Abstract
The augmentation of LH in the plasma of female 5-day cycling rats was studied after perfusion of the third ventricle with dopamine, serotonin or drugs which block its synthesis at the nerve terminals.Dopamine induces a sharp rise of LH 4 h after infusion; this may be reduced if serotonin is given before. When serotonin is infused after dopamine it induces a fall of LH in blood but to a level still much higher than in control or in rats when dopamine was given after 5 HT.When dopamine is destroyed in the medial basal hypothalamus by 6-hydroxy-dopamine, LH falls in plasma to a very low level. In this situation depletion of serotoninergic terminals by 5,6-dihydroxytryptamine does not significantly modify LH level in blood. In the absence of serotonin estrogen is still acting in the arcuate nucleus as an inhibitor of LH release.These experiments support the idea that dopamine may be the mediator for the tonic positive influence on the modulatory inhibitory influence and would act together with, but independently of, estrogen. A model for such interaction is proposed.
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