BDNF and depressive disorder: We found that social defeat stress significantly decreased levels of BDNF protein in the PFC, DG, and CA3, but not in CA1, while significantly increasing BDNF protein in the NAc (Fig. 3b), consistent with previous data from the social defeat stress model of depression (Ren et al. 2016; Yang et al. 2015b; Zhang et al. 2015b) and the rat learned helplessness model (Shirayama et al. 2015; Yang et al. 2015a).