Melatonin Stimulates the Release of Gonadotropin-Inhibitory Hormone by the Avian Hypothalamus

Abstract

Gonadotropin-inhibitory hormone (GnIH), a neuropeptide that inhibits gonadotropin synthesis and release, was first identified in quail hypothalamus. GnIH acts on the pituitary and GnRH neurons in the hypothalamus via GnIH receptor to inhibit gonadal development and maintenance. In addition, GnIH neurons express melatonin receptor and melatonin induces GnIH expression in the quail brain. Thus, it seems that melatonin is a key factor controlling GnIH neural function. In the present study, we investigated the role of melatonin in the regulation of GnIH release and the correlation of GnIH release with LH release in quail. Melatonin administration dose-dependently increased GnIH release from hypothalamic explants in vitro. GnIH release was photoperiodically controlled. A clear diurnal change in GnIH release was observed in quail, and this change was negatively correlated with changes in plasma LH concentrations. GnIH release during the dark period was greater than that during the light period in explants from quail exposed to long-day photoperiods. Conversely, plasma LH concentrations decreased during the dark period. In contrast to LD, GnIH release increased under short-day photoperiods, when the duration of nocturnal secretion of melatonin increases. These results indicate that melatonin may play a role in stimulating not only GnIH expression but also GnIH release, thus inhibiting plasma LH concentrations in quail. This is the first report describing the effect of melatonin on neuropeptide release.

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

“…A regulatory mechanism(s) governing nLPXRFa peptide mRNA expression is essential to understand the physiological significance of novel newt neuropeptides. Recently, we reported that melatonin induces GnIH expression (Ubuka et al 2005) and its release (Chowdhury et al 2010) in the quail brain. Furthermore, we also demonstrated that the expressions of fGRP and fGRP-RPs in the anuran brain are also induced by melatonin .…”

“…In both experiments, newts were kept under continuous light. To quantify the newt LPXRFa peptide precursor mRNA, competitive PCR analysis was performed as described previously (Chowdhury et al 2010), with a little modification. The newt brains were removed and snap-frozen immediately in liquid nitrogen.…”

“…We first identified a novel neuropeptide with a C-terminal LPLRFa motif in the quail brain (Tsutsui et al 2000). It was shown that this avian neuropeptide was located in the hypothalamohypophysial system (Tsutsui et al 2000, Ubuka et al 2003, Ukena et al 2003a) and decreased gonadotropin release in vitro (Tsutsui et al 2000) and in vivo (Osugi et al 2004, Chowdhury et al 2010. We therefore designated this neuropeptide as gonadotropin-inhibitory hormone (GnIH; Tsutsui et al 2000).…”

A genetically female brain is required for a regular reproductive cycle in chicken brain chimeras

“…Plasma LH levels were determined by radioimmunoassay (RIA) using a highly purified chicken LH (USDA-cLH-I-3) 52 as the radioligand and standard, and polyclonal rabbit anti-chicken LH serum (USDA-AcLH-5) 52 supplied by the US Department of Agriculture-Agricultural Research Service (USDA-ARS), Biotechnology and Germplasm laboratory (Beltsville, MD). The RIA was performed as described previously 53,54 . The antiserum against chicken LH, at a final dilution of 1:50,000, exhibited the ability to specifically bind 23% of the added radioligand in the absence of any unlabelled chicken LH.…”

Effect of Photoperiod and Melatonin on Volume and Cellular Parameters of Testis in Pinealectomized Rats

“…The effect mechanism of melatonin on reproductive system previously investigated in humans (Balik et al, 2004), other mammals (Tamarkin et al;Uyar & Alan;Yilmaz et al, 2000) and avians (Chowdhury et al, 2010). Melatonin has an inhibitory effect on reproductive system of nonseasonable polyestric animals.…”