Hormones and sexual differentiation of the brain.

Male rats castrated on the first day of life exhibited predominantly heterotypical (homosexual) behaviour after androgen substitution in adulthood. In addition, an increased evocability of a positive feedback effect of oestrogen was observed in such genetic males. In homosexual men, an increased evocability of a positive oestrogen feedback on luteinizing hormone (LH) secretion was also found as compared to heterosexual men. These findings suggest that male homosexuality may be based, at least in part, on andogen deficiency during a critical period of brain differentiation. In addition, we have found significantly increased plasma follicle-stimulating hormone (FSH) and LH levels associated with decreased plasma free testosterone levels in homosexual men, but only in effeminate homosexuals. In view of these data, sexual deviations in the human may be based, at least in part, on discrepancies between the genetic sex and a sex-specific sex-hormone level during brain differentiation in prenatal life. Methods were therefore developed for determining genetic sex and sex-specific sex-hormone level during brain differentiation in prenatal life. Methods were therefore developed for determining genetic sex and sex-specific sex-hormone levels in amniotic fluid, in order to detect and possibly correct such discrepancies. Sex hormone-dependent brain differentiation may be mediated, at least in part, by neurotransmitters, which may be regarded as local hormones of the brain. Interestingly enough, we have found permanent abnormalities of mating and other non-mating behaviour associated with permanent structural and chemical alterations in discrete brain regions of rats after neonatal treatment with psychotropic drugs known to affect neurotransmitter metabolism in the brain. Therefore, changes in neurotransmitter concentrations and/or turnover rates induced by psychosocial influences as well as by systemic hormones (particularly by sex hormones), when occurring during differentiation and maturation of the brain, may permanently affect sexual behaviour, sexual orientation and gender role behaviour throughout life.