Meeting Abstract

P3.102  Saturday, Jan. 5  Role of photoperiod and gonadal steroids in the regulation of kisspeptin in seasonally breeding Siberian hamsters GREIVES, T.J.*; HUMBER, S.A.; SCOTTI, M.; KRIEGSFELD, L.J.; DEMAS, G.E.; Department of Biology, Indiana University, Bloomington, IN 47405 USA.; Department of Psychology, University of California, Berkeley, Berkeley, CA 94720 USA. tjgreive@indiana.edu

In temperate, seasonally breeding rodents, photoperiod acts as a major environmental signal initiating marked changes in reproduction; long �summer-like� days maintain functional gonads whereas short �winter-like� days induce gonadal regression and inhibit reproduction. Recently, we demonstrated that the neuropeptide, kisspeptin, potently stimulates the reproductive endocrine axis in hamsters, and that photoperiod influences hypothalamic kisspeptin expression, indicating a potential role for kisspeptin in the regulation of seasonal reproduction. In mice, kisspeptin is down-regulated following castration and up-regulated in response to testosterone (T). Thus, it is unclear whether photoperiodic changes in kisspetpin staining is in direct response to photoperiod cues, or modulated indirectly by seasonal changes in sex steroids. The goal of the current study was to assess the relative contributions of photoperiod and gonadal steroids in regulating hypothalamic kisspeptin in seasonally breeding animals. Siberian hamsters were housed in long (L:D 16:8), or short days (L:D 8:16) for 8 weeks and were subsequently either castrated or sham operated, and received a Silastic implant containing either T or left empty. Castration reduced but did not eliminate kisspeptin staining in the anteroventral periventricular nucleus (AVPV), whereas nearly all staining in short days was eliminated. Interestingly, testosterone replacement induced long-day like kisspeptin staining. These data suggest a role for both gonadal-dependent and independent mechanisms regulating seasonal kisspeptin expression in Siberian hamsters.