MTOR and major depressive disorder: Previous studies have reported the downregulation of the mTOR signaling pathway in postmortem human brain samples from subjects with MDD [39], as well as in PFC, hippocampus, and amygdala of several animal models of depression including the olfactory bulbectomy, chronic unpredictable stress (CUS), and chronic corticosterone exposure [40,41,42,43,44].