Sexual differences in tuberoinfundibular dopamine nerve activity induced by neonatal androgen exposure

The activities of different catecholaminergic neurons in the brains of male amd female rats were estimated by measuring (1) the rate of decline of dopamine (DA) and norepinephrine (NE) after inhibition of tyrosine hydroxylase with alpha-methyltyrosine (alpha-MT) and (2) the rate of accumulation of dihydroxyphenylalanine (DOPA) after inhibition of DOPA decarboxylase with NSD 1015 in brain regions containing the terminals of these neurons. In the median eminence the accumulation of DOPA and the alpha-MT-induced decline of DA, but not NE, were higher in the female than in the male, suggesting increased activity of tuberoinfundibular DA neurons in the female. There were no sexual differences in DA neurons which terminate in any of the other brain regions (striatum, olfactory tubercle, nucleus accumbens, posterior pituitary). To determine if the sexual difference in tuberoinfundibular DA neuronal activity results from neonatal exposure to androgens, the rate of DOPA accumulation was examined in the median eminence of females, males, and androgen-sterilized females (all of which were castrated as adults) and in adult males which were castrated as neonates. Similar values for DOPA accumulation were observed in the median eminence of castrate females and neonatally castrated males, while significantly lower values were observed in castrate males and androgen-sterilized females. Thus, neonatal exposure to androgens alters the activity of tuberoinfundibular DA neurons. Neonatal androgen-induced differences in tuberoinfundibular DA neuronal activity may be responsible, in part, for sexual differences in the hypothalamic regulation of hypophyseal hormone secretion.