Through 5-HT receptors, particularly 1A and 2A, stress decreases BDNF and increases full-length TrkB (TrkB-FL) expression, respectively, in the hippocampus to modulate learning, adaptive processes, inhibition of aggression, and anxiety- and depression-like behaviors in rodents (Nibuya et al., 1999; Vaidya et al., 2001; Pizarro et al., 2004; Kozlovsky et al., 2007; Martinowich and Lu, 2007; Ito et al., 2011). Here, NTRK2 is linked to major depressive disorder.