BDNF and major depressive disorder: Zhang et al. (2017) reported that CH effectively improves the depression-like behavior of CUMS rats, improved HPA axis hyperactivity, reduced plasma CORT and CRH expression in hypothalamus, reversed CUMS-induced decrease of 5-HT1A receptor expression, and up-regulated BDNF and phosphorylated-ERK1/2 levels in the hippocampus [21].