SEXUAL-DIFFERENTIATION OF AROMATASE-ACTIVITY IN THE RAT-BRAIN - EFFECTS OF PERINATAL STEROID EXPOSURE

Androgens regulate aromatase activity in the medial preoptic area and other components of the brain circuit that mediates male sexual behavi or. The levels of aromatase activity within these brain regions are gr eater in males than in females. As the activation of copulation requir es aromatization of testosterone to estradiol, this quantitative enzym atic difference between sexes could contribute to the greater behavior al response displayed by males. The present study was designed to test the hypothesis that gender differences in brain aromatase activity of adult rats are dependent on the sexual differentiation of the brain t hat occurs during perinatal exposure to gonadal hormones. Aromatase ac tivity was measured in vitro in microdissected brain samples using a s ensitive radiometric assay. We examined the effect of pre- and postnat al treatment with testosterone propionate or diethylstilbestrol on bas al levels and androgen responsiveness of aromatase in adults. In addit ion, we examined what effect prepubertal gonadectomy exerts on enzyme regulation. Our results demonstrate that perinatal treatments with gon adal hormones that are known to differentiate sexual behavior can comp letely masculinize the capacity for aromatization in the adult female. The process that differentiates aromatase expression appears to depen d on androgen exposure and, in part, local estrogen synthesis, as diet hylstilbestrol was able to substitute for testosterone propionate. We also observed that prepubertal gonadectomy reduced the levels of aroma tase activity measured in adult brain, suggesting that gonadal hormone s that are secreted during puberty may enhance the expression of aroma tase activity in adulthood. From this study, we conclude that testoste rone and/or its estrogenic metabolites act on the developing brain to determine the gender-specific capacity for aromatization and to regula te androgen responsiveness within components of the neural circuitry t hat mediates male sexual behavior.