Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters
Section snippets
Animals and housing
Adult (> 60 days of age), intact female Siberian hamsters (P. sungorus) (n = 82) were obtained from the breeding colony maintained at Indiana University. All animals were group housed with same sex siblings in a long-day photoperiod (light:dark [LD] 16:8) prior to the start of the study. Animals were housed individually in polypropylene cages (27.8 × 17.5 × 13.0 cm) and placed in either long- (LD 16:8) or short-day (LD 8:16) photoperiods. Temperature was kept constant at 20 ± 2 °C and relative humidity
Experiment 1: effect of photoperiod on kisspeptin neurons
Kisspeptin-ir cell bodies were concentrated in the AVPV and Arc nuclei. In both nuclei, kisspeptin expression was significantly altered by photoperiodic condition (p < 0.05 in each case) (Fig. 1, Fig. 2). LD hamsters exhibited a significantly greater number of kisspeptin-ir neurons in the AVPV compared to SD animals (p < 0.05; Fig. 1, Fig. 2). The inverse was true for kisspeptin-ir expression in the Arc; females held in SD conditions had a greater number of kisspeptin-ir cells compared to LD
Discussion
The results of the present study demonstrate a critical role for kisspeptin in the interpretation and integration of reproductively relevant environmental signals and transmission of this information to the GnRH neuronal network. We observed striking differences in kisspeptin-ir expression following manipulation of photoperiod in two cell populations, the AVPV and Arc. Female Siberian hamsters maintained in “summer” photoperiods exhibited robust kisspeptin expression in the AVPV, with virtually
Acknowledgments
We thank Dr. Richard Blye of the NIH NICHD for kindly providing acyline. We also thank Stephanie Humber for technical assistance and Ilia Karatsoreos for helpful comments on an earlier version of this manuscript. Supported by NIH grant HD050470 and the UC Berkeley Committee on research grant to LJK and NSF grant IOB-0543798, a Faculty Research Support Program (FRSP) grant and a Center for the Integrative Study of Animal Behavior grant to GED.
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