Photoperiod and Reproductive Condition Are Associated with Changes in RFamide-Related Peptide (RFRP) Expression in Syrian Hamsters (Mesocricetus auratus)

Abstract

To conserve scarce energetic resources during winter, seasonal breeders inhibit reproduction and other nonessential behavioral and physiological processes. Reproductive cessation is initiated in response to declining day lengths, a stimulus represented centrally as a long-duration melatonin signal. The melatonin signal is not decoded by the reproductive axis directly, but by an unidentified neurochemical system upstream of gonadotropin-releasing hormone (GnRH). The dorsomedial nucleus of the hypothalamus (DMH) has been implicated in seasonal changes in reproductive function in Syrian hamsters (Mesocricetus auratus), although the specific-cell phenotype decoding photoperiodic information remains unknown. RFamide-related peptide (RFRP; the mammalian homolog of the gonadotropin-inhibitory hormone (GnIH) gene identified in birds) has emerged as a potent inhibitory regulator of the reproductive axis and, significantly, its expression is localized to cell bodies of the DMH in rodents. In the present study, the authors explored the relationship between RFRP expression, photoperiod exposure, and reproductive condition/hormonal status. In male hamsters that respond to short days with reproductive inhibition, RFRP-ir and mRNA expression are markedly reduced relative to long-day animals. Replacement of testosterone in short-day animals did not affect this response, suggesting that alterations in RFRP expression are not a result of changing sex steroid concentrations. A subset of the hamster population that ignores day length cues and remains reproductively competent in short days (nonresponders) exhibits RFRP-ir expression comparable to long-day hamsters. Analysis of cell body and fiber density suggests a potential interplay between peptide production and release rate in differentially regulating the reproductive axis during early and late stages of reproductive regression. Together, the present findings indicate that photoperiod-induced suppression of reproduction is associated with changes in RFRP and mRNA expression, providing opportunity for further exploration on the role that RFRP plays in this process.

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone

“…The photoperiodic variation of GnIH expression is abolished in Px male hamsters, and injections of LD hamsters with melatonin for 60 days reduced GnIH gene expression to SD levels, indicating that the regulation is dependent on melatonin (Revel et al, 2008) (Table 1). Mason et al (2010) also showed that in male Syrian hamsters that respond to SD with reproductive inhibition, GnIH-ir and mRNA expression are markedly reduced relative to LD animals ( Table 1). Replacement of testosterone in SD animals did not affect this response.…”

“…Replacement of testosterone in SD animals did not affect this response. However, a subset of the male hamsters that ignores day length cues and remains reproductively competent in SD (nonresponders) exhibited GnIH-ir similar to LD hamsters (Mason et al, 2010). Ubuka et al (2012a) showed in male Siberian hamster that GnIH mRNA expression is higher in LD than in SD (Table 1).…”

Identification, localization and expression of LPXRFamide peptides, and melatonin-dependent induction of their precursor mRNA in the newt brain

“…To understand the physiological role of LPXRFa peptides, it is essential to know the factor that regulates the expression of LPXRFa peptides. Therefore, the second aim was to determine the regulation of the expression of the identified newt GnIH orthologs (LPXRFa peptide) by melatonin because this nocturnal hormone acts to regulate the expression of GnIH and its orthologs in birds and mammals (Ubuka et al 2005, Mason et al 2010. We therefore analyzed the effect of melatonin administration on the expression of LPXRFa peptide precursor mRNA in the newt brain.…”

Dorsomedial Hypothalamic Lesions Block Syrian Hamster Testicular Regression in Short Day Lengths Without Diminishing Increased Testosterone Negative-Feedback Sensitivity1

“…In male Syrian and Siberian hamsters, mRNA expression and neuropeptide-immunoreactivity for gonadotrophin-inhibitory hormone (GnIH; also known as RFamide-related-peptide-3) are markedly reduced in short DLs [28,37]. This response is mediated by Mel, with pinealectomy abolishing SD-induced inhibition of GnIH and Mel administration to LD hamsters leading to inhibition of GnIH to values similar to those of SD hamsters.…”

“…In favoring the latter hypothesis, they pointed to the DMN as a likely target tissue; it is the only site within the mediobasal hypothalamus that both binds Mel and has abundant concentrations of androgen receptors. The DMN also contains RFamide-related peptides implicated in the control of gonadotrophin secretion [28,29]. If the DMN is an essential component of the neural mechanism that controls seasonal changes in brain sensitivity to steroid negative feedback, then ablation of this structure should ''hinder the induction of increased sensitivity to steroid negative feedback necessary for termination of the breeding season'' [17] present study evaluated this hypothesis by testing whether the DMN is a necessary component of the mechanism that increases sensitivity of SD males to negative-feedback inhibition of FSH by testosterone.…”