CRH and major depressive disorder: Corticotropin‐releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN) are over‐activated under stress, thereby releasing a large amount of CRH, promoting the release of ACTH from the pituitary gland, increasing the expression of corticosterone (CORT), leading to HPA axis excitation and depression‐like behavior.9