Hypothalamic and Raphe Serotonergic Systems in Ovulation Control*

Abstract

The role of hypothalamic and midbrain serotonergic systems in the control of ovulation in the rat has been investigated using 5,7-dihydroxytryptamine (5,7-DHT) lesioning in conjunction with desmethylimipramine pretreatment. Intracisternal injection of 5,7-DHT (100 or 200 .mu.g) produced a dose-dependent decrease in the incidence of ovulation induced by PMSG [pregnant mares serum gonadotropin] (8 IU s.c. on day 30). Intraventricular injection of 200 .mu.g 5,7-DHT via the lateral ventricles completely blocked PMSG-induced ovulation. After injection into either site, nonovulatory animals were in proestrus on day 33 and contained fluid-filled uteri. Intracerebral injection of 5,7-DHT into the dorsal or median raphe significantly decreased the numbers of animals induced to ovulate. The extent and specificity of these chemical lesions were evaluated in the suprachiasmatic (SNR) and arcuate-median eminence regions of PMSG-treated rats using an in vitro uptake model. A general feature of every case of inhibited ovulation was the significant decrease in uptake of serotonin in the SNR, indicating destruction of serotonergic inputs to this region. Serotonergic SNR input from the dorsal raphe region may be essential to ovulation. Median raphe lesions appeared to be more extensive than dorsal raphe lesions, involving serotonergic projections to the arcuate-median eminence region. In addition, ascending noradrenergic projections to the SNR were significantly destroyed, also implicating these systems in ovulation control.