Activation of a Classic Hunger Circuit Slows Luteinizing Hormone Pulsatility

Androgen receptor actions on AgRP neurons are not a major cause of reproductive and metabolic impairments in peripubertally androgenized mice

Excess levels of circulating androgens during prenatal or peripubertal development are an important cause of polycystic ovary syndrome (PCOS), with the brain being a key target. Approximately half of the women diagnosed with PCOS also experience metabolic syndrome; common features including obesity, insulin resistance and hyperinsulinemia. Although a large amount of clinical and preclinical evidence has confirmed this relationship between androgens and the reproductive and metabolic features of PCOS, the mechanisms by which androgens cause this dysregulation are unknown. Neuron-specific androgen receptor knockout alleviates some PCOS-like features in a peripubertal dihydrotestosterone (DHT) mouse model, but the specific neuronal populations mediating these effects are undefined. A candidate population is the agouti-related peptide (AgRP)-expressing neurons, which are important for both reproductive and metabolic function. We used a well-characterised peripubertal androgenized mouse model and Cre-loxP transgenics to investigate whether deleting androgen receptors specifically from AgRP neurons can alleviate the induced reproductive and metabolic dysregulation. Androgen receptors were co-expressed in 66% of AgRP neurons in control mice, but only in <2% of AgRP neurons in knockout mice. The number of AgRP neurons was not altered by the treatments. Only 20% of androgen receptor knockout mice showed rescue of DHT-induced androgen-induced anovulation and acyclicity. Furthermore, androgen receptor knockout did not rescue metabolic dysfunction (body weight, adiposity or glucose and insulin tolerance). While we cannot rule out developmental compensation in our model, these results suggest peripubertal androgen excess does not markedly influence Agrp expression and does not dysregulate reproductive and metabolic function through direct actions of androgens onto AgRP neurons.

Fasting Modulates GABAergic Synaptic Transmission to Arcuate Kisspeptin Neurons in Female Mice

It is well-established that the hypothalamic-pituitary-gonadal (HPG) axis is suppressed due to negative energy balance. However, less information is available on whether kisspeptin neuronal activity contributes to fasting-induced responses. In the present study, female and male mice were fasted for 24 hours or provided food ad libitum (fed group) to determine whether acute fasting is sufficient to modulate kisspeptin neuronal activity. In female mice, fasting attenuated luteinizing hormone (LH) and prolactin (PRL) serum levels and increased follicle-stimulating hormone levels compared with the fed group. In contrast, fasting did not affect gonadotropin or PRL secretion in male mice. By measuring genes related to LH pulse generation in micropunches obtained from the arcuate nucleus of the hypothalamus (ARH), we observed that fasting reduced Kiss1 mRNA levels in female and male mice. In contrast, Pdyn expression was upregulated only in fasted female mice, whereas no changes in the Tac2 mRNA levels were observed in both sexes. Interestingly, the frequency and amplitude of the GABAergic postsynaptic currents recorded from ARH kisspeptin neurons (ARHKisspeptin) were reduced in 24-hour fasted female mice but not in males. Additionally, neuropeptide Y induced a hyperpolarization in the resting membrane potential of ARHKisspeptin neurons of fed female mice but not in males. Thus, the response of ARHKisspeptin neurons to fasting is sexually dependent with a female bias, associated with changes in gonadotropins and PRL secretion. Our findings suggest that GABAergic transmission to ARHKisspeptin neurons modulates the activity of the HPG axis during situations of negative energy balance.

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.

Central and peripheral mechanisms involved in the control of GnRH neuronal function by metabolic factors

Gonadotropin-releasing hormone (GnRH) neurons are the final output pathway for the brain control of reproduction. The activity of this neuronal population, mainly located at the preoptic area of the hypothalamus, is controlled by a plethora of metabolic signals. However, it has been documented that most of these signal impact on GnRH neurons through indirect neuronal circuits, Kiss1, proopiomelanocortin, and neuropeptide Y/agouti-related peptide neurons being some of the most prominent mediators. In this context, compelling evidence has been gathered in recent years on the role of a large range of neuropeptides and energy sensors in the regulation of GnRH neuronal activity through both direct and indirect mechanisms. The present review summarizes some of the most prominent recent advances in our understanding of the peripheral factors and central mechanisms involved in the metabolic control of GnRH neurons.

Mechanism of leptin-NPY on the onset of puberty in male offspring rats after androgen intervention during pregnancy

OBJECTIVES

The time of onset of puberty has been increasingly earlier, but its mechanism is still unclear. This study aimed to reveal the mechanism of leptin and NPY in the onset of puberty in male offspring rats after androgen intervention during pregnancy.

METHODS

Eight-week-old specific pathogen-free (SPF) healthy male Sprague-Dawley (SD) rats and 16 female SD rats were selected and caged at 1:2. The pregnant rats were randomly divided into the olive oil control group (OOG) and testosterone intervention group (TG), with 8 rats in each group. Olive oil and testosterone were injected from the 15th day of pregnancy, for a total of 4 injections (15th, 17th, 19th, 21st day). After the onset of puberty, the male offspring rats were anesthetized with 2% pentobarbital sodium to collect blood by ventral aorta puncture and decapitated to peel off the hypothalamus and abdominal fat. Serum testosterone (T), free testosterone (FT), dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), sex hormone binding globulin (SHBG), and leptin were detected by ELISA, and then the free androgen index (FAI) was calculated. The mRNA levels of androgen receptor (AR), estrogen receptor α (ERα), NPY, leptinR, and NPY2R in the hypothalamus and abdominal fat were detected by RT-PCR. Protein expression levels of AR, ERα, NPY, leptinR, and NPY2R in the arcuate nucleus (ARC) of the hypothalamus were detected by immunohistochemistry.

RESULTS

The time of onset of puberty was significantly earlier in the TG than in the OOG (P< 0.05) and was positively correlated with body weight, body length, abdominal fat, and leptinR mRNA levels in adipose tissue in the OOG (P< 0.05), while it was positively correlated with serum DHT and DHEA concentrations and FAI and AR mRNA levels in the hypothalamus in the TG (P< 0.05). The NPY2R mRNA level and protein expression levels of ERα, NPY2R, and leptinR in the TG were significantly higher than those in the OOG, while the protein expression levels of AR and NPY in the TG were significantly lower than those in the OOG (P< 0.05).

CONCLUSIONS

Testosterone intervention during pregnancy led to an earlier onset of puberty in male offspring rats, which may render the male offspring rats more sensitive to androgens, leptin, and NPY at the onset of puberty.

Conditional Deletion of KOR (Oprk1) in Kisspeptin Cells Does Not Alter LH Pulses, Puberty, or Fertility in Mice

Classic pharmacological studies suggested that endogenous dynorphin-KOR signaling is important for reproductive neuroendocrine regulation. With the seminal discovery of an interconnected network of hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B, and dynorphin (KNDy neurons), the KNDy hypothesis was developed to explain how gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) pulses are generated. Key to this hypothesis is dynorphin released from KNDy neurons acting in a paracrine manner on other KNDy neurons via kappa opioid receptor (KOR) signaling to terminate neural "pulse" events. While in vitro evidence supports this aspect of the KNDy hypothesis, a direct in vivo test of the necessity of KOR signaling in kisspeptin neurons for proper LH secretion has been lacking. We therefore conditionally knocked out KOR selectively from kisspeptin neurons of male and female mice and tested numerous reproductive measures, including in vivo LH pulse secretion. Surprisingly, despite validating successful knockout of KOR in kisspeptin neurons, we found no significant effect of kisspeptin cell-specific deletion of KOR on any measure of puberty, LH pulse parameters, LH surges, follicle-stimulating hormone (FSH) levels, estrous cycles, or fertility. These outcomes suggest that the KNDy hypothesis, while sufficient normally, may not be the only neural mechanism for sculpting GnRH and LH pulses, supported by recent findings in humans and mice. Thus, besides normally acting via KOR in KNDy neurons, endogenous dynorphin and other opioids may, under some conditions, regulate LH and FSH secretion via KOR in non-kisspeptin cells or perhaps via non-KOR pathways. The current models for GnRH and LH pulse generation should be expanded to consider such alternate mechanisms.

Kisspeptin neuron electrophysiology: Intrinsic properties, hormonal modulation, and regulation of homeostatic circuits

The obligatory role of kisspeptin (KISS1) and its receptor (KISS1R) in regulating the hypothalamic-pituitary-gonadal axis, puberty and fertility was uncovered in 2003. In the few years that followed, an impressive body of work undertaken in many species established that neurons producing kisspeptin orchestrate gonadotropin-releasing hormone (GnRH) neuron activity and subsequent GnRH and gonadotropin hormone secretory patterns, through kisspeptin-KISS1R signaling, and mediate many aspects of gonadal steroid hormone feedback regulation of GnRH neurons. Here, we review knowledge accrued over the past decade, mainly in genetically modified mouse models, of the electrophysiological properties of kisspeptin neurons and their regulation by hormonal feedback. We also discuss recent progress in our understanding of the role of these cells within neuronal circuits that control GnRH neuron activity and GnRH secretion, energy balance and, potentially, other homeostatic and reproductive functions.

Effects of electroacupuncture on the expression of hypothalamic neuropeptide Y and ghrelin in pubertal rats with polycystic ovary syndrome

Background

Polycystic ovary syndrome often starts in puberty, and its pathogenesis is not clear. This study aimed to explore the pathogenesis of pubertal polycystic ovary syndrome (PCOS) and assess the therapeutic effect of electroacupuncture on pubertal PCOS.

Methods

Dihydrotestosterone (DHT) was used to induce rat models of pubertal PCOS. pubertal rats with PCOS were randomly divided into a model group (M), an electroacupuncture group (EA), and a sham acupuncture group (SA). Age-matched normal rats were regarded as normal controls (N). Rats were treated with EA or SA five times a week for 25 minutes during their 6th–7th week. At the end of the experiment, we observed any changes in ovarian morphology; detected levels of metabolic indices in serum, the hypothalamus and pancreas.

Results

EA significantly improved estrous cycle disorders and the ovarian polycystic morphology in pubertal rats with PCOS, but SA only improved disorders of the estrous cycle. The serum levels of insulin, neuropeptide Y(NPY) and fasting blood glucose(FBG) increased significantly (both p < 0.01), while the serum levels of ghrelin(GHRL) decreased in the model group (p < 0.01). After treatment with EA, the levels of NPY (p < 0.01) and FBG (p < 0.05) went into decrease, whereas the levels of GHRL (p < 0.05) and insulin (p < 0.01) increased. There was few differences in the hypothalamic expression of galanin (GAL), galanin-like peptide (GALP) and ghrelin receptor(GHSR) between the four groups. The upregulation of NPY mRNA and neuropeptide Y2 receptor(NPY2R) mRNA and the downregulation of GHRL protein and mRNA in the hypothalamus, and the increased expression of NPY and NPY2R as well as the decreased expression of GHRL in the arcuate nucleus (ARC) can be rescued by EA. But, surprisingly, SA seem to make no difference to the levels of FBG and insulin, and the protein expression of ghrelin in the hypothalamus and ARC. Co-expression of kisspeptin and GHSR, and co-expression of gonadotrophin releasing hormone(GnRH) and NPY2R were observed in ARC. No differences were found between groups in protein of GAL, GALP and GHRL expression in the pancreas. Neither EA nor SA can attenuate the upregulated kisspeptin protein expression in the pancreas of PCOS model rats.

Conclusions

EA and SA improved the symptoms of pubertal PCOS rats, and the mechanism might be associated with regulating hypothalamic NPY and ghrelin levels.

Polycystic Ovary Syndrome and the Neuroendocrine Consequences of Androgen Excess

Polycystic ovary syndrome (PCOS) is a major endocrine disorder strongly associated with androgen excess and frequently leading to female infertility. Although classically considered an ovarian disease, altered neuroendocrine control of gonadotropin-releasing hormone (GnRH) neurons in the brain and abnormal gonadotropin secretion may underpin PCOS presentation. Defective regulation of GnRH pulse generation in PCOS promotes high luteinizing hormone (LH) pulsatile secretion, which in turn overstimulates ovarian androgen production. Early and emerging evidence from preclinical models suggests that maternal androgen excess programs abnormalities in developing neuroendocrine circuits that are associated with PCOS pathology, and that these abnormalities are sustained by postpubertal elevation of endogenous androgen levels. This article will discuss experimental evidence, from the clinic and in preclinical animal models, that has significantly contributed to our understanding of how androgen excess influences the assembly and maintenance of neuroendocrine impairments in the female brain. Abnormal central gamma-aminobutyric acid (GABA) signaling has been identified in both patients and preclinical models as a possible link between androgen excess and elevated GnRH/LH secretion. Enhanced GABAergic innervation and drive to GnRH neurons is suspected to contribute to the pathogenesis and early manifestation of neuroendocrine derangement in PCOS. Accordingly, this article also provides an overview of GABA regulation of GnRH neuron function from prenatal development to adulthood to discuss possible avenues for future discovery research and therapeutic interventions. © 2022 American Physiological Society. Compr Physiol 12:3347-3369, 2022.

Hypothalamic Kisspeptin Neurons and the Control of Homeostasis

Hypothalamic kisspeptin (Kiss1) neurons provide indispensable excitatory transmission to gonadotropin-releasing hormone (GnRH) neurons for the coordinated release of gonadotropins, estrous cyclicity, and ovulation. But maintaining reproductive functions is metabolically demanding so there must be a coordination with multiple homeostatic functions, and it is apparent that Kiss1 neurons play that role. There are 2 distinct populations of hypothalamic Kiss1 neurons, namely arcuate nucleus (Kiss1ARH) neurons and anteroventral periventricular and periventricular nucleus (Kiss1AVPV/PeN) neurons in rodents, both of which excite GnRH neurons via kisspeptin release but are differentially regulated by ovarian steroids. Estradiol (E2) increases the expression of kisspeptin in Kiss1AVPV/PeN neurons but decreases its expression in Kiss1ARH neurons. Also, Kiss1ARH neurons coexpress glutamate and Kiss1AVPV/PeN neurons coexpress gamma aminobutyric acid (GABA), both of which are upregulated by E2 in females. Also, Kiss1ARH neurons express critical metabolic hormone receptors, and these neurons are excited by insulin and leptin during the fed state. Moreover, Kiss1ARH neurons project to and excite the anorexigenic proopiomelanocortin neurons but inhibit the orexigenic neuropeptide Y/Agouti-related peptide neurons, highlighting their role in regulating feeding behavior. Kiss1ARH and Kiss1AVPV/PeN neurons also project to the preautonomic paraventricular nucleus (satiety) neurons and the dorsomedial nucleus (energy expenditure) neurons to differentially regulate their function via glutamate and GABA release, respectively. Therefore, this review will address not only how Kiss1 neurons govern GnRH release, but how they control other homeostatic functions through their peptidergic, glutamatergic and GABAergic synaptic connections, providing further evidence that Kiss1 neurons are the key neurons coordinating energy states with reproduction.

Inhibiting Kiss1 Neurons With Kappa Opioid Receptor Agonists to Treat Polycystic Ovary Syndrome and Vasomotor Symptoms

CONTEXT

Recent evidence suggests that vasomotor symptoms (VMS) or hot flashes in the postmenopausal reproductive state and polycystic ovary syndrome (PCOS) in the premenopausal reproductive state emanate from the hyperactivity of Kiss1 neurons in the hypothalamic infundibular/arcuate nucleus (KNDy neurons).

OBJECTIVE

We demonstrate in 2 murine models simulating menopause and PCOS that a peripherally restricted kappa receptor agonist (PRKA) inhibits hyperactive KNDy neurons (accessible from outside the blood-brain barrier) and impedes their downstream effects.

DESIGN

Case/control.

SETTING

Academic medical center.

PARTICIPANTS

Mice.

INTERVENTIONS

Administration of peripherally restricted kappa receptor agonists and frequent blood sampling to determine hormone release and body temperature.

MAIN OUTCOME MEASURES

LH pulse parameters and body temperature.

RESULTS

First, chronic administration of a PRKA to bilaterally ovariectomized mice with experimentally induced hyperactivity of KNDy neurons reduces the animals' elevated body temperature, mean plasma LH level, and mean peak LH per pulse. Second, chronic administration of a PRKA to a murine model of PCOS, having elevated plasma testosterone levels and irregular ovarian cycles, suppresses circulating levels of LH and testosterone and restores normal ovarian cyclicity.

CONCLUSION

The inhibition of kisspeptin neuronal activity by activation of kappa receptors shows promise as a novel therapeutic approach to treat both VMS and PCOS in humans.

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.

Reformulation of PULSAR for Analysis of Pulsatile LH Secretion and a Revised Model of Estrogen-Negative Feedback in Mice

The recent use of the tail-tip bleeding approach in mice has enabled researchers to generate detailed pulse and surge profiles of luteinizing hormone (LH) secretion in mice. However, the analysis of pulsatile LH secretion is piecemeal across the field with each laboratory using their own methodology. We have reformulated the once-popular PULSAR algorithm of Merriam and Wachter to operate on contemporary computer systems and provide downloadable and online pulse analysis platforms. As it is now possible to record the activity of the gonadotropin-releasing hormone pulse generator in freely behaving mice, we have been able to unambiguously define LH pulses in intact and gonadectomized male and female mice. These data sets were used to determine the appropriate PULSAR parameter sets for analyzing pulsatile LH secretion in the mouse. This was then used to establish an accurate model of estrogen negative feedback in the mouse. Intact and ovariectomized mice given Silastic capsules containing 1, 2, and 4 μg 17-β-estradiol/20 g body weight were tail-tip bled at 6-min intervals, and the resultant LH profiles were analyzed with PULSAR. Only the 4 μg 17-β-estradiol capsule treatment was found to return LH pulse amplitude and frequency to that of intact diestrous mice. Ultrasensitive mass spectrometry analysis showed that the 4 μg 17-β-estradiol capsule generated circulating estradiol levels equivalent to that of diestrous mice. It is hoped that the reformulation of PULSAR and generation of a realistic model of estrogen-negative feedback will provide a platform for the more uniform assessment of pulsatile hormone secretion in mice.

Indirect Suppression of Pulsatile LH Secretion by CRH Neurons in the Female Mouse

Acute stress is a potent suppressor of pulsatile luteinizing hormone (LH) secretion, but the mechanisms through which corticotrophin-releasing hormone (CRH) neurons inhibit gonadotropin-releasing hormone (GnRH) release remain unclear. The activation of paraventricular nucleus (PVN) CRH neurons with Cre-dependent hM3Dq in Crh-Cre female mice resulted in the robust suppression of pulsatile LH secretion. Channelrhodopsin (ChR2)-assisted circuit mapping revealed that PVN CRH neuron projections existed around kisspeptin neurons in the arcuate nucleus (ARN) although many more fibers made close appositions with GnRH neuron distal dendrons in the ventral ARN. Acutely prepared brain slice electrophysiology experiments in GnRH- green fluorescent protein (GFP) mice showed a dose-dependent (30 and 300 nM CRH) activation of firing in ~20% of GnRH neurons in both intact diestrus and ovariectomized mice with inhibitory effects being uncommon (<8%). Confocal GCaMP6 imaging of GnRH neuron distal dendrons in acute para-horizontal brain slices from GnRH-Cre mice injected with Cre-dependent GCaMP6s adeno-associated viruses demonstrated no effects of 30 to 300 nM CRH on GnRH neuron dendron calcium concentrations. Electrophysiological recordings of ARN kisspeptin neurons in Crh-Cre,Kiss1-GFP mice revealed no effects of 30 -300 nM CRH on basal or neurokinin B-stimulated firing rate. Similarly, the optogenetic activation (2-20 Hz) of CRH nerve terminals in the ARN of Crh-Cre,Kiss1-GFP mice injected with Cre-dependent ChR2 had no effect on kisspeptin neuron firing. Together, these studies demonstrate that PVN CRH neurons potently suppress LH pulsatility but do not exert direct inhibitory control over GnRH neurons, at their cell body or dendron, or the ARN kisspeptin neuron pulse generator in the female mouse.

High-Fiber Diet or Combined With Acarbose Alleviates Heterogeneous Phenotypes of Polycystic Ovary Syndrome by Regulating Gut Microbiota

OBJECTIVE

Gut microbial dysbiosis is associated with high heterogeneity of polycystic ovary syndrome (PCOS); however, studies about gut microbiota targeted clinical intervention in PCOS are limited. Our study aimed to evaluate the effects of high-fiber diet or combined with acarbose on the clinical phenotypes of PCOS, focusing on the possible influence of gut microbiota in this process.

METHODS

Twenty-five patients with PCOS were recruited and randomly divided into two groups, W group (n = 14) received the WTP diet (a high-fiber diet composed of whole grains, traditional Chinese medicinal foods, and prebiotics), and A group (n = 11) received the WTP diet combined with acarbose. The follow-up time was 12 weeks. The sex hormonal and glycolipid metabolic parameters, inflammatory factors, brain-gut peptides, and alteration of gut microbiota were evaluated.

RESULTS

The PCOS clinical phenotypes, inflammatory state, and brain-gut peptides secretion were all alleviated in both groups, while the hyperandrogenism, insulin resistance, and brain-gut peptides secretion were better improved in the A group. Alpha and beta diversities were altered more significantly in the A group. Amplicon sequence variants (ASVs) were clustered into 14 co-abundant groups (CAGs) as potential functional groups that may respond to the intervention. The CAGs predominantly comprised of Bifidobacterium and Lactobacillus were more enriched, while the CAGs predominantly comprised of Bacteroides vulgatus, Alistipes, Blautia, Lachnospira, and Roseburia were more inhibited in the A group than in W group. Moreover, the CAGs enriched in the A group had a stronger negative correlation with the luteinizing hormone (LH)/follicle-stimulating hormone (FSH) ratio, testosterone, homeostasis model assessment-insulin resistance (HOMA-IR), α-1-acid glycoprotein (α-AGP), and leptin, and positive correlation with adiponectin and spexin, while the CAGs inhibited showed an opposite trend.

CONCLUSIONS

High-fiber diet could alleviate the chronic metabolic inflammation, reproductive function, and brain-gut peptides secretion of patients with PCOS, and high-fiber diet combined with acarbose could better improve the PCOS clinical phenotypes. The remodeling of gut microbiota by our intervention may play an important role in these improvements.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn/showproj.aspx?proj=4500, ChiCTR-TRC-14005075.

Hypothalamic reproductive neurons communicate through signal transduction to control reproduction

Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus coordinate fertility and puberty. In order to achieve successful reproductive capacity, they receive signals from the periphery and from other hypothalamic neurons that coordinate energy homeostasis. Hormones, such as estradiol, insulin, leptin, and adiponectin, act directly or indirectly on GnRH and its associated reproductive neurons. Nutrients like glucose and fatty acids can also affect reproductive neurons to signal nutrient availability. Additionally, acute and chronic inflammation is reported to detrimentally affect GnRH and kisspeptin expression. All of these cues activate signal transduction pathways within neurons that lead to the changes in GnRH neuronal function. The signalling pathways can also be dysregulated by endocrine disrupting chemicals, which impair fertility by misappropriating common signalling pathways. The complex mechanisms controlling the levels of GnRH during the reproductive cycle rely on a carefully orchestrated set of signal transduction events to regulate the positive and negative feedback arms of the hypothalamic-pituitary-gonadal axis. If these signalling events are dysregulated, this will result is a downregulatory event leading to hypogonadal hypogonadism with decreased or absent fertility. Therefore, an understanding of the mechanisms involved in distinct neuronal signalling could provide an advantage to inform therapeutic interventions for infertility and reproductive disorders.

Sex differences in behavioral and metabolic effects of gene inactivation: The neuropeptide Y and Y receptors in the brain

Brain and gonadal hormones interplay controls metabolic and behavioral functions in a sex-related manner. However, most translational neuroscience research related to animal models of endocrine and psychiatric disorders are often carried out in male animals only. The Neuropeptide Y (NPY) system shows sex-dependent differences and is sensitive to gonadal steroids. Based on published data from our and other laboratories, in this review we will discuss the sex related differences of NPY action on energy balance, bone homeostasis and behavior in rodents with the genetic manipulation of genes encoding NPY and its Y1, Y2 and Y5 cognate receptors. Comparative analyses of the phenotype of transgenic and knockout NPY and Y receptor rodents unravels sex dependent differences in the functions of this neurotransmission system, potentially helping to develop therapeutics for a variety of sex-related disorders including metabolic syndrome, osteoporosis and ethanol addiction.

High-Fat Diet Alters LH Secretion and Pulse Frequency in Female Mice in an Estrous Cycle-Dependent Manner

Reproductive fitness in females is susceptible to obesogenic diets. Energy balance and reproduction are tightly regulated, in part, by hypothalamic neurons in the arcuate nucleus (ARC), and high-fat diet (HFD) can steadily increase estradiol levels in rodents. Estradiol regulates the reproductive axis via negative feedback mechanisms in ARC neurons by modulating pulsatile release of the gonadotropin luteinizing hormone (LH). However, it is unclear how the circulating estradiol milieu of adult females interacts with a state of high-caloric fat intake to alter LH pulse dynamics. Here, we used serial tail-tip blood sampling to measure pulsatile LH release at different estrous cycle stages in mice fed a HFD. Starting at 21 days of age, female C57BL/6J mice were freely fed with either regular chow diet (RD) or 60% kcal HFD for 12 weeks. Blood samples were collected once at diestrus, and then again at estrus. LH was measured in 10-minute intervals for 3 hours and analyzed for pulse frequency, amplitude, and mean and basal LH levels. Compared with RD-fed controls, mice fed HFD displayed significantly increased pulse frequency at diestrus, but not at estrus. HFD-fed mice also had lower mean and basal LH levels compared with RD-fed controls, but only during estrus. These data suggest that circulating estradiol can variably contribute to the impact that HFD has on LH pulsatile release and also provide insight into how obesity impacts women's reproductive health when ovarian estradiol levels drastically change, such as during menopause or with hormone replacement therapy.

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.

Different dendritic domains of the GnRH neuron underlie the pulse and surge modes of GnRH secretion in female mice

The gonadotropin-releasing hormone (GnRH) neurons exhibit pulse and surge modes of activity to control fertility. They also exhibit an unusual bipolar morphology comprised of a classical soma-proximal dendritic zone and an elongated secretory process that can operate as both a dendrite and an axon, termed a 'dendron'. We show using expansion microscopy that the highest density of synaptic inputs to a GnRH neuron exists at its distal dendron. In vivo, selective chemogenetic inhibition of the GnRH neuron distal dendron abolishes the luteinizing hormone (LH) surge and markedly dampens LH pulses. In contrast, inhibitory chemogenetic and optogenetic strategies targeting the GnRH neuron soma-proximal dendritic zone abolish the LH surge but have no effect upon LH pulsatility. These observations indicate that electrical activity at the soma-proximal dendrites of the GnRH neuron is only essential for the LH surge while the distal dendron represents an autonomous zone where synaptic integration drives pulsatile GnRH secretion.

Animal Models to Understand the Etiology and Pathophysiology of Polycystic Ovary Syndrome

More than 1 out of 10 women worldwide are diagnosed with polycystic ovary syndrome (PCOS), the leading cause of female reproductive and metabolic dysfunction. Despite its high prevalence, PCOS and its accompanying morbidities are likely underdiagnosed, averaging > 2 years and 3 physicians before women are diagnosed. Although it has been intensively researched, the underlying cause(s) of PCOS have yet to be defined. In order to understand PCOS pathophysiology, its developmental origins, and how to predict and prevent PCOS onset, there is an urgent need for safe and effective markers and treatments. In this review, we detail which animal models are more suitable for contributing to our understanding of the etiology and pathophysiology of PCOS. We summarize and highlight advantages and limitations of hormonal or genetic manipulation of animal models, as well as of naturally occurring PCOS-like females.

New insights into anti-Müllerian hormone role in the hypothalamic-pituitary-gonadal axis and neuroendocrine development

Research into the physiological actions of anti-Müllerian hormone (AMH) has rapidly expanded from its classical role in male sexual differentiation to the regulation of ovarian function, routine clinical use in reproductive health and potential use as a biomarker in the diagnosis of polycystic ovary syndrome (PCOS). During the past 10 years, the notion that AMH could act exclusively at gonadal levels has undergone another paradigm shift as several exciting studies reported unforeseen AMH actions throughout the Hypothalamic–Pituitary–Gonadal (HPG) axis. In this review, we will focus on these findings reporting novel AMH actions across the HPG axis and we will discuss their potential impact and significance to better understand human reproductive disorders characterized by either developmental alterations of neuroendocrine circuits regulating fertility and/or alterations of their function in adult life. Finally, we will summarize recent preclinical studies suggesting that elevated levels of AMH may potentially be a contributing factor to the central pathophysiology of PCOS and other reproductive diseases.

Direct inhibition of arcuate kisspeptin neurones by neuropeptide Y in the male and female mouse

Adverse energy states exert a potent suppressive influence on the reproductive axis by inhibiting the pulsatile release of gonadotrophin-releasing hormone and luteinising hormone. One potential mechanism underlying this involves the metabolic-sensing pro-opiomelanocortin and agouti-related peptide/neuropeptide Y (AgRP/NPY) neuronal populations directly controlling the activity of the arcuate nucleus kisspeptin neurones comprising the gonadotrophin-releasing hormone pulse generator. Using acute brain slice electrophysiology and calcium imaging approaches in Kiss1-GFP and Kiss1-GCaMP6 mice, we investigated whether NPY and α-melanocyte-stimulating hormone provide a direct modulatory influence on the activity of arcuate kisspeptin neurones in the adult mouse. NPY was found to exert a potent suppressive influence upon the neurokinin B-evoked firing of approximately one-half of arcuate kisspeptin neurones in both sexes. This effect was blocked partially by the NPY1R antagonist BIBO 3304, whereas the NPY5R antagonist L152,804 was ineffective. NPY also suppressed the neurokinin B-evoked increase in intracellular calcium levels in the presence of tetrodotoxin and amino acid receptor antagonists, indicating that the inhibitory effects of NPY are direct on kisspeptin neurones. By contrast, no effects of α-melanocyte-stimulating hormone were found on the excitability of arcuate kisspeptin neurones. These studies provide further evidence supporting the hypothesis that AgRP/NPY neurones link energy status and luteinising hormone pulsatility by demonstrating that NPY has a direct suppressive influence upon the activity of a subpopulation of arcuate kisspeptin neurones.

Hyperactive LH Pulses and Elevated Kisspeptin and NKB Gene Expression in the Arcuate Nucleus of a PCOS Mouse Model

Polycystic ovary syndrome (PCOS), a common reproductive disorder in women, is characterized by hyperandrogenemia, chronic anovulation, cystic ovarian follicles, and luteinizing hormone (LH) hyper-pulsatility, but the pathophysiology isn't completely understood. We recently reported a novel mouse model of PCOS using chronic letrozole (LET; aromatase inhibitor). Letrozole-treated females demonstrate multiple PCOS-like phenotypes, including polycystic ovaries, anovulation, and elevated circulating testosterone and LH, assayed in "one-off" measures. However, due to technical limitations, in vivo LH pulsatile secretion, which is elevated in PCOS women, was not previously studied, nor were the possible changes in reproductive neurons. Here, we used recent technical advances to examine in vivo LH pulse dynamics of freely moving LET female mice versus control and ovariectomized (OVX) mice. We also determined whether neural gene expression of important reproductive regulators such as kisspeptin, neurokinin B (NKB), and dynorphin, is altered in LET females. Compared to controls, LET females exhibited very rapid, elevated in vivo LH pulsatility, with increased pulse frequency, amplitude, and basal levels, similar to PCOS women. Letrozole-treated mice also had markedly elevated Kiss1, Tac2, and Pdyn expression and increased Kiss1 neuronal activation in the hypothalamic arcuate nucleus. Notably, the hyperactive LH pulses and increased kisspeptin neuron measures of LET mice were not as elevated as OVX females. Our findings indicate that LET mice, like PCOS women, have markedly elevated LH pulsatility, which likely drives increased androgen secretion. Increased hypothalamic kisspeptin and NKB levels may be fundamental contributors to the hyperactive LH pulse secretion in the LET PCOS-like condition and, perhaps, in PCOS women.