Localization of 3 beta-hydroxysteroid dehydrogenase in rat brain as studied by in situ hybridization

Recent evidence suggests that brain cells can synthesize steroids de novo. The steroidogenic enzyme 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) gene family of enzymes is involved in the biosynthesis of all classes of active steroids. In the present study, we have used in situ hybridization performed with a 35S-labeled cDNA-encoding rat type I 3 beta-HSD to localize the expression of member(s) of this gene family in the adult rat brain. A specific hybridization signal could only be detected in a restricted area of the medulla ventrally and laterally bordering the fourth ventricle. This area contains the nucleus propositus hypoglossi as well as some vestibular nuclei: the nucleus vestibularis medialis, the nucleus vestibularis lateralis, and the nucleus vestibularis spinalis. At high resolution, the silver grains representing a hybridization signal were detected exclusively in neurons. The present data strongly suggest that a restricted population of neurons might be involved in steroid biosynthesis in the adult rat brain. The role of the member(s) of the rat 3 beta-HSD family in the nuclei of two cranial nerves remains to be investigated.