BDNF and major depressive disorder: In animal models of stress/MDD, certain micro-scale changes have been recorded which demonstrate that AE can promote hippocampal neurogenesis, vascularization, BDNF expression (both brain-wide and within the hippocampus), IGF-1 expression, VEGF expression, and hippocampal synaptic plasticity (Adlard and Cotman, 2004; Zheng et al., 2006; Bjørnebekk et al., 2010; Nakajima et al., 2010; Sartori et al., 2011; Kiuchi et al., 2012; Yau et al., 2012; Lu et al., 2014).