AROMATASE AND 5-BETA-REDUCTASE ACTIVITY IN CULTURES OF DEVELOPING ZEBRA FINCH BRAIN - AN INVESTIGATION OF SEX AND REGIONAL DIFFERENCES

Estrogen treatment of hatchling female zebra finches causes the mascul ine development of singing behavior and of the telencephalic brain reg ions involved in the control of song. However, early estrogen treatmen t of males also blocks masculine development of copulatory behavior, p resumably controlled by diencephalic regions. In an effort to determin e whether the differences in estrogen action are related to sex and re gional differences in androgen metabolism (estrogen synthesis or andro gen inactivation), we measured aromatase and 5 beta-reductase activity in dissociated-cell cultures made separately from the telencephalon, diencephalon, and also cerebellum of hatchling zebra finches under a v ariety of conditions. Cultures from all three brain regions express hi gh levels of aromatase and 5 beta-reductase activity. Comparisons betw een telencephalic and diencephalic cultures of the activity and kineti cs of aromatase suggest that the telencephalic cultures convert androg en to estrogen more efficiently than diencephalic cultures, which migh t be important in the differential action of estrogen in the two brain regions. However, the activity of neither aromatase nor 5 beta-reduct ase was significantly different between the sexes in either telencepha lic or diencephalic cultures. Thus, comparisons between the sexes do n ot support the idea that differences in posthatching aromatase or 5 be ta-reductase activity account for the pattern of sexual differentiatio n of the song and copulatory systems. (C) 1995 John Wiley & Sons, Inc.