An essential component in steroid synthesis, the steroidogenic acute regulatory protein, is expressed in discrete regions of the brain

Recent data implicate locally produced steroids, termed neurosteroids, as regulators of neuronal function. Adrenal and gonadal steroidogenesis is controlled by changes in the steroidogenic acute regulatory protein (StAR); however, little is known about the regulation of neurosteroid production. We now demonstrate unequivocally that StAR mRNA and protein are expressed within glia and neurons in discrete regions of the mouse brain, and that glial StAR expression is inducible. Con sistent with a role in de novo neurosteroidogenesis, StAR colocalizes with the cholesterol side-chain cleavage enzyme P450_scc in both mouse and human brains. These data support a role for StAR in the production of neurosteroids and identify potential sites of active de novo steroid synthesis in the brain.