BDNF and major depressive disorder: However, the neurobiology of depression is very complex, involving not only BDNF but also a lot of other members regulated by CREB, such as mammalian target of rapamycin, vascular endothelial growth factor and peroxisome proliferator-activated receptor alpha (Clark-Raymond and Halaris, 2013; Abelaira et al., 2014; Song et al., 2018).