Coitus-induced activation of c-fos and gonadotropin-releasing hormone in hypothalamic neurons in female rabbits

Copulation induces hypothalamic release of neuropeptides and catecholamines , especially gonadotropin-releasing hormone (GnRH) and norepinephrine, in f emale rabbits. The forebrain distribution of GnRH cells and the cellular ev ents responsible for the coitally induced GnRH surge have not been identifi ed. We characterized the expression of c-fos mRNA before (0 min) and up to 60 min after coitus in forebrain tissues of mated and nonmated females and compared these findings with those in which single- and double-labeled GnRH /Fos protein cells were identified by immunocytochemistry (ICC). Enhanced e xpression of fos-mRNA occurred 30 min after coitus, especially in the anter oventral periventricular nucleus (AVPV), the encapsulated portion of the be d nucleus of the stria terminalis (BNSTe) and the ventrolateral hypothalamu s (VLH); this increased fos-mRNA activity remained elevated at 60 min in th e AVPV and VLH, and was reflected by Fos protein expression 90 min postcoit us. Both ICC Fos-labeled and ICC GnRH-labeled cells were widely distributed throughout the forebrain with postcoital increased double-labeling in the preoptic-septal areas, the anterior-medial hypothalamus and the VLH. The in creased number of dual-labeled and unchanged number of single-labeled GnRH cells after coitus suggest some GnRH neurons were non-detected before coitu s. Many dual-labeled neurons were adjacent to Fos-labeled cells, suggesting enhanced interneuronal input to GnRH cells after coitus. Collectively, the results suggest that coitus activates hypothalamic GnRH neurons via severa l loci that include the AVPV, BNSTe and VLH. The distinct anatomical locati on of the AVPV, BNSTe and VLH further suggests that coital signals may reac h the hypothalamus via separate neural pathways that are likely developed w ithin the brainstem. (C) 2000 Published by Elsevier Science B.V.