RF9 powerfully stimulates gonadotrophin secretion in the ewe: evidence for a seasonal threshold of sensitivity

The anti-inflammatory potential of neuropeptide FF in vitro and in vivo

Neuropeptide FF (NPFF) has many functions in regulating various biological processes. However, little attention has been focused on the anti-inflammatory effect of this peptide. In the present study, the in vitro anti-inflammatory activity of NPFF in both primary peritoneal macrophages and RAW 264.7 macrophages was investigated. Our data showed that NPFF suppressed the nitric oxide (NO) production of macrophages in the inflammation process. RF9, a reported antagonist of NPFF receptors, completely blocked the NPFF-induced NO suppression, suggesting a NPFF receptors-mediated pathway is mainly involved. Down-regulation of the nitric oxide synthases significantly inhibited the NPFF-induced NO reduction, indicating the involvement of nitric oxide synthases. However, the nitric oxide synthases were not the only route by which NPFF modulated the NO levels of macrophages. Pharmacological antagonists of the NF-κB signal pathway also completely suppressed the NPFF-induced NO decline. Moreover, we also observed that NPFF is capable of blocking the LPS-induced nuclear translocation of p65 in macrophages, implying the involvement of the NF-κB signal pathway. Finally, we observed that NPFF markedly attenuated the carrageenan-induced mouse paw edema, indicating that NPFF is capable of exerting anti-inflammatory potency in vivo. Collectively, our findings reveal the potential role of NPFF in the anti-inflammatory field both in vitro and in vivo, which will be helpful for the further exploitation of NPFF utility therapeutically.

Review: regulatory mechanisms of gonadotropin-inhibitory hormone (GnIH) synthesis and release in photoperiodic animals

Gonadotropin-inhibitory hormone (GnIH) is a novel hypothalamic neuropeptide that was discovered in quail as an inhibitory factor for gonadotropin release. GnIH inhibits gonadotropin synthesis and release in birds through actions on gonadotropin-releasing hormone (GnRH) neurons and gonadotropes, mediated via the GnIH receptor (GnIH-R), GPR147. Subsequently, GnIH was identified in mammals and other vertebrates. As in birds, mammalian GnIH inhibits gonadotropin secretion, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal (HPG) axis across species. Identification of the regulatory mechanisms governing GnIH expression and release is important in understanding the physiological role of the GnIH system. A nocturnal hormone, melatonin, appears to act directly on GnIH neurons through its receptor to induce expression and release of GnIH in quail, a photoperiodic bird. Recently, a similar, but opposite, action of melatonin on the inhibition of expression of mammalian GnIH was shown in hamsters and sheep, photoperiodic mammals. These results in photoperiodic animals demonstrate that GnIH expression is photoperiodically modulated via a melatonin-dependent process. Recent findings indicate that GnIH may be a mediator of stress-induced reproductive disruption in birds and mammals, pointing to a broad role for this neuropeptide in assessing physiological state and modifying reproductive effort accordingly. This paper summarizes the advances made in our knowledge regarding the regulation of GnIH synthesis and release in photoperiodic birds and mammals. This paper also discusses the neuroendocrine integration of environmental signals, such as photoperiods and stress, and internal signals, such as GnIH, melatonin, and glucocorticoids, to control avian and mammalian reproduction.

Stress regulation of kisspeptin in the modulation of reproductive function

Stressful stimuli abound in modern society and have shaped evolution through altering reproductive development, behavior, and physiology. The recent identification of kisspeptin as an important component of the hypothalamic regulatory circuits involved in reproductive homeostasis sparked a great deal of research interest that subsequently implicated kisspeptin signaling in the relay of metabolic, environmental, and physiological cues to the hypothalamo-pituitary-gonadal axis. However, although it is widely recognized that exposure to stress profoundly impacts on reproductive function, the roles of kisspeptin within the complex mechanisms underlying stress regulation of reproduction remain poorly understood. We and others have recently demonstrated that a variety of experimental stress paradigms downregulate the expression of kisspeptin ligand and receptor within the reproductive brain. Coincidently, these stressors also inhibit gonadotropin secretion and delay pubertal onset-processes that rely on kisspeptin signaling. However, a modest literature is inconsistent with an exclusively suppressive influence of stress on the reproductive axis and suggests that complicated neural interactions and signaling mechanisms translate the stress response into reproductive perturbations. The purpose of this chapter is to review the evidence for a novel role of kisspeptin signaling in the modulation of reproductive function by stress and to broaden the understanding of this timely phenomenon.

Kisspeptin and seasonality of reproduction

Wild and domesticated species display seasonality in reproductive function, controlled predominantly by photoperiod. Seasonal alterations in breeding status are caused by changes in the secretion of gonadotropin-releasing hormone (GnRH) that are mediated by upstream neuronal afferents that regulate the GnRH cells. In particular, kisspeptin appears to play a major role in seasonality of reproduction, transducing the feedback effect of gonadal steroids as well as having an independent (nonsteroid dependent) circannual rhythm. A substantial body of data on this issue has been obtained from studies in sheep and hamsters and this is reviewed here in detail. Kisspeptin function is upregulated during the breeding season in sheep, stimulating reproductive function, but contradictory data are found in Siberian and Syrian hamsters. The relative quiescence of kisspeptin cells in the nonbreeding season can be counteracted by administration of the peptide, leading to activation of reproductive function. Although there is a major role for melatonin in the transduction of photoperiod to the reproductive system, kisspeptin cells do not appear to express the melatonin receptor, so the means by which seasonality changes the level of kisspeptin activity remains unknown.

Neuropeptide FF activates ERK and NF kappa B signal pathways in differentiated SH-SY5Y cells

Neuropeptide FF (NPFF) has been reported to play important roles in regulating diverse biological processes. However, little attention has been focused on the downstream signal transduction pathway of NPFF. Here, we used the differentiated neuroblastoma cell line, dSH-SY5Y, which endogenously expresses hNPFF2 receptor, to investigate the signal transduction downstream of NPFF. In particular we investigated the regulation of the extracellular signal-regulated protein kinase (ERK) and the nuclear factor kappa B (NF-κB) pathways by NPFF in these cells. NPFF rapidly and transiently stimulated ERK. H89, a selective inhibitor of cyclic AMP-dependent protein kinase A (PKA), inhibited the NPFF-activated ERK pathway, indicating the involvement of PKA in the NPFF-induced ERK activation. Down-regulation of nitric oxide synthases also attenuated NPFF-induced ERK activation, suggesting that a nitric oxide synthase-dependent pathway is involved. Moreover, the core upstream components of the NF-κB pathway were also significantly activated in response to NPFF, suggesting that the NF-κB pathway is involved in the signal transduction pathway of NPFF. Collectively, these data demonstrate that nitric oxide synthases are involved in the signal transduction pathway of NPFF, and provide the first evidence for the interaction between NPFF and the NF-κB pathway. These advances in our interpretation of the NPFF pathway mechanism will aid the comprehensive understanding of its function and provide novel molecular insight for further study of the NPFF system.

Reproductive seasonality in the mare: neuroendocrine basis and pharmacologic control

Reproductive seasonality in the mare is characterized by a marked decline in adenohypophyseal synthesis and secretion of LH beginning near the autumnal equinox. Thus, ovarian cycles have ceased in most mares by the time of the winter solstice. Endogenous reproductive rhythms in seasonal species are entrained or synchronized as a result of periodic environmental cues. In the horse, this cue is primarily day length. Hence, supplemental lighting schemes have been used managerially for decades to modify the annual timing of reproduction in the mare. Although a full characterization of the cellular and molecular bases of seasonal rhythms has not been realized in any species, many of their synaptic and humoral signaling pathways have been defined. In the mare, neuroendocrine-related studies have focused primarily on the roles of GnRH and interneuronal signaling pathways that subserve the GnRH system in the regulatory cascade. Recent studies have considered the role of a newly discovered neuropeptide, RF-related peptide 3 that could function to inhibit GnRH secretion or gonadotrope responsiveness. Although results that used native peptide sequences have been negative in the mare and mixed in all mammalian females, new studies that used an RFRP3 antagonist (RF9) in sheep are encouraging. Importantly, despite continuing deficits in some fundamental areas, the knowledge required to control seasonal anovulation pharmacologically has been available for >20 yr. Specifically, the continuous infusion of native GnRH is both reliable and efficient for accelerating reproductive transition and is uniquely applicable to the horse. However, its practical exploitation continues to await the development of a commercially acceptable delivery vehicle.

Gonadotropin-inhibitory hormone (GnIH) secretion into the ovine hypophyseal portal system

GnIH was first identified in avian species, and there is now strong evidence that it is operant in mammals as an inhibitor of reproduction. Mammalian gonadotropin-inhibitory hormone (GnIH)-3 is encoded by the RFRP gene in neurons of the dorsomedial nucleus. These neurons project to the median eminence, predicting a role as a secreted neurohormone and regulation of the pituitary gonadotropes. To determine whether GnIH-3 is a secreted neurohormone, we measured its concentration in hypophyseal portal blood in ewes during the nonbreeding (anestrous) season and during the luteal and follicular phases of the estrous cycle in the breeding season. Paired portal and jugular blood samples were collected and plasma prepared for RIA using an ovine GnIH-3 antibody. Pulsatile GnIH-3 secretion was observed in the portal blood of all animals. Mean GnIH-3 pulse amplitude and pulse frequency was higher during the nonbreeding season. GnIH-3 was virtually undetectable in peripheral blood plasma. There was a lack of association between secretory pulses of GnIH-3 (portal) and LH (peripheral). To determine the role of secreted GnIH-3, we examined its effects on GnRH-stimulated LH secretion in hypothalamo-pituitary-disconnected ewes; a significant reduction in the LH response to GnRH was observed. Finally, to identify cellular targets in the pituitary, the expression of GnIH receptor [G protein-coupled receptor 147 (GPR147)] in fractions enriched for gonadotropes somatotropes, and lactotropes was examined; expression was observed in each cell type. These data show GnIH-3 is secreted into portal blood to act on pituitary gonadotropes, reducing the action of GnRH.