The 5 alpha-reductase activity of the subcortical white matter, the cerebral cortex, and the hypothalamus of the rat and of the mouse: possible sex differences and effect of castration

Previous studies have shown that the central nervous system is able to convert testosterone into 17-beta-hydroxy-5-alpha-androstan-3-one (DHT), by the action of the enzyme 5-alpha-reductase. The data here presented show that, in the brain of the rat and the mouse of both sexes, the 5-alpha-reductase activity is more concentrated in the subcortical white matter than in the hypothalamus and in the cerebral cortex. The enzymatic activity is apparently higher in the rat than in the mouse brain. The formation of DHT in the subcortical white matter, in the hypothalamus and in the cerebral cortex of both rats and mice does not show any sexual difference. Moreover, in the rat no effect of short- or long-term castration or neonatal castration or testosterone replacement could be observed on the formation of DHT in the three brain structures considered (even in the subcortical white matter, the cerebral tissue more active in converting testosterone into DHT). The present data support the view that the 5-alpha-reductase present in the brain is not under androgenic control.