Effects of estradiol and prolactin on incertohypothalamic dopaminergic neurons in the male rat.

The activity of incertohypothalamic, tuberoinfundibular, mesolimbic and nigrostriatal dopamine (DA) neurons was estimated by measuring the rate of turnover of DA (decline of DA after alpha-methyltyrosine) in brain regions containing the cell bodies and terminals of these neurons. Estradiol benzoate (25 micrograms/kg/day X 3; s.c.), markedly increased the concentration of prolactin in plasma and increased the rate of turnover of DA in median eminence, but failed to alter DA neuronal activity in the striatum or nucleus accumbens. An intracerebroventricular injection of prolactin (10 micrograms/rat, 12 h) mimicked the effect of estradiol on the turnover of DA in the median an eminence. Within the incertohypothalamic DA system, both estradiol and prolactin increased DA turnover in the dorsomedial nucleus but decreased DA turnover in the rostral periventricular, medial preoptic and preoptico-suprachiasmatic nuclei. Hypophysectomy decreased the tonic activity of tuberoinfundibular DA neurons, but failed to alter the activity of incertohypothalamic DA neurons. The stimulatory effects of estrogen on DA turnover in the median eminence and dorsomedial nucleus, and the inhibitory effects of this hormone on rostral hypothalamus DA neurons were blocked by hypophysectomy. Taken together these results suggest that estradiol induced changes in intact male rats are mediated by prolactin. Estradiol increased incertohypothalamic DA neuronal activity in the medial preoptic and preoptic-suprachiasmatic nuclei of hypophysectomized rats suggesting that in the absence of circulating prolactin, estradiol has a direct stimulatory effect on incertohypothalamic DA neurons in the rostral, periventricular hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)