Neurons that produce gonadotropin-releasing hormone (GnRH) are the final common pathway by which the brain regulates reproduction. GnRH neurons are regulated by an afferent network of kisspeptin-producing neurons. Kisspeptin binds to its cognate receptor on GnRH neurons and stimulates their activity, which in turn provides an obligatory signal for GnRH secretion, thus gating down-stream events supporting reproduction. We have developed kisspeptin antagonists to facilitate the direct determination of the role of kisspeptin neurons in the neuroendocrine regulation of reproduction. In vitro and in vivo studies of analogues of kisspeptin-10 with amino substitutions have identified several potent and specific antagonists. A selected antagonist was shown to inhibit the firing of GnRH neurons in the brain of the mouse and to reduce pulsatile GnRH secretion in female pubertal monkeys; the later supporting a key role of kisspeptin in puberty onset. This analog also inhibited the kisspeptin-induced release of luteinizing hormone (LH) in rats and mice and blocked the postcastration rise in LH in sheep, rats, and mice, suggesting that kisspeptin neurons mediate the negative feedback effect of sex steroids on gonadotropin secretion in mammals. The development of kisspeptin antagonists provides a valuable tool for investigating the physiological and pathophysiological roles of kisspeptin in the regulation of reproduction and could offer a unique therapeutic agent for treating hormone-dependent disorders of reproduction, including precocious puberty, endometriosis, and metastatic prostate cancer.

Neurokinin B (NKB) and its cognate receptor neurokinin 3 (NK3R) play a critical role in reproduction. NKB and NK3R are coexpressed with dynorphin (Dyn) and kisspeptin (Kiss1) genes in neurons of the arcuate nucleus (Arc). However, the mechanisms of action of NKB as a cotransmitter with kisspeptin and dynorphin remain poorly understood. We explored the role of NKB in the control of LH secretion in the female rat as follows. 1) We examined the effect of an NKB agonist (senktide, 600 pmol, administered into the lateral cerebral ventricle) on luteinizing hormone (LH) secretion. In the presence of physiological levels of estradiol (E 2), senktide induced a profound increase in serum levels of LH and a 10-fold increase in the number of Kiss1 neurons expressing c-fos in the Arc (P Ͻ 0.01 for both). 2) We mapped the distribution of NKB and NK3R mRNAs in the central forebrain and found that both are widely expressed, with intense expression in several hypothalamic nuclei that control reproduction, including the Arc. 3) We studied the effect of E 2 on the expression of NKB and NK3R mRNAs in the Arc and found that E 2 inhibits the expression of both genes (P Ͻ 0.01) and that the expression of NKB and NK3R reaches its nadir on the afternoon of proestrus (when circulating levels of E 2 are high). These observations suggest that NKB/NK3R signaling in Kiss1/NKB/ Dyn-producing neurons in the Arc has a pivotal role in the control of gonadotropin-releasing hormone (GnRH)/LH secretion and its regulation by E 2-dependent negative feedback in the rat. estradiol; hypothalamus NEUROKININ B (NKB) is a member of the tachykinin family that has recently emerged as a key neuropeptide in the control of reproductive function. Humans bearing loss-of-function mutations of TAC3 or TAC3R, which are homologous to NKB and its cognate receptor neurokinin 3 (NK3R, aka Tac2 and Tac3r), respectively, in rodents, exhibit hypogonadotropic hypogonadism and infertility (34,38). Clues regarding NKB's specific role in the regulation of reproduction come from studies in animals. In rodents, the compensatory rise of luteinizing hormone (LH) following ovariectomy (OVX) is ablated by treatment with the NKB agonist senktide (24,30). In addition, the expression of NKB and its receptor NK3R in the hypothalamic arcuate nucleus (Arc) is inhibited by estradiol (E 2 ) via estrogen receptor-␣ (9, 24). Together, these observations suggest that NKB/NK3R signaling plays an important role in the E 2 -dependent negative-feedback control of gonadotropin-releasing hormone (GnRH) and LH in mammals.In the Arc of sheep and rodents, NKB is coexpressed with kisspeptin and dynorphin, which are encoded by the Kiss1 and preprodynorphin (Dyn) genes, respectively (4, 15, 24). Kisspeptin is a potent GnRH secretagogue (25), and GnRH neurons express the kisspeptin receptor (Kiss1r, aka GPR54) (17), which plays a critical role in the neuroendocrine regulation of GnRH and LH secretion (8,25,31). Kisspeptin neurons in the Arc express estrogen receptor-␣ and are thought to be direct targets f...

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Hypogonadotropism is a common feature of uncontrolled diabetes, for which the ultimate mechanism remains to be elucidated. Kisspeptins, ligands of G protein-coupled receptor 54 (GPR54) encoded by the KiSS-1 gene, have recently emerged as major gatekeepers of the gonadotropic axis. Alteration in the hypothalamic KiSS-1 system has been reported in adverse metabolic conditions linked to suppressed gonadotropins, such as undernutrition. However, its potential contribution to defective gonadotropin secretion in diabetes has not been evaluated. We report herein analyses of luteinizing hormone (LH) responses to kisspeptin and hypothalamic expression of the KiSS-1 gene in streptozotocin (STZ)-induced diabetic male rats. In addition, functional studies involving kisspeptin replacement or continuous administration of leptin and insulin to diabetic male rats are presented. Kisspeptin administration evoked robust LH and testosterone bursts and enhanced postgonadectomy LH concentrations, despite prevailing attenuation of gonadotropic axis in diabetic animals. In addition, hypothalamic KiSS-1 mRNA levels were unambiguously decreased in diabetic male rats, and the postorchidectomy rise in KiSS-1 mRNA was severely blunted. Repeated administration of kisspeptin to diabetic rats evoked persistent LH and testosterone responses and partially rescued prostate and testis weights. In addition, central infusion of leptin, but not insulin, was sufficient to normalize hypothalamic KiSS-1 mRNA levels, as well as LH and testosterone concentrations. In summary, we provide evidence for altered expression of the hypothalamic KiSS-1 system in a model of uncontrolled diabetes. This observation, together with the ability of exogenous kisspeptin to rescue defective LH responses in diabetic rats, unravel the physiopathological implication, and potential therapeutic intervention, of the KiSS-1 system in altered gonadotropin secretion of type 1 diabetes. Diabetes

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that operates as sensor of cellular energy status and effector for its coupling to cell growth and proliferation. At the hypothalamic arcuate nucleus, mTOR signaling has been recently proposed as transducer for leptin effects on energy homeostasis and food intake. However, whether central mTOR also participates in metabolic regulation of fertility remains unexplored. We provide herein evidence for the involvement of mTOR in the control of puberty onset and LH secretion, likely via modulation of hypothalamic expression of Kiss1. Acute activation of mTOR by l-leucine stimulated LH secretion in pubertal female rats, whereas chronic l-leucine infusion partially rescued the state of hypogonadotropism induced by food restriction. Conversely, blockade of central mTOR signaling by rapamycin caused inhibition of the gonadotropic axis at puberty, with significantly delayed vaginal opening, decreased LH and estradiol levels, and ovarian and uterine atrophy. Inactivation of mTOR also blunted the positive effects of leptin on puberty onset in food-restricted females. Yet the GnRH/LH system retained their ability to respond to ovariectomy and kisspeptin-10 after sustained blockade of mTOR, ruling out the possibility of unspecific disruption of GnRH function by rapamycin. Finally, mTOR inactivation evoked a significant decrease of Kiss1 expression at the hypothalamus, with dramatic suppression of Kiss1 mRNA levels at the arcuate nucleus. Altogether our results unveil the role of central mTOR signaling in the control of puberty onset and gonadotropin secretion, a phenomenon that involves the regulation of Kiss1 and may contribute to the functional coupling between energy balance and gonadal activation and function.

Kisspeptins (Kp) have recently emerged as master regulators of the reproductive axis and among the most potent elicitors of GnRH-gonadotropin secretion. Despite their paramount importance in reproductive physiology and their potential therapeutic implications, development of Kp antagonists has remained elusive, and only recently has the first compound with the ability to block Kp actions in vitro and in vivo, namely p234, been reported. However, previous in vivo studies all used acute central injections, whereas characterization of the effects of the antagonist after continuous or systemic administration, which poses pharmacological challenges, is still pending. We report herein a comprehensive series of analyses on the impact of continuous intracerebroventricular infusion of p234 on puberty onset and the preovulatory surge of gonadotropins in the female rat. In addition, the effects of systemic (ip) administration of a tagged p234-penetratin, with a predicted higher permeability at the blood-brain barrier, on Kp-10 induced gonadotropin secretion were evaluated. Central infusion of p234 to pubertal females delayed vaginal opening and decreased uterine and ovarian weights at the expected time of puberty, without affecting body weight. Likewise, chronic intracerebroventricular administration of p234 for 4 d prevented the preovulatory surges of LH and FSH. In addition, systemic (ip) administration of p234-penetratin significantly attenuated acute LH and FSH responses to Kp-10, either after intracerebroventricular or ip injection of Kp. Our data document the validity of p234 for antagonizing Kp actions in vivo and provide direct experimental evidence for the important role of Kp signaling in the key events of female reproduction, such as puberty onset and the preovulatory surge of gonadotropins.

The hypothalamic peptide, nesfatin-1, derived from the precursor NEFA/nucleobindin 2 (NUCB2), was recently identified as anorexigenic signal, acting in a leptin-independent manner. Yet its participation in the regulation of other biological functions gated by body energy status remains unexplored. We show herein that NUCB2/nesfatin-1 is involved in the control of female puberty. NUCB2/nesfatin mRNA and protein were detected at the hypothalamus of pubertal female rats, with prominent signals at lateral hypothalamus (LHA), paraventricular (PVN), and supraoptic (SON) nuclei. Hypothalamic NUCB2 expression raised along pubertal transition, with detectable elevations of its mRNA levels at LHA, PVN, and SON, and threefold increase of its total protein content between late-infantile and peripubertal periods. Conditions of negative energy balance, such as 48 h fasting or sustained subnutrition, decreased hypothalamic NUCB2 mRNA and/or protein levels in pubertal females. At this age, central administration of nesfatin-1 induced modest but significant elevations of circulating gonadotropins, whose magnitude was notably augmented in conditions of food deprivation. Continuous intracerebroventricular infusion of antisense morpholino oligonucleotides (as-MONs) against NUCB2 along pubertal maturation, which markedly reduced hypothalamic NUCB2 protein content, delayed vaginal opening and decreased ovarian weights and serum luteinizing hormone (LH) levels. In contrast, in adult female rats, intracerebroventricular injection of nesfatin did not stimulate LH or folliclestimulating hormone secretion; neither did central as-MON infusion alter preovulatory gonadotropin surges, despite suppression of hypothalamic NUCB2. In sum, our data are the first to disclose the indispensable role of NUCB2/nesfatin-1 in the central networks driving puberty onset, a function that may contribute to its functional coupling to energy homeostasis.

van Noort PI, Tena-Sempere M. Characterization of the inhibitory roles of RFRP3, the mammalian ortholog of GnIH, in the control of gonadotropin secretion in the rat: in vivo and in vitro studies. Am J Physiol Endocrinol Metab 299: E39 -E46, 2010. First published April 27, 2010; doi:10.1152/ajpendo.00108.2010.-RF-amide related peptides (RFRP), as putative mammalian orthologs of the avian gonadotropin-inhibitory hormone (GnIH), have been proposed as key regulators of gonadotropin secretion in higher vertebrates. Yet considerable debate has arisen recently on their physiological relevance and potential mechanisms and sites of action. Present studies were undertaken to further characterize the effects of RFRP on LH and FSH secretion by a combination of in vivo and in vitro approaches in male and female rats. Initial screening via intracerebroventricular (icv) administration of different analogs of RFRP1 (RFRP1-12 and RFRP1-20) and RFRP3 (RFRP3-8 and RFRP3-17), as well as the related neuropeptide FF (NPFF8), to gonadectomized (GNX) female rats evidenced significant, albeit modest, inhibitory effects on LH secretion only for RFRP3-8 and RFRP3-17, which were detectable at the high dose rage (1 nmol for RFRP3-8, 5 nmol for RFRP3-17). This moderate inhibitory action was also documented after icv administration of RFRP3-8 to intact and GNX male rats. In addition, systemic (intravenous) administration of RFRP3-8 decreased the circulating levels of both gonadotropins in GNX male rats. Likewise, RFRP3-8 inhibited basal and GnRH-stimulated LH secretion by pituitaries from GNX males in vitro. This inhibitory effect was blocked by the antagonist of RFRP receptors, RF9. In summary, our results support a putative inhibitory role of RFRP3 as ortholog of GnIH in the regulation of gonadotropin secretion in mammals, which appears to involve direct pituitary actions as well as potential central (hypothalamic) effects.RF-amide related peptide; gonadotropin-inhibitory hormone; gonadotropin-releasing hormone; neuropeptide FF; receptor; RF9 THE NEUROENDOCRINE CONTROL of the gonadotropic axis relies on a complex array of stimulatory and inhibitory signals that primarily, but not exclusively, impinge onto a subset of hypothalamic neurons producing the decapeptide gonadotropinreleasing hormone (GnRH) (7, 15). Our knowledge on the nature and mechanisms of action of these neuroendocrine regulators has enlarged considerably recently, with the identification of novel factors (e.g., kisspeptins) and unsuspected biological effects of classical signals (e.g., excitatory actions of putative inhibitory neurotransmitters such as GABA) (7,22). In this context, a 12-amino acid neuropeptide, with a distinctive RF-amide (RFa) motif at its COOH terminus, was isolated from the avian brain in 2000 and termed gonadotropin-inhibitory hormone (GnIH) due to its capacity to suppress gonadotropin release by quail pituitaries (30). This finding boosted a considerable interest in the field, as this was thought to represent the physiological counterpart of GnRH or on...