STEROIDOGENIC ACUTE REGULATORY PROTEIN (STAR) TRANSCRIPTS CONSTITUTIVELY EXPRESSED IN THE ADULT-RAT CENTRAL-NERVOUS-SYSTEM - COLOCALIZATIONOF STAR, CYTOCHROME P-450(SCC) (CYP XIA1), AND 3-BETA-HYDROXYSTEROID DEHYDROGENASE IN THE RAT-BRAIN

Steroidogenic acute regulatory protein (StAR) is a 30-kDa protein invo lved in the transport of cholesterol to the inner mitochondrial membra ne and thus plays a key role in steroid biosynthesis. To clarify the i mplications of this protein in neurosteroid biosynthesis, we examined the possible expression of a StAR transcript in the adult rat CNS and detected it. cDNA cloning and sequencing analysis revealed that two fo rms of StAR mRNAs are expressed in the brain in the same manner as in the adrenal gland, indicating that they are fully functional and not m inor gene transcripts. An RNase protection assay quantitatively reveal ed that the amount of the rat StAR transcript in brain was two to thre e orders of magnitude lower than that in the adrenal gland. An in situ hybridization study, involving antisense riboprobes, revealed that St AR transcripts were abundant in the cerebral cortex, hippocampus, dent ate gyrus, olfactory bulb, cerebellar granular layer, and Purkinje cel ls. Furthermore, other steroidogenic enzymes, side-chain cleavage cyto chrome P-450scc (CYP XIA1) and 3 beta-hydroxysteroid dehydrogenase/Del ta(5-)Delta(4) isomerase (EC 1.1.1.145), were found to be coexpressed in the hippocampus, dentate gyrus, cerebellar granular layer, and Purk inje cells. These findings strongly indicate that neurosteroids are sy nthesized in a region-specific manner in the brain.