DISTRIBUTION AND ONTOGENY OF 3-ALPHA-HYDROXYSTEROID DEHYDROGENASE IN THE RAT-BRAIN

3 alpha-Hydroxysteroid dehydrogenase in the brain is responsible for p roduction of neuroactive tetrahydrosteroids that interact with the maj or inhibitory gamma-aminobutyric acid receptor complexes. Distribution of 3 alpha-hydroxysteroid dehydrogenase in different regions of the b rain in rats was evaluated by activity assay and by Western immunoblot ting using a monoclonal antibody against liver 3 alpha-hydroxysteroid dehydrogenase as the probe. The olfactory bulb was found to contain th e highest level of 3 alpha-hydroxysteroid dehydrogenase activity, whil e moderate levels of the enzyme activity were found in other regions s uch as cerebellum, cerebral cortex, hypothalamus and pituitary. Some a ctivities were found in the rest of the brain such as amygdala, brain stem, caudate putamen, cingulate cortex, hippocampus, midbrain, and th alamus. The protein levels of 3 alpha-hydroxysteroid dehydrogenase in different regions of the brain as detected by Western immunoblotting a re comparable to those of the enzyme activity. No sexual dimorphism wa s found in either the concentration levels or the activities of the br ain 3 alpha-hydroxysteroid dehydrogenase. At the time of birth, the ra t brain already expresses a significant level of 3 alpha-hydroxysteroi d dehydrogenase; the levels of brain 3 alpha-hydroxysteroid dehydrogen ase activity in rats continue to rise during the first week after thei r birth, and reach a plateau thereafter.