Figure 2.

Schematic representation of the HPA axis with the neurosteroid allopregnanolone as a modulator of the stress response. Through positive allosteric modulation of the GABA_A receptors (GABA_ARs) present in corticotropin-releasing hormone (CRH) neurons, allopregnanolone participates in the negative feedback that eventually terminates the acute stress response. ACTH: adrenocorticotropic hormone; GRs: glucocorticoid receptors; MDD; major depressive disorder; PTSD: post-traumatic stress disorder; PPD: postpartum depression. Red arrows (−) indicate negative feedback.