BDNF and major depressive disorder: In contrast, Xu and Liang (2021) provided direct mechanistic evidence for a BDNF-mediated effect of active vitamin D. In a Post-stroke depression model (MCAO combined with UCMS), daily intracerebroventricular administration of calcitriol (25 μg/kg) over 4 weeks significantly increased hippocampal BDNF expression and reversed depression-like behaviors, including reduced sucrose preference and increased immobility in the forced swim test [46].