BDNF and major depressive disorder: The products of BDNF may promote neurogenesis and protect against excitotoxicity in both the hippocampus (Khaspekov et al., 2004; Scharfman et al., 2005) and striatum (Perez-Navarro et al., 1999; Mohapel et al., 2005) and mediates the increase of amygdala volume in samples of patients with drug-induced depression.