAuthor":false,"prefix":"","firstName":"Lily","middleName":"","lastName":"Vu","suffix":""},{"id":485261561,"identity":"075eaee5-aa45-4d9f-af80-03cbaa13e8d5","order_by":2,"name":"Christopher Driskill","email":"","orcid":"","institution":"The University of Texas at Dallas","correspondingAuthor":false,"prefix":"","firstName":"Christopher","middleName":"","lastName":"Driskill","suffix":""},{"id":485261562,"identity":"226fca00-0cb2-4eb3-a050-b7da1951f2a5","order_by":3,"name":"Sven Kroener","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4klEQVRIiWNgGAWjYBACCSgtB8QGDA8KwBwDorQYM7ABVSYYkKAlsYFoLZKzDx98XFBxL33D/eaNHxIM7OwZ2Ju3SeDTIs2Xlmw840xx7oZjbMUSCQbJiQ08x8rwapHj4TGT5m1LAGrhMQBqYU5gkMgxI6TF/Dfvv4R0g2M8xj8SDOrtGeTf4NciDbSFmbchIQGoxQxoy2HGBgke/Foke9iSpXmOJRjOPJZWZpFgcDyxjSet2AKfFokzzAc/89QkyPMdPrz5xoeKant+9sMbb+DTggnYSFM+CkbBKBgFowAbAAC4QT+TexdlgAAAAABJRU5ErkJggg==","orcid":"","institution":"The University of Texas at Dallas","correspondingAuthor":true,"prefix":"","firstName":"Sven","middleName":"","lastName":"Kroener","suffix":""}],"badges":[],"createdAt":"2025-06-30 21:23:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7014180/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7014180/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-27577-7","type":"published","date":"2025-12-11T15:57:51+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86858828,"identity":"e7ba0b19-f6eb-4210-9cb9-f5764705255f","added_by":"auto","created_at":"2025-07-16 11:41:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1075659,"visible":true,"origin":"","legend":"\u003cp\u003eVagus nerve stimulation (VNS) facilitates extinction from cocaine seeking and reduces cue-induced reinstatement. (A) Active lever presses in rats self-administering cocaine (COC, red circles) and their yoked-saline controls (YS, black circles) during the last 10 days of self-administration. (B) Responses at the active lever during self-administration, extinction, and cue-induced reinstatement in rats receiving VNS (green triangles) or sham stimulation (SHAM, gray triangles) during extinction on days 11–20. (C) VNS-treated rats displayed reduced active lever presses during the first day of extinction. (D) An unpaired t-test revealed significantly fewer responses on the previously active lever during cue-induced reinstatement in VNS rats. \u003cem\u003eP\u003c/em\u003e values are (***) \u0026lt;0.001, and (****) \u0026lt;0.0001.\u003c/p\u003e","description":"","filename":"Fig.1.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/e5ca641a4b714bd2a7872878.jpg"},{"id":86859003,"identity":"5160c64e-46c4-48de-817f-a2fb886f86eb","added_by":"auto","created_at":"2025-07-16 11:49:42","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1087275,"visible":true,"origin":"","legend":"\u003cp\u003eVNS reverses drug-induced LTP in the BLA-IL pathway. (A) Diagram of stimulation and recording sites in the IL and BLA. (B) Single-pulse stimulation in the BLA elicited negative field potentials in the IL that peaked after ~10 ms. Representative traces (averages of ten consecutive sweeps) of an input–output curve from a YS rat are shown. (C) Input–output curves in the four treatment groups. Cocaine self-administering (COC) and sham-stimulated (SHAM) groups showed increased baseline responses relative to eLFPs in yoked-saline (YS). VNS treatment modified changes induced by drug-seeking and decreased eLFP amplitudes. (D-G) Representative experiments showing eLFPs in all four treatment groups before and after HFS (50 Hz; arrow indicates delivery). Insets are averages of eight consecutive eLFPs before and after HFS. (H) Comparison of synaptic plasticity changes across the four treatment groups. HFS induced LTP in all groups, with the greatest change in COC and SHAM rats (\u003cem\u003eP\u003c/em\u003e\u0026lt; 0.0001 and \u003cem\u003eP\u003c/em\u003e= 0.024, respectively). Extinction paired with VNS reversed drug-seeking-induced LTP, restoring it to YS control levels (\u003cem\u003eP\u003c/em\u003e= 0.004, VNS vs SHAM). BLA: basolateral amygdala, IL: infralimbic cortex.\u003c/p\u003e","description":"","filename":"Fig.2.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/2f595ede18267e9cf82ac96f.jpg"},{"id":86858034,"identity":"31628299-346f-4ca4-a23d-b81757a1b2c4","added_by":"auto","created_at":"2025-07-16 11:33:42","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1028004,"visible":true,"origin":"","legend":"\u003cp\u003eVNS modulates drug-induced changes in synaptic plasticity in the PL-NAc core pathway. (A) Diagram of stimulation and recording sites in the PL and NAc core. (B) Single-pulse stimulation in the PL elicited negative field potentials in the NAc core peaking at 20–25 ms. Representative traces (average of ten consecutive sweeps) from a yoked-saline (YS) rat. (C) Input–output curves from rats in four treatment groups. Cocaine self-administration (COC) and cue-induced reinstatement (SHAM) increased baseline responses compared to YS rats (\u003cem\u003eP\u003c/em\u003e \u0026lt;0.05). VNS treatment partially reversed this effect, resulting in smaller amplitudes than in COC and SHAM rats (\u003cem\u003eP\u003c/em\u003e \u0026lt;0.05). (D–G) Representative experiments showing plasticity induced by HFS (50 Hz; arrow indicates delivery) in the four treatment groups. Insets show the average of eight consecutive eLFPs before and after HFS. (H) Comparison of average plasticity changes across the four treatment groups. HFS induced LTP in YS rats (\u003cem\u003eP\u003c/em\u003e\u0026lt;0.0001) but caused LTD in COC and SHAM rats (\u003cem\u003eP\u003c/em\u003e= 0.012 and \u003cem\u003eP\u003c/em\u003e= 0.0005, respectively). In VNS-treated rats, HFS failed to induce either LTP or LTD which was significantly different from the LTD induced in COC and SHAM-treated rats (\u003cem\u003eP\u003c/em\u003e= 0.025 and \u003cem\u003eP\u003c/em\u003e= 0.001, respectively). PL: prelimbic cortex, NAc: nucleus accumbens.\u003c/p\u003e","description":"","filename":"Fig.3.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/87f5636f983d87aa5a106e7a.jpg"},{"id":86858830,"identity":"fa8b419c-be20-4789-87cc-83aa0c4d6c9e","added_by":"auto","created_at":"2025-07-16 11:41:42","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1062473,"visible":true,"origin":"","legend":"\u003cp\u003eVNS induces synaptic plasticity in the IL-NAc shell pathway. (A) Diagram of stimulation and recording sites in the IL and NAc shell. (B) Single-pulse stimulation targeted to the IL elicited negative field potentials in the NAc shell peaking at ~10 ms. Representative traces (average of ten consecutive sweeps) from a YS rat. (C) Input–output curves from rats in the four treatment groups. VNS treatment significantly enhanced baseline amplitudes (\u003cem\u003eP\u003c/em\u003e\u0026lt; 0.01, VNS vs YS). (D–G) Representative experiments showing plasticity induced by HFS (50 Hz; arrow indicates delivery) in the four treatment groups. Insets show the average of eight consecutive eLFPs before and after HFS. (D) HFS failed to induce LTP in YS rats. (E, F) In COC and SHAM rats, HFS induced LTD instead of LTP (\u003cem\u003eP\u003c/em\u003e= 0.043 and \u003cem\u003eP\u003c/em\u003e= 0.042, respectively). (G) In VNS-treated rats, HFS successfully induced LTP in the NAc shell compared to both the baseline and SHAM group (\u003cem\u003eP\u003c/em\u003e= 0.001 and \u003cem\u003eP\u003c/em\u003e\u0026lt;0.0001 respectively). (H) Group comparisons of plasticity outcomes. COC use and reinstatement shifted IL–NAc plasticity toward LTD, whereas VNS paired with extinction changed this pathway to induction of LTP. IL: infralimbic, NAc: nucleus accumbens.\u003c/p\u003e","description":"","filename":"Fig.4.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/8cee53bff1fde625d54423bf.jpg"},{"id":86858831,"identity":"3f28e74b-ce7b-474b-ac81-637bf478d82e","added_by":"auto","created_at":"2025-07-16 11:41:42","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":375008,"visible":true,"origin":"","legend":"\u003cp\u003eDrug-seeking and VNS change synaptic strength and metaplasticity across extinction and drug-seeking pathways. Summary of the effects of cocaine self-administration (COC) and extinction paired with either sham stimulation (SHAM) or VNS (VNS) followed by cue-induced reinstatement on baseline synaptic strength (filled arrows) and metaplasticity (open arrows) in three key pathways: BLA- IL, PL–NAc core (drug-seeking pathway), IL–NAc shell (extinction pathway). Arrows indicate relative changes in synaptic strength across treatments compared to yoked-saline (YS) groups, as well as changes relative to baseline in the case of synaptic plasticity. See text for details.\u003c/p\u003e","description":"","filename":"Fig.5.tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/f8fce66f9c2470d326ce0ea0.jpg"},{"id":98244842,"identity":"d1af37d3-54ec-4fe4-be5b-d001068f8dbe","added_by":"auto","created_at":"2025-12-15 16:15:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5420346,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7014180/v1/852c5a99-144c-4192-b58f-7f87f5d9266a.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Vagus nerve stimulation modulates synaptic plasticity induced by cocaine- seeking in reward-related circuitry","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCocaine addiction is a chronic and relapsing disorder characterized by maladaptive neuroplasticity within cortical-limbic circuits. These circuits, which include the prefrontal cortex (PFC), nucleus accumbens (NAc), and amygdala, are critical for regulating reward processing, emotional responses, and decision-making \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Chronic cocaine exposure disrupts the balance of synaptic plasticity in these pathways, including impairment in induction of LTP and LTD, resulting in heightened sensitivity to drug-related cues and impaired behavioral control \u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. These changes underlie the persistent drug-seeking behaviors and high relapse rates observed in cocaine addiction \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. The infralimbic cortex (IL) and prelimbic cortex (PL), two subregions of the PFC, play largely opposing roles in drug-seeking behavior. The IL inhibits drug-seeking by projecting to the NAc shell or PL, while the PL drives drug-seeking and facilitates reinstatement of drug-seeking through its connections to the NAc core \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. The basolateral amygdala (BLA) is another key structure in this network, encoding the salience of drug-related cues and influencing the activity of other brain areas involved in drug-seeking including PFC and NAc \u003csup\u003e\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e .\u003c/p\u003e\u003cp\u003eChronic cocaine use induces significant molecular and cellular changes in reward-related brain regions, leading to disruptions in normal brain function, including impairments in synaptic plasticity \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Cocaine induces neuroadaptations within cortical-limbic pathways, which is strongly implicated in the persistence of addictive behaviors. Cocaine induces metaplasticity, a phenomenon linked to increased vulnerability to relapse \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Metaplasticity, defined as a change in threshold or rule for inducing synaptic plasticity, represents a higher-order form of plasticity that is not expressed as a change in synaptic transmission efficacy but rather as a change in the direction or degree of plasticity induced by specific stimulation patterns \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. This concept is essential for understanding drug addiction mechanisms. Effective treatments for relapse should normalize synaptic transmission and reverse cocaine-induced metaplasticity in reward-related brain areas.\u003c/p\u003e\u003cp\u003eVagus nerve stimulation (VNS) is FDA-approved for use in epilepsy and depression and considered for the treatment of an expanding range of psychiatric diseases including substance use disorders \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. VNS causes the release of several neuromodulators which modulate cortical plasticity. This plasticity can increase learning and memory in rats \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e and humans \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Recently we showed that VNS facilitates extinction and reduces cue‐induced reinstatement in cocaine self‐administering rats \u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Also, we have shown that pairing VNS with extinction of conditioned fear potentiates evoked field responses in the BLA, resulting in LTP in the IL-BLA pathway, suggesting that VNS promotes plasticity in this pathway to facilitate extinction of conditioned fear responses \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e. VNS has been shown to reduce relapse in reinstatement models of drug-seeking as well as modulate synaptic transmission and metaplasticity \u003csup\u003e\u003cspan additionalcitationids=\"CR15 CR16 CR17 CR18\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eHere we determined how cocaine self-administration and reinstatement induce metaplasticity in key cortical-limbic circuits involved in drug-seeking, including the BLA-IL, IL-NAc shell and PL-NAc core pathways. We also show that extinction training paired with VNS can modulate these changes to reduce reinstatement.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cb\u003eVNS facilitates extinction and reduces cue-induced reinstatement\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo examine the effects of cocaine self-administration on neuroplasticity, 30 rats of both sexes (16 males; 14 females) were trained to self-administer either cocaine (COC, n\u0026thinsp;=\u0026thinsp;16) or which received yoked-saline infusions (YS, n\u0026thinsp;=\u0026thinsp;14) for at least 10 days. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA shows active lever presses in a cohort of COS and YS rats. Cocaine self-administering animals consistently exhibited significantly higher active lever responses compared to yoked-saline animals (F(1, 28)\u0026thinsp;=\u0026thinsp;46.56, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). To evaluate the impact of VNS on drug-seeking behavior, a separate group of rats underwent cocaine self-administration for a minimum of 10 days, followed by 10 days of extinction training paired with either VNS (n\u0026thinsp;=\u0026thinsp;18, 10 males and 8 females) or sham stimulation (SHAM; n\u0026thinsp;=\u0026thinsp;16, 9 males and 7 females). After 10 days of extinction, drug-seeking behavior was assessed in a cued reinstatement session through the presentation of conditioned drug cues (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). A two-way ANOVA revealed no significant differences between groups in active lever responses during the final 10 days of self-administration (F (1, 33)\u0026thinsp;=\u0026thinsp;0.013, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.9). During extinction training and the cue-induced reinstatement session, responses at the previously active lever were used as a measure of extinction learning. A repeated-measures two-way ANOVA, with time (sessions) and treatment (SHAM or VNS) as factors, revealed a significant effect of extinction (main effect of time: F (9, 330)\u0026thinsp;=\u0026thinsp;57.67, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), a significant difference between treatment groups (main effect of treatment: F (1, 330)\u0026thinsp;=\u0026thinsp;46.59, p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), and a significant interaction between these factors (F (9, 330)\u0026thinsp;=\u0026thinsp;8.52, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Post hoc analysis showed that rats receiving VNS pressed the active lever significantly less than the sham group on the first two days of extinction (Day 1, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB; Day 2, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB, C), suggesting that VNS facilitates extinction learning. Twenty-four hours after the final extinction session, drug-seeking was assessed in a cue-induced reinstatement session. An unpaired t-test revealed that VNS animals exhibited significantly fewer responses on the previously active lever during cue-induced reinstatement (t(32)\u0026thinsp;=\u0026thinsp;7.79, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB, D), demonstrating the effectiveness of VNS in inhibiting cue-induced reinstatement.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eVNS reverses drug-induced LTP in the pathway from the BLA to the IL\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo determine how cocaine self-administration, reinstatement, and VNS influence synaptic plasticity in the pathway from the BLA to the IL, we performed \u003cem\u003ein vivo\u003c/em\u003e recordings in anesthetized rats following the final session of either self-administration or reinstatement in the four treatment groups (YS, n\u0026thinsp;=\u0026thinsp;6; COC, n\u0026thinsp;=\u0026thinsp;9; SHAM, n\u0026thinsp;=\u0026thinsp;6; VNS, n\u0026thinsp;=\u0026thinsp;9). We placed a stimulation electrode into the BLA and performed recordings of eLFPs in the IL (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Single-pulse stimulation in the BLA evoked a characteristic field potential response in the IL which peaked after 10ms (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). A two-way ANOVA examining the current-voltage relationship of eLFPs revealed a main effect of I\u0026ndash;O curves (F (3, 140)\u0026thinsp;=\u0026thinsp;7.185; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0002, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). In the BLA-IL pathway, cocaine self-administration and cue-induced reinstatement significantly altered the current-voltage relationship of eLFPs, resulting in a marked increase in baseline responses relative to eLFPs in YS rats (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). VNS treatment reversed these changes and reduced baseline responses, resulting in no significant difference between the VNS and YS groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC). After obtaining stable baseline recordings for a minimum of 10 minutes we used HFS in the BLA to induce LTP to further examine the effect of drug-seeking and VNS treatment on synaptic plasticity in this pathway. Tetanic stimulation delivered to the BLA induced a persistent increase in amplitude of BLA-evoked responses in the IL in all groups (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD- H); however, the magnitude of LTP was significantly greater in COC rats compared to LTP in the other groups F (3, 50)\u0026thinsp;=\u0026thinsp;6.827; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0006, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE, H). SHAM animals exhibited smaller LTP compared to rats in the COC group (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.021; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eF, H), but larger amplitudes than rats in the YS group (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.024; 2H). Pairing extinction training with VNS significantly reversed the drug-seeking-induced LTP, restoring it to YS control levels (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eG, H). These results show that drug-seeking behavior strengthens this pathway, and that extinction training by itself can partially reverse these changes. Pairing extinction training with VNS further reduces drug-induced changes resulting in plasticity similar to that observed in YS controls.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eVNS modulates drug-induced changes in synaptic plasticity in the PL-NAc core pathway\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe PL can drive reinstatement of drug-seeking via its projection to the NAc core \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. To determine how cocaine self-administration and cue-induced reinstatement alter synaptic plasticity in the PL-NAc core pathway, and how pairing extinction training with VNS can modulate these changes, we recorded eLFPs in this pathway in our four treatment groups (YS, n\u0026thinsp;=\u0026thinsp;6; COC, n\u0026thinsp;=\u0026thinsp;7; SHAM, n\u0026thinsp;=\u0026thinsp;9; VNS, n\u0026thinsp;=\u0026thinsp;9) after the last self-administration session or the reinstatement session, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA, B, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Stimulation of the PL elicited negative field potentials in the NAc core, which peaked after 20\u0026ndash;25ms (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). The current-voltage relationship between stimulation intensity in the PL and eLFP amplitude in the NAc core were significantly different between the four groups F (3, 135)\u0026thinsp;=\u0026thinsp;6.509; \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0004; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). The COC and SHAM groups showed increased baseline eLFP amplitudes compared to the YS group (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In addition, eLFP amplitudes in the VNS group were significantly reduced compared to those in COC and SHAM rats (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC). To further examine the effect of drug-seeking and VNS treatment on synaptic plasticity we used HFS (50 Hz) of the PL to induce LTP in this pathway. Our results showed a main effect of treatment F (3, 56)\u0026thinsp;=\u0026thinsp;26.04, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). Consistent with previous reports \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, this protocol induced synaptic plasticity in YS rats (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, H). In contrast, in COC and SHAM animals, HFS consistently induced LTD rather than LTP in this pathway (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.012 and \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0005, respectively, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE, F, H). In VNS rats, HFS did not induce synaptic plasticity (baseline vs. post HFS, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.9), which was significantly different from the LTD induced in COC and SHAM-treated rats (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.025 and \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001, respectively, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF, H). These results show that VNS can modulate drug-seeking induced changes in metaplasticity in the PL-NAc core pathway.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eVNS Induces synaptic plasticity in the IL-NAc shell pathway\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe IL facilitates extinction learning and suppresses cocaine-seeking behavior through its projections to the NAc shell \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. To determine how cocaine self-administration, reinstatement, and VNS influence synaptic plasticity we recorded eLFPs in this pathway in the four treatment groups after the last self-administration or the reinstatement session (YS, n\u0026thinsp;=\u0026thinsp;8; COC, n\u0026thinsp;=\u0026thinsp;9) or reinstatement (SHAM, n\u0026thinsp;=\u0026thinsp;7; VNS, n\u0026thinsp;=\u0026thinsp;8) (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). IL stimulation elicited eLFPs in the NAc shell, characterized by a negative potential peaking at 10ms (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). The shape, amplitude, and latency of these eLFPs were highly reproducible and remained stable over time. A two-way ANOVA assessing the relationship between stimulation intensity (0.2 mA\u0026ndash;2.5 mA) and baseline eLFP amplitude revealed a significant main effect of treatment on I\u0026ndash;O curves (F(3,144)\u0026thinsp;=\u0026thinsp;19.91, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001). Specifically, rats in the VNS group exhibited significantly larger baseline responses compared to YS (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as well as COC and SHAM rats (P\u0026thinsp;\u0026lt;\u0026thinsp;0.01, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC). After obtaining stable baseline recordings, we applied HFS to induce LTP. In YS rats, HFS of the IL failed to induce synaptic plasticity in the NAc shell, showing no significant difference between baseline and post-HFS amplitudes (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0. 0.88, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD, H). In both COC and SHAM rats, post-HFS amplitudes remained consistently lower, indicating that cocaine self-administration and reinstatement facilitated induction of LTD rather than LTP in this pathway (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.043 and \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.042 respectively, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eE, F, H). In contrast, pairing extinction training with VNS modified metaplasticity in the NAc shell so that HFS of the IL induced LTP in the NAc shell compared to both the baseline and SHAM group (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001 and \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001 respectively).Taken together, these findings demonstrate that both cocaine-seeking behavior and VNS significantly alter synaptic plasticity in the IL-to-NAc shell pathway (F (3, 56)\u0026thinsp;=\u0026thinsp;4.475, \u003cem\u003eP\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0.0069). While drug-seeking behavior weakens this pathway, pairing extinction training with VNS strengthens it.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eCorticolimbic pathways connecting the PFC, amygdala, and NAc play a crucial role in drug-seeking behavior by integrating emotional cues, reward anticipation, and decision-making \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Dysregulation in these pathways reinforces maladaptive behaviors and impairs inhibitory control, perpetuating addiction \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. While extinction training can reverse drug-induced changes, it alone is often insufficient to prevent reinstatement. We replicate previous findings showing that pairing extinction training with VNS accelerates extinction learning during the initial session and reduces cue-induced reinstatement, suggesting enhanced consolidation of extinction memories \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. We determined changes in synaptic metaplasticity induced by drug-taking and cue-induced reinstatement in key cortical-limbic circuits, including the BLA-IL, IL-NAc shell, and PL-NAc core pathways. We show that drug-seeking behavior disrupts synaptic plasticity in each of these circuits and that pairing extinction with VNS effectively reverses these neuroplastic changes in ways consistent with VNS-induced suppression of drug-seeking.\u003c/p\u003e\u003cp\u003eThe BLA mediates the consolidation of both cocaine-stimulus association and extinction learning, two processes with opposite effects on subsequent cue-induced cocaine-seeking behavior \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. The BLA processes the salience of drug-related stimuli within the corticolimbic circuit \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, contributing to cue-induced reinstatement of cocaine-seeking \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Inactivation of the BLA, along with dorsomedial PFC inactivation, inhibits conditioned cue-induced reinstatement of cocaine-seeking behavior \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, while cocaine-associated cues trigger c-Fos activation in BLA-to-mPFC pathways \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. The BLA also plays a crucial role in extinction of drug-seeking through its involvement in extinction memory consolidation and influence on related neural circuits \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Extinction of conditioned fear requires neuronal activity in the BLA \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e and IL \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, as well as functional connectivity between the mPFC and amygdala \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eHowever, how drug-seeking alters synaptic plasticity between the BLA and the IL remains unknown, and our LFP recordings are the first to directly examine synaptic changes in this pathway in-vivo. Our results show that both cocaine self-administration and cue-induced reinstatement paired with SHAM stimulation significantly strengthened baseline synaptic responses (measured as I-O curves) and enhanced LTP induction in the BLA-IL pathway. This suggests cocaine-seeking behavior hyperactivates this pathway to drive maladaptive cue-driven responses. How these changes in synaptic strength relate to the IL's role in extinction learning remains unclear. Extinction paired with SHAM stimulation partially reduced cocaine self-administration effects as the amplitude of LTP in SHAM-stimulated rats following reinstatement was significantly smaller than in the COC group (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH). Importantly, pairing extinction with VNS reversed both the increase in baseline responses in the BLA-IL projection and the amplification of LTP in this pathway that accompanied drug-seeking, resulting in only a small LTP resembling HFS-induced changes in synaptic plasticity seen in YS-control rats (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eH). Projections from the BLA to the mPFC contact both pyramidal projection neurons \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e and inhibitory interneurons \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. In the IL, interneuron activation drives robust feedforward inhibition \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, so the overall impact of the BLA projection may be predominantly inhibitory. Thus, increased strength and plasticity in the BLA-IL projection induced by cocaine self-administration and reinstatement may lead to IL inhibition and increased drug-seeking behavior \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. In contrast, extinction (alone or paired with VNS) may reduce this projection's strength, leading to IL disinhibition and improved extinction memory expression. The reduction in synaptic strength in the BLA-IL pathway following VNS is noteworthy for another reason: Several studies show that VNS potentiates synaptic responses relative to control conditions \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e or enhances LTP \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Our study provides the first evidence that pairing behavior with VNS can also lead to synaptic response weakening, even if other pathways' strength was enhanced in the same subject. The mechanisms remain unclear, but they underscore the pathway-specificity of VNS modulation.\u003c/p\u003e\u003cp\u003eThe NAc core regulates reward evaluation and motor activity. Drug-seeking is associated with increased excitability of PL-NAc core projecting neurons \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, and drug-induced changes in PL-NAc glutamate transmission drive drug-taking, relapse, and withdrawal. Repeated cocaine exposure strengthens glutamatergic transmission in the PL-NAc pathway \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e, while PL inhibition can attenuate cue-induced reinstatement of cocaine seeking \u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Multiple lines of evidence support that chronic cocaine exposure induces LTP-like changes in nucleus accumbens medium spiny neurons \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, including increased AMPA/NMDA ratios of synaptic currents \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, upregulated membrane insertion of AMAP receptors into synaptic membranes \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e, and heightened behavioral sensitivity to locally administered AMPA \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. Consistent with these findings, we show that cocaine self-administration and reinstatement significantly increased baseline eLFP amplitudes relative to YS group levels, suggesting drug-seeking strengthened the PL-NAc core pathway. High frequency stimulation induced persistent LTP in YS control animals, consistent with previous findings \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. In contrast, cocaine self-administration and reinstatement in SHAM-stimulated rats altered metaplasticity in this pathway, not only reducing LTP induction ability as previously shown \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, but causing LTD emergence. This suggests LTP induction in this pathway occurs on a sliding scale where prior drug exposure creates a condition where synapses are already potentiated (in an LTP-like state, evidenced by increased baseline responses in I-O curves), making further potentiation difficult due to ceiling effects, while depression remains inducible \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eSimilar drug-induced deficits in LTP or LTD induction in the NAc core have been shown for cocaine \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e or heroin \u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. These synaptic changes likely underlie heightened sensitivity to drug-associated cues and increased relapse vulnerability \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. Importantly, we show that VNS modulates drug-induced alterations in synaptic plasticity within the PL to NAc core pathway. Pairing extinction with VNS reduced baseline eLFP amplitudes compared to recordings in COC and SHAM-treated rats, suggesting VNS reversed drug-induced changes in synaptic strength. VNS also partially reversed drug-induced metaplasticity changes seen in SHAM or COC groups, so that in the VNS group, HFS did not result in LTD. Together, these VNS-induced changes may attenuate pathological neuroplasticity associated with addiction, restoring the circuit's capacity for bidirectional plasticity and countering the cocaine-induced \"ceiling effect\" that favors LTD over LTP. By normalizing exaggerated responsiveness to drug-associated cues, VNS might reduce the conditioned craving that drives relapse.\u003c/p\u003e\u003cp\u003eThe IL plays a crucial role in the consolidation and expression of extinction memories \u003csup\u003e\u003cspan additionalcitationids=\"CR44\" citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e, and it inhibits drug-seeking behavior through its projections to the NAc shell and/or the PL \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. Cocaine-seeking induced by IL inactivation is reversed by concurrent inactivation of the PL or BLA, suggesting that during extinction expression, IL actively competes with the cocaine-seeking circuitry \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Extinction training induces plasticity in the IL-NAc shell projection \u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e, increasing AMPA receptor expression in the NA shell, with GluA1 levels negatively correlating with reinstatement susceptibility \u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. Conversely, during drug seeking, activity in the IL-NAc shell connection may decrease \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e, enabling the return of drug-seeking behavior following extinction. Our results provide further support for these ideas as rats in both COC and SHAM groups showed LTD, suggesting that drug-seeking weakened this pathway, consistent with previous studies demonstrating that IL inactivation induces cocaine-seeking \u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. In contrast, VNS strengthened both the baseline response and increased metaplasticity in this pathway so that HFS of the IL caused pronounced LTP in the NAc shell. Together, these findings suggest drug-seeking behavior disrupts connections between the IL and NAc shell, whereas VNS strengthens the connection and enhances synaptic plasticity to aid extinction memory expression.\u003c/p\u003e\u003cp\u003eActivation of ascending vagus nerve fibers triggers release of various neuromodulators, including norepinephrine, acetylcholine, and BDNF, within the central nervous system, resulting in widespread cortical and subcortical activation \u003csup\u003e\u003cspan additionalcitationids=\"CR53 CR54 CR55 CR56\" citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e. This release creates permissive conditions for synaptic plasticity, modulating cognitive and motivational states and influencing both sensory processing and encoding, as well as learning and memory-related processes \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. Specifically, long-term VNS increases norepinephrine and dopamine levels in the PFC and NAc, potentially influencing addiction-related neuroplasticity \u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. VNS delivered during extinction from cocaine self-administration also increases BDNF levels in the mPFC, modulating glutamatergic transmission in the IL. Blocking TrkB receptors prevented both VNS' effect on synaptic transmission and its beneficial effects on cue-induced relapse behavior \u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. Consistent with our findings of VNS-induced network reorganization, studies in human patients with major depression indicate that VNS normalizes activity within the ventromedial prefrontal cortex, cingulate cortex, and limbic regions \u003csup\u003e\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e and modulates pathways relevant for reward and motivation, strengthening the functional connectivity between the NAc, mPFC, and ACC \u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e,\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e. The VNS-induced changes in metaplasticity in the three pathways examined in our study similarly enhance capacity for adaptive plasticity in the corticolimbic network and contribute to VNS' inhibitory effects on drug-seeking behavior (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOur study suggests that VNS modulates drug-seeking behavior by modulating drug-induced neuroplasticity within key corticolimbic circuits. VNS effectively enhanced extinction learning and suppressed drug-seeking behavior by reversing maladaptive synaptic changes induced by cocaine use and reinstatement. Specifically, VNS strengthened the IL-NAc shell pathway, crucial for extinction memory expression, and partially reversed synaptic plasticity in the PL-NAc core pathway that drives drug-seeking. These findings support the idea that VNS might serve as an adjunct to addiction treatment, offering a means for targeted synaptic plasticity to reduce relapse vulnerability.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003e\u003cb\u003eAnimals and surgical procedures\u003c/b\u003e\u003c/p\u003e\u003cp\u003eMale and female Sprague Dawley rats (Envigo, \u0026ge;\u0026thinsp;90 days old) were assigned to four groups: cocaine self-administration (COC, n\u0026thinsp;=\u0026thinsp;16), yoked-saline control (YS, n\u0026thinsp;=\u0026thinsp;14), and cocaine self-administration followed by extinction training with either sham-stimulation (SHAM, n\u0026thinsp;=\u0026thinsp;16) or vagus nerve stimulation (VNS, n\u0026thinsp;=\u0026thinsp;18). Rats were individually housed on a 12-hour reverse light/dark cycle with ad libitum food and water access. All protocols complied with the NIH Guide for Laboratory Animal Care and were approved by The University of Texas at Dallas IACUC committee and were conducted in accordance with the ARRIVE guidelines for reporting animal research. Rats were anesthetized with ketamine HCl (87.5 mg/kg) and xylazine (5 mg/kg) and implanted with jugular vein catheters and a custom cuff electrode around the left vagus nerve for VNS delivery \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. Catheters were flushed daily with gentamicin (2\u0026ndash;3 mg/day/animal) and heparin (0.2 ml of 100 units) to prevent infection and maintain catheter patency. Ketoprofen was also administered to reduce pain and discomfort.\u003c/p\u003e\u003cp\u003e\u003cb\u003eDrug self-administration, extinction training, and VNS treatment\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDrug self-administration and extinction training were performed as previously described \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e\u003c/sup\u003e. After 7\u0026ndash;10 days of recovery, rats learned to self-administer food pellets in a single overnight session before beginning daily cocaine self-administration sessions in operant conditioning chambers (Med Associates). During the 2 hr. self-administration sessions, each active lever press delivered 0.25 mg cocaine (NIDA Drug Supply Program) in 0.05 ml saline over 3 seconds and the presentation of drug-paired cues (illumination of the light over the active lever and the presentation of a 2900 Hz tone), followed by a 20-second timeout. Subjects completed at least 10 days of self-administration with \u0026ge;\u0026thinsp;20 infusions per session. Rats in the YS groups received saline infusions contingent on lever presses by cocaine-administering rats. Extinction groups underwent 10 days of training where lever presses no longer produced cocaine infusions or presentation of drug-paired cues. During extinction, rats received either sham stimulation or noncontingent VNS (0.4 mA for 30 seconds every 5 minutes). Following 10 days of extinction training, drug-seeking behavior was reinstated in a cue-induced reinstatement session during which presses on the active lever triggered the presentation of the previously drug-paired tone and light but did not result in drug delivery or VNS.\u003c/p\u003e\u003cp\u003e\u003cb\u003eIn vivo LFP recording\u003c/b\u003e\u003c/p\u003e\u003cp\u003eEvoked local field potentials (eLFPs) were recorded after either the final self-administration session (COC, YS) or after cue-induced reinstatement (SHAM, VNS). Under urethane anesthesia (1.5 g/kg, i.p.) we recorded eLFPs in three pathways: For recordings of eLFPs in the BLA-IL pathway, a bipolar matrix stimulation electrode (FHC) was placed in the BLA (DV: 7.3, AP: -2.7, ML: 4.9 from bregma) and eLFPs were recorded in the IL (DV: 5, AP: +3, ML: 0.6 from bregma) using a tungsten microelectrode (WPI). For recordings in the IL-NAc shell pathway, the stimulation electrode was placed in the IL (DV: 5, AP: +3, ML: 0.6 from bregma), and eLFPs were recorded in the NAc shell (DV: 7.3, AP: +1.5, ML: 0.8 from bregma). Field potentials in the BLA-IL and IL-NAc shell pathways were recorded in opposing hemispheres in the same rats. We alternated both hemispheres and the order of the recordings across all animals. For recordings of eLFPs in the PL-NAc core pathway, the stimulation electrode was placed in the PL (DV: 3.5, AP: +3, ML: 0.6 from bregma) and recordings were performed in the NAc core (DV: 7, AP: +1.5, ML: 1.4 from bregma). Field responses were evoked every 15 s using a 0.3 ms stimulation pulse, and the basal stimulation intensity corresponded to 40% of the minimum current intensity that evoked a maximum field response, based on an input\u0026ndash;output curve determined before collection of baseline data. Signals were amplified using a Model 1600 Neuropore Amplifier (A-M Systems) and a BMA 200 Portable Bioamplifier (CWE, cwe-inc.com). Signals were digitized using a CED 1401 interface (Cambridge Electronic Design, Cambridge, England) and analyzed using Spike-2 (CED). Baseline data were collected for a minimum of 10 min before synaptic plasticity was induced using high-frequency stimulation (HFS) consisting of three bursts of 100 pulses at 50 Hz (2 s), with 20 s inter-burst intervals at the minimum current intensity that evoked the maximum field response. Field potential amplitude was measured as the difference between the mean of a 5 ms window before the stimulation artifact and the negative peak of the field potential after the stimulation artifact. Responses were averaged across 2 min for analysis. Data were normalized to baseline, and the average of a 10 min baseline was set as 100%, and the 10 min period 40\u0026ndash;50 min after plasticity induction was used to analyze long-term synaptic changes.\u003c/p\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003eData analysis\u003c/h2\u003e\u003cp\u003eStatistical analyses used GraphPad Prism 7.0.5. Active lever presses during self-administration and extinction were compared using separate two-way ANOVAs with the factors of treatment and time following with Post hoc analyses. An independent t-test was conducted on the cue-induced reinstatement session to compare reinstatement between VNS and SHAM animals. Changes in eLFP amplitudes following induction of synaptic plasticity were analyzed using repeated-measures ANOVA with a treatment group \u0026times; time interaction. Input-output curves of eLFPs were analyzed using two-way repeated measures ANOVA with the factors of treatment group \u0026times; current intensity. \u003cem\u003eP\u003c/em\u003e values\u0026thinsp;\u0026lt;\u0026thinsp;0.05 were considered significant.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflict of interest:\u003c/h2\u003e\u003cp\u003eThe authors of this manuscript have no conflicts of interest.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthical approval:\u003c/strong\u003e\u003cp\u003e This study has been conducted based on ethical approval from the University of Texas at Dallas.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding information:\u003c/h2\u003e\u003cp\u003eThis work was supported by a grant from the NIH to SK (Grant number:1R01DA055008).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eR.A. conceptualization, data acquisition, statistical analysis, writing, reviewing, and editing the manuscript. L.V. and C.D. data acquisition. S.K. funding acquisition, conceptualization, writing, review, and editing of the manuscript. All authors reviewed the manuscript and approved the final version for publication.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors are grateful to the following undergraduates in the Kroener lab for their contribution: Mansi Madaik, Zarin Tasnim Hasan, Dravin Raj and Neissa Molin. Cocaine HCl was provided by the NIDA Drug Supply Program. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institute on Drug Abuse or the National Institutes of Health.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKoob, G. F. \u0026amp; Volkow, N. D. J. T. l. p. Neurobiology of addiction: a neurocircuitry analysis. \u003cstrong\u003e3\u003c/strong\u003e, 760-773 (2016).\u003c/li\u003e\n\u003cli\u003eMoussawi, K.\u003cem\u003e et al.\u003c/em\u003e N-Acetylcysteine reverses cocaine-induced metaplasticity. \u003cem\u003eNature neuroscience\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 182-189 (2009).\u003c/li\u003e\n\u003cli\u003eKnackstedt, L. A.\u003cem\u003e et al.\u003c/em\u003e Extinction training after cocaine self-administration induces glutamatergic plasticity to inhibit cocaine seeking. \u003cem\u003eJournal of Neuroscience\u003c/em\u003e \u003cstrong\u003e30\u003c/strong\u003e, 7984-7992 (2010).\u003c/li\u003e\n\u003cli\u003ePeters, J., Kalivas, P. W. \u0026amp; Quirk, G. J. Extinction circuits for fear and addiction overlap in prefrontal cortex. \u003cem\u003eLearning \u0026amp; memory\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 279-288 (2009).\u003c/li\u003e\n\u003cli\u003eFuchs, R. A., Feltenstein, M. W. \u0026amp; See, R. E. The role of the basolateral amygdala in stimulus-reward memory and extinction memory consolidation and in subsequent conditioned cued reinstatement of cocaine seeking. \u003cem\u003eThe European journal of neuroscience\u003c/em\u003e \u003cstrong\u003e23\u003c/strong\u003e, 2809-2813, doi:10.1111/j.1460-9568.2006.04806.x (2006).\u003c/li\u003e\n\u003cli\u003eMcLaughlin, J. \u0026amp; See, R. E. Selective inactivation of the dorsomedial prefrontal cortex and the basolateral amygdala attenuates conditioned-cued reinstatement of extinguished cocaine-seeking behavior in rats. \u003cem\u003ePsychopharmacology\u003c/em\u003e \u003cstrong\u003e168\u003c/strong\u003e, 57-65 (2003).\u003c/li\u003e\n\u003cli\u003eMiller, C. A. \u0026amp; Marshall, J. F. Altered Fos expression in neural pathways underlying cue‐elicited drug seeking in the rat. \u003cem\u003eEuropean Journal of Neuroscience\u003c/em\u003e \u003cstrong\u003e21\u003c/strong\u003e, 1385-1393 (2005).\u003c/li\u003e\n\u003cli\u003eSmith, A. C.\u003cem\u003e et al.\u003c/em\u003e Synaptic plasticity mediating cocaine relapse requires matrix metalloproteinases. \u003cem\u003eNature neuroscience\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 1655-1657 (2014).\u003c/li\u003e\n\u003cli\u003eAbraham, W. C. Metaplasticity: tuning synapses and networks for plasticity. \u003cem\u003eNat Rev Neurosci\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 387, doi:10.1038/nrn2356 (2008).\u003c/li\u003e\n\u003cli\u003eCimpianu, C.-L., Strube, W., Falkai, P., Palm, U. \u0026amp; Hasan, A. Vagus nerve stimulation in psychiatry: a systematic review of the available evidence. \u003cem\u003eJournal of neural transmission\u003c/em\u003e \u003cstrong\u003e124\u003c/strong\u003e, 145-158 (2017).\u003c/li\u003e\n\u003cli\u003eClark, K., Krahl, S., Smith, D. \u0026amp; Jensen, R. Post-training unilateral vagal stimulation enhances retention performance in the rat. \u003cem\u003eNeurobiology of learning and memory\u003c/em\u003e \u003cstrong\u003e63\u003c/strong\u003e, 213-216 (1995).\u003c/li\u003e\n\u003cli\u003eClark, K.\u003cem\u003e et al.\u003c/em\u003e Posttraining electrical stimulation of vagal afferents with concomitant vagal efferent inactivation enhances memory storage processes in the rat. \u003cem\u003eNeurobiology of learning and memory\u003c/em\u003e \u003cstrong\u003e70\u003c/strong\u003e, 364-373 (1998).\u003c/li\u003e\n\u003cli\u003eSun, L.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation improves working memory performance. \u003cem\u003eJournal of Clinical and Experimental Neuropsychology\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, 954-964 (2017).\u003c/li\u003e\n\u003cli\u003eChilds, J. E., DeLeon, J., Nickel, E. \u0026amp; Kroener, S. Vagus nerve stimulation reduces cocaine seeking and alters plasticity in the extinction network. \u003cem\u003eLearning \u0026amp; Memory\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 35-42 (2017).\u003c/li\u003e\n\u003cli\u003eChilds, J. E., Kim, S., Driskill, C. M., Hsiu, E. \u0026amp; Kroener, S. Vagus nerve stimulation during extinction learning reduces conditioned place preference and context-induced reinstatement of cocaine seeking. \u003cem\u003eBrain stimulation\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 1448-1455 (2019).\u003c/li\u003e\n\u003cli\u003eDriskill, C. M.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation (VNS) modulates synaptic plasticity in the rat infralimbic cortex via Trk-B receptor activation to reduce drug-seeking. \u003cem\u003ebioRxiv\u003c/em\u003e (2024).\u003c/li\u003e\n\u003cli\u003ePe\u0026ntilde;a, D. F.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation enhances extinction of conditioned fear and modulates plasticity in the pathway from the ventromedial prefrontal cortex to the amygdala. \u003cem\u003eFrontiers in behavioral neuroscience\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 327 (2014).\u003c/li\u003e\n\u003cli\u003eKeute, M. \u0026amp; Gharabaghi, A. Brain plasticity and vagus nerve stimulation. \u003cem\u003eAutonomic neuroscience : basic \u0026amp; clinical\u003c/em\u003e \u003cstrong\u003e236\u003c/strong\u003e, 102876, doi:10.1016/j.autneu.2021.102876 (2021).\u003c/li\u003e\n\u003cli\u003eOlsen, L. K.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation-induced cognitive enhancement: Hippocampal neuroplasticity in healthy male rats. \u003cem\u003eBrain Stimul\u003c/em\u003e \u003cstrong\u003e15\u003c/strong\u003e, 1101-1110, doi:10.1016/j.brs.2022.08.001 (2022).\u003c/li\u003e\n\u003cli\u003ePeters, J., LaLumiere, R. T. \u0026amp; Kalivas, P. W. Infralimbic prefrontal cortex is responsible for inhibiting cocaine seeking in extinguished rats. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 6046-6053, doi:10.1523/JNEUROSCI.1045-08.2008 (2008).\u003c/li\u003e\n\u003cli\u003eKoob, G. F. \u0026amp; Volkow, N. D. Neurobiology of addiction: a neurocircuitry analysis. \u003cem\u003eThe Lancet Psychiatry\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 760-773 (2016).\u003c/li\u003e\n\u003cli\u003eSee, R. E., Kruzich, P. J. \u0026amp; Grimm, J. W. Dopamine, but not glutamate, receptor blockade in the basolateral amygdala attenuates conditioned reward in a rat model of relapse to cocaine-seeking behavior. \u003cem\u003ePsychopharmacology\u003c/em\u003e \u003cstrong\u003e154\u003c/strong\u003e, 301-310 (2001).\u003c/li\u003e\n\u003cli\u003eCiccocioppo, R., Sanna, P. P. \u0026amp; Weiss, F. Cocaine-predictive stimulus induces drug-seeking behavior and neural activation in limbic brain regions after multiple months of abstinence: reversal by D1 antagonists. \u003cem\u003eProceedings of the National Academy of Sciences\u003c/em\u003e \u003cstrong\u003e98\u003c/strong\u003e, 1976-1981 (2001).\u003c/li\u003e\n\u003cli\u003eKim, J. H. \u0026amp; Richardson, R. The effect of temporary amygdala inactivation on extinction and reextinction of fear in the developing rat: unlearning as a potential mechanism for extinction early in development. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 1282-1290, doi:10.1523/JNEUROSCI.4736-07.2008 (2008).\u003c/li\u003e\n\u003cli\u003eLaurent, V. \u0026amp; Westbrook, R. F. Inactivation of the infralimbic but not the prelimbic cortex impairs consolidation and retrieval of fear extinction. \u003cem\u003eLearn Mem\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 520-529, doi:10.1101/lm.1474609 (2009).\u003c/li\u003e\n\u003cli\u003eBloodgood, D. W., Sugam, J. A., Holmes, A. \u0026amp; Kash, T. L. Fear extinction requires infralimbic cortex projections to the basolateral amygdala. \u003cem\u003eTransl Psychiatry\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 60, doi:10.1038/s41398-018-0106-x (2018).\u003c/li\u003e\n\u003cli\u003eCho, J. H., Deisseroth, K. \u0026amp; Bolshakov, V. Y. Synaptic encoding of fear extinction in mPFC-amygdala circuits. \u003cem\u003eNeuron\u003c/em\u003e \u003cstrong\u003e80\u003c/strong\u003e, 1491-1507, doi:10.1016/j.neuron.2013.09.025 (2013).\u003c/li\u003e\n\u003cli\u003eCheriyan, J., Kaushik, M. K., Ferreira, A. N. \u0026amp; Sheets, P. L. Specific Targeting of the Basolateral Amygdala to Projectionally Defined Pyramidal Neurons in Prelimbic and Infralimbic Cortex. \u003cem\u003eeNeuro\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, doi:10.1523/ENEURO.0002-16.2016 (2016).\u003c/li\u003e\n\u003cli\u003eMcGarry, L. M. \u0026amp; Carter, A. G. Inhibitory gating of basolateral amygdala inputs to the prefrontal cortex. \u003cem\u003eJournal of Neuroscience\u003c/em\u003e \u003cstrong\u003e36\u003c/strong\u003e, 9391-9406 (2016).\u003c/li\u003e\n\u003cli\u003eChilds, J. E., DeLeon, J., Nickel, E. \u0026amp; Kroener, S. Vagus nerve stimulation reduces cocaine seeking and alters plasticity in the extinction network. \u003cem\u003eLearning \u0026amp; memory\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 35-42, doi:10.1101/lm.043539.116 (2017).\u003c/li\u003e\n\u003cli\u003eZuo, Y., Smith, D. C. \u0026amp; Jensen, R. A. Vagus nerve stimulation potentiates hippocampal LTP in freely-moving rats. \u003cem\u003ePhysiol Behav\u003c/em\u003e \u003cstrong\u003e90\u003c/strong\u003e, 583-589, doi:10.1016/j.physbeh.2006.11.009 (2007).\u003c/li\u003e\n\u003cli\u003eWayman, W. N. \u0026amp; Woodward, J. J. Chemogenetic excitation of accumbens-projecting infralimbic cortical neurons blocks toluene-induced conditioned place preference. \u003cem\u003eJournal of Neuroscience\u003c/em\u003e \u003cstrong\u003e38\u003c/strong\u003e, 1462-1471 (2018).\u003c/li\u003e\n\u003cli\u003eGipson, C. D., Kupchik, Y. M. \u0026amp; Kalivas, P. W. Rapid, transient synaptic plasticity in addiction. \u003cem\u003eNeuropharmacology\u003c/em\u003e \u003cstrong\u003e76\u003c/strong\u003e, 276-286 (2014).\u003c/li\u003e\n\u003cli\u003eStefanik, M. T.\u003cem\u003e et al.\u003c/em\u003e Optogenetic inhibition of cocaine seeking in rats. \u003cem\u003eAddiction biology\u003c/em\u003e \u003cstrong\u003e18\u003c/strong\u003e, 50-53 (2013).\u003c/li\u003e\n\u003cli\u003eKourrich, S., Rothwell, P. E., Klug, J. R. \u0026amp; Thomas, M. J. Cocaine experience controls bidirectional synaptic plasticity in the nucleus accumbens. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e27\u003c/strong\u003e, 7921-7928, doi:10.1523/JNEUROSCI.1859-07.2007 (2007).\u003c/li\u003e\n\u003cli\u003eGipson, C. D.\u003cem\u003e et al.\u003c/em\u003e Relapse induced by cues predicting cocaine depends on rapid, transient synaptic potentiation. \u003cem\u003eNeuron\u003c/em\u003e \u003cstrong\u003e77\u003c/strong\u003e, 867-872, doi:10.1016/j.neuron.2013.01.005 (2013).\u003c/li\u003e\n\u003cli\u003eConrad, K. L.\u003cem\u003e et al.\u003c/em\u003e Formation of accumbens GluR2-lacking AMPA receptors mediates incubation of cocaine craving. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e454\u003c/strong\u003e, 118-121, doi:10.1038/nature06995 (2008).\u003c/li\u003e\n\u003cli\u003eLoweth, J. A., Tseng, K. Y. \u0026amp; Wolf, M. E. Adaptations in AMPA receptor transmission in the nucleus accumbens contributing to incubation of cocaine craving. \u003cem\u003eNeuropharmacology\u003c/em\u003e \u003cstrong\u003e76 Pt B\u003c/strong\u003e, 287-300, doi:10.1016/j.neuropharm.2013.04.061 (2014).\u003c/li\u003e\n\u003cli\u003ePierce, R. C., Bell, K., Duffy, P. \u0026amp; Kalivas, P. W. Repeated cocaine augments excitatory amino acid transmission in the nucleus accumbens only in rats having developed behavioral sensitization. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 1550-1560, doi:10.1523/JNEUROSCI.16-04-01550.1996 (1996).\u003c/li\u003e\n\u003cli\u003eSuto, N.\u003cem\u003e et al.\u003c/em\u003e Previous exposure to psychostimulants enhances the reinstatement of cocaine seeking by nucleus accumbens AMPA. \u003cem\u003eNeuropsychopharmacology\u003c/em\u003e \u003cstrong\u003e29\u003c/strong\u003e, 2149-2159, doi:10.1038/sj.npp.1300533 (2004).\u003c/li\u003e\n\u003cli\u003eShen, H. \u0026amp; Kalivas, P. W. Reduced LTP and LTD in prefrontal cortex synapses in the nucleus accumbens after heroin self-administration. \u003cem\u003eInternational Journal of Neuropsychopharmacology\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 1165-1167 (2013).\u003c/li\u003e\n\u003cli\u003eKalivas, P. W. The glutamate homeostasis hypothesis of addiction. \u003cem\u003eNature reviews neuroscience\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 561-572 (2009).\u003c/li\u003e\n\u003cli\u003eLaLumiere, R. T., Niehoff, K. E. \u0026amp; Kalivas, P. W. The infralimbic cortex regulates the consolidation of extinction after cocaine self-administration. \u003cem\u003eLearn Mem\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 168-175, doi:10.1101/lm.1576810 (2010).\u003c/li\u003e\n\u003cli\u003eLaLumiere, R. T., Smith, K. C. \u0026amp; Kalivas, P. W. Neural circuit competition in cocaine‐seeking: roles of the infralimbic cortex and nucleus accumbens shell. \u003cem\u003eEuropean Journal of Neuroscience\u003c/em\u003e \u003cstrong\u003e35\u003c/strong\u003e, 614-622 (2012).\u003c/li\u003e\n\u003cli\u003eGutman, A. L.\u003cem\u003e et al.\u003c/em\u003e Extinction of Cocaine Seeking Requires a Window of Infralimbic Pyramidal Neuron Activity after Unreinforced Lever Presses. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e37\u003c/strong\u003e, 6075-6086, doi:10.1523/JNEUROSCI.3821-16.2017 (2017).\u003c/li\u003e\n\u003cli\u003eNett, K. E.\u003cem\u003e et al.\u003c/em\u003e Infralimbic Projections to the Nucleus Accumbens Shell and Amygdala Regulate the Encoding of Cocaine Extinction Learning. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e43\u003c/strong\u003e, 1348-1359, doi:10.1523/JNEUROSCI.2023-22.2022 (2023).\u003c/li\u003e\n\u003cli\u003eFuchs, R. A., Ramirez, D. R. \u0026amp; Bell, G. H. Nucleus accumbens shell and core involvement in drug context-induced reinstatement of cocaine seeking in rats. \u003cem\u003ePsychopharmacology (Berl)\u003c/em\u003e \u003cstrong\u003e200\u003c/strong\u003e, 545-556, doi:10.1007/s00213-008-1234-4 (2008).\u003c/li\u003e\n\u003cli\u003eLaLumiere, R. T., Smith, K. C. \u0026amp; Kalivas, P. W. Neural circuit competition in cocaine-seeking: roles of the infralimbic cortex and nucleus accumbens shell. \u003cem\u003eThe European journal of neuroscience\u003c/em\u003e \u003cstrong\u003e35\u003c/strong\u003e, 614-622, doi:10.1111/j.1460-9568.2012.07991.x (2012).\u003c/li\u003e\n\u003cli\u003eVan den Oever, M. C., Spijker, S., Smit, A. B. \u0026amp; De Vries, T. J. Prefrontal cortex plasticity mechanisms in drug seeking and relapse. \u003cem\u003eNeurosci Biobehav Rev\u003c/em\u003e \u003cstrong\u003e35\u003c/strong\u003e, 276-284, doi:10.1016/j.neubiorev.2009.11.016 (2010).\u003c/li\u003e\n\u003cli\u003eSutton, M. A.\u003cem\u003e et al.\u003c/em\u003e Extinction-induced upregulation in AMPA receptors reduces cocaine-seeking behaviour. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e421\u003c/strong\u003e, 70-75, doi:10.1038/nature01249 (2003).\u003c/li\u003e\n\u003cli\u003eWu, X., Kobeissi, A. M., Phillips, H. L., Dai, H. \u0026amp; Yao, W. D. A Prefrontal Cortex-Nucleus Accumbens Circuit Attenuates Cocaine-conditioned Place Preference Memories. \u003cem\u003ebioRxiv\u003c/em\u003e, doi:10.1101/2025.03.21.644656 (2025).\u003c/li\u003e\n\u003cli\u003eCao, J., Lu, K.-H., Powley, T. L. \u0026amp; Liu, Z. Vagal nerve stimulation triggers widespread responses and alters large-scale functional connectivity in the rat brain. \u003cem\u003ePloS one\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, e0189518 (2017).\u003c/li\u003e\n\u003cli\u003eCollins, L., Boddington, L., Steffan, P. J. \u0026amp; McCormick, D. Vagus nerve stimulation induces widespread cortical and behavioral activation. \u003cem\u003eCurrent Biology\u003c/em\u003e \u003cstrong\u003e31\u003c/strong\u003e, 2088-2098. e2083 (2021).\u003c/li\u003e\n\u003cli\u003eNichols, J. A.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation modulates cortical synchrony and excitability through the activation of muscarinic receptors. \u003cem\u003eNeuroscience\u003c/em\u003e \u003cstrong\u003e189\u003c/strong\u003e, 207-214, doi:10.1016/j.neuroscience.2011.05.024 (2011).\u003c/li\u003e\n\u003cli\u003eFurmaga, H., Carreno, F. R. \u0026amp; Frazer, A. Vagal nerve stimulation rapidly activates brain-derived neurotrophic factor receptor TrkB in rat brain. \u003cem\u003ePLoS One\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, e34844, doi:10.1371/journal.pone.0034844 (2012).\u003c/li\u003e\n\u003cli\u003eFollesa, P.\u003cem\u003e et al.\u003c/em\u003e Vagus nerve stimulation increases norepinephrine concentration and the gene expression of BDNF and bFGF in the rat brain. \u003cem\u003eBrain Res\u003c/em\u003e \u003cstrong\u003e1179\u003c/strong\u003e, 28-34, doi:10.1016/j.brainres.2007.08.045 (2007).\u003c/li\u003e\n\u003cli\u003eRoosevelt, R. W., Smith, D. C., Clough, R. W., Jensen, R. A. \u0026amp; Browning, R. A. Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat. \u003cem\u003eBrain Res\u003c/em\u003e \u003cstrong\u003e1119\u003c/strong\u003e, 124-132, doi:10.1016/j.brainres.2006.08.048 (2006).\u003c/li\u003e\n\u003cli\u003eBorland, M. S.\u003cem\u003e et al.\u003c/em\u003e Pairing vagus nerve stimulation with tones drives plasticity across the auditory pathway. \u003cem\u003eJournal of neurophysiology\u003c/em\u003e (2019).\u003c/li\u003e\n\u003cli\u003eManta, S., El Mansari, M., Debonnel, G. \u0026amp; Blier, P. Electrophysiological and neurochemical effects of long-term vagus nerve stimulation on the rat monoaminergic systems. \u003cem\u003eInternational Journal of Neuropsychopharmacology\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 459-470 (2013).\u003c/li\u003e\n\u003cli\u003eDriskill, C. M.\u003cem\u003e et al.\u003c/em\u003e Vagus Nerve Stimulation (VNS) Modulates Synaptic Plasticity in the Infralimbic Cortex via Trk-B Receptor Activation to Reduce Drug-Seeking in Male Rats. \u003cem\u003eThe Journal of neuroscience : the official journal of the Society for Neuroscience\u003c/em\u003e \u003cstrong\u003e44\u003c/strong\u003e, doi:10.1523/jneurosci.0107-24.2024 (2024).\u003c/li\u003e\n\u003cli\u003ePardo, J. V.\u003cem\u003e et al.\u003c/em\u003e Chronic vagus nerve stimulation for treatment-resistant depression decreases resting ventromedial prefrontal glucose metabolism. \u003cem\u003eNeuroimage\u003c/em\u003e \u003cstrong\u003e42\u003c/strong\u003e, 879-889 (2008).\u003c/li\u003e\n\u003cli\u003eWang, Z.\u003cem\u003e et al.\u003c/em\u003e Frequency-dependent functional connectivity of the nucleus accumbens during continuous transcutaneous vagus nerve stimulation in major depressive disorder. \u003cem\u003eJournal of psychiatric research\u003c/em\u003e \u003cstrong\u003e102\u003c/strong\u003e, 123-131 (2018).\u003c/li\u003e\n\u003cli\u003eZhang, S.\u003cem\u003e et al.\u003c/em\u003e Prolonged longitudinal transcutaneous auricular vagus nerve stimulation effect on striatal functional connectivity in patients with major depressive disorder. \u003cem\u003eBrain Sciences\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 1730 (2022).\u003c/li\u003e\n\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Cocaine, Vagus nerve stimulation, Local field potentials, LTP, Prefrontal cortex","lastPublishedDoi":"10.21203/rs.3.rs-7014180/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7014180/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eCocaine use alters brain networks and connections, impairing inhibitory control over drug-seeking. Cortical-limbic circuits, including the infralimbic (IL), prelimbic (PL) cortices, and basolateral amygdala (BLA), regulate extinction learning and drug-seeking via projections to the nucleus accumbens (NAc). Vagus nerve stimulation (VNS) paired with extinction enhances learning and reduces reinstatement, but its effects on extinction-related networks remain unclear. This study examined how cocaine and VNS affect plasticity in relapse-related pathways. Evoked local field potentials (eLFP) were recorded in the IL, NAc core, and NAc shell following self-administration or reinstatement sessions. In the BLA-IL pathway, cocaine-treated (COC) and sham-VNS (SHAM) groups exhibited the highest baseline eLFP amplitudes and increased long-term potentiation (LTP) induction, which VNS restored to yoked-saline (YS) levels. In the PL-NAc core pathway, high-frequency stimulation (HFS) had no effect on EFPs in VNS-treated animals, significantly differing from the long-term depression (LTD) observed in COC and SHAM groups, which had the highest baseline eLFP amplitudes. In the IL-NAc shell pathway, VNS-treated rats displayed the largest baseline amplitudes, and unlike YS, COC, and SHAM groups, HFS in the IL induced persistent LTP in the NAc shell. These findings suggest cocaine use and craving induce maladaptive neuroplasticity within cortical-limbic circuits, and VNS may modulate these changes, contributing its beneficial effects in preventing reinstatement.\u003c/p\u003e","manuscriptTitle":"Vagus nerve stimulation modulates synaptic plasticity induced by cocaine- seeking in reward-related circuitry","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-16 11:33:37","doi":"10.21203/rs.3.rs-7014180/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-25T06:09:15+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-07T08:42:02+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-25T08:57:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"90318698127409964807267292326882362253","date":"2025-07-16T08:42:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"221841611679649173461019970756910720144","date":"2025-07-14T14:54:55+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-14T12:07:28+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-14T12:04:37+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-07-09T16:20:12+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-07-03T20:55:15+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-07-03T20:51:09+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3f780eb1-d868-4b4f-8023-7429dfa1bde0","owner":[],"postedDate":"July 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":51514494,"name":"Biological sciences/Neuroscience"},{"id":51514495,"name":"Biological sciences/Physiology"}],"tags":[],"updatedAt":"2025-12-15T16:10:18+00:00","versionOfRecord":{"articleIdentity":"rs-7014180","link":"https://doi.org/10.1038/s41598-025-27577-7","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-12-11 15:57:51","publishedOnDateReadable":"December 11th, 2025"},"versionCreatedAt":"2025-07-16 11:33:37","video":"","vorDoi":"10.1038/s41598-025-27577-7","vorDoiUrl":"https://doi.org/10.1038/s41598-025-27577-7","workflowStages":[]},"version":"v1","identity":"rs-7014180","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7014180","identity":"rs-7014180","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}