Effects of vitamin D in an animal model of Alzheimer's disease: behavioral assessment with biochemical investigation of Hippocampus and serum.

Regulatory role of vitamin D (VitD) in cognitive memory and learning has been proposed. Here, we examine the behavioral and biochemical effects of VitD in Alzheimer's disease (AD), as the most common form of dementia, in male Wistar rats. Animals (n = 48) were randomly divided into six groups: control, sham solvent, sham surgery, VitD (by intraperitoneal injection), AD (receiving intrahippocampal injection of amyloid-beta peptide, Aβ), and combination of VitD and Aβ. Learning and memory functions were investigated through the passive avoidance and the Morris water maze (MWM) tasks. Moreover, oxidative stress biomarkers including total antioxidant capacity (TAC), total thiol groups (TTG), lipid peroxidation (LPO), and DNA damage were assessed in hippocampus and serum. In passive avoidance task, Aβ significantly impaired the step-through latency and time in dark compartment. It also increased escape latency and time spent in the target quadrant in the MWM. VitD administration attenuated the Aβ-induced memory impairment in passive avoidance and MWM tests. Furthermore, VitD reduced deleterious biochemical effect of Aβ by enhancing the levels of TAC and TTG in addition to decreasing LPO and DNA damage levels in both hippocampus and serum. We showed, for the first time, that VitD administration improves the impaired Aβ-induced memory and that, by acting as a strong antioxidant, it can attenuate the stress oxidative biomarkers in hippocampus and serum of rats with AD. Altogether, our results provide evidence for further application of VitD in neurodegenerative disorders such as AD to enlighten the involved mechanisms.