Dorsal raphe lesion alters the estrous cycle and the preovulatory gonadotropin release

The purpose of this study was to examine the role that the dorsal raphe (DR)-median eminence (ME) serotonergic projection may have in the proestrous gonadotropin and prolactin (PRL) release. DR electrolytic lesions were performed in cycling rats during the first day of diestrus. The effect of DR lesions after 48-72 h of survival (short-term lesioned animals) or after 35-40 days of survival (long-term lesioned animals) on estrous cyclicity, preovulatory gonadotropin and PRL releasing pattern, ovulation and serotonin (5-HT) content of the ME were studied. Following DR lesions the estrous cycle became irregular, remaining in the diestrus phase for several days. Preovulatory gonadotropin release in short-term lesioned animals was increased; on the contrary, in long-term lesioned rats a delay in the surge of these two hormones and a decrease in LH secretion were detected. Long-term lesioned animals also showed a diminished secretion of PRL. The number of ova did not differ between control and lesioned animals. DR lesions in both short- and long-term lesioned rats reduced 5-HT levels in the ME by about 50% and nullified the normal 5-HT decline during the afternoon of proestrus. Our results suggest that the DR exerts a stimulatory influence on the preovulatory gonadotropin release by means of its 5-HT projection to the ME. As the pattern of hormonal secretion in lesioned animals remains similar to that of controls, it may be suggested that this pathway acts as a fine modulator of the mechanisms involved in the regulation of LH and FSH release in cycling rats.(ABSTRACT TRUNCATED AT 250 WORDS)