Elsevier

Hormones and Behavior

Volume 52, Issue 4, November 2007, Pages 492-498
Hormones and Behavior

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

https://doi.org/10.1016/j.yhbeh.2007.07.004Get rights and content

Abstract

To avoid breeding during unsuitable environmental or physiological circumstances, the reproductive axis adjusts its output in response to fluctuating internal and external conditions. The ability of the reproductive system to alter its activity appropriately in response to these cues has been well established. However, the means by which reproductively relevant cues are interpreted, integrated and relayed to the reproductive axis remain less well specified. The neuropeptide kisspeptin has been shown to be a potent positive stimulator of the hypothalamo–pituitary–gonadal (HPG) axis, suggesting a possible neural locus for the interpretation/integration of these cues. Because a failure to inhibit reproduction during winter would be maladaptive for short-lived female rodents, female Siberian hamsters (Phodopus sungorus) housed in long and short days were examined. In long “summer” photoperiods, kisspeptin is highly expressed in the anteroventral periventricular nucleus (AVPV), with low expression in the arcuate nucleus (Arc). A striking reversal in this pattern is observed in animals held in short, “winter” photoperiods, with negligible kisspeptin expression in the AVPV and marked staining in the Arc. Although all studies to date suggest that both populations act to stimulate the reproductive axis, these contrasting expression patterns of AVPV and Arc kisspeptin point to disparate roles for these two cell populations. Additionally, we found that the stimulatory actions of exogenous kisspeptin are blocked by acyline, a gonadotropin-releasing hormone (GnRH) receptor antagonist, suggesting an action of kisspeptin on the GnRH system rather than pituitary gonadotropes. Finally, females held in short day lengths exhibit a reduced response to exogenous kisspeptin treatment relative to long-day animals. Together, these findings indicate a role for kisspeptin in the AVPV and Arc as an upstream integration center for reproductively relevant stimuli and point to a dual mechanism of reproductive inhibition in which kisspeptin expression is reduced concomitant with reduced sensitivity of the HPG axis to this peptide.

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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