PGRMC1 and major depressive disorder: Generally, oestrogen acts on neurons and glial cells by binding to the nuclear oestrogen receptors ERα and exhibit an antidepressant effect [69], proven by enhancing the antidepressant-effect of ketamine; In contrast, progesterone led to depression by binding to progesterone receptor membrane component 1 (PGRMC1) on microglia, lowering BDNF expression as reported [70].