Immunocytochemical localization of 5 alpha-reductase in rat brain

The presence of steroid 5 alpha-reductase in brain tissue is well-documented. In order to determine with precision the brain areas and nerve cell types containing this enzyme in adult rat, we have studied its immunocytochemical localization using antibodies to the sequence peptide comprising amino acids 227 to 240 of the enzyme. At the light microscopic level, 5 alpha-reductase immunoreactive material appeared to be present only in glial and ependymal cells, including tanycytes. Immunolabeled cells were found in high concentration in the hypothalamus, thalamus, hippocampus, cerebral cortex, cerebral cortex, and circumventricular organs. Immunoelectron microscopic studies demonstrated that immunoreactive material was diffusely distributed throughout the cytoplasm of glial and ependymal cells, thus confirming the association of 5 alpha-reductase immunoreactivity with nonneuronal cells. These data suggest that glial cells play an important role in the conversion of testosterone to dihydrotestosterone or progesterone to dihydroprogesterone under in vivo conditions in adult rat.