Kisspeptin Signalling in the Hypothalamic Arcuate Nucleus Regulates GnRH Pulse Generator Frequency in the Rat

Abstract

BackgroundKisspeptin and its G protein-coupled receptor (GPR) 54 are essential for activation of the hypothalamo-pituitary-gonadal axis. In the rat, the kisspeptin neurons critical for gonadotropin secretion are located in the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV) nuclei. As the ARC is known to be the site of the gonadotropin-releasing hormone (GnRH) pulse generator we explored whether kisspeptin-GPR54 signalling in the ARC regulates GnRH pulses.Methodology/Principal FindingsWe examined the effects of kisspeptin-10 or a selective kisspeptin antagonist administration intra-ARC or intra-medial preoptic area (mPOA), (which includes the AVPV), on pulsatile luteinizing hormone (LH) secretion in the rat. Ovariectomized rats with subcutaneous 17β-estradiol capsules were chronically implanted with bilateral intra-ARC or intra-mPOA cannulae, or intra-cerebroventricular (icv) cannulae and intravenous catheters. Blood samples were collected every 5 min for 5–8 h for LH measurement. After 2 h of control blood sampling, kisspeptin-10 or kisspeptin antagonist was administered via pre-implanted cannulae. Intranuclear administration of kisspeptin-10 resulted in a dose-dependent increase in circulating levels of LH lasting approximately 1 h, before recovering to a normal pulsatile pattern of circulating LH. Both icv and intra-ARC administration of kisspeptin antagonist suppressed LH pulse frequency profoundly. However, intra-mPOA administration of kisspeptin antagonist did not affect pulsatile LH secretion.Conclusions/SignificanceThese data are the first to identify the arcuate nucleus as a key site for kisspeptin modulation of LH pulse frequency, supporting the notion that kisspeptin-GPR54 signalling in this region of the mediobasal hypothalamus is a critical neural component of the hypothalamic GnRH pulse generator.

Food restriction during lactation suppresses Kiss1 mRNA expression and kisspeptin-stimulated LH release in rats

“…However, pulsatile LH release was attenuated during lactation in both the AL-fed and food-restricted dams, and this suppression of pulsatility was still observed on days 20-22 pp despite an increase in basal LH concentrations (Walker et al 1995). It has been demonstrated that the administration of a kisspeptin antagonist directly into the arcuate nucleus results in a decrease in LH pulse frequency without affecting pulse amplitude in rats, suggesting a role for arcuate nucleus kisspeptin in the regulation of LH pulse frequency (Li et al 2009). Therefore, it is tempting to speculate that low arcuate nucleus Kiss1 mRNA may contribute to the reduction in the pulsatile release of LH during lactation.…”

Synchronous activation of gonadotropin-releasing hormone gene transcription and secretion by pulsatile kisspeptin stimulation

“…We analyzed the kinetics of GnRH gene transcription in association with secretion of the neurohormone in response to the secretagogue kisspeptin in hypothalamic GnRH neurons. Although inhibition of kisspeptin signaling modulates pulsatile GnRH secretion in several species (24,25), the role of kisspeptin in episodic GnRH gene expression remains elusive. We examined the effects of kisspeptin pulses on ultradian GnRH gene transcription in individual GnRH neurons and examined neuronal synchronization and secretion of the decapeptide.…”

“…However, continuous administration of kisspeptin abolishes gonadotropin secretion after an acute stimulatory effect, presumably owing to receptor desensitization (21)(22)(23). Thus, kisspeptin may participate in GnRH pulse generation, although the underlying mechanisms remain elusive (24,25).…”

Current and future applications of GnRH, kisspeptin and neurokinin B analogues

“…In another study in prepubertal female monkeys, GnRH was suppressed for 90 minutes by peptide 234 suggesting that there is a lower KP tone 119 . Peptide 234 was also effective in suppressing LH (GnRH) pulsatility in ovariectomised ewes without affecting basal LH 109 and decreased LH pulse frequency, but not basal LH, when administered intra ARC in ovariectomised female rats 120 .…”

“…In these treatments steroid hormones are lowered to castrate levels resulting in side effects such as hot flushes, reduced lean body mass, loss of libido and bone loss. The demonstration that KP antagonists reduce LH pulsatility 109,120 and inhibit the ovulatory LH surge 116 , but do not appear to affect basal LH, suggests that they may find clinical utility in conditions where maximal suppression of sex steroids is contra-indicated. Examples are benign prostatic hyperplasia, endometriosis and uterine fibroids where lowering of gonadal steroids could improve the conditions without the side effects of reducing steroid hormones to castrate levels.…”