Kisspeptin/neurokinin B/dynorphin Research Articles

7985 Insights into the Menopausal Transition: A Comparative Analysis of Hypothalamic Reproductive Aging in Women and a Mouse Model of Menopause

Abstract Disclosure: J.C. Bloom: None. S.A. Pereira: None. E. Torres Jimenez: None. D.C. Page: None. V.M. Navarro: None. Menopause onset is the major determinant of reproductive lifespan in women and is characterized by the decline in estrogen production from the ovary. While much of our current understanding of the menopause transition in humans comes from a series of observational longitudinal studies initiated in the 1980s and 1990s, the mechanisms by which reproductive aging impacts healthy brain aging remains a profoundly under-studied aspect of women’s health. The hypothalamus, a hub of homeostatic and temperature regulation, is highly sensitive to changes in sex steroid levels. Recently, activation of the neurokinin 3 receptor (NK3R) by neurokinin B (NKB) has been linked to the onset of vasomotor symptoms (VMS) during menopausal transition. NKB is secreted by hypothalamic Kisspeptin, NKB, Dynorphin (KNDy) neurons in response to decreasing estradiol levels. Here, we present a comparative study of the expression trajectories of the KNDy genes (KISS1, TAC3, PDYN, respectively) and NK3R (TACR3) in hypothalamic samples of humans across menopause and a mouse model of peri- and post-menopause (short- and long-term ovariectomy (OVX), respectively). RNA-sequencing data of human and mouse hypothalamic samples revealed a high correlation in the expression profile of the KNDy/NK3R genes between both species. Further investigation has revealed a highly conserved pool of genes in human and mouse hypothalami that correlate with TACR3 upon decline of circulating sex steroids. Thus, by examining conserved gene expression patterns across this critical reproductive period, we have been able to identify novel candidate targets involved in menopausal transition which may serve to better elucidate the biology of menopause-associated conditions affecting the brain, such as VMS and cognitive decline. Presentation: 6/2/2024

7985 Insights into the Menopausal Transition: A Comparative Analysis of Hypothalamic Reproductive Aging in Women and a Mouse Model of Menopause

Abstract Disclosure: J.C. Bloom: None. S.A. Pereira: None. E. Torres Jimenez: None. D.C. Page: None. V.M. Navarro: None. Menopause onset is the major determinant of reproductive lifespan in women and is characterized by the decline in estrogen production from the ovary. While much of our current understanding of the menopause transition in humans comes from a series of observational longitudinal studies initiated in the 1980s and 1990s, the mechanisms by which reproductive aging impacts healthy brain aging remains a profoundly under-studied aspect of women’s health. The hypothalamus, a hub of homeostatic and temperature regulation, is highly sensitive to changes in sex steroid levels. Recently, activation of the neurokinin 3 receptor (NK3R) by neurokinin B (NKB) has been linked to the onset of vasomotor symptoms (VMS) during menopausal transition. NKB is secreted by hypothalamic Kisspeptin, NKB, Dynorphin (KNDy) neurons in response to decreasing estradiol levels. Here, we present a comparative study of the expression trajectories of the KNDy genes (KISS1, TAC3, PDYN, respectively) and NK3R (TACR3) in hypothalamic samples of humans across menopause and a mouse model of peri- and post-menopause (short- and long-term ovariectomy (OVX), respectively). RNA-sequencing data of human and mouse hypothalamic samples revealed a high correlation in the expression profile of the KNDy/NK3R genes between both species. Further investigation has revealed a highly conserved pool of genes in human and mouse hypothalami that correlate with TACR3 upon decline of circulating sex steroids. Thus, by examining conserved gene expression patterns across this critical reproductive period, we have been able to identify novel candidate targets involved in menopausal transition which may serve to better elucidate the biology of menopause-associated conditions affecting the brain, such as VMS and cognitive decline. Presentation: 6/2/2024

30 Central Regulation of Kndy Neurons During Undernutrition in Sheep

Abstract Adequate energy intake is essential for reproduction. While we have known for decades that feed restriction inhibits gonadotropin-releasing hormone/luteinizing hormone (GnRH/LH) secretion, the central mechanisms that govern this reduction during undernutrition remain to be fully elucidated. The past few years, we have focused on examining central mechanisms whereby chronic feed restriction in young sheep results in the inhibition of LH secretion. This presentation will focus on our current understanding of how feed restriction impacts kisspeptin/neurokinin B/dynorphin (KNDy) neurons in young sheep and will give a glimpse into our next few years as we examine how input to KNDy neurons could play a key role in regulating reproduction during undernutrition.

FRI280 Partial Loss Of KNDy Neurons In Prenatally Androgen Treated Female Rats Alters The LH Secretion And Ovarian Morphology In A Model Of Polycystic Ovary Syndrome

Abstract Disclosure: N.S. Aquino: None. A. Campideli-Santana: None. L.M. Antunes: None. R. Araújo-Lopes: None. K.S. Silva: None. P.C. Henriques: None. D.D. Gusmão: None. M.P. Bernuci: None. R.E. Szawka: None. A.M. dos Reis: None. Polycystic Ovary Syndrome (PCOS) is a high-prevalent endocrine dysfunction, causing metabolic disorders and infertility. Women with PCOS show a disrupted hypothalamus-pituitary-gonadal (HPG) axis, which results in increased luteinizing hormone (LH) secretion, LH pulse frequency, and LH/follicle stimulating hormone (FSH) ratio. These changes are related to an impaired negative-feedback effect of ovarian steroids, estradiol and progesterone, on the gonadotrophin releasing-hormone (GnRH) neurons. Because the kisspeptin/neurokinin-B/dynorphin (KNDy) neurons of the arcuate (ARC) nucleus are responsible for mediating the ovarian steroid negative feedback, we investigated whether the ablation of KNDy neurons would change the LH secretion and ovarian morphology in a rat model of PCOS. Pregnant dams were treated with dihydrotestosterone (DHT, 3 mg/day; s.c) from days 16 to 19 of pregnancy. Three months after birth, the prenatally androgen-treated (PNA) offspring received intra-ARC stereotaxic injections of the neurokinin-3 receptor agonist conjugated with saporin (NK3-SAP) to induce the lesion of KNDy neurons and were submitted to serial blood sampling for LH measurement. PNA NK3-SAP rats had a moderate loss of ARC neurokinin-B-immunoreactive neurons (between 50-70%) compared with the Blank-SAP-injected PNA group. The PNA Blank-SAP rats displayed LH pulse frequency, pulse amplitude, and mean LH levels similar to control rats on diestrus. Remarkably, the partial loss of KNDy neurons increased the LH pulse amplitude and mean LH without changing the pulse frequency. Histological analysis was performed to investigate the outcome of the partial loss of KNDy neurons on the ovarian morphology in PNA rats. The numbers of primordial, primary, and secondary health follicles were decreased in PNA Blank-SAP compared with diestrus rats. Notably, the number of primordial follicles was partially restored in NK3-SAP rats. On the other hand, neither the number of atretic follicles nor the number of corpora lutea was changed in PNA Blank or NK3-SAP rats, indicating no change in the ovulatory function. Therefore, we provide evidence that KNDy neurons negatively modulate LH release and LH pulse amplitude in PNA rats. Moreover, the results suggest that KNDy neurons are involved in the reduction of the primordial follicle pool and ovarian reserve in PNA rats. Financial Support: Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG), Brazilian National Council for Scientific and Technological Development (CNPq), British Society for Neuroendocrinology (BSN). Presentation: Friday, June 16, 2023

Effects of electroacupuncture on the kisspeptin-gonadotropin-releasing hormone (GnRH) /luteinizing hormone (LH) neural circuit abnormalities and androgen receptor expression of kisspeptin/neurokinin B/dynorphin neurons in PCOS rats

BackgroundPolycystic ovary syndrome (PCOS) is characterized by hyperandrogenism, anovulation, and polycystic ovaries. Electroacupuncture (EA) can effectively improve hyperandrogenism and increase ovulation frequency in patients with PCOS. Pieces of suggest that androgen activity in the brain is associated with impaired steroid negative feedback in such patients. Studies have shown that EA regulated androgen receptor (AR) expression and local factor levels (such as anti-Müllerian hormone and inhibin B) in the ovary of PCOS rats. However, few studies have explored the effect of EA on androgen activity in the brain.ObjectiveThis study investigated the effect of EA on the kisspeptin-gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) neural circuit and sex hormone receptor expression in the hypothalamus of PCOS rats.MethodsPCOS signs were induced by letrozole administration, and the induced rats were treated with low-frequency EA at Guan Yuan acupoint (CV4). The effect of EA on PCOS-like signs was evaluated by observing changes in the body weight, ovarian quality, ovarian morphology, and serum sex hormone levels in rats. To explore the mechanism of the effect of EA on PCOS-like signs, the neuropeptide content of the kisspeptin-GnRH/LH neural circuit was assessed using enzyme-linked immunosorbent assay(ELISA); AR and estrogen receptor α (ERα) coexpression on kisspeptin/neurokinin B/dynorphin (KNDy) neurons was determined via triple-label immunofluorescence; and protein and mRNA expression of Kiss1, Ar, Esr1, and kisspeptin receptor (Kiss1r) was evaluated via western blotting and Reverse Transcription-Polymerase Chain Reaction (RT-PCR).ResultsThe results revealed that the estrous cycle of rats in the EA treatment group recovered, and their body and ovary weight reduced; ovarian morphology improved; serum testosterone and LH levels significantly decreased; and kisspeptin, GnRH, and dynorphin levels in hypothalamic arcuate nucleus significantly decreased. Compared with controls, the number of AR/Kiss1-positive cells increased, number of ERα/Kiss1-positive cells decreased, and protein and mRNA expression of Kiss1, Ar, and Kiss1r significantly increased in PCOS rats. However, EA treatment reversed these changes and reduced the expression of Kiss1, Ar, and Kiss1r significantly.ConclusionImprovement in the reproductive hallmarks of PCOS rats via EA may be achieved by regulating the kisspeptin-GnRH/LH circuit via androgen activity attenuation. Thus, the results provide an experimental basis for acupuncture as an adjuvant medical therapy on PCOS.

Short-term depletion of plasma estrogen affects hypothalamic kisspeptin-neurokinin B-dynorphin A neurons, gonadotrophs, and pulsatile luteinizing hormone secretion in female rats

Kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the arcuate nucleus (ARC) regulate pulsatile luteinizing hormone (LH) secretion. These neurons express estrogen receptors and are negatively regulated by estrogen. This study aimed to determine whether estrogen supplementation after short-term ovariectomy-induced estrogen depletion has different effects on KNDy neurons depending on the timing of the supplementation. To decrease endogenous estradiol (E2) for a short time, adult female rats received a tube filled with E2 one week after ovariectomy and utilized it one week later (O1w + E). From the results of immunohistochemistry, the response to E2 was attenuated in KNDy neurons of O1w + E rats. Enlarged LH-secreting cells in the anterior pituitary were found in O1w + E rats; however, such enlarged LH cells were not found in ones without previous short-term E2 depletion. From the analysis of LH pulses, plasma LH levels were increased in O1w + E rats relative to ones without previous short-term E2 depletion. These results suggested that once endogenous sex steroids were depleted, the response to E2 in hypothalamic KNDy neurons did not fully recover in one week. Thus, short-term sex steroid depletion due to gonadectomy could alter the response to the sex steroids in KNDy neurons even though the period without sex steroids is only one week, and the alteration is likely to affect plasma hormone levels.

Kisspeptin-neuron control of LH pulsatility and ovulation.

Feedback from oestradiol (E2) plays a critical role in the regulation of major events in the physiological menstrual cycle including the release of gonadotrophins to stimulate follicular growth, and the mid-cycle luteinising hormone (LH) surge that leads to ovulation. E2 predominantly exerts its action via oestrogen receptor-alpha (ERα), however, as gonadotrophin releasing hormone (GnRH) neurons lack ERα, E2-feedback is posited to be indirectly mediated via upstream neurons. Kisspeptin (KP) is a neuropeptide expressed in hypothalamic KP-neurons that control GnRH secretion and plays a key role in the central mechanism regulating the hypothalamic-pituitary-gonadal (HPG) axis. In the rodent arcuate (ARC) nucleus, KP is co-expressed with Neurokinin B and Dynorphin; and thus, these neurons are termed 'Kisspeptin-Neurokinin B-Dynorphin' (KNDy) neurons. ARC KP-neurons function as the 'GnRH pulse generator' to regulate GnRH pulsatility, as well as mediating negative feedback from E2. A second KP neuronal population is present in the rostral periventricular area of the third ventricle (RP3V), which includes anteroventral periventricular (AVPV) nucleus and preoptic area neurons. These RP3V KP-neurons mediate positive feedback to induce the mid-cycle luteinising hormone (LH) surge and subsequent ovulation. Here, we describe the role of KP-neurons in these two regions in mediating this differential feedback from oestrogens. We conclude by considering reproductive diseases for which exploitation of these mechanisms could yield future therapies.

ODP330 Long-term Effects of Prenatal Undernutrition on Hypothalamic KNDy Gene Expression in Female Rats

Abstract Accumulating evidence suggested that the nutritional environment during development periods induces metabolic programming, leading to metabolic disorders and detrimental influences on human reproductive health. The purpose of this study was to determine whether intrauterine malnutrition has a long-term adverse effect on a reproductive center, kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus (ARC) of the female offspring. In female offspring from 50% undernutrition (UN) dams, first virginal estrus tended to be advanced, and hypothalamic neurokinin B gene (Tac3) expression was increased in adolescents. Conversely, the UN caused the significant suppression of ARC kisspeptin (Kiss1) and Tac3 gene expression after 29 weeks of age. These results suggested that intrauterine undernutrition stress caused developmental programming in KNDy neurons, which changed in their gene expression depending on life stages. Furthermore, our data showed obesogenic effects of prenatal undernutrition in the female rats; UN offspring showed low birth weight, rapid catch-up growth at four weeks of age, visceral fat accumulation, and an increase in calorie intake and plasma triglyceride levels at adulthood. The current study demonstrated that intrauterine undernutrition affected hypothalamic developmental programming in female rats, which induced long-term effects on hypothalamic KNDy gene expression and could influence metabolism and reproductive function later in life. Presentation: No date and time listed

Deletion of Growth Hormone Secretagogue Receptor in Kisspeptin Neurons in Female Mice Blocks Diet-Induced Obesity.

The gut peptide, ghrelin, mediates energy homeostasis and reproduction by acting through its receptor, growth hormone secretagogue receptor (GHSR), expressed in hypothalamic neurons in the arcuate (ARC). We have shown 17β-estradiol (E2) increases Ghsr expression in Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons, enhancing sensitivity to ghrelin. We hypothesized that E2-induced Ghsr expression augments KNDy sensitivity in a fasting state by elevating ghrelin to disrupt energy expenditure in females. We produced a Kiss1-GHSR knockout to determine the role of GHSR in ARC KNDy neurons. We found that changes in ARC gene expression with estradiol benzoate (EB) treatment were abrogated by the deletion of GHSR and ghrelin abolished these differences. We also observed changes in metabolism and fasting glucose levels. Additionally, knockouts were resistant to body weight gain on a high fat diet (HFD). Behaviorally, we found that knockouts on HFD exhibited reduced anxiety-like behavior. Furthermore, knockouts did not refeed to the same extent as controls after a 24 h fast. Finally, in response to cold stress, knockout females had elevated metabolic parameters compared to controls. These data indicate GHSR in Kiss1 neurons modulate ARC gene expression, metabolism, glucose homeostasis, behavior, and thermoregulation, illustrating a novel mechanism for E2 and ghrelin to control Kiss1 neurons.

The influence of estro-progestin therapy on neurohormonal activity in functional hypothalamic amenorrhea

Background: Functional hypothalamic amenorrhea (FHA) is a chronic endocrine disorder caused by the abnormal pulsatile secretion of neurohormones in the hypothalamus. Secretion of GnRH is regulated by kisspeptin/neurokinin B/dynorphin (KNDy) neurons. These neurons produce, among other neurohormones, neurokinin B (NKB) which regulates the coordinated stimulation or inhibition of GnRH secreting neurons. Aim of the study: Assessment and comparison of serum NKB in patients with FHA at baseline, and following 6 months of estrogen-progestagen therapy. Materials and methods: Fifty-five patients with functional hypothalamic amenorrhea were included in the study group. Serum concentrations of neurokinin B (NKB), follicle stimulating hormone (FSH), luteinizing hormone (LH), 17-β-estradiol (E2), prolactin (PRL), cortisol, testosterone (T), dehydroepiandrosterone sulfate (DHEA-S), thyroid-stimulating hormone (TSH), free thyroxine (fT4), fasting glucose and insulin, as well as lipid profile were measured at baseline. At the time of diagnosis, patients with FHA were prescribed a course of 2 mg 17-β-estradiol and 10 mg dydrogesterone for duration of 6 months. Serum NKB was then reassessed following treatment at 6 months. Results: At baseline, the FHA group was found to have a decreased serum NKB concentration when compared to a healthy control group. Following 6 months of sequential estrogen-progestogen hormone therapy, this study did not find any statistically significant difference in serum NKB concentration in the treatment arm compared to baseline. Conclusions: For the first time, NKB secretion has been studied in patients with FHA. A significantly lower level of serum NKB was observed in these patients at baseline, when compared to a control group. After 6 months of combination estrogen-progesterone therapy, no significant changes in NKB levels were observed in these patients. These findings, for the first time in the literature, provide insight into the perceived benefit of HRT, calling into question its benefit in addressing the underlying etiopathogenetic contributors of FHA. These new findings may contribute to more targeted and appropriate treatment of such patients in the future.

Opioidergic pathways and kisspeptin in the regulation of female reproduction in mammals.

Endogenous opioid peptides have attracted attention as critical neuropeptides in the central mechanism regulating female reproduction ever since the discovery that arcuate dynorphin neurons that coexpress kisspeptin and neurokinin B (NKB), which are also known as kisspeptin/neurokinin B/dynorphin (KNDy) neurons, play a role as a master regulator of pulsatile gonadotropin-releasing hormone (GnRH) release in mammals. In this study, we first focus on the role of dynorphin released by KNDy neurons in the GnRH pulse generation. Second, we provide a historical overview of studies on endogenous opioid peptides. Third, we discuss how endogenous opioid peptides modulate tonic GnRH/gonadotropin release in female mammals as a mediator of inhibitory internal and external cues, such as ovarian steroids, nutritional status, or stress, on reproduction. Then, we discuss the role of endogenous opioid peptides in GnRH surge generation in female mammals.

Synergistic Control of KNDy Neuronal Influence on Energy Balance by Ghrelin and Estradiol

The gut peptide, ghrelin, mediates negative energy homeostasis and the neuroendocrine control of energy homeostasis by acting through its receptor, growth hormone secretagogue receptor (GHSR). GHSR, expressed in hypothalamic Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons in the arcuate (ARC), is well known to regulate energy balance. We have previously shown 17-beta-estradiol (E2) robustly increases Ghsr expression in KNDy neurons, enhancing their sensitivity to ghrelin. We hypothesize that E2-induced increase in GHSR expression augments KNDy sensitivity in a fasting state by elevating ghrelin to reduce energy expenditure in females. We developed a Kiss1-specific GHSR knockout to determine the role of GHSR in ARC KNDy neurons and fed them either a low-fat diet (LFD) or a high-fat diet (HFD). Knockout (experimental) females were resistant to HFD in terms of body weight gain, adiposity, and food intake compared to HFD-fed controls. HFD-fed experimental females also exhibited slower glucose clearance compared to HFD-fed controls. Experimental females, regardless of diet, exhibited elevated fasting (5h) glucose. Metabolic rates (V.O2, V.CO2) and energy expenditure (heat) were not different. Respiratory Exchange Ratio (RER) was elevated in LFD-fed females, indicating the utilization of carbohydrates over fat for energy. Further meal pattern analysis revealed a reduction in meal duration in HFD-fed females, but elevated meal frequency, while HFD-fed experimental females exhibited a reduced meal size. In two separate meal pattern experiments, experimental and control females were fasted for 24h and refed or injected with ghrelin (I.P. 1mg/kg) or saline. We observed a striking delay in refeeding behavior in experimental females compared to controls during the refeeding period after fasting. After injection, control females responded to ghrelin with a rapid and sustained increase in food intake which was blunted in experimentals. Collectively, these data suggest that GHSR activation in KNDy neurons modulates metabolism, glucose homeostasis, and feeding behavior, illustrating a novel mechanism for E2 and ghrelin to synergistically control KNDy neuronal output and their subsequent behavioral and physiological outcomes.

Effects of Diet-Induced Obesity on Hypothalamic Kisspeptin-Neurokinin-Dynorphin (KNDy) Neurons and Luteinizing Hormone Secretion in Sex Hormone-Primed Male and Female Rats

Metabolic stress resulting from a nutrient excess causes infertility in both sexes. Kisspeptin-neurokinin B-dynorphin (KNDy) neurons in the arcuate nucleus (ARC) have been suggested to be key players in reproduction via direct stimulation of gonadotropin-releasing hormone (GnRH) and subsequent gonadotropin release in mammalian species. In this study, we investigated the sex differences in the effects of a high-fat diet (HFD) on KNDy-associated gene expression in the ARC to determine the pathogenic mechanism underlying obesity-induced infertility. Wistar-Imamichi strain male and female rats (7 weeks of age) were fed either a standard diet (10% calories from fat) or high-fat diet (45% calories from fat) for 4 months. In male rats, the HFD caused a significant suppression of Kiss1(encoding kisspeptin), Tac3(encoding neurokinin B), and Pdyn(encoding dynorphin A) gene expression in the ARC, resulting in a decrease in plasma luteinizing hormone (LH) levels. In female rats, 58% of the HFD-fed female rats exhibited irregular estrous cycles, while the other rats showed regular cycles. LH pulses were found, and the numbers of ARC Kiss1-,Tac3-, and Pdyn-expressing cells were high in control animals and almost allHFD-fed female rats, but two out of 10 rats showed profound HFD-induced suppression of LH pulse frequency and reduction in these cells. No statistical differences in LH secretion or ARC KNDy gene expression were observed between HFD-fed and control female rats. Additionally, the number of Gnrh1-expressing cells in the preoptic area was comparable between the groups in both sexes. Our findings revealed that HFD-fed male rats showed KNDy-dependent infertility, while irregular menstruation was mainly induced by KNDy-independent pathways during the incipient stage of obese infertility in female rats. Taken together, hypothalamic kisspeptin neurons in male rats may be susceptible to HFD-induced obesity compared with those in female rats.

Effect of diet-induced obesity on kisspeptin-neurokinin B-dynorphin A neurons in the arcuate nucleus and luteinizing hormone secretion in sex hormone-primed male and female rats

Metabolic stress resulting from either lack or excess of nutrients often causes infertility in both sexes. Kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the arcuate nucleus (ARC) has been suggested to be a key players in reproduction via direct stimulation of the pulsatile gonadotropin-releasing hormone (GnRH) and subsequent gonadotropin release in mammalian species. In this study, we investigated the effect of high-fat diet (HFD) on hypothalamic KNDy gene expression to examine the pathogenic mechanism underlying obesity-induced infertility in male and female rats. Male and female rats at 7 weeks of age were fed with either a standard or HFD for 4 months. In the male rats, the HFD caused a significant suppression of ARC Kiss1 and Pdyn gene expressions, but did not affect the plasma luteinizing hormone (LH) levels and sizes of the morphology of the testis and epididymis. In the female rats, 58% of the HFD-fed female rats exhibited irregular estrous cycles, whereas the remaining rats showed regular cycles. Two of the 10 rats that showed HFD-induced irregular estrous cycles showed profound suppression of LH pulse frequency and the number of ARC Kiss1-expressing cells, whereas the other females showed normal LH pulses and ARC Kiss1 expression. Our finding shows that suppression of ARC Kiss1 expression might be the initial pathological change of hypogonadotropic hypogonadism in HFD-fed male rats, while the obese-related infertility in the female rats may be mainly induced by KNDy-independent pathways. Taken together, ARC kisspeptin neurons in male rats may be susceptible to HFD-induced obesity compared with those in female rats.

A review of the pathophysiology of functional hypothalamic amenorrhoea in women subject to psychological stress, disordered eating, excessive exercise or a combination of these factors.

Functional hypothalamic amenorrhoea (FHA) is a common form of secondary amenorrhoea without an identifiable structural cause. Suppression of gonadotrophin-releasing hormone (GnRH) pulsatility results in reduced luteinizing hormone (LH) levels, with subsequent reduction in oestradiol, anovulation and cessation of menstruation. GnRH pulsatility suppression is a recognized complication of psychological stress, disordered eating, low body weight, excessive exercise or a combination of these factors. Individuals with FHA demonstrate low energy availability (EA), body fat percentage and energy expenditure. Documented adipocytokine changes notably, raised adiponectin, ghrelin, PYY, and decreased leptin, are associated with GnRH suppression. Other endocrine responses seen in this low EA state include low insulin levels, low total T3, increased basal cortisol levels and a reduced response to corticotrophin-releasing hormone (CRH) administration. FHA is associated with raised growth hormone (GH) and low insulin-like growth factor (IGF-1), suggesting relative GH resistance. Kisspeptins are a group of polypeptides, recently discovered to play a major role in the regulation of the reproductive axis through influencing GnRH release. KNDy (kisspeptin/neurokinin B/dynorphin) act on GnRH neurons and a multitude of factors result in their release. Management of FHA is imperative to prevent adverse outcomes in bone density, cardiovascular risk profile, psychological well-being and fertility. Outwith modification of nutritional intake and exercise, limited therapeutic strategies are currently available for women with FHA. Advancements in the understanding of the pathophysiological basis of this under-recognized and under-treated clinical entity will aid management and may result in the development of novel therapeutic approaches.

Evidence that Nitric Oxide Is Critical for LH Surge Generation in Female Sheep.

Elevated and sustained estradiol concentrations cause a gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) surge that is necessary for ovulation. In sheep, several different neural systems have been implicated in this stimulatory action of estradiol and this study focused on somatostatin (SST) neurons in the ventral lateral region of the ventral medial nucleus (vlVMN) which express c-Fos during the surge. First, we determined if increased activity of SST neurons could be related to elevated GnRH secretion by assessing SST synapses onto GnRH neurons and neurons coexpressing kisspeptin, neurokinin B, dynorphin (KNDy). We found that the percentage of preoptic area GnRH neurons that receive SST input increased during the surge compared with other phases of the cycle. However, since SST is generally inhibitory, and pharmacological manipulation of SST signaling did not alter the LH surge in sheep, we hypothesized that nitric oxide (NO) was also produced by these neurons to account for their activation during the surge. In support of this hypothesis we found that (1) the majority of SST cells in the vlVMN (>80%) contained neuronal nitric oxide synthase (nNOS); (2) the expression of c-Fos in dual-labeled SST-nNOS cells, but not in single-labeled cells, increased during the surge compared with other phases of the cycle; and (3) intracerebroventricular (ICV) infusion of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester, completely blocked the estrogen-induced LH surge. These data support the hypothesis that the population of SST-nNOS cells in the vlVMN are a source of NO that is critical for the LH surge, and we propose that they are an important site of estradiol positive feedback in sheep.

Kisspeptin/Neurokinin B/Dynorphin (KNDy) cells as integrators of diverse internal and external cues: evidence from viral-based monosynaptic tract-tracing in mice

Neurons in the hypothalamic arcuate nucleus (ARC) that co-express kisspeptin, neurokinin B and dynorphin (KNDy cells) are essential for mammalian reproduction as key regulators of gonadotropin-releasing hormone (GnRH) secretion. Although multiple endogenous and exogenous signals act indirectly via KNDy neurons to regulate GnRH, the identity of upstream neurons that provide synaptic input to this subpopulation is unclear. We used rabies-mediated tract-tracing in transgenic Kiss1-Cre mice combined with whole-brain optical clearing and multiple-label immunofluorescence to create a comprehensive and quantitative brain-wide map of neurons providing monosynaptic input to KNDy cells, as well as identify the estrogen receptor content and peptidergic phenotype of afferents. Over 90% of monosynaptic input to KNDy neurons originated from hypothalamic nuclei in both male and female mice. The greatest input arose from non-KNDy ARC neurons, including proopiomelanocortin-expressing cells. Significant female-dominant sex differences in afferent input were detected from estrogen-sensitive hypothalamic nuclei critical for reproductive endocrine function and sexual behavior in mice, indicating KNDy cells may provide a unique site for the coordination of sex-specific behavior and gonadotropin release. These data provide key insight into the structural framework underlying the ability of KNDy neurons to integrate endogenous and environmental signals important for the regulation of reproductive function.

Prenatal Testosterone Exposure Alters GABAergic Synaptic Inputs to GnRH and KNDy Neurons in a Sheep Model of Polycystic Ovarian Syndrome.

Prenatal testosterone (T)-treated female sheep display reproductive deficits similar to women with polycystic ovarian syndrome (PCOS), including an increase in LH pulse frequency due to actions of the central GnRH pulse generator. In this study, we used multiple-label immunocytochemistry to investigate the possibility of changes in the γ-aminobutyric acid (GABA) neurotransmitter system at two key components of the GnRH pulse generator in prenatal T-treated sheep: kisspeptin/neurokinin B/dynorphin (KNDy) neurons of the arcuate nucleus, and GnRH neurons in the preoptic area (POA) and mediobasal hypothalamus (MBH). We observed a significant decrease and increase, respectively, in the number of GABAergic synapses onto POA and MBH GnRH neurons in prenatal T-treated ewes; additionally, there was a significant increase in the number of GABAergic inputs onto KNDy neurons. To determine the actions of GABA on GnRH and KNDy neurons, we examined colocalization with the chloride transporters NKCC1 and KCC2, which indicate stimulatory or inhibitory activation of neurons by GABA, respectively. Most GnRH neurons in both POA and MBH colocalized NKCC1 cotransporter whereas none contained the KCC2 cotransporter. Most KNDy neurons colocalized either NKCC1 or KCC2, and 28% of the KNDy population contained NKCC1 alone. Therefore, we suggest that, as in the mouse, GABA in the sheep is stimulatory to GnRH neurons, as well as to a subset of KNDy neurons. Increased numbers of stimulatory GABAergic inputs to both MBH GnRH and KNDy neurons in prenatal T-treated animals may contribute to alterations in steroid feedback control and increased GnRH/LH pulse frequency seen in this animal model of PCOS.

SAT-426 Rabies-Mediated Monosynaptic Tract-Tracing of Sexually Dimorphic Estrogen-Sensitive Afferents to KNDy Neurons in the Mouse

Estradiol controls reproductive status and sexual behavior by acting upon a variety of neurochemical systems in the brain to mediate the sexually dimorphic release of gonadotrophins. However, the neural pathways that transmit steroid hormone information to gonadotropin-releasing hormone (GnRH) neurons are unclear. Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons of the arcuate nucleus (ARC) are critical for reproductive status and implicated to relay a number of peripheral signals, including gonadal steroids, to regulate GnRH secretion. We recently reported the distribution of primary afferents to KNDy neurons (Moore et al, International Congress for Neuroendocrinology, 2018), however, it is not known if KNDy neurons receive synaptic input from steroid hormone-sensitive cells. To address this, we utilized rabies-mediated tract-tracing to unequivocally determine the distribution of estradiol-sensitive monosynaptic inputs to KNDy neurons. Adult male (n=6) and female (n=4) Kiss1-Cre mice were stereotaxically injected in the ARC with Cre-dependent adenoassociated viruses (AAVs) to express avian receptor protein with GFP (TVA-GFP) and rabies glycoprotein (G) in ARC kisspeptin (KNDy) neurons. After three weeks, the glycoprotein-deleted rabies virus (RVdG) containing mCherry was injected in the same location. RVdG exclusively infects KNDy cells expressing TVA, and, as G is required for rabies to cross transynaptically, RVdG crosses into primary afferents of KNDy neurons to express mCherry. As RVdG induces toxicity in cells, a time-point trial determined mCherry-positive cells retain protein expression after 5 days. Mice were perfused and coronal sections immunolabeled for GFP to identify KNDy cells, mCherry to visualize KNDy afferents and estrogen receptor alpha (ERα). Immunoreactivity was mapped using fluorescent microscopy and slide scanning software (MBFbioscience) and dual labeled mCherry- and ERα- positive cells analyzed using confocal microscopy. Male and female mice were statistically compared using students t tests. Dual-labeled cells were detected within the bed nucleus of the stria terminalis and the hypothalamic rostral periventricular area, medial preoptic nucleus (MPON), ventromedial and anterior hypothalamus, ARC and premammillary nucleus. Compared to male mice, females exhibited a significantly higher percentage of dual-labeled cells in the periventricular nucleus (PeN, 46.7±16.4% in females, 7.8±5.1% in males, p<0.05) and MPON (34.3±7.2% in females, 10.9±6% in males, p<0.05). The PeN and MPON are critical for reproductive endocrine function and sexual behavior in the mouse, respectively. Together, these data indicate that sexually dimorphic estradiol-sensitive neuronal populations in the rostral hypothalamus may directly relay steroid hormone signals to KNDy neurons to regulate GnRH secretion and perhaps other functions.

Determining the relationship between hot flushes and LH pulses in menopausal women using mathematical modelling

BackgroundHypothalamic kisspeptin/neurokinin B/dynorphin (KNDy) neurones regulate LH pulsatility. It is widely accepted that the menopausal hot flush (HF) consistently synchronizes with the LH pulse, implicating the hypothalamic KNDy neurones in generating LH pulsatility and HF. Using a modern immunoassay and mathematical modeling, we investigated if the HF and LH pulse were consistently synchronized in menopausal women.MethodsEleven menopausal women (51 to 62 years of age and experiencing ≥7 HF in 24 hours) participated in an 8-hour study. Subjects self-reported HF and underwent peripheral blood sampling every 10 minutes. LH pulsatility was determined using two mathematical models: blinded deconvolution analysis and Bayesian spectrum analysis. The probability that the LH pulse and HF event intervals matched was estimated using the interval distributions observed in our data.ResultsNinety-six HFs were self-reported, and 82 LH pulses were identified by blinded deconvolution analysis. Using both models, the probability that the two event intervals matched was low in the majority of participants (mean P = 0.24; P = 1 reflects perfect association).InterpretationOur data challenge the widely accepted dogma that HFs consistently synchronize with an LH pulse and therefore have clinically important therapeutic and mechanistic implications.