Neuroanatomical distribution of testosterone-metabolizing enzymes in the Japanese quail.

We describe a very sensitive and precise assay which allows one to study the metabolism of testosterone (T) in small brain nuclei dissected out according to the method of Palkovits and Brownstein. With this method, the neuroanatomical distributions of aromatase, and 5 alpha- and 5 beta-reductase activities were studied in adult male quail (Coturnix coturnix japonica). The different enzymes show different neuroanatomical distributions. Production of estradiol-17 beta (E2) was highest in the sexually dimorphic nucleus preopticus medialis (POM). We showed previously that the preoptic aromatase activity is higher in male than in female quail. As the POM is a central and very large structure within the preoptic area, the present results suggest a relationship between the neuroanatomical and the biochemical sex differences. By contrast, the production of 5 alpha-DHT was highest in the lateral hypothalamic area (LHY), the bed nucleus of the pallial commissure (BPC) and the lateral septum (SL). The 5 beta-reductase activity was highest in the lateral septum and in the ventral part of the archistriatum (AV). Moreover, there was a rostral to caudal decrease in 5 beta-reductase activity in the hypothalamus.