Cytochrome P450-dependent neurosteroid synthesis in the rat brain hippocampal neurons

We have demonstrated the neuronal localization of neurosteroidogenic systems as well as the regulation of neurosteroidogenic activity in an adult rat hippocampus. The expressions of steroidogenic enzymes (cytochrome P450scc, adrenodoxin (ADX), NADPH-adrenodoxin reductase (ADR), hydroxysteroid sulfotransferase and steroidogenic acute regulatory protein (StAR)) were observed principally in pyramidal neurons and granule neurons by means of immunohistochemical staining. The expression of P450scc, redox partners, sulfotransferase and StAR was also confirmed by Western blot analysis.Exposing the neurons to N-methyl-D-aspartate (NMDA) stimulated the process of active neurosteroidogenesis. Upon stimulation with NMDA, the significant net production of pregnenolone (PREG) and pregnenolone sulfate (PREGS) was observed in the hippocampus. This neurosteroid production was considerably suppressed by the addition of antagonists of NMDA receptors, by Ca²⁺ depletion or by the addition of an inhibitor of P450scc. Upon stimulation with NMDA, the processing of full-length StAR (37-kDa) to the truncated 30-kDa StAR was observed. Taken together, these observations imply that hippocampal neurons synthesize neurosteroids. This synthesis may be stimulated and regulated by glutamate-mediated synaptic communication. We also discuss the possibility that PREGS may act as a paracrine modulator of NMDA receptors.