Effects of a prenatal androgen peak on rat brain sexual differentiation

Exposure of the developing female brain to a 5 alpha-dihydrotestosterone surge on day 18 of gestation resulted in defeminization and slight masculinization of the brain. In contrast, abolition of the androgenic effects of the testosterone peak naturally occurring in male fetuses on day 18 of gestation by exposure of the developing male brain to cyproterone acetate, at that time, resulted in demasculinization while feminization was not affected. On the basis of these results, we suggest that both the prenatal testosterone peak and the high testosterone levels occurring in males neonatally are necessary for aromatization sufficient to effect complete male rat brain sexual differentiation.