[Effect of 5,6-hydroxytryptamine and various light schedules on the hypothalamo-hypophyseo-gonadal system of the female rat].

Hypothalamic luliberin and plasma lutropin concentration were studied under normal light-darkness cycle or under constant illumination in rats. Some of them were injected with 5,6-dihydroxytryptamine (5,6-HTA) into the lateral brain ventricle. Constant illumination led to a persistent oestrus with a significant drop in plasma lutropin and a decrease in hypothalamic luliberin. Destruction of serotoninergic terminals with 5,6-HTA resulted in an opposite effect and prevented to some extent inhibiting influence of constant illumination. Luliberin synthesis and secretion seem to be suppressed by serotoninergic nerve terminals on the luliberin producing cells as well as by serotonin reaching the hypothalamus from the pineal gland.