Protective role of vitamin-D on chronic stress induced-learning and memory deficits in rats

Long-term stress disturbs HPA axis and increases glucocorticoids release, which disturbs neural plasticity in the hippocampus and may lead to learning and memory deficits. Noticeably, vitamin D plays a protective role in the nervous system and has receptors in the hippocampus. This behavioral study investigates the possible protective role of vitamin-D against the negative effects of chronic stress on learning and memory.

All the Rats were randomly divided to two groups; stress and control groups (each had 3 subgroups). Stress-group animals were exposed to restraint stress for 28 days, 3 hours/day. During 28 days, vitamin D (5 or 10 mg/kg), or vehicle was injected (IP) twice weekly to both groups. At day 29, blood sample collected for serum corticosterone assay. Morris water maze (MWM) test was performed in the order of 4 days training, one-day probe testing and finally working memory test. Passive avoidance test was performed after MWM.

Stress group revealed higher levels of serum corticosterone (P <0.0001) relative to controls. In MWM test, all groups learned the location of the platform during training. Latency in reaching the platform was reduced by the training days (P = 0.0001) for all the groups. Probe test indicated that stress groups reached the platform sooner than the control groups. Higher dose of vitamin D reduced this latency (P = 0.0002). Conversely, in passive avoidance test, stress groups spent less time in the dark than the control group (P = 0.0997).  Vitamin D (10 μg / kg) did not change the results.

In this study, chronic restraint stress increased blood corticosterone levels and changed the behavioral effects of long and short term spatial and conditional memory. Treatment with vitamin D improved spatial learning.