BDNF and major depressive disorder: In addition to hippocampal BDNF, BDNF in several other brain regions including the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) play important roles in the pathogenesis of depression as well (Berton et al., 2006; Xu et al., 2017; Xu et al., 2018; Chen et al., 2021).