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 masculine development of singing behavior and of the telencephalic brain regions involved in the control of song. However, early estrogen treatment of males also blocks masculine development of copulatory behavior, presumably controlled by diencephalic regions. In an effort to determine whether the differences in estrogen action are related to sex and regional differences in androgen metabolism (estrogen synthesis or androgen 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 variety of conditions. Cultures from all three brain regions express high levels of aromatase and 5 beta-reductase activity. Comparisons between telencephalic and diencephalic cultures of the activity and kinetics of aromatase suggest that the telencephalic cultures convert androgen to estrogen more efficiently than diencephalic cultures, which might be important in the differential action of estrogen in the two brain regions. However, the activity of neither aromatase nor 5 beta-reductase was significantly different between the sexes in either telencephalic or diencephalic cultures. Thus, comparisons between the sexes do not support the idea that differences in posthatching aromatase or 5 beta-reductase activity account for the pattern of sexual differentiation of the song and copulatory systems.