Differential response patterns of kisspeptin and RFRP to photoperiod and sex steroid feedback in the Djungarian hamster (Phodopus sungorus)

Abstract

Many animals synchronize their reproductive activity with the seasons to optimize their offspring's survival. This synchronization involves switching on and off their gonadotropic axis. Ever since their discovery as key regulators of GnRH neurons, the hypothalamic RF-amide peptides kisspeptin and RFRP have been a major focus of research on the seasonal regulation of the gonadotropic axis. In this study we investigated the regulation of both neuropeptides in the Djungarian hamster, a major animal model for the study of seasonal reproduction. During the long day breeding period, kisspeptin neurons in the anteroventral periventricular area are solely controlled by a positive sex steroid feedback, and in the arcuate nucleus they are subject to a very strong negative sex steroid feedback associated with a minor photoperiodic effect. During short day sexual quiescence, the disappearance of this hormonal feedback leads to high levels of kisspeptin in arcuate neurons. Notably, chronic central administration of kisspeptin is able to override the photoperiodic inhibition of the gonadotropic axis and reactivate the reproductive function. Therefore our data suggest that the kisspeptin secretion by arcuate neurons during sexual quiescence is inhibited by mechanisms upstream of kisspeptin neurons. RFRP expression is solely controlled by photoperiod, being strongly reduced in short days independently of the sex steroid feedback. Thus kisspeptin and RFRP display contrasting patterns of expression and regulation. Upstream mechanisms controlling these neurons should be the focus of further studies on the roles of these RFamide neuropeptides in the seasonal control of reproduction.

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