The effects of stimulation and lesion of raphe nuclei on luteinizing hormone release in estrogen-progesterone-treated ovariectomized rats.

A study was made of the effects of electrochemically stimulating (ECS) and destroying the midbrain dorsal and median raphe nuclei on the estrogen-progesterone- (EP) induced surge of pituitary LH release in ovariectomized rats. ECS and lesions were produced simultaneously with anodal direct current through a chronically implanted stimulation-lesion electrode. Blood for LH assay was collected through a chronic intra-atrial cannula positioned on the day of first treatment with progesterone. ECS of the raphe nuclei exerted a strong inhibition of the LH surge when compared with sham stimulation. On the second EP treatment the onset of the LH surge was advanced both in sham-stimulated animals and in rats with raphe lesions resulting from the anodal direct current of the initial ECS. It was suggested that this apparent facilitation of the LH surge on the second EP treatment was the results of reduced stress or an altered hormonal milieu and not a consequence of destroying the raphe nuclei. The results confirm in a chronic preparation that stimulation of raphe nuclei depresses the EP-induced LH surge and that subsequently in the absence of the raphe nuclei the LH response to EP treatment is apparently normal.