Chronic stress exerts negative effects on cognitive functions through inducing changes in the hippocampus. Brain-derived neurotrophic factor (BDNF) is an essential factor in cognitive activities, which is considerably reduced under chronic stress. 1,25(OH)2 vitamin D plays neuroprotective roles partially by regulating the expression of various neurotrophic factors.

 Since few studies have studied the impact of vitamin D on BDNF level, we conducted this brief experiment to understand the role of vitamin D in maintaining hippocampal BDNF protein levels by using restraint as a model of chronic stress in rats.

 Rats underwent restraint stress 3 h/day for 28 days, during which they received vitamin D (5, 10 μg/kg) or its vehicle (IP, twice weekly). After the stress period, serum corticosterone (CORT) and hippocampus BDNF protein levels were measured.

 Restraint stress increased serum CORT (P < 0.001) and reduced BDNF protein levels (P < 0.001) as compared to the non-stress group. Vitamin D markedly maintained BDNF level close to normal (P < 0.001), but did not change CORT level significantly.

 This study demonstrated that 3h/day of chronic restraint stress for 28 days boosted serum CORT and declined hippocampal BDNF levels, similar to stronger restraint stress models. Vitamin D maintained BDNF level close to normal in the hippocampus, but it did not affect CORT level significantly.