Sex hormone-dependent brain maturation and sexual behaviour in rats.

In male and female rats the endogenous steroid and gonadotrophin secretion was inhibited by injecting high doses of chlormadinone acetate (CmAc) from day 14 to 24 of life, i. e. during the period of brain maturation. In adulthood the males treated prepubertally with CmAc exhibited reduced sexual activity and fertility, whereas the females did not differ from the controls. More complete sex hormone deficiency during brain maturation was achieved by castration on day 14 of life. Controls were castrated at normal puberty time (40--60 days). Both groups were then substituted with androgens or oestrogens. In the females castrated on day 14 no impairment of sexual behaviour was observed as compared to the later castrated controls. In contrast, the early castrated males showed delayed onset of mounting behaviour. At autopsy, the weights of their sex organs were found to be lower than in the controls despite equal testosterone replacement for several months. These findings speak in favour of a permanently diminished responsiveness to androgens in males having been exposed to more or less severe androgen deficiency during sex specific brain maturation. Hence, the maturation of a male hypothalamus as well as the differentiation appears to depend at least in part on the presence of androgens, whereas in females it runs without hormonal influence.