Neuropeptide Y directly inhibits neuronal activity in a subpopulation of gonadotropin-releasing hormone-1 neurons via Y1 receptors

Investigating GABA Neuron-Specific Androgen Receptor Knockout in two Hyperandrogenic Models of PCOS

Androgen excess is a hallmark feature of polycystic ovary syndrome (PCOS), the most common form of anovulatory infertility. Clinical and preclinical evidence links developmental or chronic exposure to hyperandrogenism with programming and evoking the reproductive and metabolic traits of PCOS. While critical androgen targets remain to be determined, central GABAergic neurons are postulated to be involved. Here, we tested the hypothesis that androgen signaling in GABAergic neurons is critical in PCOS pathogenesis in 2 well-characterized hyperandrogenic mouse models of PCOS. Using cre-lox transgenics, GABA-specific androgen receptor knockout (GABARKO) mice were generated and exposed to either acute prenatal androgen excess (PNA) or chronic peripubertal androgen excess (PPA). Females were phenotyped for reproductive and metabolic features associated with each model and brains of PNA mice were assessed for elevated GABAergic input to gonadotropin-releasing hormone (GnRH) neurons. Reproductive and metabolic dysfunction induced by PPA, including acyclicity, absence of corpora lutea, obesity, adipocyte hypertrophy, and impaired glucose homeostasis, was not different between GABARKO and wild-type (WT) mice. In PNA mice, acyclicity remained in GABARKO mice while ovarian morphology and luteinizing hormone secretion was not significantly impacted by PNA or genotype. However, PNA predictably increased the density of putative GABAergic synapses to GnRH neurons in adult WT mice, and this PNA-induced plasticity was absent in GABARKO mice. Together, these findings suggest that while direct androgen signaling in GABA neurons is largely not required for the development of PCOS-like traits in androgenized models of PCOS, developmental programming of GnRH neuron innervation is dependent upon androgen signaling in GABA neurons.

Potential for NPY receptor-related therapies for polycystic ovary syndrome: an updated review

Polycystic ovary syndrome (PCOS) is a complex endocrine disease that can cause female infertility and bring economic burden to families and to society. The clinical and/or biochemical manifestations include hyperandrogenism, persistent anovulation, and polycystic ovarian changes, often accompanied by insulin resistance and obesity. Although its pathogenesis is unclear, PCOS involves the abnormal regulation of the hypothalamic-pituitary-ovarian axis and the abnormal activation of GnRH neurons. Neuropeptide Y (NPY) is widely distributed in the arcuate nucleus of the hypothalamus and functions as the physiological integrator of two neuroendocrine systems, one governing feeding and the other controlling reproduction. In recent years, an increasing number of studies have focused on the improvement of the reproductive and metabolic status of PCOS through the therapeutic application of NPY and its receptors. In this review, we summarize the central and peripheral regulation of NPY and its receptors in the development of PCOS and discuss the potential for NPY receptor-related therapies for PCOS.

Acetylcholine regulation of GnRH neuronal activity: A circuit in the medial septum

In vertebrates, gonadotropin-releasing hormone (GnRH)-secreting neurons control fertility by regulating gonadotrophs in the anterior pituitary. While it is known that acetylcholine (ACh) influences GnRH secretion, whether the effect is direct or indirect, and the specific ACh receptor (AChR) subtype(s) involved remain unclear. Here, we determined 1) whether ACh can modulate GnRH cellular activity and 2) a source of ACh afferents contacting GnRH neurons. Calcium imaging was used to assay GnRH neuronal activity. With GABAergic and glutamatergic transmission blocked, subtype-specific AChR agonists and antagonists were applied to identify direct regulation of GnRH neurons. ACh and nicotine caused a rise in calcium that declined gradually back to baseline after 5-6 min. This response was mimicked by an alpha3-specific agonist. In contrast, muscarine inhibited GnRH calcium oscillations, and blocking M2 and M4 together prevented this inhibition. Labeling for choline acetyltransferase (ChAT) and GnRH revealed ChAT fibers contacting GnRH neurons, primarily in the medial septum (MS), and in greater number in females than males. ChAT positive cells in the MS are known to express p75NGFRs. Labeling for p75NGFR, ChAT and GnRH indicated that ChAT fibers contacting GnRH cells originate from cholinergic cells within these same rostral areas. Together, these results indicate that cholinergic cells in septal areas can directly regulate GnRH neurons.

Exogenous Melatonin Regulates Puberty and the Hypothalamic GnRH-GnIH System in Female Mice

In recent years, the age of children entering puberty is getting lower and the incidence of central precocious puberty is increasing. It is known that melatonin plays an increasingly important role in regulating animal reproduction, but the specific role and mechanism of melatonin in regulating the initiation of puberty remain unclear. The purpose of the current study was to investigate the effect of subcutaneous melatonin injection on pubertal development in female mice and its mechanism of action. Female mice that were 22 days old received 1 mg/kg doses of melatonin subcutaneously every day for 10, 15 and 20 days. The vaginal opening was checked daily. Hematoxylin and eosin (HE) stain was used to determine the growth of the uterus and ovaries. Enzyme-linked immunosorbent assay (ELISA) was used to determine the levels of follicle-stimulating hormone (FSH), gonadotropin-inhibiting hormone (GnIH), and gonadotropin-releasing hormone (GnRH) in serum. By using RT-PCR and Western blotting, the mRNA and protein expression of the hypothalamus GnRH, GnIH, Kisspeptin (Kp), Proopiomelanocortin (POMC), Neuropeptide Y (NPY), as well as G protein-coupled receptor 147 (GPR147) were identified. The findings demonstrated that melatonin could suppress ovarian follicle and uterine wall growth as well as delay vaginal opening, decrease serum levels of GnRH and FSH and increase levels of GnIH. Melatonin increased GnIH and GPR147 expression in the hypothalamus in comparison to the saline group, while decreasing the expression of GnRH, Kisspeptin, POMC, and NPY. In conclusion, exogenous melatonin can inhibit the onset of puberty in female mice by modulating the expression of hypothalamic GnRH, GnIH, Kisspeptin, POMC and NPY neurons and suppressing the hypothalamic–pituitary–gonadal axis.

How does apelin affect LH levels? An investigation at the level of GnRH and KNDy neurons

Hypothalamic control of reproduction relies on GnRH and kisspeptin (KP) secretions. KP neurons are sensitive to sex steroids and metabolic status and their distribution overlaps with neurons producing apelin, a metabolic hormone known to decrease LH secretion in rats. Here, we observed neuroanatomical contacts between apelin fibers and both KP and GnRH neurons in the hypothalamus of male rodents. Intracerebroventricular apelin infusion for 2 weeks in male mice did not decrease LH levels nor did it affect gene expression for KP, neurokinin B and dynorphin. Finally, increasing apelin concentrations did not modulate Ca²⁺ levels of cultured GnRH neurons, while 10 μM apelin infusion on forskolin pretreated GnRH neurons revoked a rhythmic activity in 18% of GnRH neurons. These results suggest that acute apelin effect on LH secretion does not involve modulation of gene expression in KP neurons but may affect the secretory activity of GnRH neurons.

Neural programming of seasonal physiology in birds and mammals: A modular perspective

Most animals in the temperate zone exhibit robust seasonal rhythms in neuroendocrine, physiological and behavioral processes. The integration of predictive and supplementary environmental cues (e.g., nutrients) involves a series of discrete, and interconnected brain regions that span hypothalamic, thalamic, mesencephalic, and limbic regions. Species-specific adaptive changes in these neuroendocrine structures and cellular plasticity have likely evolved to support seasonal life-history transitions. Despite significant advances in our understanding of ecological responses to predictive and supplementary environmental cues, there remains a paucity of literature on how these diverse cues impact the underlying neural and cellular substrates. To date, most scientific approach has focused on neuroendocrine responses to annual changes in daylength, referred to as photoperiod, due to the robust physiological changes to light manipulations in laboratory settings. In this review, we highlight the relatively few animal models that have been effectively used to investigate how predictive day lengths, and supplementary cues are integrated across hypothalamic nuclei, and discuss key findings of how seasonal rhythms in physiology are governed by adaptive neuroendocrine changes. We discuss how specific brain regions integrate environmental cues to form a complex multiunit or 'modular' system that has evolved to optimize the timing of seasonal physiology. Overall, the review aims to highlight the existence of a modular network of neural regions that independently contribute to timing seasonal physiology. This paper proposes that a multi-modular neuroendocrine system has evolved in which independent neural 'units' operate to support species-specific seasonal rhythms.

The electrophysiologic properties of gonadotropin-releasing hormone neurons

For about two decades, recordings of identified gonadotropin-releasing hormone (GnRH) neurons have provided a wealth of information on their properties. We describe areas of consensus and debate the intrinsic electrophysiologic properties of these cells, their response to fast synaptic and neuromodulatory input, Ca2+ imaging correlates of action potential firing, and signaling pathways regulating these aspects. How steroid feedback and development change these properties, functions of GnRH neuron subcompartments and local networks, as revealed by chemo- and optogenetic approaches, are also considered.

The Dopamine D4 Receptor Regulates Gonadotropin-Releasing Hormone Neuron Excitability in Male Mice

Gonadotropin-releasing hormone (GnRH)-secreting neurons control fertility. The release of GnRH peptide regulates the synthesis and release of both luteinizing hormone (LH) and Follicle stimulation hormone (FSH) from the anterior pituitary. While it is known that dopamine regulates GnRH neurons, the specific dopamine receptor subtype(s) involved remain unclear. Previous studies in adult rodents have reported juxtaposition of fibers containing tyrosine hydroxylase (TH), a marker of catecholaminergic cells, onto GnRH neurons and that exogenous dopamine inhibits GnRH neurons postsynaptically through dopamine D1-like and/or D2-like receptors. Our microarray data from GnRH neurons revealed a high level of Drd4 transcripts [i.e., dopamine D4 receptor (D4R)]. Single-cell RT-PCR and immunocytochemistry confirmed GnRH cells express the Drd4 transcript and protein, respectively. Calcium imaging identified changes in GnRH neuronal activity during application of subtype-specific dopamine receptor agonists and antagonists when GABAergic and glutamatergic transmission was blocked. Dopamine, dopamine with D1/5R-specific or D2/3R-specific antagonists or D4R-specific agonists decreased the frequency of calcium oscillations. In contrast, D1/5R-specific agonists increased the frequency of calcium oscillations. The D4R-mediated inhibition was dependent on Gαi/o protein coupling, while the D1/5R-mediated excitation required Gαs protein coupling. Together, these results indicate that D4R plays an important role in the dopaminergic inhibition of GnRH neurons.

Inverse age-related changes between hypothalamic NPY and KISS1 gene expression during pubertal initiation in male rhesus monkey

The neuroendocrine mechanism underlying the sinusoidal wave nature of gonadotropin-releasing hormone pulse generator activity from infantile to adult age still needs to be meticulously defined. Direct inhibition of kisspeptin neurons by neuropeptide Y (NPY) and close intimacy between the two rekindle the importance of these two neuropeptides controlling reproductive axis activity. Thus, the present study was undertaken to decipher simultaneous fluctuations and to profile correlative changes in the relative expression of KISS1, NPY, and their receptor genes from the mediobasal hypothalamus of infant (n = 3), juvenile, pre-pubertal, and adult (n = 4 in each stage) male rhesus monkey (Macaca mulatta) by RT-qPCR. Significant elevation (p < 0.05-0.01) in KISS1 and KISS1R and low (p < 0.05) expression in NPY and NPY1R mRNA in the adult group as compared to the pre-pubertal group was observed. Moreover, significantly high (p < 0.05) expression of NPY and NPY1R mRNA with non-significant (p> 0.05) decline in KISS1 and KISS1R in pre-pubertal animals in comparison to infants describe inverse correlative age-associated changes during pubertal development. Current findings imply that NPY may contribute as a neurobiological brake for the dormancy of kisspeptin neurons before pubertal onset, while dwindling of this brake is likely to occasion kisspeptin dependent hypothalamic-pituitary-gonadal axis activation at puberty. These findings may help in the development of clinical and therapeutic strategies to regulate fertility in humans.

Heterogeneity in GnRH and kisspeptin neurons and their significance in vertebrate reproductive biology

Vertebrate reproduction is essentially controlled by the hypothalamus-pituitary-gonadal (HPG) axis, which is a central dogma of reproductive biology. Two major hypothalamic neuroendocrine cell groups containing gonadotropin-releasing hormone (GnRH) and kisspeptin are crucial for control of the HPG axis in vertebrates. GnRH and kisspeptin neurons exhibit high levels of heterogeneity including their cellular morphology, biochemistry, neurophysiology and functions. However, the molecular foundation underlying heterogeneities in GnRH and kisspeptin neurons remains unknown. More importantly, the biological and physiological significance of their heterogeneity in reproductive biology is poorly understood. In this review, we first describe the recent advances in the neuroendocrine functions of kisspeptin-GnRH pathways. We then view the recent emerging progress in the heterogeneity of GnRH and kisspeptin neurons using morphological and single-cell transcriptomic analyses. Finally, we discuss our views on the significance of functional heterogeneity of reproductive endocrine cells and their potential relevance to reproductive health.

Hydrogen peroxide suppresses excitability of gonadotropin-releasing hormone neurons in adult mouse

It has been reported that reactive oxygen species (ROS) derived from oxygen molecule reduction can interfere with the cross-talk between the hypothalamic-pituitary-gonadal (HPG) axis and other endocrine axes, thus affecting fertility. Furthermore, ROS have been linked to GnRH receptor signaling in gonadotropes involved in gonadotropin release. There has been evidence that ROS can interfere with the HPG axis and gonadotropin release at various levels. However, the direct effect of ROS on gonadotropin-releasing hormone (GnRH) neuron remains unclear. Thus, the objective of this study was to determine the effect of hydrogen peroxide (H₂O₂), an ROS source, on GnRH neuronal excitabilities in transgenic GnRH-green fluorescent protein-tagged mice using the whole-cell patch-clamp electrophysiology. In adults, H₂O₂ at high concentrations (mM level) hyperpolarized most GnRH neurons tested, whereas low concentrations (pM to μM) caused slight depolarization. In immature GnRH neurons, H₂O₂ exposure induced excitation. The sensitivity of GnRH neurons to H₂O₂ was increased with postnatal development. The effect of H₂O₂ on adult female GnRH neurons was found to be estrous cycle-dependent. Hyperpolarization mediated by H₂O₂ persisted in the presence of tetrodotoxin, a voltage-gated Na⁺ channel blocker, and amino-acids receptor blocking cocktail containing blockers for the ionotropic glutamate receptors, glycine receptors, and GABA_A receptors, indicating that H₂O₂ could act on GnRH neurons directly. Furthermore, glibenclamide, an ATP-sensitive K⁺ (K_ATP) channel blocker, completely blocked H₂O₂-mediated hyperpolarization. Increasing endogenous H₂O₂ by inhibiting glutathione peroxidase decreased spontaneous activities of most GnRH neurons. We conclude that ROS can act as signaling molecules for regulating GnRH neuron's excitability and that adult GnRH neurons are sensitive to increased ROS concentration. Results of this study demonstrate that ROS have direct modulatory effects on the HPG axis at the hypothalamic level to regulate GnRH neuron's excitabilities.

The neuroendocrine pathways and mechanisms for the control of the reproduction in female pigs

Within the hypothalamic-pituitary-gonad (HPG) axis, the major hierarchical component is gonadotropin-releasing hormone (GnRH) neurons, which directly or indirectly receive regulatory inputs from a wide array of regulatory signals and pathways, involving numerous circulating hormones, neuropeptides, and neurotransmitters, and which operate as a final output for the brain control of reproduction. In recent years, there has been an increasing interest in neuropeptides that have the potential to stimulate or inhibit GnRH in the hypothalamus of pigs. Among them, Kisspeptin is a key component in the precise regulation of GnRH neuron secretion activity. Besides, other neuropeptides, including neurokinin B (NKB), neuromedin B (NMB), neuromedin S (NMS), α-melanocyte-stimulating hormone (α-MSH), Phoenixin (PNX), show potential for having a stimulating effect on GnRH neurons. On the contrary, RFamide-related peptide-3 (RFRP-3), endogenous opioid peptides (EOP), neuropeptide Y (NPY), and Galanin (GAL) may play an inhibitory role in the regulation of porcine reproductive nerves and may directly or indirectly regulate GnRH neurons. By combining data from suitable model species and pigs, we aim to provide a comprehensive summary of our current understanding of the neuropeptides acting on GnRH neurons, with a particular focus on their central regulatory pathways and underlying molecular basis.

Spexin: Its role, regulation, and therapeutic potential in the hypothalamus

Spexin is the most recently discovered member of the galanin/kisspeptin/spexin family of peptides. This 14-amino acid peptide is highly conserved and is implicated in homeostatic functions including, but not limited to, metabolism, energy homeostasis, and reproduction. Spexin is expressed by neurons in the hypothalamus, which coordinate energy homeostasis and reproduction. Critically, levels of spexin appear to be altered in disorders related to energy homeostasis and reproduction, such as obesity, diabetes, and polycystic ovarian syndrome. In this review, we discuss the evidence for the involvement of spexin in the hypothalamic control of energy homeostasis and reproduction. The anorexigenic properties of spexin have been attributed to its effects on the energy-regulating neuropeptide Y/agouti-related peptide neurons and proopiomelanocortin neurons. While the role of spexin in reproduction remains unclear, there is evidence that gonadotropin-releasing hormone expressing neurons may produce and respond to spexin. Furthermore, we discuss the disorders and concomitant treatments, which have been reported to alter spexin expression, as well as the underlying signaling mechanisms that may be involved. Finally, we discuss the biochemical basis of spexin, its interaction with its cognate receptors, and how this information can be adapted to develop therapeutics for disorders related to the alteration of energy homeostasis and reproduction.

Β-endorphin-immunoreactive perikarya appear to receive innervation from NPY-immunoreactive fiber varicosities in the human hypothalamus

Morphological and pharmacological studies indicate that hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons communicate with each other in rats and regulate a variety of hypothalamic and extrahypothalamic functions. Indeed, electron microscopic studies revealed NPY-immunoreactive (NPI-IR) synapses on β-endorphin-IR neurons in the hypothalamus. However, no such connections have been reported in humans. Here, we studied the putative NPY-β-endorphin associations with high-resolution light microscopic double-label immunocytochemistry in the human hypothalamus. The majority of β-endorphin-IR perikarya appear to be innervated by abutting NPY-IR fibers in the infundibulum/median eminence, receiving more than 6 contacts (38% of the counted neurons) or three to six contacts (42% of the counted neurons). The rest of the β-endorphin-IR neurons are lightly innervated by NPY fibers (14%, one-three contacts) or do not receive any detectable NPY-IR axon varicosities (6% of the counted neurons). Since β-endorphin is cleaved from the proopiomelanocortin (POMC) precursor, the NPY-β-endorphin connections also provide the foundation for NPY-α-MSH and NPY-ACTH connections and their subsequent physiology. The close anatomical connections between NPY-IR nerve terminals and β-endorphin-IR neurons reported herein may represent functional synapses and provide the foundation for NPY-stimulated β-endorphin release. By interacting with β-endorphin, NPY may have a more widespread regulatory capacity than acting alone on different neurotransmitter systems.

GnRH pulse frequency and irregularity play a role in male aging

Gonadotropin-releasing hormone (GnRH) has a role in hypothalamic control of aging, but the underlying patterns and relationship with downstream reproductive hormones are still unclear. Here we report that hypothalamic GnRH pulse frequency and irregularity increase before GnRH pulse amplitude slowly decreases during aging. GnRH is inhibited by nuclear factor (NF)-κB, and GnRH pulses were controlled by oscillations in the transcriptional activity of NF-κB. Exposure to testosterone under pro-inflammatory conditions stimulated both NF-κB oscillations and GnRH pulses. While castration of middle-aged mice induced short-term anti-aging effects, preventing elevation of luteinizing hormone (LH) levels after castration led to long-term anti-aging effects and lifespan extension, indicating that high-frequency GnRH pulses and high-magnitude LH levels coordinately mediate aging. Reprogramming the endogenous GnRH pulses of middle-aged male mice via an optogenetic approach revealed that increasing GnRH pulses frequency causes LH excess and aging acceleration, while lowering the frequency of and stabilizing GnRH pulses can slow down aging. In conclusion, GnRH pulses are important for aging in male mice.

An Inhibitory Circuit From Brainstem to GnRH Neurons in Male Mice: A New Role for the RFRP Receptor

RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal, and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges, such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found (1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly rectifying potassium channels), (2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, (3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and (4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

Estradiol Priming Potentiates the Kisspeptin-Induced Release of LH in Ovariectomized Cows

The present study examined whether priming with estradiol benzoate (EB) for 12 h increased both the peak and duration of LH release in response to kisspeptin (KISS1, KP) in cows. In a Latin square design, ovariectomized Nelore cows (n = 8) received: Control, i.m. 4 mL of 0.9% saline; KP, i.m. 4 mg murine KISS1-10; EBKP, i.m. 4 mg KISS1-10 + i.m. 2 mg EB simultaneously; EB12KP, i.m. 4 mg KISS1-10 + i.m. 2 mg EB 12 h before KISS1-10. Concentrations of LH were determined in blood samples obtained at time 0 (treatment), 20, 40, 60, 90, 120, 150, 180, 210 and 270 min. Concentrations of LH were analyzed by Proc GLIMMIX for repeated measures. In case of significance, the adjusted Tukey test was used to test for differences among treatments. GraphPad 8.0 PRISM® was used to determine the area under the LH-response curve (AUC) after injection of KISS1-10. Plasma LH remained relatively constant throughout sampling after treatment with saline. The peak in LH after injection of KISS1-10 occurred at 20 min in Groups KP and EBKP and at 40 min in Group EB12KP. The peak LH response (∆LH, ng/mL) was greater (p < 0.01) in Group EB12KP (5.6 ± 0.9) than in Groups KP (2.4 ± 0.9) and EBKP (3.5 ± 0.9), which did not differ. AUC (LH ng/mL*min) was greater (p = 0.02) in Group EB12KP (439 ± 73) than in Groups KP (176 ± 73) and EBKP (241 ± 73), with the latter two groups not differing. The findings indicated that 12 h priming with EB increased both the peak and duration of the LH response to treatment with KISS1. The incorporation of EB priming and KISS1 could improve the efficiency of estrus synchronization with fixed-time AI in cows. This would have an important practical application in assisted breeding in beef and dairy cattle.

Reproductive health in women with type 2 diabetes mellitus

As type 2 diabetes mellitus (T2DM) reaches epidemic proportions in the developed world and the age at diagnosis decreases, more women of reproductive age are being affected. In this article, we provide a synoptic view on potential mechanisms and relevant factors underlying menstrual cycle disorders and fertility issues in women with T2DM. The article discusses the function of the hypothalamic-pituitary-ovarian (HPO) axis, the central role of the hypothalamus in the homeostasis of this system, the central modulators of the axis, and the peripheral metabolic signals involved in neuroendocrine control of reproduction. The available literature on the relationship between T2DM and the female reproductive lifespan, menstrual cycle disorders, fertility issues, and gestational health in women with T2DM are also discussed. The data so far indicate that there is a "U-shaped" relationship between menarche, menopause, and T2DM, both early and late menarche/menopause being risk factors for T2DM. Hyperglycemia and its consequences may be responsible for the effects of T2DM on reproductive health in women, but the exact mechanisms are not as yet fully understood; thus, more studies are needed in order to identify factors causing disruption of the HPO axis.

Investigating the NPY/AgRP/GABA to GnRH Neuron Circuit in Prenatally Androgenized PCOS-Like Mice

Polycystic ovary syndrome (PCOS), the most common form of anovulatory infertility, is associated with altered signaling within the hormone-sensitive neuronal network that regulates gonadotropin-releasing hormone (GnRH) neurons, leading to a pathological increase in GnRH secretion. Circuit remodeling is evident between GABAergic neurons in the arcuate nucleus (ARN) and GnRH neurons in a murine model of PCOS. One-third of ARN GABA neurons co-express neuropeptide Y (NPY), which has a known yet complex role in regulating GnRH neurons and reproductive function. Here, we investigated whether the NPY-expressing subpopulation (NPY^ARN) of ARN GABA neurons (GABA^ARN) is also affected in prenatally androgenized (PNA) PCOS-like NPY^ARN reporter mice [Agouti-related protein (AgRP)-Cre;τGFP]. PCOS-like mice and controls were generated by exposure to di-hydrotestosterone or vehicle (VEH) in late gestation. τGFP-expressing NPY^ARN neuron fiber appositions with GnRH neurons and gonadal steroid hormone receptor expression in τGFP-expressing NPY^ARN neurons were assessed using confocal microscopy. Although GnRH neurons received abundant close contacts from τGFP-expressing NPY^ARN neuron fibers, the number and density of putative inputs was not affected by prenatal androgen excess. NPY^ARN neurons did not co-express progesterone receptor or estrogen receptor α in either PNA or VEH mice. However, the proportion of NPY^ARN neurons co-expressing the androgen receptor was significantly elevated in PNA mice. Therefore, NPY^ARN neurons are not remodeled by prenatal androgen excess like the wider GABA^ARN population, indicating GABA-to-GnRH neuron circuit remodeling occurs in a presently unidentified non-NPY/AgRP population of GABA^ARN neurons. NPY^ARN neurons do, however, show independent changes in the form of elevated androgen sensitivity.

NPY Deficiency Prevents Postmenopausal Adiposity by Augmenting Estradiol-Mediated Browning

The orexigenic hormone neuropeptide Y (NPY) plays a pivotal role in the peripheral regulation of fat metabolism. However, the mechanisms underlying the effects of sex on NPY function have not been extensively analyzed. In this study, we examined the effects of NPY deficiency on fat metabolism in male and female mice. Body weight was slightly decreased, whereas white adipose tissue (WAT) mass was significantly decreased as the thermogenic program was upregulated in NPY-/- female mice compared with that in wild-type mice; these factors were not altered in response to NPY deficiency in male mice. Moreover, lack of NPY resulted in an increase in luteinizing hormone (LH) expression in the pituitary gland, with concomitant activation of the estradiol-mediated thermogenic program in inguinal WAT, and alleviated age-related modification of adiposity in female mice. Taken together, these data revealed a novel intracellular mechanism of NPY in the regulation of fat metabolism and highlighted the sexual dimorphism of NPY as a promising target for drug development to reduce postmenopausal adiposity.

Activation of a Classic Hunger Circuit Slows Luteinizing Hormone Pulsatility

INTRODUCTION

The central regulation of fertility is carefully coordinated with energy homeostasis, and infertility is frequently the outcome of energy imbalance. Neurons in the hypothalamus expressing neuropeptide Y and agouti-related peptide (NPY/AgRP neurons) are strongly implicated in linking metabolic cues with fertility regulation.

OBJECTIVE

We aimed here to determine the impact of selectively activating NPY/AgRP neurons, critical regulators of metabolism, on the activity of luteinizing hormone (LH) pulse generation.

METHODS

We employed a suite of in vivo optogenetic and chemogenetic approaches with serial measurements of LH to determine the impact of selectively activating NPY/AgRP neurons on dynamic LH secretion. In addition, electrophysiological studies in ex vivo brain slices were employed to ascertain the functional impact of activating NPY/AgRP neurons on gonadotropin-releasing hormone (GnRH) neurons.

RESULTS

Selective activation of NPY/AgRP neurons significantly decreased post-castration LH secretion. This was observed in males and females, as well as in prenatally androgenized females that recapitulate the persistently elevated LH pulse frequency characteristic of polycystic ovary syndrome (PCOS). Reduced LH pulse frequency was also observed when optogenetic stimulation was restricted to NPY/AgRP fiber projections surrounding GnRH neuron cell bodies in the rostral preoptic area. However, electrophysiological studies in ex vivo brain slices indicated these effects were likely to be indirect.

CONCLUSIONS

These data demonstrate the ability of NPY/AgRP neuronal signaling to modulate and, specifically, reduce GnRH/LH pulse generation. The findings suggest a mechanism by which increased activity of this hunger circuit, in response to negative energy balance, mediates impaired fertility in otherwise reproductively fit states, and highlight a potential mechanism to slow LH pulsatility in female infertility disorders, such as PCOS, that are associated with hyperactive LH secretion.

Knockout of the Gnrh genes in zebrafish: effects on reproduction and potential compensation by reproductive and feeding-related neuropeptides

Gonadotropin-releasing hormone (GNRH) is known as a pivotal upstream regulator of reproduction in vertebrates. However, reproduction is not compromised in the hypophysiotropic Gnrh3 knockout line in zebrafish (gnrh3-/-). In order to determine if Gnrh2, the only other Gnrh isoform in zebrafish brains, is compensating for the loss of Gnrh3, we generated a double Gnrh knockout zebrafish line. Surprisingly, the loss of both Gnrh isoforms resulted in no major impact on reproduction, indicating that a compensatory response, outside of the Gnrh system, was evoked. A plethora of factors acting along the reproductive hypothalamus-pituitary axis were evaluated as possible compensators based on neuroanatomical and differential gene expression studies. In addition, we also examined the involvement of feeding factors in the brain as potential compensators for Gnrh2, which has known anorexigenic effects. We found that the double knockout fish exhibited upregulation of several genes in the brain, specifically gonadotropin-inhibitory hormone (gnih), secretogranin 2 (scg2), tachykinin 3a (tac3a), and pituitary adenylate cyclase-activating peptide 1 (pacap1), and downregulation of agouti-related peptide 1 (agrp1), indicating the compensation occurs outside of Gnrh cells and therefore is a noncell autonomous response to the loss of Gnrh. While the differential expression of gnih and agrp1 in the double knockout line was confined to the periventricular nucleus and hypothalamus, respectively, the upregulation of scg2 corresponded with a broader neuronal redistribution in the lateral hypothalamus and hindbrain. In conclusion, our results demonstrate the existence of a redundant reproductive regulatory system that comes into play when Gnrh2 and Gnrh3 are lost.

One-month of high-intensity exercise did not change the food intake and the hypothalamic arcuate nucleus proopiomelanocortin and neuropeptide Y expression levels in male Wistar rats

OBJECTIVE

The hypothalamic arcuate nucleus proopiomelanocortin (POMC) and neuropeptide Y (NPY) circuitries are involved in the inhibition and stimulation of the appetite, respectively. The aim of this study was to investigate the effects of one-month lasting high-intensity exercise on the POMC mRNA and NPY mRNA expression in the above-mentioned brain structure and appetite and food intake levels.

METHODS

Fourteen male Wistar rats (250±50 g) were used and kept in the well-controlled conditions (22±2 °C, 50±5% humidity, and 12 h dark/light cycle) with food and water ad libitum. The rats were divided into two groups (n=7): 1) control group (C, these rats served as controls) and 2) exercised group (RIE, these rats performed a high-intensity exercise for one month (5 days per week) 40 min daily with speed 35 m/min. The total exercise time was 60 min. The body weight and food intake were recorded continuously during the experiments.

RESULTS

The results showed relative mRNA expression of POMC and NPY estimated in the hypothalamic arcuate nucleus. There were no significant differences in the NPY and POMC mRNAs expression levels and food intake between C and RIE groups.

CONCLUSIONS

The present data indicate that one-month regular intensive exercise did not alter the levels of NPY and POMC mRNAs expression (as two important factors in the regulation of appetite) in the hypothalamic arcuate nucleus and food intake suggesting that this type of exercise itself is not an appropriate procedure for the body weight reduction.

Functional Implications of RFRP-3 in the Central Control of Daily and Seasonal Rhythms in Reproduction

Adaptation of reproductive activity to environmental changes is essential for breeding success and offspring survival. In mammals, the reproductive system displays regular cycles of activation and inactivation which are synchronized with seasonal and/or daily rhythms in environmental factors, notably light intensity and duration. Thus, most species adapt their breeding activity along the year to ensure that birth and weaning of the offspring occur at a time when resources are optimal. Additionally, female reproductive activity is highest at the beginning of the active phase during the period of full oocyte maturation, in order to improve breeding success. In reproductive physiology, it is therefore fundamental to delineate how geophysical signals are integrated in the hypothalamo-pituitary-gonadal axis, notably by the neurons expressing gonadotropin releasing hormone (GnRH). Several neurochemicals have been reported to regulate GnRH neuronal activity, but recently two hypothalamic neuropeptides belonging to the superfamily of (Arg)(Phe)-amide peptides, RFRP-3 and kisspeptin, have emerged as critical for the integration of environmental cues within the reproductive axis. The goal of this review is to survey the current understanding of the role played by RFRP-3 in the temporal regulation of reproduction, and consider how its effect might combine with that of kisspeptin to improve the synchronization of reproduction to environmental challenges.

Nociceptin/Orphanin-FQ Inhibits Gonadotropin-Releasing Hormone Neurons via G-Protein-Gated Inwardly Rectifying Potassium Channels

The pulsatile release of gonadotropin-releasing hormone (GnRH) is a key feature of the hypothalamic-pituitary-gonadal axis. Kisspeptin neurons in the arcuate nucleus (ARC) trigger GnRH neuronal activity, but how GnRH neurons return to baseline electrical activity is unknown. Nociceptin/orphanin-FQ (OFQ) is an inhibitory neuromodulator. ARC proopiomelanocortin (POMC) neurons, known to receive inputs from ARC kisspeptin neurons, contact GnRH neurons and coexpress OFQ in the rat. In the present study, the effect of OFQ(1-13) on GnRH neurons was determined in the mouse. We identified transcripts for the OFQ receptor [opioid receptor like 1 (ORL1)] in GnRH neurons, and, using two-model systems (explants and slices), we found that OFQ exerted a potent inhibition on GnRH neurons, with or without excitatory inputs. We confirmed that the inhibition was mediated by ORL1 via Gi/o-protein coupling. The inhibition, occurring independently of levels of intracellular cyclic adenosine monophosphate, was sensitive to inwardly rectifying potassium channels. The only specific blocker of Gi/o-protein-coupled inwardly rectifying potassium (GIRK) channels, tertiapin-Q (TPNQ), was ineffective in the inhibition of OFQ. Two GIRK activators, one sharing the binding site of TPNQ and one active only on GIRK1-containing GIRK channels, failed to trigger an inhibition. In contrast, protein kinase C phosphorylation activation, known to inhibit GIRK2-mediated currents, prevented the OFQ inhibition. These results indicate a specific combination of GIRK subunits, GIRK2/3 in GnRH neurons. In vivo, double-labeled OFQ/POMC fibers were found in the vicinity of GnRH neurons, and OFQ fibers apposed GnRH neurons. Together, this study brings to light a potent neuromodulator of GnRH neurons.

Emerging insights into hypothalamic-pituitary-gonadal axis regulation and interaction with stress signalling

Reproduction and fertility are regulated via hormones of the hypothalamic-pituitary-gonadal (HPG) axis. Control of this reproductive axis occurs at all levels, including the brain and pituitary, and allows for the promotion or inhibition of gonadal sex steroid secretion and function. In addition to guiding proper gonadal development and function, gonadal sex steroids also act in negative- and positive-feedback loops to regulate reproductive circuitry in the brain, including kisspeptin neurones, thereby modulating overall HPG axis status. Additional regulation is also provided by sex steroids made within the brain, including neuroprogestins. Furthermore, because reproduction and survival need to be coordinated and balanced, the HPG axis is able to modulate (and be modulated by) stress hormone signalling, including cortiscosterone, from the hypothalamic-pituitary-adrenal (HPA) axis. This review covers recent data related to the neural, hormonal and stress regulation of the HPG axis and emerging interactions between the HPG and HPA axes, focusing on actions at the level of the brain and pituitary.

Long non-coding RNAs could act as vectors for paternal heredity of high fat diet-induced obesity

Long non-coding RNAs (lncRNAs) play an important role in epigenetic regulation, and abnormalities may lead to male infertility. To investigate whether lncRNAs are involved in intergenerational inheritance of obesity and obesity-induced decline in fertility, we divided mice into obesity (F0 mice fed a high-fat diet, F0-HFD) and non-obese (F0 mice fed normal chow, F0-NC) model groups and their male offspring (F1-HFD and F1-NC, respectively). We examined the differences in the expression levels of lncRNAs and mRNAs in the F0-HFD/F0-NC and F1-HFD/F1-NC groups. The results revealed similar expression patterns in the F1-HFD/F0-HFD groups at both the lncRNA and mRNA levels. The maximum difference in the lncRNA expression was observed between the F0-HFD and F0-NC groups. The differentially expressed lncRNA targets and mRNAs identified in our study are mainly involved in GnRH signalling pathway, metabolic process, and Hippo signalling pathway; similarly expressed lncRNAs and mRNAs in F1-HFD/F0-HFD are closely linked with G-protein coupled receptor signalling pathway, pancreatic polypeptide receptor activity, and lysine biosynthesis, which may play an important role in the molecular mechanism of intergenerational inheritance of obesity. Furthermore, potential genes that might play important roles in the pathogenesis of obesity-related low fertility were revealed by lncRNA-and mRNA-interaction studies based on the microarray expression profiles. In conclusion, we found that lncRNA could be involved in obesity-induced infertility by expressing abnormalities, which could act as genetic vectors of paternal inheritance of obesity.

Increased high molecular weight adiponectin, but decreased total adiponectin and kisspeptin, in central precocious puberty compared with aged-matched prepubertal girls

The aim of the present study was to compare serum leptin, kisspeptin, total adiponectin, high molecular weight (HMW) adiponectin and neuropeptide Y (NPY) levels between girls with central precocious puberty (CPP; n = 26, 7–9.5 years old) and age-matched controls (n = 29) including or excluding obese girls. Leptin and NPY levels were comparable between CPP and control girls. Kisspeptin levels were lower in the CPP than control group, and were positively correlated with oestrogen in the control group and with systolic and diastolic blood pressure in the CPP group. Kisspeptin levels were negatively correlated with FSH and LH in the CPP group. Total adiponectin levels were lower in CPP than control girls, and were negatively correlated with Tanner stage and body mass index, but positively correlated with the quantitative insulin sensitivity check index in the control group. HMW adiponectin was higher in the CPP than control group, and was positively correlated with Tanner stage and LH in all girls. Total adiponectin had a strong positive correlation with HMW adiponectin in the CPP group (r = 0.915) compared with the control group (r = 0.371). In conclusion, kisspeptin may be associated with increased oestrogen in prepubertal girls, but with increased blood pressure in girls with CPP. In girls entering puberty, HMW adiponectin was increased and associated with reproductive parameters. Based on these observations, HMW adiponectin probably plays an essential role in the initiation of puberty and is a candidate marker for the prediction of CPP.

Obese Neuronal PPARγ Knockout Mice Are Leptin Sensitive but Show Impaired Glucose Tolerance and Fertility

The peroxisome-proliferator activated receptor γ (PPARγ) is expressed in the hypothalamus in areas involved in energy homeostasis and glucose metabolism. In this study, we created a deletion of PPARγ brain-knockout (BKO) in mature neurons in female mice to investigate its involvement in metabolism and reproduction. We observed that there was no difference in age at puberty onset between female BKOs and littermate controls, but the BKOs gave smaller litters when mated and fewer oocytes when ovulated. The female BKO mice had regular cycles but showed an increase in the number of cycles with prolonged estrus. The mice also had increased luteinizing hormone (LH) levels during the LH surge and histological examination showed hemorrhagic corpora lutea. The mice were challenged with a 60% high-fat diet (HFD). Metabolically, the female BKO mice showed normal body weight, glucose and insulin tolerance, and leptin levels but were protected from obesity-induced leptin resistance. The neuronal knockout also prevented the reduction in estrous cycles due to the HFD. Examination of ovarian histology showed a decrease in the number of primary and secondary follicles in both genotypes due to the HFD, but the BKO ovaries showed an increase in the number of hemorrhagic follicles. In summary, our results show that neuronal PPARγ is required for optimal female fertility but is also involved in the adverse effects of diet-induced obesity by creating leptin resistance potentially through induction of the repressor Socs3.

Prenatal testosterone exposure decreases colocalization of insulin receptors in kisspeptin/neurokinin B/dynorphin and agouti-related peptide neurons of the adult ewe

Insulin serves as a link between the metabolic and reproductive systems, communicating energy availability to the hypothalamus and enabling reproductive mechanisms. Adult Suffolk ewes prenatally exposed to testosterone (T) display an array of reproductive and metabolic dysfunctions similar to those seen in women with polycystic ovarian syndrome (PCOS), including insulin resistance. Moreover, prenatal T treatment alters neuropeptide expression in KNDy (co-expressing kisspeptin, neurokinin B/dynorphin) and agouti-related peptide (AgRP) neurons in the arcuate nucleus, two populations that play key roles in the control of reproduction and metabolism, respectively. In this study, we determined whether prenatal T treatment also altered insulin receptors in KNDy and AgRP neurons, as well as in preoptic area (POA) kisspeptin, pro-opiomelanocortin (POMC), and gonadotropin-releasing hormone (GnRH) neurons of the adult sheep brain. Immunofluorescent detection of the beta subunit of insulin receptor (IRβ) revealed that KNDy, AgRP and POMC neurons, but not GnRH or POA kisspeptin neurons, colocalize IRβ in control females. Moreover, prenatal T treatment decreased the percentage of KNDy and AgRP neurons that colocalized IRβ, consistent with reduced insulin sensitivity. Administration of the anti-androgen drug, Flutamide, during prenatal T treatment, prevented the reduction in IRβ colocalization in AgRP, but not in KNDy neurons, suggesting that these effects are programmed by androgenic and oestrogenic actions, respectively. These findings provide novel insight into the effects of prenatal T treatment on hypothalamic insulin sensitivity and raise the possibility that decreased insulin receptors, specifically within KNDy and AgRP neurons, may contribute to the PCOS-like phenotype of this animal model.

Galanin Activates G Protein Gated Inwardly Rectifying Potassium Channels and Suppresses Kisspeptin-10 Activation of GnRH Neurons

GnRH neurons are regulated by hypothalamic kisspeptin neurons. Recently, galanin was identified in a subpopulation of kisspeptin neurons. Although the literature thoroughly describes kisspeptin activation of GnRH neurons, little is known about the effects of galanin on GnRH neurons. This study investigated whether galanin could alter kisspeptin signaling to GnRH neurons. GnRH cells maintained in explants, known to display spontaneous calcium oscillations, and a long-lasting calcium response to kisspeptin-10 (kp-10), were used. First, transcripts for galanin receptors (GalRs) were examined. Only GalR1 was found in GnRH neurons. A series of experiments was then performed to determine the action of galanin on kp-10 activated GnRH neurons. Applied after kp-10 activation, galanin 1-16 (Gal1-16) rapidly suppressed kp-10 activation. Applied with kp-10, Gal1-16 prevented kp-10 activation until its removal. To determine the mechanism by which galanin inhibited kp-10 activation of GnRH neurons, Gal1-16 and galanin were applied to spontaneously active GnRH neurons. Both inhibited GnRH neuronal activity, independent of GnRH neuronal inputs. This inhibition was mimicked by a GalR1 agonist but not by GalR2 or GalR2/3 agonists. Although Gal1-16 inhibition relied on Gi/o signaling, it was independent of cAMP levels but sensitive to blockers of G protein-coupled inwardly rectifying potassium channels. A newly developed bioassay for GnRH detection showed Gal1-16 decreased the kp-10-evoked GnRH secretion below detection threshold. Together, this study shows that galanin is a potent regulator of GnRH neurons, possibly acting as a physiological break to kisspeptin excitation.

BPA Directly Decreases GnRH Neuronal Activity via Noncanonical Pathway

Peripheral feedback of gonadal estrogen to the hypothalamus is critical for reproduction. Bisphenol A (BPA), an environmental pollutant with estrogenic actions, can disrupt this feedback and lead to infertility in both humans and animals. GnRH neurons are essential for reproduction, serving as an important link between brain, pituitary, and gonads. Because GnRH neurons express several receptors that bind estrogen, they are potential targets for endocrine disruptors. However, to date, direct effects of BPA on GnRH neurons have not been shown. This study investigated the effects of BPA on GnRH neuronal activity using an explant model in which large numbers of primary GnRH neurons are maintained and express many of the receptors found in vivo. Because oscillations in intracellular calcium have been shown to correlate with electrical activity in GnRH neurons, calcium imaging was used to assay the effects of BPA. Exposure to 50μM BPA significantly decreased GnRH calcium activity. Blockage of γ-aminobutyric acid ergic and glutamatergic input did not abrogate the inhibitory BPA effect, suggesting direct regulation of GnRH neurons by BPA. In addition to estrogen receptor-β, single-cell RT-PCR analysis confirmed that GnRH neurons express G protein-coupled receptor 30 (G protein-coupled estrogen receptor 1) and estrogen-related receptor-γ, all potential targets for BPA. Perturbation studies of the signaling pathway revealed that the BPA-mediated inhibition of GnRH neuronal activity occurred independent of estrogen receptors, GPER, or estrogen-related receptor-γ, via a noncanonical pathway. These results provide the first evidence of a direct effect of BPA on GnRH neurons.

Leptin Responsive and GABAergic Projections to the Rostral Preoptic Area in Mice

The adipocyte-derived hormone leptin plays a critical role in the control of reproduction via signalling in hypothalamic neurones. The drivers of the hypothalamic-pituitary-gonadal axis, the gonadotrophin-releasing hormone (GnRH) neurones, do not have the receptors for leptin. Therefore, intermediate leptin responsive neurones must provide leptin-to-GnRH signalling. We investigated the populations of leptin responsive neurones that provide input to the rostral preoptic area (rPOA) where GnRH cell bodies reside. Fluorescent retrograde tracer beads (RetroBeads; Lumafluor Inc., Naples, FL, USA) were injected into the rPOA of transgenic leptin receptor enhanced green fluorescent protein (Lepr-eGFP) reporter mice. Uptake of the RetroBeads by Lepr-eGFP neurones was assessed throughout the hypothalamus. RetroBead uptake was most evident in the medial arcuate nucleus (ARC), the dorsomedial nucleus (DMN) and the ventral premammillary nucleus (PMV) of the hypothalamus. The uptake of RetroBeads specifically by Lepr-eGFP neurones was highest in the medial ARC (18% of tracer-labelled neurones Lepr-eGFP-positive). Because neurones that are both leptin responsive and GABAergic play a critical role in the regulation of fertility by leptin, we next focussed on the location of these populations. To address whether GABAergic neurones in leptin-responsive hypothalamic regions project to the rPOA, the experiment was repeated in GABA neurone reporter mice (Vgat-tdTomato). Between 10% and 45% of RetroBead-labelled neurones in the ARC were GABAergic, whereas uptake of tracer by GABAergic neurones in the DMN and PMV was very low (< 5%). These results show that both leptin responsive and GABAergic neurones from the ARC project to the region of the GnRH cell bodies. Our findings suggest that LEPR-expressing GABA neurones from the ARC may be mediators of leptin-to-GnRH signalling.

Chloride Accumulators NKCC1 and AE2 in Mouse GnRH Neurons: Implications for GABAA Mediated Excitation

A developmental “switch” in chloride transporters occurs in most neurons resulting in GABA_A mediated hyperpolarization in the adult. However, several neuronal cell subtypes maintain primarily depolarizing responses to GABA_A receptor activation. Among this group are gonadotropin-releasing hormone-1 (GnRH) neurons, which control puberty and reproduction. NKCC1 is the primary chloride accumulator in neurons, expressed at high levels early in development and contributes to depolarization after GABA_A receptor activation. In contrast, KCC2 is the primary chloride extruder in neurons, expressed at high levels in the adult and contributes to hyperpolarization after GABA_A receptor activation. Anion exchangers (AEs) are also potential modulators of responses to GABA_A activation since they accumulate chloride and extrude bicarbonate. To evaluate the mechanism(s) underlying GABA_A mediated depolarization, GnRH neurons were analyzed for 1) expression of chloride transporters and AEs in embryonic, pre-pubertal, and adult mice 2) responses to GABA_A receptor activation in NKCC1^-/- mice and 3) function of AEs in these responses. At all ages, GnRH neurons were immunopositive for NKCC1 and AE2 but not KCC2 or AE3. Using explants, calcium imaging and gramicidin perforated patch clamp techniques we found that GnRH neurons from NKCC1^-/- mice retained relatively normal responses to the GABA_A agonist muscimol. However, acute pharmacological inhibition of NKCC1 with bumetanide eliminated the depolarization/calcium response to muscimol in 40% of GnRH neurons from WT mice. In the remaining GnRH neurons, HCO₃^- mediated mechanisms accounted for the remaining calcium responses to muscimol. Collectively these data reveal mechanisms responsible for maintaining depolarizing GABA_A mediated transmission in GnRH neurons.

Actions of NPY, and its Y1 and Y2 receptors on pulsatile growth hormone secretion during the fed and fasted state

The hypothalamic NPY system plays an important role in regulating food intake and energy expenditure. Different biological actions of NPY are assigned to NPY receptor subtypes. Recent studies demonstrated a close relationship between food intake and growth hormone (GH) secretion; however, the mechanism through which endogenous NPY modulates GH release remains unknown. Moreover, conclusive evidence demonstrating a role for NPY and Y-receptors in regulating the endogenous pulsatile release of GH does not exist. We used genetically modified mice (germline Npy, Y1, and Y2 receptor knock-out mice) to assess pulsatile GH secretion under both fed and fasting conditions. Deletion of NPY did not impact fed GH release; however, it reversed the fasting-induced suppression of pulsatile GH secretion. The recovery of GH secretion was associated with a reduction in hypothalamic somatotropin release inhibiting factor (Srif; somatostatin) mRNA expression. Moreover, observations revealed a differential role for Y1 and Y2 receptors, wherein the postsynaptic Y1 receptor suppresses GH secretion in fasting. In contrast, the presynaptic Y2 receptor maintains normal GH output under long-term ad libitum-fed conditions. These data demonstrate an integrated neural circuit that modulates GH release relative to food intake, and provide essential information to address the differential roles of Y1 and Y2 receptors in regulating the release of GH under fed and fasting states.

A Multi-Oscillatory Circadian System Times Female Reproduction

Rhythms in female reproduction are critical to insure that timing of ovulation coincides with oocyte maturation and optimal sexual arousal. This fine tuning of female reproduction involves both the estradiol feedback as an indicator of oocyte maturation, and the master circadian clock of the suprachiasmatic nuclei (SCN) as an indicator of the time of the day. Herein, we are providing an overview of the state of knowledge regarding the differential inhibitory and stimulatory effects of estradiol at different stages of the reproductive axis, and the mechanisms through which the two main neurotransmitters of the SCN, arginine vasopressin, and vasoactive intestinal peptide, convey daily time cues to the reproductive axis. In addition, we will report the most recent findings on the putative functions of peripheral clocks located throughout the reproductive axis [kisspeptin (Kp) neurons, gonadotropin-releasing hormone neurons, gonadotropic cells, the ovary, and the uterus]. This review will point to the critical position of the Kp neurons of the anteroventral periventricular nucleus, which integrate both the stimulatory estradiol signal, and the daily arginine vasopressinergic signal, while displaying a circadian clock. Finally, given the critical role of the light/dark cycle in the synchronization of female reproduction, we will discuss the impact of circadian disruptions observed during shift-work conditions on female reproductive performance and fertility in both animal model and humans.

Reciprocal changes in leptin and NPY during nutritional acceleration of puberty in heifers

Feeding a high-concentrate diet to heifers during the juvenile period, resulting in increased body weight (BW) gain and adiposity, leads to early-onset puberty. In this study, we tested the hypothesis that the increase in GnRH/LH release during nutritional acceleration of puberty is accompanied by reciprocal changes in circulating leptin and central release of neuropeptide Y (NPY). The heifers were weaned at 3.5 months of age and fed to gain either 0.5 (Low-gain; LG) or 1.0 kg/day (High-gain; HG) for 30 weeks. A subgroup of heifers was fitted surgically with third ventricle guide cannulas and was subjected to intensive cerebrospinal fluid (CSF) and blood sampling at 8 and 9 months of age. Mean BW was greater in HG than in LG heifers at week 6 of the experiment and remained greater thereafter. Starting at 9 months of age, the percentage of pubertal HG heifers was greater than that of LG heifers, although a replicate effect was observed. During the 6-h period in which CSF and blood were collected simultaneously, all LH pulses coincided with or shortly followed a GnRH pulse. At 8 months of age, the frequency of LH pulses was greater in the HG than in the LG group. Beginning at 6 months of age, concentrations of leptin were greater in HG than in LG heifers. At 9 months of age, concentrations of NPY in the CSF were lesser in HG heifers. These observations indicate that increased BW gain during juvenile development accelerates puberty in heifers, coincident with reciprocal changes in circulating concentrations of leptin and hypothalamic NPY release.

Metabolic influences on reproduction: adiponectin attenuates GnRH neuronal activity in female mice

Metabolic dysfunctions are often linked to reproductive abnormalities. Adiponectin (ADP), a peripheral hormone secreted by white adipose tissue, is important in energy homeostasis and appetite regulation. GnRH neurons are integral components of the reproductive axis, controlling synthesis, and release of gonadotropins. This report examined whether ADP can directly act on GnRH neurons. Double-label immunofluorescence on brain sections from adult female revealed that a subpopulation of GnRH neurons express ADP receptor (AdipoR)2. GnRH/AdipoR2+ cells were distributed throughout the forebrain. To determine the influence of ADP on GnRH neuronal activity and the signal transduction pathway of AdipoR2, GnRH neurons maintained in explants were assayed using whole-cell patch clamping and calcium imaging. This mouse model system circumvents the dispersed distribution of GnRH neurons within the forebrain, making analysis of large numbers of GnRH cells possible. Single-cell PCR analysis and immunocytochemistry confirmed the presence of AdipoR2 in GnRH neurons in explants. Functional analysis revealed 20% of the total GnRH population responded to ADP, exhibiting hyperpolarization or decreased calcium oscillations. Perturbation studies revealed that ADP activates AMP kinase via the protein kinase Cζ/liver kinase B1 pathway. The modulation of GnRH neuronal activity by ADP demonstrated in this report directly links energy balance to neurons controlling reproduction.

Evidence that hypothalamic RFamide related peptide-3 neurones are not leptin-responsive in mice and rats

Leptin, a permissive hormonal regulator of fertility, provides information about the body's energy reserves to the hypothalamic gonadotrophin-releasing hormone (GnRH) neuronal system that drives reproduction. Leptin does not directly act on GnRH neurones, and the neuronal pathways that it uses remain unclear. RFamide-related peptide-3 (RFRP-3) neurones project to GnRH neurones and primarily inhibit their activity. We tested whether leptin could act via RFRP-3 neurones to potentially modulate GnRH activity. First, the effects of leptin deficiency or high-fat diet-induced obesity on RFRP-3 cell numbers and gene expression were assessed in male and female mice. There was no significant difference in Rfrp mRNA levels or RFRP-3-immunoreactive cell counts in wild-type versus leptin-deficient ob/ob animals, or in low-fat versus high-fat diet fed wild-type mice. Second, the presence of leptin-induced signalling in RFRP-3 neurones was examined in male and female wild-type mice and rats. Dual label immunohistochemistry revealed leptin-induced phosphorylated signal transducer and activator of transcription-3 in close proximity to RFRP-3 neurones, although there was very little (2-13%) colocalisation and no significant differences between vehicle and leptin-treated animals. Furthermore, we were unable to detect leptin receptor mRNA in a semi-purified RFRP-3 cell preparation. Because GABA neurones form critical leptin-responsive GnRH inputs, we also determined whether RFRP-3 and GABA cells were colocalised. No such colocalisation was detected. These results support the concept that leptin has little or no effects on RFRP-3 neurones, and that these neurones are unlikely to be an important neuronal pathway for the metabolic regulation of fertility by leptin.

Leptin signaling in GABA neurons, but not glutamate neurons, is required for reproductive function

The adipocyte-derived hormone leptin acts in the brain to modulate the central driver of fertility: the gonadotropin releasing hormone (GnRH) neuronal system. This effect is indirect, as GnRH neurons do not express leptin receptors (LEPRs). Here we test whether GABAergic or glutamatergic neurons provide the intermediate pathway between the site of leptin action and the GnRH neurons. Leptin receptors were deleted from GABA and glutamate neurons using Cre-Lox transgenics, and the downstream effects on puberty onset and reproduction were examined. Both mouse lines displayed the expected increase in body weight and region-specific loss of leptin signaling in the hypothalamus. The GABA neuron-specific LEPR knock-out females and males showed significantly delayed puberty onset. Adult fertility observations revealed that these knock-out animals have decreased fecundity. In contrast, glutamate neuron-specific LEPR knock-out mice displayed normal fertility. Assessment of the estrogenic hypothalamic-pituitary-gonadal axis regulation in females showed that leptin action on GABA neurons is not necessary for estradiol-mediated suppression of tonic luteinizing hormone secretion (an indirect measure of GnRH neuron activity) but is required for regulation of a full preovulatory-like luteinizing hormone surge. In conclusion, leptin signaling in GABAergic (but not glutamatergic neurons) plays a critical role in the timing of puberty onset and is involved in fertility regulation throughout adulthood in both sexes. These results form an important step in explaining the role of central leptin signaling in the reproductive system. Limiting the leptin-to-GnRH mediators to GABAergic cells will enable future research to focus on a few specific types of neurons.

Paradoxical effect of gonadotrophin-inhibiting hormone to negatively regulate neuropeptide Y neurones in mouse arcuate nucleus

Regulation of reproduction and energy homeostasis are linked, although our understanding of the central neural mechanisms subserving this connection is incomplete. Gonadotrophin-inhibiting hormone (GnIH) is a neuropeptide that negatively regulates reproduction and stimulates food intake. Neuropeptide Y (NPY) and products of the pro-opiomelanocortin (POMC) precursor (β-endorphin melanocortins) are appetite regulating peptides produced in the neurones of the arcuate nucleus; these peptides also regulate reproduction. In the present study, we determined the effects of GnIH on NPY and POMC neurones. Using brain slices from mice with transgenes for fluorescent tags in the two types of neurone and patch clamp electrophysiology, a predominant inhibitory effect of GnIH was observed. GnIH (100 nM) inhibited the firing rate in POMC cells, confirming the results of previous studies and consistent with the stimulatory effect of GnIH on food intake. Paradoxically (i.e. because both GnIH and NPY stimulate food intake), GnIH also had a predominantly inhibitory effect on action potential activity in NPY cells. GnIH also inhibited the secretion of NPY and α-melanocyte-stimulating hormone secretion in incubated hypothalamic blocks. GnIH (100 ng) injected into the cerebral ventricles of mice did not increase the number of NPY cells that were positively immunostained for c-Fos. Finally, dual label immunocytochemistry showed that 20% of NPY neurones had close contacts from GnIH fibres/varicosities. In conclusion, we confirm a negative effect of GnIH on POMC cells and demonstrate a paradoxical reduction of electrophysiological and functional activity in NPY cells.

Neuropeptide y gates a stress-induced, long-lasting plasticity in the sympathetic nervous system

Acute stress evokes the fight-or-flight reflex, which via release of the catecholamine hormones affects the function of every major organ. Although the reflex is transient, it has lasting consequences that produce an exaggerated response when stress is reexperienced. How this change is encoded is not known. We investigated whether the reflex affects the adrenal component of the sympathetic nervous system, a major branch of the stress response. Mice were briefly exposed to the cold-water forced swim test (FST) which evoked an increase in circulating catecholamines. Although this hormonal response was transient, the FST led to a long-lasting increase in the catecholamine secretory capacity measured amperometrically from chromaffin cells and in the expression of tyrosine hydroxylase. A variety of approaches indicate that these changes are regulated postsynaptically by neuropeptide Y (NPY), an adrenal cotransmitter. Using immunohistochemistry, RT-PCR, and NPY(GFP) BAC mice, we find that NPY is synthesized by all chromaffin cells. Stress failed to increase secretory capacity in NPY knock-out mice. Genetic or pharmacological interference with NPY and Y1 (but not Y2 or Y5) receptor signaling attenuated the stress-induced change in tyrosine hydroxylase expression. These results indicate that, under basal conditions, adrenal signaling is tonically inhibited by NPY, but stress overrides this autocrine negative feedback loop. Because acute stress leads to a lasting increase in secretory capacity in vivo but does not alter sympathetic tone, these postsynaptic changes appear to be an adaptive response. We conclude that the sympathetic limb of the stress response exhibits an activity-dependent form of long-lasting plasticity.

Modulation of the arcuate nucleus-medial preoptic nucleus lordosis regulating circuit: a role for GABAB receptors

Estradiol rapidly activates a microcircuit in the arcuate nucleus of the hypothalamus (ARH) that is needed for maximal female sexual receptivity. Membrane estrogen receptor-α complexes with and signals through the metabotropic glutamate receptor-1a stimulating NPY release within the ARH activating proopiomelanocortin (POMC) neurons. These POMC neurons project to the medial preoptic nucleus (MPN) and release β-endorphin. Estradiol treatment induces activation/internalization of MPN μ-opioid receptors (MOR) to inhibit lordosis. Estradiol membrane action modulates ARH gamma-aminobutyric acid receptor-B (GABAB) activity. We tested the hypothesis that ARH GABAB receptors mediate estradiol-induced MOR activation and facilitation of sexual receptivity. Double-label immunohistochemistry revealed expression of GABAB receptors in NPY, ERα and POMC expressing ARH neurons. Approximately 70% of POMC neurons expressed GABAB receptors. Because estradiol initially activates an inhibitory circuit and maintains activation of this circuit, the effects of blocking GABAB receptors were evaluated before estradiol benzoate (EB) treatment and after at the time of lordosis testing. Bilateral infusions of the GABAB receptor antagonist, CGP52432, into the ARH prior to EB treatment of ovariectomized rats prevented estradiol-induced activation/internalization of MPN MOR, and the rats remained unreceptive. However, in EB-treated rats, bilateral CGP52432 infusions 30 min before behavior testing attenuated MOR internalization and facilitated lordosis. These results indicated that GABAB receptors were located within the lordosis-regulating ARH microcircuit and are necessary for activation and maintenance of the estradiol inhibition of lordosis behavior. Although GABAB receptors positively influence estradiol signaling, they negatively regulate lordosis behavior since GABAB activity maintains the estradiol-induced inhibition.

Role of GnRH Neurons and Their Neuronal Afferents as Key Integrators between Food Intake Regulatory Signals and the Control of Reproduction

Reproductive function is regulated by a plethora of signals that integrate physiological and environmental information. Among others, metabolic factors are key components of this circuit since they inform about the propitious timing for reproduction depending on energy availability. This information is processed mainly at the hypothalamus that, in turn, modulates gonadotropin release from the pituitary and, thereby, gonadal activity. Metabolic hormones, such as leptin, insulin, and ghrelin, act as indicators of the energy status and convey this information to the reproductive axis regulating its activity. In this review, we will analyse the central mechanisms involved in the integration of this metabolic information and their contribution to the control of the reproductive function. Particular attention will be paid to summarize the participation of GnRH, Kiss1, NPY, and POMC neurons in this process and their possible interactions to contribute to the metabolic control of reproduction.

Direct regulation of GnRH neuron excitability by arcuate nucleus POMC and NPY neuron neuropeptides in female mice

Hypothalamic neuropeptide Y (NPY) and proopiomelanocortin (POMC) neurons act to sense and coordinate the brain's responses to metabolic cues. One neuronal network that is very sensitive to metabolic status is that controlling fertility. In this study, we investigated the impact of neuropeptides released by NPY and POMC neurons on the cellular excitability of GnRH neurons, the final output cells of the brain controlling fertility. The majority (∼70%) of GnRH neurons were activated by α-melanocyte-stimulating hormone, and this resulted from the direct postsynaptic activation of melanocortin receptor 3 and melanocortin receptor 4. A small population of GnRH neurons (∼15%) was excited by cocaine and amphetamine-regulated transcript or inhibited by β-endorphin. Agouti-related peptide, released by NPY neurons, was found to have variable inhibitory (∼10%) and stimulatory (∼25%) effects upon subpopulations of GnRH neurons. A variety of NPY and pancreatic polypeptide analogs was used to examine potential NPY interactions with GnRH neurons. Although porcine NPY (Y1/Y2/Y5 agonist) directly inhibited the firing of approximately 45% of GnRH neurons, [Leu(31),Pro(34)]-NPY (Y1/Y4/Y5 agonist) could excite (56%) or inhibit (19%). Experiments with further agonists indicated that Y1 receptors were responsible for suppressing GnRH neuron activity, whereas postsynaptic Y4 receptors were stimulatory. These results show that the activity of GnRH neurons is regulated in a complex manner by neuropeptides released by POMC and NPY neurons. This provides a direct route through which different metabolic cues can regulate fertility.

SDF and GABA interact to regulate axophilic migration of GnRH neurons

Stromal derived growth factor (SDF-1) and gamma-aminobutyric acid (GABA) are two extracellular cues that regulate the rate of neuronal migration during development and may act synergistically. The molecular mechanisms of this interaction are still unclear. Gonadotropin releasing hormone-1 (GnRH) neurons are essential for vertebrate reproduction. During development, these neurons emerge from the nasal placode and migrate through the cribriform plate into the brain. Both SDF-1 and GABA have been shown to regulate the rate of GnRH neuronal migration by accelerating and slowing migration, respectively. As such, this system was used to explore the mechanism by which these molecules act to produce coordinated cell movement during development. In the present study, GABA and SDF-1 are shown to exert opposite effects on the speed of cell movement by activating depolarizing or hyperpolarizing signaling pathways, GABA via changes in chloride and SDF-1 via changes in potassium. GABA and SDF-1 were also found to act synergistically to promote linear rather than random movement. The simultaneous activation of these signaling pathways, therefore, results in tight control of cellular speed and improved directionality along the migratory pathway of GnRH neurons.

The GTPase activating Rap/RanGAP domain-like 1 gene is associated with chicken reproductive traits

Background

Abundant evidence indicates that chicken reproduction is strictly regulated by the hypothalamic-pituitary-gonad (HPG) axis, and the genes included in the HPG axis have been studied extensively. However, the question remains as to whether any other genes outside of the HPG system are involved in regulating chicken reproduction. The present study was aimed to identify, on a genome-wide level, novel genes associated with chicken reproductive traits.

Methodology/Principal Finding

Suppressive subtractive hybridization (SSH), genome-wide association study (GWAS), and gene-centric GWAS were used to identify novel genes underlying chicken reproduction. Single marker-trait association analysis with a large population and allelic frequency spectrum analysis were used to confirm the effects of candidate genes. Using two full-sib Ningdu Sanhuang (NDH) chickens, GARNL1 was identified as a candidate gene involved in chicken broodiness by SSH analysis. Its expression levels in the hypothalamus and pituitary were significantly higher in brooding chickens than in non-brooding chickens. GWAS analysis with a NDH two tail sample showed that 2802 SNPs were significantly associated with egg number at 300 d of age (EN300). Among the 2802 SNPs, 2 SNPs composed a block overlapping the GARNL1 gene. The gene-centric GWAS analysis with another two tail sample of NDH showed that GARNL1 was strongly associated with EN300 and age at first egg (AFE). Single marker-trait association analysis in 1301 female NDH chickens confirmed that variation in this gene was related to EN300 and AFE. The allelic frequency spectrum of the SNP rs15700989 among 5 different populations supported the above associations. Western blotting, RT-PCR, and qPCR were used to analyze alternative splicing of the GARNL1 gene. RT-PCR detected 5 transcripts and revealed that the transcript, which has a 141 bp insertion, was expressed in a tissue-specific manner.

Conclusions/Significance

Our findings demonstrate that the GARNL1 gene contributes to chicken reproductive traits.

Culturing embryonic nasal explants for developmental and physiological study

Primary cultures obtained from embryonic nasal placodes can maintain olfactory neurons, olfactory ensheathing cells, and large numbers of gonadotropin releasing hormone-1 (GnRH) neurons. Depending on the age of the starting material, one can examine cell interactions important for placode formation or neuronal migration and axonal outgrowth. When generated at E11.5 in mouse, neuronal migration and axon outgrowth away from the main tissue mass occurs. This area of the explant, the periphery, is only a few cells thick. This characteristic offers the opportunity to image single cells and axons and allows pharmacological and molecular manipulations as well as physiological recordings to be performed. Here, we describe a system for culturing nasal explants used in our laboratory. This model system provides a method for obtaining physiological cellular responses with post hoc immunohistochemistry, or gene expression studies, on cells arising from the nasal placode.