Immunohistochemical localization of 3 beta-hydroxysteroid dehydrogenase and 5 alpha-reductase in the brain of the African lungfish Protopterus annectens

The localization of the enzymes responsible for the biosynthesis of neurost eroids in the brain of dipnoans has not yet been determined. In the present study, we investigated the immunohistochemical distribution of 3 beta -hyd roxysteroid dehydrogenase (3 beta -HSD) and 5 alpha -reductase (5 alpha -R) in the brain and pituitary of the African lungfish Protopterus annectens b y using antibodies raised against type I human 3 beta -HSD and type I human 5 alpha -R. The 3 beta -HSD and 5 alpha -R immunoreactivities were detecte d in cell bodies and fibers located in the same areas of the lungfish brain , namely, in the pallium, thalamus, hypothalamus, tectum, and periaqueducta l gray. Identification of astrocytes, oligodendrocytes, and neurons with an tisera against glial fibrillary acidic protein, galactocerebroside and neur ofilaments revealed that, in the lungfish brain, 3 beta -HSD immunolabeling is expressed exclusively by neurons, whereas the 5 alpha -R-immunoreactive material is contained in both neurons and glial cells. In the pituitary gl and, 3 beta -HSD- and 5 alpha -R-like immunoreactivity was localized in bot h the pars distalis and the pars intermedia. The present study provides the first immunocytochemical mapping of two key steroidogenic enzymes in the b rain and pituitary of a lungfish. These data strongly suggest that neuroste roid biosynthesis occurs in the brain of fishes, as previously shown for am phibians, birds, and mammals. J. Comp. Neurol. 438:123-135, 2001. (C) 2001 Wiley-Liss, Inc.