Apparent effects of neurotransmitters on sexual differentiation of the brain without mediation of sex hormones.

Male sexual behaviour was found to be permanently decreased in neonatally reserpinized or paragylinized male rats. On the other hand, hypoplasia of sex organs was only observed in reserpinized, but not in pargylinized newborn males. Furthermore, male sexual behavior was found to be permanently increased in neonatally pyridostigminized males which showed even a slight hypoplasia of seminal vesicles in neonatal life. These findings suggest that changes of neurotransmitter concentrations and/or turnover rates apparently induced by psychotrophic drugs can affect sex-specific brain differentiation by direct action without mediation of sex hormones. Hence, neurotransmitters may be regarded as organizers of the brain.