Reversal by estrogen of the effect of dorsal raphe stimulation on release of LH but not prolactin.

Electrical stimulation of the dorsal raphe nucleus (DRN) was administered to rats 2-4 weeks after ovariectomy and at least 7 days following implantation of a bipolar electrode. During stimulation the concentration of luteinizing hormone (LH) decreased whereas that of prolactin (Prl) increased in serial plasma samples obtained from the unanesthetized animals via a cannula chronically implanted in the right external jugular vein. Administration of estradiol benzoate (5 micrograms/100 g BW) for 2 days prior to the experiment reversed the effect of stimulation on LH but augmented the Prl response, suggesting modulation by estrogen of the relative effectiveness of opposing pathways ascending from DRN to influence LH release. It is also apparent that LH and Prl release are controlled by distinct mechanisms since estrogen exerted opposite influences on the responses of these two hormones to stimulation of DRN.