Effects of Pinealectomy and Short Day Lengths on Reproduction and Neuronal RFRP-3, Kisspeptin, and GnRH in Female Turkish Hamsters

Abstract

Long days (LDs) stimulate and short days (SDs) inhibit reproduction in photoperiodic rodents by modifying nocturnal pineal melatonin secretion. In LD Turkish hamsters, unlike other rodents, pinealectomy induces reproductive quiescence comparable to that produced by SDs. We assessed whether SDs and pinealectomy induce similar or different patterns of kisspeptin and gonadotropin-inhibitory hormone (also known as RFamide-related peptide-3 [RFRP-3] in mammals) expression, important mediators of seasonal reproductive changes in other species. Brains were harvested from sham-operated female Turkish hamsters maintained in LDs and SDs and LD-pealectomized (pinx) females, all housed in their respective photoperiods for 12 weeks. Uterine weights were substantially higher in LD-sham than in LD-pinx and SD-sham females. RFRP-3-immunoreactive(-ir) cells in the dorsomedial hypothalamic nucleus were greater in number and size in the reproductively competent LD-sham hamsters than in both reproductively suppressed SD-sham and LD-pinx hamsters. LD-sham hamsters had more kisspeptin-ir cells in the anteroventral periventricular nucleus than did LD-pinx hamsters. Reproductive quiescence, whether induced by short-day lengths or pinealectomy, was generally accompanied by comparable changes in RFRP-3 and kisspeptin, suggesting that long-duration melatonin signaling and withdrawal of melatonin by pinealectomy may act through the same neural substrates to induce gonadal quiescence.

Seasonal control of gonadotropin-inhibitory hormone (GnIH) in birds and mammals

“…Similar results are seen following several weeks of melatonin administration to long-day animals and pinealectomy prevents the suppression of GnIH in short days [81,113]. Analogous seasonal patterns of GnIH expression have been observed in European [90] and Turkish [74] hamsters as well as the semi-desert rodent, Jerboa [42]. In male hamsters, the short-day-induced reduction in GnIH is not the result of low circulating gonadal steroid concentrations; castration of long-day hamsters or providing testosterone implants to short-day hamsters does not alter the pattern of GnIH protein or mRNA [59,81,113].…”

Gonadotrophin‐inhibitory hormone and its mammalian orthologue RFamide‐related peptide‐3: Discovery and functional implications for reproduction and stress

“…By contrast to expectation, extended exposure to inhibitory day lengths leads to reductions in RFRP‐3 peptide and mRNA as well as decreased fibre density and projections to GnRH cells in Syrian and Siberian hamsters . Analogous seasonal patterns of RFRP‐3 expression are seen in European and Turkish hamsters, as well as the semi‐desert rodent, jerboa . Recently, a study in Syrian hamsters revealed that expression RFRP‐3 receptor, GPR147, also varies seasonally .…”

GnIH Control of Feeding and Reproductive Behaviors

“…These photoperiodic changes in GnIH expression disappear in Px hamsters; however, melatonin injections to LD hamsters reduce GnIH expression to SD levels (43, 83). Seasonal GnIH expression patterns were similar in European and Turkish hamsters (85, 86) and the semi-desert rodent, Jerboa (87). Although these results suggest a role for GnIH in seasonal breeding, it is inconsistent with the seasonal reproductive control model.…”