EXPRESSION OF THE STEROIDOGENIC ENZYME P450SCC IN THE CENTRAL AND PERIPHERAL NERVOUS SYSTEMS DURING RODENT EMBRYOGENESIS

Neurosteroids are steroids that are synthesized de novo in the brain a nd include some classical (adrenal and gonadal) steroids and some uniq ue brain-specific steroids. Neurosteroids are thought to mediate their action through ion-gated channel receptors, such as gamma-aminobutyri c acid, and N-methyl-D-aspartate rather than through classical nuclear steroid hormone receptors. Some enzymes involved in neurosteroidogene sis have been identified as those found in steroidogenic tissues, and some may be unique to the brain. We previously demonstrated that the m essenger RNAs for the cholesterol side-chain cleavage enzyme, P450scc, and one form of 11 beta-hydroxylase, P450c11 beta, are regionally exp ressed in the adult rat brain. We now demonstrate that P450scc is expr essed in the nervous system of the developing rodent embryo in cell li neages derived from the neural crest. Despite the presence of readily detectable P450scc protein, a ribonuclease protection assay detected P 450scc messenger RNA only in the trunks and not in the heads of male a nd female rat embryos. P450scc immunoreactive protein is continuously expressed in the central and peripheral nervous systems from embryonic day 9.5 in the rat. The sites of expression of P450scc are located ma inly in sensory structures of the peripheral nervous system during emb ryogenesis, suggesting a possible function in coordinating environment al cues and behavior and in the development and organization of the ne rvous system.