Neonatal catecholaminergic influence on behaviour and sexual hormones

There is evidence of a sexually dimorphic effect of serotonin administration during the critical period of sexual differentiation on gonadal hormone secretion in adulthood. To investigate the possible involvement of catecholamines on these mechanisms, we have injected dopamine or noradrenaline intraventricularly into neonatal male and female rats to examine the influence, during the critical period, of this single treatment on the adulthood. Gonadal sex hormone contents, sexually dimorphic behaviours, and catecholaminergic distribution in hypothalamic and extrahypothalamic areas were studied. Both catecholaminergic treatments in females resulted in a reduced striatal dopaminergic activity and an increase in the hypothalamic noradrenergic ratio, while a reduction in the open field activity occurred in the same groups. These results suggest the possible involvement of striatal dopamine and hypothalamic noradrenaline in the differentiation of exploratory activity in females. A reduction in copulatory behaviour was shown in adults of both sexes after neonatal dopaminergic administration, but gonadal hormone levels were not affected in the same way. This indicates the existence of different facets of sexual differentiation, with striatal dopamine and hypothalamic noradrenaline playing important roles in neurobehavioural differentiation.