Effects of estradiol on brain aminergic turnover of the female rainbow trout (Oncorhynchus mykiss) at the beginning of vitellogenesis.

Brain serotonin and dopamine (DA) turnovers in the female rainbow trout were studied at the beginning of the vitellogenesis and related to blood estradiol (E2) levels; pituitary and plasma gonadotropin (GtH) were also assayed. Ovariectomy did not modify brain aminergic turnover. E2 replacement on ovariectomized fish increased hypothalamic DA turnover (increased DA and increased DA metabolites). E2 stimulated GtH synthesis (positive feedback) but did not enhance GtH release; hypothalamic E2-mediated aminergic inhibition upon release was suspected. Individual relations between blood E2 levels and catecholaminergic neurotransmitters were determined. A linear positive correlation (r = 0.82) was found for the hypothalamus, but not for the pituitary, the preoptic area, or the telencephalon. These data suggest that an activation of hypothalamic tyrosine hydroxylase (the limiting step of catecholamines synthesis) by E2 could develop as vitellogenesis proceeds.