Figure 4.

Mitochondrial steroidogenesis. (A) Cholesterol is translocated across the mitochondrial membrane by the steroidogenic acute regulatory protein (StAR). Thereafter, cholesterol is converted to pregnenolone by the side-chain cleavage enzyme CYP11A1. Pregnenolone is trafficked then to the endoplasmaic reticulum (ER), where it can be converted into various neurosteroids including allopregnanolone. (B) Most GABA_A-receptors contain two α and β subunits each together with a single copy of the γ2 subunit. These subunits arrange around a central pore to form a chloride ion-conducting channel. Allopregnanolone is a positive allosteric regulator of GABA_A-receptors leading to prolonged channel opening and hyperpolarization.