GABAergic integration of progesterone and androgen feedback to gonadotropin-releasing hormone neurons

[Neuroendocrine features of the pathogenesis of polycystic ovary syndrome (literature review)]

Polycystic ovary syndrome (PCOS) is one of the most pressing problems in endocrine gynecology. The main signs of the disease are hyperandrogenism, menstrual and/or ovulatory dysfunction, and polycystic ovarian structure according to ultrasound. Women with PCOS are at risk for developing metabolic syndrome, type 2 diabetes, cardiovascular disease, and endometrial cancer. In this connection, the pathogenetic mechanisms of the occurrence of this syndrome are continuously studied and new methods of treatment are being sought. PCOS is characterized by a wide range of various disorders of the neuroendocrine regulation of the reproductive system. The main focus of the review is aimed at summarizing information about the etiological role of neuropeptides and neurotransmitters, such as phoenixin, galanins, orexins, GABA, in the pathophysiology of PCOS and about the possibility of their use for diagnostic and therapeutic purposes. In recent decades, the interest of scientists has been focused on the study of KNDy neurons, because it is the kisspeptin synthesized by them that is one of the main regulators of the hypothalamic-pituitary-ovarian axis. This article discusses data on the significance of KNDy neurons in the pathogenesis of the syndrome. Information is provided on the effect of elevated levels of androgens and anti-Müllerian hormone on GnRH neurons. Also analyzed are studies on functional and structural disorders in the hypothalamus in PCOS. Literature search was carried out in national (eLibrary, CyberLeninka.ru) and international (PubMed, Cochrane Library) databases in Russian and English. The priority was free access to the full text of articles. The choice of sources was prioritized for the period from 2018 to 2023.However, taking into account the insufficient knowledge of the chosen topic, the choice of sources dates back to 1998.

Impaired steroid hormone feedback in polycystic ovary syndrome: Evidence from preclinical models for abnormalities within central circuits controlling fertility

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy and cause of infertility in women of reproductive age worldwide. Despite diagnostic features of anovulation, polycystic ovarian morphology, and high androgen secretion indicating the syndrome are the result of ovarian dysfunction, alterations to central neuroendocrine circuits that control reproductive capacity may drive PCOS symptoms. Resistance of gonadotrophin-releasing hormone (GnRH) neurons in the hypothalamus to inhibition by sex steroid hormone-negative feedback leads to a rapid frequency of pulsatile gonadotrophin secretion, which, in turn, drives the ovarian features of the disease. As GnRH neurons do not express steroid hormone receptors, impaired negative feedback is hypothesized to occur within an upstream network that controls GnRH pulse generation. This review will discuss the latest work from preclinical animal models of PCOS used to dissect the specific central mechanisms involved in impaired steroid hormone feedback. In particular, this review will focus on research that indicates neurons in the arcuate nucleus of the hypothalamus that express Kisspeptin, Neurokinin B and Dynorphin (KNDy cells) or γ-aminobutyric acid are targets of androgen-mediated impairment of steroid hormone feedback. Finally, this review will explore the development of therapeutic agents targeting neurons that control LH pulse frequency to resolve PCOS symptoms in the clinic.

The role of gonadotropin-releasing hormone neurons in polycystic ovary syndrome

Given the critical central role of gonadotropin-releasing hormone (GnRH) neurons in fertility, it is not surprising that the GnRH neural network is implicated in the pathology of polycystic ovary syndrome (PCOS), the most common cause of anovulatory infertility. Although many symptoms of PCOS relate most proximately to ovarian dysfunction, the central reproductive neuroendocrine system ultimately drives ovarian function through its regulation of anterior pituitary gonadotropin release. The typical cyclical changes in frequency of GnRH release are often absent in women with PCOS, resulting in a persistent high-frequency drive promoting gonadotropin changes (i.e., relatively high luteinizing hormone and relatively low follicle-stimulating hormone concentrations) that contribute to ovarian hyperandrogenemia and ovulatory dysfunction. However, the specific mechanisms underpinning GnRH neuron dysfunction in PCOS remain unclear. Here, we summarize several preclinical and clinical studies that explore the causes of aberrant GnRH secretion in PCOS and the role of disordered GnRH secretion in PCOS pathophysiology.

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.

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.

A review of the hormones involved in the endocrine dysfunctions of polycystic ovary syndrome and their interactions

Polycystic ovary syndrome (PCOS) affects up to 20% of women but remains poorly understood. It is a heterogeneous condition with many potential comorbidities. This review offers an overview of the dysregulation of the reproductive and metabolic systems associated with PCOS. Review of the literature informed the development of a comprehensive summarizing 'wiring' diagram of PCOS-related features. This review provides a justification for each diagram aspect from the relevant academic literature, and explores the interactions between the hypothalamus, ovarian follicles, adipose tissue, reproductive hormones and other organ systems. The diagram will provide an efficient and useful tool for those researching and treating PCOS to understand the current state of knowledge on the complexity and variability of PCOS.

Prenatal androgenization causes expression changes of progesterone and androgen receptor mRNAs in the arcuate nucleus of female mice across development

Prenatal exposure to excess androgens is associated with the development of polycystic ovary syndrome (PCOS). In prenatally androgenised (PNA) mice, a model of PCOS, progesterone receptor (PR) protein expression is reduced in arcuate nucleus (ARC) GABA neurons. This suggests a mechanism for PCOS-related impaired steroid hormone feedback and implicates androgen excess with respect to inducing transcriptional repression of the PR-encoding gene Pgr in the ARC. However, the androgen sensitivity of ARC neurons and the relative gene expression of PRs over development and following prenatal androgen exposure remain unknown. Here, we used a quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) of microdissected ARC to determine the relative androgen receptor (Ar) and progesterone receptor (Pgr) gene expression in PNA and control mice at five developmental timepoints. In a two-way analysis of variance, none of the genes examined showed expression changes with a statistically significant interaction between treatment and age, although PgrA showed a borderline interaction. For all genes, there was a statistically significant main effect of age on expression levels, reflecting a general increase in expression with increasing age, regardless of treatment. For PgrB and Ar, there was a statistically significant main effect of treatment, indicating a change in expression following PNA (increased for PgrB and decreased for Ar), regardless of age. For PgrA, there was a borderline main effect of treatment, suggesting a possible change in expression following PNA, regardless of age. PgrAB gene expression changes showed no significant main effect of treatment. We additionally examined androgen and progesterone responsiveness specifically in P60 ARC GABA neurons using RNAScope® (Advanced Cell Diagnostics, Inc.) in situ hybridization. This analysis revealed that Pgr and Ar were expressed in the majority of ARC GABA neurons in normal adult females. However, our RNAScope® analysis did not show significant changes in Pgr or Ar expression within ARC GABA neurons following PNA. Lastly, because GABA drive to gonadotropin-releasing hormone neurons is increased in PNA, we hypothesised that PNA mice would show increased expression of glutamic acid decarboxylase (GAD), the rate-limiting enzyme in GABA production. However, the RT-qPCR showed that the expression of GAD encoding genes (Gad1 and Gad2) was unchanged in adult PNA mice compared to controls. Our findings indicate that PNA treatment can impact Pgr and Ar mRNA expression in adulthood. This may reflect altered circulating steroid hormones in PNA mice or PNA-induced epigenetic changes in the regulation of Pgr and Ar gene expression in ARC neurons.

Neuroendocrine interactions of the stress and reproductive axes

Reproduction is controlled by a sequential regulation of the hypothalamo-pituitary-gonadal (HPG) axis. The HPG axis integrates multiple inputs to maintain proper reproductive functions. It has long been demonstrated that stress alters fertility. Nonetheless, the central mechanisms of how stress interacts with the reproductive system are not fully understood. One of the major pathways that is activated during the stress response is the hypothalamo-pituitary-adrenal (HPA) axis. In this review, we discuss several aspects of the interactions between these two neuroendocrine systems to offer insights to mechanisms of how the HPA and HPG axes interact. We have also included discussions of other systems, for example GABA-producing neurons, where they are informative to the overall picture of stress effects on reproduction.

Prenatal Androgen Treatment Does Not Alter the Firing Activity of Hypothalamic Arcuate Kisspeptin Neurons in Female Mice

Neuroendocrine control of reproduction is disrupted in many individuals with polycystic ovary syndrome (PCOS), who present with increased luteinizing hormone (LH), and presumably gonadotropin-releasing hormone (GnRH), release frequency, and high androgen levels. Prenatal androgenization (PNA) recapitulates these phenotypes in primates and rodents. Female offspring of mice injected with dihydrotestosterone (DHT) on gestational days 16-18 exhibit disrupted estrous cyclicity, increased LH and testosterone, and increased GnRH neuron firing rate as adults. PNA also alters the developmental trajectory of GnRH neuron firing rates, markedly blunting the prepubertal peak in firing that occurs in three-week (3wk)-old controls. GnRH neurons do not express detectable androgen receptors and are thus probably not the direct target of DHT. Rather, PNA likely alters GnRH neuronal activity by modulating upstream neurons, such as hypothalamic arcuate neurons co-expressing kisspeptin, neurokinin B (gene Tac2), and dynorphin, also known as KNDy neurons. We hypothesized PNA treatment changes firing rates of KNDy neurons in a similar age-dependent manner as GnRH neurons. We conducted targeted extracellular recordings (0.5-2 h) of Tac2-identified KNDy neurons from control and PNA mice at 3wks of age and in adulthood. About half of neurons were quiescent (<0.005 Hz). Long-term firing rates of active cells varied, suggestive of episodic activity, but were not different among groups. Short-term burst firing was also similar. We thus reject the hypothesis that PNA alters the firing rate of KNDy neurons. This does not preclude altered neurosecretory output of KNDy neurons, involvement of other neuronal populations, or in vivo networks as critical drivers of altered GnRH firing rates in PNA mice.

Functions of the GABAergic system on serum LH concentrations in pre-pubertal Nellore heifers

This study was conducted to evaluate the luteinizing hormone (LH) secretion pattern after gamma-aminobutyric acid (GABA_A) antagonist to determine the effects of the GABAergic system on LH secretion during reproductive maturation in pre-pubertal Nellore heifers. Nellore heifers (n = 10) were administered a picrotoxin injection of 0.18 mg/kg, i.v. Blood samples were collected every 15 min for 3 h at different developmental stages (8, 10, 14 and 17 mo of age). Plasma concentrations of LH were quantified using an RIA (sensitivity of 0.04 ng/mL and CV of 15 %). There was an interaction between treatment and age (P = 0.034). Picrotoxin-treated heifers had lesser (P ≤  0.05) LH mean concentrations during a 3 h period at 10 and 17 mo of age compared to control heifers (P ≤  0.05). Comparing the period before and after Picrotoxin injection in the same animals, there was a 33 % decrease in LH concentration at 8 mo of age (P = 0.0165). These results indicate the GABAergic system has a stimulatory function in inducing LH secretion in pre-pubertal Nellore heifers. These findings corroborate previous results that GABA increases GnRH/LH secretion in other species during the pre-pubertal period.

Central Regulation of PCOS: Abnormal Neuronal-Reproductive-Metabolic Circuits in PCOS Pathophysiology

Polycystic ovary syndrome (PCOS) is a common reproductive endocrine disease. PCOS patients are characterized by hyperandrogenemia, anovulation, and metabolic dysfunction. Hypothalamus-pituitary-ovary axis imbalance is considered as an important pathophysiology underlying PCOS, indicating that central modulation, especially the abnormal activation of hypothalamic GnRH neurons plays a vital role in PCOS development. Increased GnRH pulse frequency can promote LH secretion, leading to ovarian dysfunction and abnormal sex steroids synthesis. By contrast, peripheral sex steroids can modulate the action of GnRH neurons through a feedback effect, which is impaired in PCOS, thus forming a vicious cycle. Additionally, hypothalamic GnRH neurons not only serve as the final output pathway of central control of reproductive axis, but also as the central connection point where reproductive function and metabolic state inter-regulate with each other. Metabolic factors, such as insulin resistance and obesity in PCOS patients can regulate GnRH neurons activity, and ultimately regulate reproductive function. Besides, gut hormones act on both brain and peripheral organs to modify metabolic state. Gut microbiota disturbance is also related to many metabolic diseases and has been reported to play an essential part in PCOS development. This review concludes with the mechanism of central modulation and the interaction between neuroendocrine factors and reproductive or metabolic disorders in PCOS development. Furthermore, the role of the gut microenvironment as an important part involved in the abnormal neuronal-reproductive-metabolic circuits that contribute to PCOS is discussed, thus offering possible central and peripheral therapeutic targets for PCOS patients.

Research Progress on the Effect of Epilepsy and Antiseizure Medications on PCOS Through HPO Axis

Epilepsy is a common chronic neurological disease that manifests as recurrent seizures. The incidence and prevalence of epilepsy in women are slightly lower than those in men. Polycystic ovary syndrome (PCOS), a reproductive endocrine system disease, is a complication that women with epilepsy are susceptible to, and its total prevalence is 8%-13% in the female population and sometimes as high as 26% in female epilepsy patients. The rate of PCOS increased markedly in female patients who chose valproate (VPA), to 1.95 times higher than that of other drugs. In addition, patients receiving other anti-seizure medications (ASMs), such as lamotrigine (LTG), oxcarbazepine (OXC), and carbamazepine (CBZ), also have reproductive endocrine abnormalities. Some scholars believe that the increase in incidence is related not only to epilepsy itself but also to ASMs. Epileptiform discharges can affect the activity of the pulse generator and then interfere with the reproductive endocrine system by breaking the balance of the hypothalamic-pituitary-ovarian (HPO) axis. ASMs may also cause PCOS-like disorders of the reproductive endocrine system through the HPO axis. Moreover, other factors such as hormone metabolism and related signalling pathways also play a role in it.

A CRH Receptor Type 1 Agonist Increases GABA Transmission to GnRH Neurons in a Circulating-Estradiol-Dependent Manner

GnRH neurons are central regulators of reproduction and respond to factors affecting fertility, such as stress. Corticotropin-releasing hormone (CRH) is released during stress response. In brain slices from unstressed controls, CRH has opposite, estradiol-dependent effects on GnRH neuron firing depending on the CRH receptor activated; activating CRHR-1 stimulates whereas activating CRHR-2 suppresses activity. We investigated possible direct and indirect mechanisms. Mice were ovariectomized and either not treated further (OVX) or given a capsule producing high positive feedback (OVX + E) or low negative feedback (OVX + low E) physiologic circulating estradiol levels. We tested possible direct effects on GnRH neurons by altering voltage-gated potassium currents. Two types of voltage-gated potassium currents (transient IA and sustained IK) were measured; neither CRHR-1 nor CRHR-2 agonists altered potassium current density in GnRH neurons from OVX + E mice. Further, neither CRH nor receptor-specific agonists altered action potential generation in response to current injection in GnRH neurons from OVX + E mice. To test the possible indirect actions, GABAergic postsynaptic currents were monitored. A CRHR-1 agonist increased GABAergic transmission frequency to GnRH neurons from OVX + E, but not OVX, mice, whereas a CRHR-2 agonist had no effect. Finally, we tested if CRH alters the firing rate of arcuate kisspeptin neurons, which provide an important excitatory neuromodulatory input to GnRH neurons. CRH did not acutely alter firing activity of these neurons from OVX, OVX + E or OVX + low E mice. These results suggest CRH increases GnRH neuron activity in an estradiol-dependent manner in part by activating GABAergic afferents. Mechanisms underlying inhibitory effects of CRH remain unknown.

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.

Abnormal GnRH Pulsatility in Polycystic Ovary Syndrome: Recent Insights

Although the fundamental symptoms of polycystic ovary syndrome (PCOS) relate most directly to ovarian dysfunction, central neuroendocrine systems play a prominent role in its pathophysiology. Gonadotropin-releasing hormone (GnRH) pulse generator resistance to negative feedback contributes to rapid GnRH pulse secretion, which promotes gonadotropin abnormalities that foster ovarian hyperandrogenemia and ovulatory dysfunction. The causes of GnRH neuron dysfunction, however, have remained enigmatic. In this review, we highlight a number of recent preclinical and clinical studies pertinent to the neuroendocrine abnormalities of PCOS, including those that have provided important insights into the relevance of animal models with PCOS-like features, the potential roles of kisspeptin and γ-aminobutyric acid (GABA)-ergic neurons, and the potential role of anti-Müllerian hormone.

Ovarian Androgens Maintain High GnRH Neuron Firing Rate in Adult Prenatally-Androgenized Female Mice

Changes in gonadotropin-releasing hormone (GnRH) release frequency from the brain help drive reproductive cycles. In polycystic ovary syndrome (PCOS), persistent high GnRH/luteinizing hormone (LH) frequency disrupts cycles and exacerbates hyperandrogenemia. Adult prenatally-androgenized (PNA) mice exhibit increased GnRH neuron firing rate, elevated ovarian androgens, and disrupted cycles, but before puberty, GnRH neuron activity is reduced in PNA mice compared with controls. We hypothesized that ovarian feedback mediates the age-dependent change in GnRH neuron firing rate in PNA vs control mice. Extracellular recordings of green fluorescent protein (GFP)-identified GnRH neurons were made 5 to 7 days after sham-surgery, ovariectomy (OVX), or, in adults, after OVX plus replacement of sub-male androgen levels with dihydrotestosterone implants (OVX + DHT). In 3-week-old mice, OVX did not affect GnRH neuron firing rate in either group. In adult controls, OVX increased GnRH neuron firing rate, which was further enhanced by DHT. In adult PNA mice, however, OVX decreased GnRH neuron firing rate, and DHT restored firing rate to sham-operated levels. In contrast to the differential effects of ovarian feedback on GnRH neuron firing rate, serum LH increased after OVX in both control and PNA mice and was not altered by DHT. Pituitary gene expression largely reflected changes expected with OVX, although in PNA but not control mice, DHT treatment increased Lhb expression. These results suggest prenatal androgen exposure programs marked changes in GnRH neuron regulation by homeostatic steroid feedback. PNA lowers GnRH neuron activity in low-steroid states (before puberty, OVX), and renders activity in adulthood dependent upon ongoing exposure to elevated ovarian androgens.

Neurotransmitter, neuropeptide and gut peptide profile in PCOS-pathways contributing to the pathophysiology, food intake and psychiatric manifestations of PCOS

Polycystic ovary syndrome (PCOS) is a major health problem with a heterogeneous hormone-imbalance and clinical presentation across the lifespan of women. Increased androgen production and abnormal gonadotropin-releasing hormone (GnRH) release and gonadotropin secretion, resulting in chronic anovulation are well-known features of the PCOS. The brain is both at the top of the neuroendocrine axis regulating ovarian function and a sensitive target of peripheral gonadal hormones and peptides. Current literature illustrates that neurotransmitters regulate various functions of the body, including reproduction, mood and body weight. Neurotransmitter alteration could be one of the reasons for disturbed GnRH release, consequently directing the ovarian dysfunction in PCOS, since there is plenty evidence for altered catecholamine metabolism and brain serotonin or opioid activity described in PCOS. Further, the dysregulated neurotransmitter and neuropeptide profile in PCOS could also be the reason for low self-esteem, anxiety, mood swings and depression or obesity, features closely associated with PCOS women. Can these altered central brain circuits, or the disrupted gut-brain axis be the tie that would both explain and link the pathogenesis of this disorder, the occurrence of depression, anxiety and other mood disorders as well as of obesity, insulin resistance and abnormal appetite in PCOS? This review intends to provide the reader with a comprehensive overview of what is known about the relatively understudied, but very complex role that neurotransmitters, neuropeptides and gut peptides play in PCOS. The answer to the above question may help the development of drugs to specifically target these central and peripheral circuits, thereby providing a valuable treatment for PCOS patients that present to the clinic with GnRH/LH hypersecretion, obesity or psychiatric manifestations.

Pathological pulses in PCOS

Polycystic ovary syndrome (PCOS) is a highly prevalent endocrine disorder associated with hyperandrogenism and anovulation. Although a spectrum disorder, many women with PCOS exhibit elevated luteinizing hormone (LH) pulse frequency and an elevated LH to follicle stimulating hormone ratio. This aberrant pattern of gonadotrophin signalling drives many of the downstream ovarian features of PCOS, including increased androgen synthesis, and indicates neuroendocrine impairments upstream. Decreased responsiveness to gonadal steroid hormone negative feedback in PCOS patients points toward dysfunction within the gonadotropin-releasing hormone (GnRH) neuronal network in the brain. Excessive androgen exposure during development or over pubertal onset can recapitulate the neuroendocrine pathology of PCOS in pre-clinical models, and these models have been fundamental in beginning to pick apart the specific central mechanisms involved. This mini-review will briefly describe the pathology of PCOS associated with high frequency GnRH/LH pulses and then highlight what is currently known, and yet to be discovered, about the central mechanisms involved.

Origin and Evolution of the Neuroendocrine Control of Reproduction in Vertebrates, With Special Focus on Genome and Gene Duplications

In humans, as in the other mammals, the neuroendocrine control of reproduction is ensured by the brain-pituitary gonadotropic axis. Multiple internal and environmental cues are integrated via brain neuronal networks, ultimately leading to the modulation of the activity of gonadotropin-releasing hormone (GnRH) neurons. The decapeptide GnRH is released into the hypothalamic-hypophysial portal blood system and stimulates the production of pituitary glycoprotein hormones, the two gonadotropins luteinizing hormone and follicle-stimulating hormone. A novel actor, the neuropeptide kisspeptin, acting upstream of GnRH, has attracted increasing attention in recent years. Other neuropeptides, such as gonadotropin-inhibiting hormone/RF-amide related peptide, and other members of the RF-amide peptide superfamily, as well as various nonpeptidic neuromediators such as dopamine and serotonin also provide a large panel of stimulatory or inhibitory regulators. This paper addresses the origin and evolution of the vertebrate gonadotropic axis. Brain-pituitary neuroendocrine axes are typical of vertebrates, the pituitary gland, mediator and amplifier of brain control on peripheral organs, being a vertebrate innovation. The paper reviews, from molecular and functional perspectives, the evolution across vertebrate radiation of some key actors of the vertebrate neuroendocrine control of reproduction and traces back their origin along the vertebrate lineage and in other metazoa before the emergence of vertebrates. A focus is given on how gene duplications, resulting from either local events or from whole genome duplication events, and followed by paralogous gene loss or conservation, might have shaped the evolutionary scenarios of current families of key actors of the gonadotropic axis.

Neuroendocrine Impairments of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a prevalent and distressing disorder of largely unknown etiology. Although PCOS defined by ovarian dysfunction, accumulating evidence supports a critical role for the brain in the ontogeny and pathophysiology of PCOS. A critical pathological feature of PCOS is impaired gonadal steroid hormone negative feedback to the GnRH neuronal network in the brain that regulates fertility. This impairment is associated with androgen excess, a cardinal feature of PCOS. Impaired steroid hormone feedback to GnRH neurons is thought to drive hyperactivity of the neuroendocrine axis controlling fertility, leading to a vicious cycle of androgen excess and reproductive dysfunction. Decades of clinical research have been unable to uncover the mechanisms underlying this impairment, because of the extreme difficulty in studying the brain in humans. It is only recently, with the development of preclinical models of PCOS, that we have begun to unravel the role of the brain in the development and progression of PCOS. Here, we provide a succinct overview of what is known about alterations in the steroid hormone-sensitive GnRH neuronal network that may underlie the neuroendocrine defects in clinical PCOS, with a particular focus on those that may contribute to impaired progesterone negative feedback, and the likely role of androgens in driving this impairment.

Does kisspeptin participate in GABA-mediated modulation of GnRH and GnRH receptor biosynthesis in the hypothalamic-pituitary unit of follicular-phase ewes?

BACKGROUND

The inverse relationship between GnRH transcript level and GABA neurons activity has suggested that GABA at the hypothalamic level may exert a suppressive effect on subsequent steps of the GnRH biosynthesis. In the present study, we analyzed the effects of GABA type A receptor agonist (muscimol) or antagonist (bicuculline) on molecular mechanisms governing GnRH/LH secretion in follicular-phase sheep.

METHODS

ELISA technique was used to investigate the effects of muscimol and/or bicuculline on levels of post-translational products of genes encoding GnRH ligand and GnRH receptor (GnRHR) in the preoptic area (POA), anterior (AH) and ventromedial (VMH) hypothalamus, stalk/median eminence (SME), and GnRHR in the anterior pituitary (AP). Real-time PCR was chosen for determination of the effect of drugs on kisspeptin (Kiss 1) mRNA level in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by RIA method for measurement of plasma LH concentration.

RESULTS

The study demonstrated that muscimol and bicuculline significantly decreased or increased GnRH biosynthesis in all analyzed structures, respectively, and led to analogous changes in plasma LH concentration. Similar muscimol- and bicuculline-related alterations were observed in levels of GnRHR. However, the expression of Kiss 1 and Kiss1r mRNAs in selected POA-hypothalamic areas of either muscimol- and bicuculline-treated animals remained unaltered.

CONCLUSIONS

Our data suggest that GABAergic neurotransmission is involved in the regulatory pathways of GnRH/GnRHR biosynthesis and then GnRH/LH release in follicular-phase sheep conceivably via indirect mechanisms that exclude involvement of Kiss 1 neurons.

Changes in Both Neuron Intrinsic Properties and Neurotransmission Are Needed to Drive the Increase in GnRH Neuron Firing Rate during Estradiol-Positive Feedback

Central output of gonadotropin-releasing hormone (GnRH) neurons controls fertility and is sculpted by sex-steroid feedback. A switch of estradiol action from negative to positive feedback initiates a surge of GnRH release, culminating in ovulation. In ovariectomized mice bearing constant-release estradiol implants (OVX+E), GnRH neuron firing is suppressed in the morning (AM) by negative feedback and activated in the afternoon (PM) by positive feedback; no time-of-day-dependent changes occur in OVX mice. In this daily surge model, GnRH neuron intrinsic properties are shifted to favor increased firing during positive feedback. It is unclear whether this shift and the observed concomitant increase in GABAergic transmission, which typically excites GnRH neurons, are independently sufficient for increasing GnRH neuron firing rate during positive feedback or whether both are needed. To test this, we used dynamic clamp to inject selected previously recorded trains of GABAergic postsynaptic conductances (PSgs) collected during the different feedback states of the daily surge model into GnRH neurons from OVX, OVX+E AM, and OVX+E PM mice. PSg trains mimicking positive feedback initiated more action potentials in cells from OVX+E PM mice than negative feedback or OVX (open feedback loop) trains in all three animal models, but the positive-feedback train was most effective when applied to cells during positive feedback. In silico studies of model GnRH neurons in which >1000 PSg trains were tested exhibited the same results. These observations support the hypothesis that GnRH neurons integrate fast-synaptic and intrinsic changes to increase firing rates during positive feedback.SIGNIFICANCE STATEMENT Infertility affects 15%-20% of couples; failure to ovulate is a common cause. Understanding how the brain controls ovulation is critical for new developments in both infertility treatment and contraception. Ovarian estradiol alters both the intrinsic properties of gonadotropin-releasing hormone (GnRH) neurons and synaptic inputs to these cells coincident with production of sustained GnRH release that ultimately triggers ovulation. We demonstrate here using dynamic clamp and mathematical modeling that estradiol-induced shifts in synaptic transmission alone can increase firing output, but that the intrinsic properties of GnRH neurons during positive feedback further poise these cells for increased response to higher frequency synaptic transmission. These data suggest that GnRH neurons integrate fast-synaptic and intrinsic changes to increase firing rates during the preovulatory GnRH surge.

Dynamic and Sex-Specific Changes in Gonadotropin-Releasing Hormone Neuron Activity and Excitability in a Mouse Model of Temporal Lobe Epilepsy

Reproductive endocrine disorders are prominent comorbidities of temporal lobe epilepsy (TLE) in both men and women. The neural mechanisms underlying these comorbidities remain unclear, but hypothalamic gonadotropin-releasing hormone (GnRH) neurons may be involved. Here, we report the first direct demonstrations of aberrant GnRH neuron function in an animal model of epilepsy. Recordings of GnRH neuron firing and excitability were made in acute mouse brain slices prepared two months after intrahippocampal injection of kainate (KA) or control saline, a well-established TLE model in which most females develop comorbid estrous cycle disruption. GnRH neurons from control females showed elevated firing and excitability on estrus compared with diestrus. By contrast, cells from KA-injected females that developed prolonged, disrupted estrous cycles (KA-long) showed the reverse pattern. Firing rates of cells from KA-injected females that maintained regular cycles (KA-regular) were not different from controls on diestrus, but were reduced on estrus. In KA-injected males, only GnRH neurons in the medial septum displayed elevated firing. In contrast to the diestrus versus estrus and sex-specific changes in firing, GnRH neuron intrinsic excitability was elevated in all KA-injected groups, indicating a role for afferent synaptic and neuromodulatory inputs in shaping overall changes in firing activity. Furthermore, KA-injected females showed cycle-stage-specific changes in circulating sex steroids on diestrus and estrus that also differed between KA-long and KA-regular groups. Together, these findings reveal that the effects of epilepsy on the neural control of reproduction are dynamic across the estrous cycle, distinct in association with comorbid estrous cycle disruption severity, and sex-specific.

Prepubertal Development of GABAergic Transmission to Gonadotropin-Releasing Hormone (GnRH) Neurons and Postsynaptic Response Are Altered by Prenatal Androgenization

Gonadotropin-releasing hormone (GnRH) neurons regulate reproduction through pulsatile GnRH release. Women with polycystic ovary syndrome (PCOS) have persistently elevated luteinizing hormone release frequency, reflecting GnRH release; this exacerbates hyperandrogenemia and disrupted reproductive cycles that are characteristic of this disorder. Clinical evidence suggests that neuroendocrine features of PCOS may manifest peripubertally. Adult mice prenatally exposed to androgens (PNA) mimic several reproductive features of PCOS. GnRH neurons from these mice have increased firing activity and receive increased GABAergic transmission, which is excitatory. When changes emerge during development is unknown. To study the typical postnatal development of GABAergic transmission and the effects of PNA treatment and sex, whole-cell voltage-clamp recordings were made of GABAergic postsynaptic currents (PSCs) in GnRH neurons in brain slices from prepubertal through adult control and PNA female and male mice. GABAergic transmission was present by 1 week of age in females and males and increased in frequency, reaching adult levels at 3 and 4 weeks, respectively. GABAergic PSC frequency was elevated in 3-week-old PNA versus control females. PSC frequency in both controls and PNA mice was activity independent, suggesting that PNA induces changes in synapse organization. PNA also alters the functional response of GnRH neurons to GABA. GABA induced firing in fewer neurons from 3-week-old PNA than control females; membrane potential depolarization induced by GABA was also reduced in cells from PNA mice at this age. PNA thus induces changes during development in the presynaptic organization of the GABAergic network afferent to GnRH neurons as well as the postsynaptic GnRH neuron response, both of which may contribute to adult reproductive dysfunction.SIGNIFICANCE STATEMENT The central neuronal network that regulates reproduction is overactive in polycystic ovary syndrome (PCOS), a leading cause of infertility. Recent evidence of neuroendocrine dysfunction in midpubertal girls suggests that the pathophysiological mechanisms underlying PCOS may arise before pubertal maturation. Prenatal exposure to androgens (PNA) in mice mimics several neuroendocrine features of PCOS. GABAergic transmission to gonadotropin-releasing hormone (GnRH) neurons is important for reproduction and is increased in adult PNA mice. The typical development of this network and when changes with PNA and sex arise relative to puberty are unknown. These studies provide evidence that PNA alters prepubertal development of the GABAergic network afferent to GnRH neurons, including both the presynaptic organization and postsynaptic response. These changes may contribute to reproductive dysfunction in adults.

Prepubertal Development of Gonadotropin-Releasing Hormone Neuron Activity Is Altered by Sex, Age, and Prenatal Androgen Exposure

Gonadotropin-releasing hormone (GnRH) neurons regulate reproduction though pulsatile hormone release. Disruption of GnRH release as measured via luteinizing hormone (LH) pulses occurs in polycystic ovary syndrome (PCOS), and in young hyperandrogenemic girls. In adult prenatally androgenized (PNA) mice, which exhibit many aspects of PCOS, increased LH is associated with increased GnRH neuron action potential firing. How GnRH neuron activity develops over the prepubertal period and whether this is altered by sex or prenatal androgen treatment are unknown. We hypothesized GnRH neurons are active before puberty and that this activity is sexually differentiated and altered by PNA. Dams were injected with dihydrotestosterone (DHT) on days 16 to 18 post copulation to generate PNA mice. Action potential firing of GFP-identified GnRH neurons in brain slices from 1-, 2-, 3-, and 4-week-old and adult mice was monitored. GnRH neurons were active at all ages tested. In control females, activity increased with age through 3 weeks, then decreased to adult levels. In contrast, activity did not change in PNA females and was reduced at 3 weeks. Activity was higher in control females than males from 2 to 3 weeks. PNA did not affect GnRH neuron firing rate in males at any age. Short-term action potential patterns were also affected by age and PNA treatment. GnRH neurons are thus typically more active during the prepubertal period than adulthood, and PNA reduces prepubertal activity in females. Prepubertal activity may play a role in establishing sexually differentiated neuronal networks upstream of GnRH neurons; androgen-induced changes during this time may contribute to the adult PNA, and possibly PCOS, phenotype.

Polycystic ovary syndrome: Understanding the role of the brain

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder and the leading cause of anovulatory infertility. Characterised by hyperandrogenism, menstrual dysfunction and polycystic ovaries, PCOS is a broad-spectrum disorder unlikely to stem from a single common origin. Although commonly considered an ovarian disease, the brain is now a prime suspect in both the ontogeny and pathology of PCOS. We discuss here the neuroendocrine impairments present in PCOS that implicate involvement of the brain and review evidence gained from pre-clinical models of the syndrome about the specific brain circuitry involved. In particular, we focus on the impact that developmental androgen excess and adult hyperandrogenemia have in programming and regulating brain circuits important in the central regulation of fertility. The studies discussed here provide compelling support for the importance of the brain in PCOS ontogeny and pathophysiology and highlight the need for a better understanding of the underlying mechanisms involved.

Increased cerebrospinal fluid levels of GABA, testosterone and estradiol in women with polycystic ovary syndrome

STUDY QUESTION

Do cerebrospinal fluid (CSF) concentrations of gamma-aminobutyric acid (GABA), testosterone (T) and estradiol (E2) differ in women with polycystic ovary syndrome (PCOS) as compared to eumenorrheic, ovulatory women (EW)?

SUMMARY ANSWER

Women with PCOS displayed higher CSF levels of GABA and E2, and possibly T, than EW.

WHAT IS KNOWN ALREADY

The chronic anovulation characteristic of PCOS has been attributed to increased central GnRH drive and resulting gonadotropin aberrations. Androgens are thought to regulate GABA, which in turn regulates the neural cascade that modulates GnRH drive.

STUDY DESIGN, SIZE, DURATION

This cross-sectional observational study included 15 EW and 12 non-obese women with PCOS who consented to a lumbar puncture in addition to 24 h of serum blood collection at 15-min intervals.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 27 women were studied at a the General Clinical Research Center (GCRC) at the University of Pittsburgh. Serum analytes included T, E2 and androstenedione. CSF analytes included GABA, glutamate, glucose, T and E2.

MAIN RESULTS AND THE ROLE OF CHANCE

Women with PCOS had higher CSF GABA as compared to EW (9.04 versus 7.04 μmol/L, P < 0.05). CSF glucose and glutamate concentrations were similar between the two groups. CSF T was 52% higher (P = 0.1) and CSF E2 was 30% higher (P < 0.01) in women with PCOS compared to EW. Circulating T was 122% higher (P < 0.01) and circulating E2 was 75% higher (P < 0.01) in women with PCOS than in EW.

LIMITATIONS REASONS FOR CAUTION

The study is limited by its small sample size and the technical limitations of measuring CSF analytes that are pulsatile and have short half-lives.

WIDER IMPLICATIONS OF THE FINDINGS

Women with PCOS displayed significantly higher circulating levels of T and E2, significantly higher CSF levels of E2, and higher levels of CSF testosterone, although the latter was not statistically significant. A better understanding of the central milieu informs our understanding of the mechanisms mediating increased the GnRH drive in PCOS and lends a new perspective for understanding the presentation, pathogenesis and potential health consequences of PCOS, including gender identity issues.

STUDY FUNDING/COMPETING INTEREST(S)

No conflicts of interest. The study was funded by NIH grants to SLB (RO1-MH50748, U54-HD08610) and NIH RR-00056 to the General Clinical Research Center of the University of Pittsburgh.

TRIAL REGISTRATION NUMBER

NCT01674426.

The impact of postnatal leuprolide acetate treatment on reproductive characteristics in a rodent model of polycystic ovary syndrome

In this study, a GnRH agonist, leuprolide acetate (LA), was given as a single depot injection before 48 h of life to Wistar female rats allotted to prenatal (E16-18) and postnatal androgenization (day 5 of life) by the use of testosterone propionate, looking for reproductive endpoints. Remarkably, a single injection of LA increased the estrus cycles in the postnatal group (PostN) from 0% to 25% of the estrus cycles in the postnatal LA treated group (PostN L). LA also reduced the serum testosterone levels and cysts and atretic follicles in PostN L in contrast with rats (>100 days) from the PostN group (p = 0.04). Prenatally androgenized rats (PreN) exhibited significant modifications in the hypothalamic genes, such as Gnrh. To the best of our knowledge, this is the first study to show that blockage of the GnRH axis with leuprolide acetate depot prevented the development of typical features (anovulation, cysts, atretic follicles) in a postnatal testosterone propionate rat model of PCOS.

Long-term treatment with testosterone alters ovary innervation in adult pigs

BACKGROUND

Intraovarian distribution and density of nerve fibres immunoreactive (IR) to protein gene product 9.5 (PGP 9.5) and containing dopamine-β-hydroxylase (DβH), neuropeptide Y (NPY), somatostatin (SOM), galanin (GAL) were determined.

METHODS

From day 4 of the first oestrous cycle to day 20 of the second studied cycle, experimental gilts (n = 3) were injected with testosterone (T), while control gilts (n = 3) received corn oil.

RESULTS

After T administration the numbers of fibres IR to PGP 9.5 and fibres IR to DβH, NPY and SOM were decreased. Fewer PGP 9.5- and DβH-IR terminals were observed within the ground plexus and around arteries and medullar veins, and medium tertiary follicles, and DβH-IR terminals in the vicinity of small tertiary follicles. T decreased the density of NPY-IR fibres in the medullar part of the ground plexus, and SOM-IR in the cortical part of the ground plexus.

CONCLUSIONS

The obtained data show that long-term T treatment of gilts decreases the total number of intraovarian fibres, including sympathetic ones. These results suggest that elevated T levels that occur during pathological states may affect the innervation pattern of ovaries, and their function(s).

Role of the PI3K-Akt Signaling Pathway in the Pathogenesis of Polycystic Ovary Syndrome

This review aimed to focus on the recent progress of the understanding of the role of phosphatidylinositol 3-kinase (PI3K) in polycystic ovary syndrome (PCOS). In recent years, it has been increasingly recognized that PI3K plays an important role in PCOS whose pathogenesis is unclear. However, research continues into revealing the details of how PI3Ks are involved in developing PCOS. Previous studies have shown that activation of the PI3K-protein kinase B (Akt) signaling pathway has important effects on insulin resistance and endometrial cancer. Knowledge of the action of PI3K in PCOS might provide valuable information to further validate the pathogenesis of PCOS and suggest new methods of treatment.

The neuroendocrine genesis of polycystic ovary syndrome: A role for arcuate nucleus GABA neurons

Polycystic ovary syndrome (PCOS) is a prevalent and distressing endocrine disorder lacking a clearly identified aetiology. Despite its name, PCOS may result from impaired neuronal circuits in the brain that regulate steroid hormone feedback to the hypothalamo-pituitary-gonadal axis. Ovarian function in all mammals is controlled by the gonadotropin-releasing hormone (GnRH) neurons, a small group of neurons that reside in the pre-optic area of the hypothalamus. GnRH neurons drive the secretion of the gonadotropins from the pituitary gland that subsequently control ovarian function, including the production of gonadal steroid hormones. These hormones, in turn, provide important feedback signals to GnRH neurons via a hormone sensitive neuronal network in the brain. In many women with PCOS this feedback pathway is impaired, resulting in the downstream consequences of the syndrome. This review will explore what is currently known from clinical and animal studies about the identity, relative contribution and significance of the individual neuronal components within the GnRH neuronal network that contribute to the pathophysiology of PCOS. We review evidence for the specific neuronal pathways hypothesised to mediate progesterone negative feedback to GnRH neurons, and discuss the potential mechanisms by which androgens may evoke disruptions in these circuits at different developmental time points. Finally, this review discusses data providing compelling support for disordered progesterone-sensitive GABAergic input to GnRH neurons, originating specifically within the arcuate nucleus in prenatal androgen induced forms of PCOS.

Both Estrogen and Androgen Modify the Response to Activation of Neurokinin-3 and κ-Opioid Receptors in Arcuate Kisspeptin Neurons From Male Mice

Gonadal steroids regulate the pattern of GnRH secretion. Arcuate kisspeptin (kisspeptin, neurokinin B, and dynorphin [KNDy]) neurons may convey steroid feedback to GnRH neurons. KNDy neurons increase action potential firing upon the activation of neurokinin B receptors (neurokinin-3 receptor [NK3R]) and decrease firing upon the activation of dynorphin receptors (κ-opioid receptor [KOR]). In KNDy neurons from intact vs castrated male mice, NK3R-mediated stimulation is attenuated and KOR-mediated inhibition enhanced, suggesting gonadal secretions are involved. Estradiol suppresses spontaneous GnRH neuron firing in male mice, but the mediators of the effects on firing in KNDy neurons are unknown. We hypothesized the same gonadal steroids affecting GnRH firing pattern would regulate KNDy neuron response to NK3R and KOR agonists. To test this possibility, extracellular recordings were made from KNDy neurons in brain slices from intact, untreated castrated or castrated adult male mice treated in vivo with steroid receptor agonists. As observed previously, the stimulation of KNDy neurons by the NK3R agonist senktide was attenuated in intact vs castrated mice and suppression by dynorphin was enhanced. In contrast to observations of steroid effects on the GnRH neuron firing pattern, both estradiol and DHT suppressed senktide-induced KNDy neuron firing and enhanced the inhibition caused by dynorphin. An estrogen receptor-α agonist but not an estrogen receptor-β agonist mimicked the effects of estradiol on NK3R activation. These observations suggest the steroid modulation of responses to activation of NK3R and KOR as mechanisms for negative feedback in KNDy neurons and support the contribution of these neurons to steroid-sensitive elements of a GnRH pulse generator.

Enhancement of a robust arcuate GABAergic input to gonadotropin-releasing hormone neurons in a model of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS), the leading cause of female infertility, is associated with an increase in luteinizing hormone (LH) pulse frequency, implicating abnormal steroid hormone feedback to gonadotropin-releasing hormone (GnRH) neurons. This study investigated whether modifications in the synaptically connected neuronal network of GnRH neurons could account for this pathology. The PCOS phenotype was induced in mice following prenatal androgen (PNA) exposure. Serial blood sampling confirmed that PNA elicits increased LH pulse frequency and impaired progesterone negative feedback in adult females, mimicking the neuroendocrine abnormalities of the clinical syndrome. Imaging of GnRH neurons revealed greater dendritic spine density that correlated with increased putative GABAergic but not glutamatergic inputs in PNA mice. Mapping of steroid hormone receptor expression revealed that PNA mice had 59% fewer progesterone receptor-expressing cells in the arcuate nucleus of the hypothalamus (ARN). To address whether increased GABA innervation to GnRH neurons originates in the ARN, a viral-mediated Cre-lox approach was taken to trace the projections of ARN GABA neurons in vivo. Remarkably, projections from ARN GABAergic neurons heavily contacted and even bundled with GnRH neuron dendrites, and the density of fibers apposing GnRH neurons was even greater in PNA mice (56%). Additionally, this ARN GABA population showed significantly less colocalization with progesterone receptor in PNA animals compared with controls. Together, these data describe a robust GABAergic circuit originating in the ARN that is enhanced in a model of PCOS and may underpin the neuroendocrine pathophysiology of the syndrome.

Reproductive neuroendocrine dysfunction in polycystic ovary syndrome: insight from animal models

Polycystic ovary syndrome (PCOS) is a common endocrinopathy with elusive origins. A clinically heterogeneous disorder, PCOS is likely to have multiple etiologies comprised of both genetic and environmental factors. Reproductive neuroendocrine dysfunction involving increased frequency and amplitude of gonadotropin-releasing hormone (GnRH) release, as reflected by pulsatile luteinizing hormone (LH) secretion, is an important pathophysiologic component in PCOS. Whether this defect is primary or secondary to other changes in PCOS is unclear, but it contributes significantly to ongoing reproductive dysfunction. This review highlights recent work in animal models, with a particular emphasis on the mouse, demonstrating the ability of pre- and postnatal steroidal and metabolic factors to drive changes in GnRH/LH pulsatility and GnRH neuron function consistent with the observed abnormalities in PCOS. This work has begun to elucidate how a complex interplay of ovarian, metabolic, and neuroendocrine factors culminates in this syndrome.

Gonadal steroids differentially modulate the actions of orphanin FQ/nociceptin at a physiologically relevant circuit controlling female sexual receptivity

Orphanin FQ/nociceptin (OFQ/N) inhibits the activity of pro-opiomelanocortin (POMC) neurones located in the hypothalamic arcuate nucleus (ARH) that regulate female sexual behaviour and energy balance. We tested the hypothesis that gonadal steroids differentially modulate the ability of OFQ/N to inhibit these cells via presynaptic inhibition of transmitter release and postsynaptic activation of G protein-gated, inwardly-rectifying K(+) (GIRK)-1 channels. Whole-cell patch clamp recordings were performed in hypothalamic slices prepared from ovariectomised rats. OFQ/N (1 μm) decreased the frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs), and also caused a robust outward current in the presence of tetrodotoxin, in ARH neurones from vehicle-treated animals. A priming dose of oestradiol benzoate (EB; 2 μg) increased basal mEPSC frequency, markedly diminished both the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents, and potentiated the OFQ/N-induced decrease in mIPSC frequency. Steroid treatment regimens that facilitate sexual receptivity reinstate the basal mEPSC frequency, the OFQ/N-induced decrease in mEPSC frequency and the activation of GIRK-1 currents to levels observed in vehicle-treated controls, and largely abolish the ability of OFQ/N to decrease mIPSC frequency. These effects were observed in an appreciable population of identified POMC neurones, almost one-half of which projected to the medial preoptic nucleus. Taken together, these data reveal that gonadal steroids influence the pleiotropic actions of OFQ/N on ARH neurones, including POMC neurones, in a disparate manner. These temporal changes in OFQ/N responsiveness further implicate this neuropeptide system as a critical mediator of the gonadal steroid regulation of reproductive behaviour.

Uncovering steroidopathy in women with autism: a latent class analysis

Background

Prenatal exposure to increased androgens has been implicated in both polycystic ovary syndrome (PCOS) and autism spectrum conditions (ASC), suggesting that PCOS may be increased among women with ASC. One study suggested elevated steroidopathic symptoms (‘steroidopathy’) in women with ASC. As the symptoms are not independent, we conducted a latent class analysis (LCA). The objectives of the current study are: (1) to test if these findings replicate in a larger sample; and (2) to use LCA to uncover affected clusters of women with ASC.

Methods

We tested two groups of women, screened using the Autism Spectrum Quotient - Group 1: n = 415 women with ASC (mean age 36.39 ± 11.98 years); and Group 2: n = 415 controls (mean age 39.96 ± 11.92 years). All participants completed the Testosterone-related Medical Questionnaire online. A multiple-group LCA was used to identify differences in latent class structure between women with ASC and controls.

Results

There were significant differences in frequency of steroid-related conditions and symptoms between women with ASC and controls. A two-class semi-constrained model best fit the data. Based on response patterns, we identified the classes as ‘Typical’ and ‘Steroidopathic’. The prevalence of the ‘Steroidopathic’ class was significantly increased within the ASC group (ΔG² = 15, df =1, P = 0.0001). In particular, we confirmed higher frequencies of epilepsy, amenorrhea, dysmenorrhea, severe acne, gender dysphoria, and transsexualism, and differences in sexual preference in women with ASC.

Conclusions

Women with ASC are at increased risk for symptoms and conditions linked to steroids. LCA revealed this steroidopathy despite the apparent underdiagnosis of PCOS.

Androgens regulate ovarian follicular development by increasing follicle stimulating hormone receptor and microRNA-125b expression

Although androgen excess is considered detrimental to women's health and fertility, global and ovarian granulosa cell-specific androgen-receptor (AR) knockout mouse models have been used to show that androgen actions through ARs are actually necessary for normal ovarian function and female fertility. Here we describe two AR-mediated pathways in granulosa cells that regulate ovarian follicular development and therefore female fertility. First, we show that androgens attenuate follicular atresia through nuclear and extranuclear signaling pathways by enhancing expression of the microRNA (miR) miR-125b, which in turn suppresses proapoptotic protein expression. Second, we demonstrate that, independent of transcription, androgens enhance follicle-stimulating hormone (FSH) receptor expression, which then augments FSH-mediated follicle growth and development. Interestingly, we find that the scaffold molecule paxillin regulates both processes, making it a critical regulator of AR actions in the ovary. Finally, we report that low doses of exogenous androgens enhance gonadotropin-induced ovulation in mice, further demonstrating the critical role that androgens play in follicular development and fertility. These data may explain reported positive effects of androgens on ovulation rates in women with diminished ovarian reserve. Furthermore, this study demonstrates mechanisms that might contribute to the unregulated follicle growth seen in diseases of excess androgens such as polycystic ovary syndrome.

Estradiol negative and positive feedback in a prenatal androgen-induced mouse model of polycystic ovarian syndrome

Gonadal steroid hormone feedback is impaired in polycystic ovarian syndrome (PCOS), a common endocrine disorder characterized by hyperandrogenism and an associated increase in LH pulse frequency. Using a prenatal androgen (PNA)-treated mouse model of PCOS, we aimed to investigate negative and positive feedback effects of estrogens on the hypothalamic-pituitary axis regulation of LH. PNA-treated mice exhibited severely disrupted estrous cycles, hyperandrogenism, significantly reduced fertility, and altered ovarian morphology. To assess the negative feedback effects of estrogens, LH was measured before and after ovariectomy and after estradiol (E2) administration. Compared with controls, PNA-treated mice exhibited a blunted postcastration rise in LH (P < .001) and an absence of LH suppression after E2 administration. To assess E2-positive feedback, control and PNA-treated GnRH-green fluorescent protein transgenic mice were subjected to a standard ovariectomy with E2-replacement regimen, and both plasma and perfusion-fixed brains were collected at the time of the expected GnRH/LH surge. Immunocytochemistry and confocal imaging of cFos and green fluorescent protein were used to assess GnRH neuron activation and spine density. In the surged group, both control and PNA-treated mice had significantly increased LH and cFos activation in GnRH neurons (P < .05) compared with nonsurged animals. Spine density was quantified in cFos-positive and -negative GnRH neurons to examine whether there was an increase in spine density in cFos-expressing GnRH neurons of surged mice as expected. A significant increase in spine density in cFos-expressing GnRH neurons was evident in control animals; however, no significant increase was observed in the PNA-treated mice because spine density was elevated across all GnRH neurons. These data support that PNA treatment results in a PCOS-like phenotype that includes impaired E2-negative feedback. Additionally, although E2-positive feedback capability is retained in PNA mice, elevated GnRH neuron spine density may reflect altered synaptic regulation.

Glutamatergic and GABAergic innervation of human gonadotropin-releasing hormone-I neurons

Amino acid (aa) neurotransmitters in synaptic afferents to hypothalamic GnRH-I neurons are critically involved in the neuroendocrine control of reproduction. Although in rodents the major aa neurotransmitter in these afferents is γ-aminobutyric acid (GABA), glutamatergic axons also innervate GnRH neurons directly. Our aim with the present study was to address the relative contribution of GABAergic and glutamatergic axons to the afferent control of human GnRH neurons. Formalin-fixed hypothalamic samples were obtained from adult male individuals (n = 8) at autopsies, and their coronal sections processed for dual-label immunohistochemical studies. GABAergic axons were labeled with vesicular inhibitory aa transporter antibodies, whereas glutamatergic axons were detected with antisera against the major vesicular glutamate transporter (VGLUT) isoforms, VGLUT1 and VGLUT2. The relative incidences of GABAergic and glutamatergic axonal appositions to GnRH-immunoreactive neurons were compared quantitatively in two regions, the infundibular and paraventricular nuclei. Results showed that GABAergic axons established the most frequently encountered type of axo-somatic apposition. Glutamatergic contacts occurred in significantly lower numbers, with similar contributions by their VGLUT1 and VGLUT2 subclasses. The innervation pattern was different on GnRH dendrites where the combined incidence of glutamatergic (VGLUT1 + VGLUT2) contacts slightly exceeded that of the GABAergic appositions. We conclude that GABA represents the major aa neurotransmitter in axo-somatic afferents to human GnRH neurons, whereas glutamatergic inputs occur somewhat more frequently than GABAergic inputs on GnRH dendrites. Unlike in rats, the GnRH system of the human receives innervation from the VGLUT1, in addition to the VGLUT2, subclass of glutamatergic neurons.

Membrane progesterone receptors: evidence for neuroprotective, neurosteroid signaling and neuroendocrine functions in neuronal cells

Membrane progesterone receptors (mPRs) are novel G protein-coupled receptors belonging to the progestin and adipoQ receptor family (PAQR) that mediate a variety of rapid cell surface-initiated progesterone actions in the reproductive system involving activation of intracellular signaling pathways (i.e. nonclassical actions). The mPRs are highly expressed in the brain, but research on their neural functions has only been conducted in a single neuronal cell line, GT1-7 cells, which have negligible nuclear progesterone receptor (PR) expression. GT1-7 cells express mPRα and mPRβ on their plasma membranes which is associated with the presence of high-affinity, specific [(3)H]-progesterone receptor binding. The neurosteroid, allopregnanolone, is an effective ligand for recombinant mPRα with a relative binding affinity of 7.6% that of progesterone. Allopregnanolone acts as a potent mPR agonist on GT1-7 cells, mimicking the progesterone-induced decrease in cAMP accumulation and its antiapoptotic actions at low nanomolar concentrations. The decrease in cAMP levels is associated with rapid progesterone-induced downregulation of GnRH pulsatile secretion from perifused GT1-7 cells. The recent suggestion that mPRs are alkaline ceramidases and mediate sphingolipid signaling is not supported by empirical evidence that TNFα does not bind to mPRs overexpressed in human cells and that exogenous sphingomyelinase is ineffective in mimicking progestin actions through mPRs to induce meiotic maturation of fish oocytes. Taken together, these recent studies indicate that mPRs mediate neuroprotective effects of progesterone and allopregnanolone and are also the likely intermediaries in progesterone-induced inhibition of pulsatile GnRH secretion in GT1-7 cells.

Developmental programming: reproductive endocrinopathies in the adult female sheep after prenatal testosterone treatment are reflected in altered ontogeny of GnRH afferents

The GnRH system represents a useful model of long-term neural plasticity. An unexplored facet of this plasticity relates to the ontogeny of GnRH neural afferents during critical periods when the hypothalamic-pituitary-gonadal axis is highly susceptible to perturbation by sex steroids. Sheep treated with testosterone (T) in utero exhibit profound reproductive neuroendocrine dysfunctions during their lifespan. The current study tested the hypothesis that these changes are associated with alterations in the normal ontogeny of GnRH afferents and glial associations. Adult pregnant sheep (n=50) were treated with vehicle [control (CONT)] or T daily from gestational day (GD)30 to GD90. CONT and T fetuses (n=4-6/treatment per age group) were removed by cesarean section on GD90 and GD140 and the brains frozen at -80°C. Brains were also collected from CONT and T females at 20-23 wk (prepubertal), 10 months (normal onset of puberty and oligo-anovulation), and 21 months (oligo-anovulation in T females). Tissue was analyzed for GnRH immunoreactivity (ir), total GnRH afferents (Synapsin-I ir), glutamate [vesicular glutamate transporter-2 (VGLUT2)-ir], and γ-aminobutyric acid [GABA, vesicular GABA transporter (VGAT)-ir] afferents and glial associations (glial fibrillary acidic protein-ir) with GnRH neurons using optical sectioning techniques. The results revealed that: 1) GnRH soma size was slightly reduced by T, 2) the total (Synapsin-I) GnRH afferents onto both somas and dendrites increased significantly with age and was reduced by T, 3) numbers of both VGAT and VGLUT inputs increased significantly with age and were also reduced by T, and 4) glial associations with GnRH neurons were reduced (<10%) by T. Together, these findings reveal a previously unknown developmental plasticity in the GnRH system of the sheep. The altered developmental trajectory of GnRH afferents after T reinforces the notion that prenatal programming plays an important role in the normal development of the reproductive neuroendocrine axis.

Endocannabinoids and prostaglandins both contribute to GnRH neuron-GABAergic afferent local feedback circuits

Gonadotropin-releasing hormone (GnRH) neurons form the final common pathway for central control of fertility. Regulation of GnRH neurons by long-loop gonadal steroid feedback through steroid receptor-expressing afferents such as GABAergic neurons is well studied. Recently, local central feedback circuits regulating GnRH neurons were identified. GnRH neuronal depolarization induces short-term inhibition of their GABAergic afferents via a mechanism dependent on metabotropic glutamate receptor (mGluR) activation. GnRH neurons are enveloped in astrocytes, which express mGluRs. GnRH neurons also produce endocannabinoids, which can be induced by mGluR activation. We hypothesized the local GnRH-GABA circuit utilizes glia-derived and/or cannabinoid mechanisms and is altered by steroid milieu. Whole cell voltage-clamp was used to record GABAergic postsynaptic currents (PSCs) from GnRH neurons before and after action potential-like depolarizations were mimicked. In GnRH neurons from ovariectomized (OVX) mice, this depolarization reduced PSC frequency. This suppression was blocked by inhibition of prostaglandin synthesis with indomethacin, by a prostaglandin receptor antagonist, or by a specific glial metabolic poison, together suggesting the postulate that prostaglandins, potentially glia-derived, play a role in this circuit. This circuit was also inhibited by a CB1 receptor antagonist or by blockade of endocannabinoid synthesis in GnRH neurons, suggesting an endocannabinoid element, as well. In females, local circuit inhibition persisted in androgen-treated mice but not in estradiol-treated mice or young ovary-intact mice. In contrast, local circuit inhibition was present in gonad-intact males. These data suggest GnRH neurons interact with their afferent neurons using multiple mechanisms and that these local circuits can be modified by both sex and steroid feedback.

Depolarising and hyperpolarising actions of GABA(A) receptor activation on gonadotrophin-releasing hormone neurones: towards an emerging consensus

The gonadotrophin-releasing hormone (GnRH) neurones represent the final output neurones of a complex neuronal network that controls fertility. It is now appreciated that GABAergic neurones within this network provide an important regulatory influence on GnRH neurones. However, the consequences of direct GABA(A) receptor activation on adult GnRH neurones have been controversial for nearly a decade now, with both hyperpolarising and depolarising effects being reported. This review provides: (i) an overview of GABA(A) receptor function and its investigation using electrophysiological approaches and (ii) re-examines the past and present results relating to GABAergic regulation of the GnRH neurone, with a focus on mouse brain slice data. Although it remains difficult to reconcile the results of the early studies, there is a growing consensus that GABA can act through the GABA(A) receptor to exert both depolarising and hyperpolarising effects on GnRH neurones. The most recent studies examining the effects of endogenous GABA release on GnRH neurones indicate that the predominant action is that of excitation. However, we are still far from a complete understanding of the effects of GABA(A) receptor activation upon GnRH neurones. We argue that this will require not only a better understanding of chloride ion homeostasis in individual GnRH neurones, and within subcellular compartments of the GnRH neurone, but also a more integrative view of how multiple neurotransmitters, neuromodulators and intrinsic conductances act together to regulate the activity of these important cells.

Glucosensing by GnRH neurons: inhibition by androgens and involvement of AMP-activated protein kinase

GnRH neurons integrate steroidal and metabolic cues to regulate fertility centrally. Central glucoprivation reduces LH secretion, which is governed by GnRH release, suggesting GnRH neuron activity is modulated by glucose availability. Here we tested whether GnRH neurons can sense changes in extracellular glucose, and whether glucosensing is altered by the steroids dihydrotestosterone (DHT) and/or estradiol (E). Extracellular recordings were made from GnRH neurons in brain slices from ovariectomized (OVX) mice ± DHT and/or E implants. Firing rate was reduced by a switch from 4.5 to 0.2 mm glucose in cells from OVX, OVX+E, and OVX+DHT+E mice, but not OVX+DHT mice. This suggests that androgens reduce the sensitivity of GnRH neurons to changes in extracellular glucose, but E mitigates this effect. Next we investigated potential mechanisms. In the presence of the ATP-sensitive potassium channel antagonist tolbutamide, glucosensing persisted. In contrast, glucosensing was attenuated in the presence of compound C, an antagonist of AMP-activated protein kinase (AMPK), suggesting a role for AMPK in glucosensing. The AMPK activator N1-(b-D-ribofuranosyl)-5-aminoimidazole-4-carboxamide (AICAR) mimicked the effect of low glucose and was less effective in cells from DHT-treated mice. The effect of DHT to diminish responses to low glucose and AICAR was abolished by blockade of fast synaptic transmission. Both AICAR and low glucose activated a current with a reversal potential near -50 mV, suggesting a nonspecific cation current. These studies indicate that glucosensing is one mechanism by which GnRH neurons sense fuel availability and point to a novel role for AMPK in the central regulation of fertility.

Retrograde endocannabinoid signaling reduces GABAergic synaptic transmission to gonadotropin-releasing hormone neurons

Cannabinoids suppress fertility via reducing hypothalamic GnRH output. γ-Aminobutyric acid (GABA)(A) receptor (GABA(A)-R)-mediated transmission is a major input to GnRH cells that can be excitatory. We hypothesized that cannabinoids act via inhibiting GABAergic input. We performed loose-patch electrophysiological studies of acute slices from adult male GnRH-green fluorescent protein transgenic mice. Bath application of type 1 cannabinoid receptor (CB1) agonist WIN55,212 decreased GnRH neuron firing rate. This action was detectable in presence of the glutamate receptor antagonist kynurenic acid but disappeared when bicuculline was also present, indicating GABA(A)-R involvement. In immunocytochemical experiments, CB1-immunoreactive axons formed contacts with GnRH neurons and a subset established symmetric synapses characteristic of GABAergic neurotransmission. Functional studies were continued with whole-cell patch-clamp electrophysiology in presence of tetrodotoxin. WIN55,212 decreased the frequency of GABA(A)-R-mediated miniature postsynaptic currents (mPSCs) (reflecting spontaneous vesicle fusion), which was prevented with the CB1 antagonist AM251, indicating collectively that activation of presynaptic CB1 inhibits GABA release. AM251 alone increased mPSC frequency, providing evidence that endocannabinoids tonically inhibit GABA(A)-R drive onto GnRH neurons. Increased mPSC frequency was absent when diacylglycerol lipase was blocked intracellularly with tetrahydrolipstatin, showing that tonic inhibition is caused by 2-arachidonoylglycerol production of GnRH neurons. CdCl(2) in extracellular solution can maintain both action potentials and spontaneous vesicle fusion. Under these conditions, when endocannabinoid-mediated blockade of spontaneous vesicle fusion was blocked with AM251, GnRH neuron firing increased, revealing an endogenous endocannabinoid brake on GnRH neuron firing. Retrograde endocannabinoid signaling may represent an important mechanism under physiological and pathological conditions whereby GnRH neurons regulate their excitatory GABAergic inputs.

Identified GnRH neuron electrophysiology: a decade of study

Over the past decade, the existence of transgenic mouse models in which reporter genes are expressed under the control of the gonadotropin-releasing hormone (GnRH) promoter has made possible the electrophysiological study of these cells. Here, we review the intrinsic and synaptic properties of these cells that have been revealed by these approaches, with a particular regard to burst generation. Advances in our understanding of neuromodulation of GnRH neurons and synchronization of this network are also discussed.

Progesterone treatment inhibits and dihydrotestosterone (DHT) treatment potentiates voltage-gated calcium currents in gonadotropin-releasing hormone (GnRH) neurons

GnRH neurons are central regulators of fertility, and their activity is modulated by steroid feedback. In normal females, GnRH secretion is regulated by estradiol and progesterone (P). Excess androgens present in hyperandrogenemic fertility disorders may disrupt communication of negative feedback signals from P and/or independently stimulate GnRH release. Voltage-gated calcium channels (VGCCs) are important in regulating excitability and hormone release. Estradiol alters VGCCs in a time-of-day-dependent manner. To further elucidate ovarian steroid modulation of GnRH neuron VGCCs, we studied the effects of dihydrotestosterone (DHT) and P. Adult mice were ovariectomized (OVX) or OVX and treated with implants containing DHT (OVXD), estradiol (OVXE), estradiol and DHT (OVXED), estradiol and P (OVXEP), or estradiol, DHT, and P (OVXEDP). Macroscopic calcium current (I(Ca)) was recorded in the morning or afternoon 8-12 d after surgery using whole-cell voltage-clamp. I(Ca) was increased in afternoon vs. morning in GnRH neurons from OVXE mice but this increase was abolished in cells from OVXEP mice. I(Ca) in cells from OVXD mice was increased regardless of time of day; there was no additional effect in OVXED mice. P reduced N-type and DHT potentiated N- and R-type VGCCs; P blocked the DHT potentiation of N-type-mediated current. These data suggest P and DHT have opposing actions on VGCCs in GnRH neurons, but in the presence of both steroids, P dominates. VGCCs are targets of ovarian steroid feedback modulation of GnRH neuron activity and, more specifically, a potential mechanism whereby androgens could activate GnRH neuronal function.

Neuroendocrine regulation of GnRH release and expression of GnRH and GnRH receptor genes in the hypothalamus-pituitary unit in different physiological states

This review is focused on the relationship between neuroendocrine regulation of GnRH/LH secretion and the expression of GnRH and GnRH receptor (GnRHR) genes in the hypothalamic-pituitary unit during different physiological states of animals and under stress. Moreover, the involvement of hypothalamic GABA-ergic, Beta-endorphinergic, CRH-ergic, noradrenergic, dopaminergic and GnRH-ergic systems in the regulation of expression of the GnRH and GnRHR genes as well as secretion of GnRH/LH is analyzed. It appears that the neural mechanisms controlling GnRH gene expression in different physiological states may be distinct from those regulating GnRH/LH release. The hypothalamic GnRHR gene is probably located in different neural systems and may act in a specific way on GnRH gene expression and GnRH release.

Knockdown of GABA(A) receptor signaling in GnRH neurons has minimal effects upon fertility

The amino acid gamma-aminobutyric acid (GABA) is thought to play a key role in shaping the activity of the GnRH neurons throughout embryonic and postnatal life. However, the physiological roles of direct GABA inputs to GnRH neurons remain unknown. Using a Cre-LoxP strategy, we generated a targeted mouse line, in which all (98 +/- 1%) GnRH neurons had the gamma2-subunit of the GABA(A) receptor deleted. Electrophysiological recordings of GABA(A)-mediated postsynaptic currents from green fluorescent protein-tagged GnRH neurons with the gamma2-subunit knocked out (GnRH gamma2 KO) showed that the amplitude and frequency of GABA(A) postsynaptic currents were reduced by 70% (P < 0.01) and 77% (P < 0.05), respectively, and that the response to exogenous GABA was reduced by 90% (P < 0.01). Evaluation of male and female GnRH gamma2 KO mice revealed completely normal fecundity, estrous cycles, and puberty onset. Further investigation with gonadectomy and different steroid replacement regimens showed normal basal levels of LH in both sexes, and a normal estradiol-evoked positive feedback mechanism in females. However, the increment in LH after gonadectomy in GnRH gamma2 KO female mice was double that of controls (P < 0.05) and also more potently suppressed by 17-beta-estradiol (P < 0.05). A similar but nonsignificant trend was observed in GnRH gamma2 KO male mice. Together, these findings show that 70-90% reductions in the normal levels of GABA(A) receptor activity at the GnRH neuron appear to impact upon the estrogen negative feedback mechanism but are, nevertheless, compatible with normal fertility in mice.