Androgens increase gonadotropin-releasing hormone neuron firing activity in females and interfere with progesterone negative feedback

Overactivation of GnRH neurons is sufficient to trigger polycystic ovary syndrome-like traits in female mice

BACKGROUND

Polycystic ovary syndrome (PCOS) is the most common endocrine disorder leading to anovulatory infertility. Abnormalities in the central neuroendocrine system governed by gonadotropin-releasing hormone (GnRH) neurons might be related to ovarian dysfunction in PCOS, although the link in this disordered brain-to-ovary communication remains unclear. Here, we manipulated GnRH neurons using chemogenetics in adult female mice to unveil whether chronic overaction of these neurons would trigger PCOS-like hormonal and reproductive impairments.

METHODS

We used adult Gnrh1cre female mice to selectively target and express the designer receptors exclusively activated by designer drugs (DREADD)-based chemogenetic tool hM3D(Gq) in hypophysiotropic GnRH neurons. Chronic chemogenetic activation protocol was carried out with clozapine N-oxide (CNO) i.p. injections every 48 h over a month. We evaluated the reproductive and hormonal profile before, during, and two months after chemogenetic manipulations.

FINDINGS

We discovered that the overactivation of GnRH neurons was sufficient to disrupt reproductive cycles, promote hyperandrogenism, and induce ovarian dysfunction. These PCOS features were detected with a long-lasting neuroendocrine dysfunction through abnormally high luteinizing hormone (LH) pulse secretion. Additionally, the GnRH-R blockade prevented the establishment of long-term neuroendocrine dysfunction and androgen excess in these animals.

INTERPRETATION

Taken together, our results show that hyperactivity of hypothalamic GnRH neurons is a major driver of reproductive and hormonal impairments in PCOS and suggest that antagonizing the aberrant GnRH signaling could be an efficient therapeutic venue for the treatment of PCOS.

FUNDING

European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement n◦ 725149).

Gonadal Feedback Alters the Relationship between Action Potentials and Hormone Release in Gonadotropin-Releasing Hormone Neurons in Male Mice

In vertebrates, the pulsatile release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus triggers secretion of anterior pituitary gonadotropins, which activate steroidogenesis, and steroids in turn exert typically homeostatic negative feedback on GnRH release. Although long-term episodic firing patterns of GnRH neurons in brain slices resemble the pulsatile release of GnRH and LH in vivo, neither the relationship between GnRH neuron firing and release nor whether this relationship is influenced by gonadal feedback are known. We combined fast-scan cyclic voltammetry and patch-clamp to perform simultaneous measurements of neuropeptide release with either spontaneous action potential firing or in response to neuromodulator or action-potential-spike templates in brain slice preparations from male mice. GnRH release increased with higher frequency spontaneous firing to a point; release reached a plateau after which further increases in firing rate did not elicit further increased release. Kisspeptin, a potent GnRH neuron activator via a Gq-coupled signaling pathway, triggered GnRH release before increasing firing rate, whether globally perfused or locally applied. Increasing the number of spikes in an applied burst template increased release; orchidectomized mice had higher sensitivity to the increased action potential number than sham-operated mice. Similarly, Ca2+ currents triggered by these burst templates were increased in GnRH neurons of orchidectomized mice. These results suggest removal of gonadal feedback increases the efficacy of the stimulus-secretion coupling mechanisms, a phenomenon that may extend to other steroid-sensitive regions of the brain.SIGNIFICANCE STATEMENT Pulsatile secretion of GnRH plays a critical role in fertility. The temporal relationship between GnRH neuron action potential firing and GnRH release remains unknown as does whether this relationship is influenced by gonadal feedback. By combining techniques of fast-scan cyclic voltammetry and patch-clamp we, for the first time, monitored GnRH concentration changes during spontaneous and neuromodulator-induced GnRH neuron firing. We also made the novel observation that gonadal factors exert negative feedback on excitation-secretion coupling to reduce release in response to the same stimulus. This has implications for the control of normal fertility, central causes of infertility, and more broadly for the effects of sex steroids in the brain.

Caring for Patients With Congenital Adrenal Hyperplasia Throughout the Lifespan

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder affecting cortisol and aldosterone biosynthesis, which can lead to virilization in fetuses with a 46,XX karyotype. 21-hydroxylase deficiency is the most common cause of CAH, accounting for 90-99% of all patients with the condition. The management of patients with CAH should be done with a multidisciplinary team, which would address all of the complex components of their care throughout their lifespans. Many multidisciplinary teams have adopted shared decision-making approaches to genital surgery in which parents and patients can be part of the decision-making process. Continued research is needed to best serve these patients throughout their lifespans.

The Impact of Obesity on the Excretion of Steroid Metabolites in Boys and Girls: A Comparison with Normal-Weight Children

Obesity in childhood is associated with several steroid changes, which result from excess body mass. The aim of this study was to evaluate steroid metabolism in children with obesity compared with those with normal weight, especially in relation to sex and puberty progress. We analyzed the clinical data of 191 children, aged between 5 and 18 years, with 115 affected (64 girls and 51 boys) and 76 unaffected (35 girls and 41 boys) by obesity. Routine clinical assessment and pubertal stage evaluation based upon Tanner's scale were performed. In addition, to evaluate the impact of puberty, children with pre-adolescence and advanced puberty were divided into separate subgroups. Then, 24 h urine steroid excretion profiles were analyzed by gas chromatography/mass spectrometry. Significant differences in the excretion of steroid metabolites were found between normal weight children and children with obesity, especially in the prepubertal cohort. In this group, we observed enhanced activity in all the pathways of adrenal steroidogenesis. Raised excretion of mineralocorticoid derivatives such as tetrahydro-11-deoxycorticosterone, tetrahydrocorticosterone, and 5α-tetrahydrocorticosterone supported increased activity of this track. No significant differences were detected in the excreted free forms of cortisol and cortisone, while the excretion of their characteristic tetrahydro-derivatives was different. In pre-adolescent children with obesity, α-cortol and especially α-cortolone appeared to be excreted more abundantly than β-cortol or β-cortolone. Furthermore, in children with obesity, we observed elevated androgen excretion with an enhanced backdoor pathway. As puberty progressed, remarkable reduction in the differences between adolescents with and without obesity was demonstrated.

Oxidative stress and antioxidant imbalance in ovulation disorder in patients with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common reproductive endocrine disease that is characterized by oligo-ovulation or anovulation, hyperandrogenism, and polycystic ovaries observed using ultrasound with high clinical heterogeneity. At present, the etiology of PCOS is not clear but is thought to be related to genetic, metabolic, endocrine and environmental factors. Hyperandrogenism interacts with insulin resistance and overweight/obesity, forming a vicious cycle of mutual promotion and participating in the occurrence and progression of PCOS. Oxidative stress (OS) refers to the imbalance between the oxidation system and antioxidation system in the human body, which is associated with the occurrence and development of various diseases. Recent studies have shown that OS may be closely related to ovulation disorders in PCOS, and antioxidants can improve the oxidative stress state of PCOS. However, previous studies did not examine the effect of the interaction between OS and hyperandrogenism, insulin resistance or overweight/obesity on ovulation disorders in PCOS. This article reviews the interaction between OS and hyperandrogenism, insulin resistance and overweight/obesity; the effects of OS, hyperandrogenism, insulin resistance and overweight/obesity on ovulation disorders in PCOS; and the application of antioxidants in PCOS.

Daughters of polycystic ovary syndrome pregnancies and androgen levels in puberty: a Meta-analysis

Purpose: To provide an overview and critical analysis of the literature related to the circulating androgen levels of daughters of PCOS mothers during prepubertal and pubertal stage who have not yet been diagnosed with PCOS or precocious puberty. Methods: We critically considered and meta-analyzed observational studies comparing androgens concentration in daughters of PCOS mothers compared to daughters of mothers without PCOS. A literature search was conducted in MEDLINE, Scopus and other sources from 01/09/2021 until 01/12/2021. The study followed the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). The primary outcome included total testosterone levels whereas the secondary outcomes included 17a-hydroxyprogesterone (17-OHP), androstenedione (Δ4Α) and Sex Hormone Binding Globulin (SHBG) levels respectively. Results: Our search yielded 1073 studies, 9 of which were included in our analysis. The results are presented differently according to pubertal stage. Pubertal daughters of PCOS mothers exhibited significantly higher total testosterone (pooled mean difference 14.95 (95%CI: 6.98 to 22.93), higher 17-OHP (pooled mean difference 0.11 (95%CI: 0.02 to 0.20) and lower SHBG levels (pooled mean difference -10.48 (95%CI: -16.46 to -4.61). Instead, prepubertal daughters of PCOS mothers presented greater SHBG levels (pooled mean difference 7.79 (95%CI: 0.03 to 15.54) compared to controls. No difference was found in Δ4Α levels in both groups. Conclusion: The onset of puberty is a critical point in the development of the disease and an early intervention may be imperative.

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.

Chronic androgen excess in female mice does not impact luteinizing hormone pulse frequency or putative GABAergic inputs to GnRH neurons

Polycystic ovary syndrome (PCOS) is associated with androgen excess and, frequently, hyperactive pulsatile luteinizing hormone (LH) secretion. Although the origins of PCOS are unclear, evidence from pre-clinical models implicates androgen signalling in the brain in the development of PCOS pathophysiology. Chronic exposure of female mice to dihydrotestosterone (DHT) from 3 weeks of age drives both reproductive and metabolic impairments that are ameliorated by selective androgen receptor (AR) loss from the brain. This suggests centrally driven mechanisms in hyperandrogen-mediated PCOS-like pathophysiology that remain to be defined. Acute prenatal DHT exposure can also model the hyperandrogenism of PCOS, and this is accompanied by increased LH pulse frequency and increased GABAergic innervation of gonadotrophin-releasing hormone (GnRH) neurons. We aimed to determine the impact of chronic exposure of female mice to DHT, which models the hyperandrogenism of PCOS, on pulsatile LH secretion and putative GABAergic input to GnRH neurons. To do this, GnRH-green fluorescent protein (GFP) female mice received either DHT or blank capsules for 90 days from postnatal day 21 (n = 6 or 7 per group). Serial tail-tip blood sampling was used to measure LH dynamics and perfusion-fixed brains were collected and immunolabelled for vesicular GABA transporter (VGAT) to assess putative GABAergic terminals associated with GFP-labelled GnRH neurons. As expected, chronic DHT resulted in acyclicity and significantly increased body weight. However, no differences in LH pulse frequency or the density of VGAT appositions to GnRH neurons were identified between ovary-intact DHT-treated females and controls. Chronic DHT exposure significantly increased the number of AR expressing cells in the hypothalamus, whereas oestrogen receptor α-expressing neuron number was unchanged. Therefore, although chronic DHT exposure from 3 weeks of age increases AR expressing neurons in the brain, the GnRH neuronal network changes and hyperactive LH secretion associated with prenatal androgen excess are not evident. These findings suggest that unique central mechanisms are involved in the reproductive impairments driven by exposure to androgen excess at different developmental stages.

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.

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.

Randomized Controlled Trial of Neurokinin 3 Receptor Antagonist Fezolinetant for Treatment of Polycystic Ovary Syndrome

CONTEXT

Polycystic ovary syndrome (PCOS), a highly prevalent endocrine disorder characterized by hyperandrogenism, is the leading cause of anovulatory infertility.

OBJECTIVE

This proof-of-concept study evaluated clinical efficacy and safety of the neurokinin 3 (NK3) receptor antagonist fezolinetant in PCOS.

METHODS

This was a phase 2a, randomized, double-blind, placebo-controlled, multicenter study (EudraCT 2014-004409-34). The study was conducted at 5 European clinical centers. Women with PCOS participated in the study. Interventions included fezolinetant 60 or 180 mg/day or placebo for 12 weeks. The primary efficacy end point was change in total testosterone. Gonadotropins, ovarian hormones, safety and tolerability were also assessed.

RESULTS

Seventy-three women were randomly assigned, and 64 participants completed the study. Adjusted mean (SE) changes in total testosterone from baseline to week 12 for fezolinetant 180 and 60 mg/day were -0.80 (0.13) and -0.39 (0.12) nmol/L vs -0.05 (0.10) nmol/L with placebo (P < .001 and P < .05, respectively). Adjusted mean (SE) changes from baseline in luteinizing hormone (LH) for fezolinetant 180 and 60 mg/d were -10.17 (1.28) and -8.21 (1.18) vs -3.16 (1.04) IU/L with placebo (P < .001 and P = .002); corresponding changes in follicle-stimulating hormone (FSH) were -1.46 (0.32) and -0.92 (0.30) vs -0.57 (0.26) IU/L (P = .03 and P = .38), underpinning a dose-dependent decrease in the LH-to-FSH ratio vs placebo (P < .001). Circulating levels of progesterone and estradiol did not change significantly vs placebo (P > .10). Fezolinetant was well tolerated.

CONCLUSION

Fezolinetant had a sustained effect to suppress hyperandrogenism and reduce the LH-to-FSH ratio in women with PCOS.

Morphological evidence indicates a role for microglia in shaping the PCOS-like brain

Although polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility worldwide, the aetiology of the disorder remains poorly defined. Animal-based evidence highlights the brain as a prime suspect in both the development and maintenance of PCOS. Prenatally androgenised (PNA) models of PCOS exhibit excessive GABAergic wiring associated with PCOS-like reproductive deficits in adulthood, with aberrant brain wiring detected as early as postnatal day (P) 25, prior to disease onset, in the PNA mouse. The mechanisms underlying this aberrant brain wiring remain unknown. Microglia, the immune cells of the brain, are regulators of neuronal wiring across development, mediating both the formation and removal of neuronal inputs. Here, we tested the hypothesis that microglia play a role in the excessive GABAergic wiring that leads to PCOS-like features in the PNA brain. Using specific immunolabelling, microglia number and morphology associated with activation states were analysed in PNA and vehicle-treated controls across developmental timepoints, including embryonic day 17.5, P0, P25 and P60 (n = 7-14 per group), and in two regions of the hypothalamus implicated in fertility regulation. At P0, fewer amoeboid microglia were observed in the rostral preoptic area (rPOA) of PNA mice. However, the greatest changes were observed at P25, with PNA mice exhibiting fewer total microglia, and specifically fewer "sculpting" microglia, in the rPOA. Based on these findings, we assessed microglia-mediated refinement of GABAergic synaptic terminals at two developmental stages of peak synaptic refinement: P7 and P15 (n = 7 per group). PNA mice showed a reduction in the uptake of GABAergic synaptic material at P15. These findings reveal time-specific changes in the microglia population and refinement of GABAergic inputs in a mouse model of PCOS driven by prenatal androgen excess and suggest a role for microglia in shaping the atypical brain wiring associated with the development of PCOS features.

Gonadotropin-Releasing Hormone (GnRH) Neuron Potassium Currents and Excitability in Both Sexes Exhibit Minimal Changes upon Removal of Negative Feedback

Gonadotropin-releasing hormone (GnRH) drives pituitary secretion of luteinizing hormone and follicle-stimulating hormone, which in turn regulate gonadal functions including steroidogenesis. The pattern of GnRH release and thus fertility depend on gonadal steroid feedback. Under homeostatic (negative) feedback conditions, removal of the gonads from either females or males increases the amplitude and frequency of GnRH release and alters the long-term firing pattern of these neurons in brain slices. The neurobiological mechanisms intrinsic to GnRH neurons that are altered by homeostatic feedback are not well studied and have not been compared between sexes. During estradiol-positive feedback, which is unique to females, there are correlated changes in voltage-gated potassium currents and neuronal excitability. We thus hypothesized that these same mechanisms would be engaged in homeostatic negative feedback. Voltage-gated potassium channels play a direct role in setting excitability and action potential properties. Whole-cell patch-clamp recordings of GFP-identified GnRH neurons in brain slices from sham-operated and castrated adult female and male mice were made to assess fast and slow inactivating potassium currents as well as action potential properties. Surprisingly, no changes were observed among groups in most potassium current properties, input resistance, or capacitance, and this was reflected in a lack of differences in excitability and specific action potential properties. These results support the concept that, in contrast to positive feedback, steroid-negative feedback regulation of GnRH neurons in both sexes is likely conveyed to GnRH neurons via mechanisms that do not induce major changes in the biophysical properties of these cells.

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.

The role of non-neuronal cells in hypogonadotropic hypogonadism

The hypothalamic-pituitary-gonadal axis is controlled by gonadotropin-releasing hormone (GnRH) released by the hypothalamus. Disruption of this system leads to impaired reproductive maturation and function, a condition known as hypogonadotropic hypogonadism (HH). Most studies to date have focused on genetic causes of HH that impact neuronal development and function. However, variants may also impact the functioning of non-neuronal cells known as glia. Glial cells make up 50% of brain cells of humans, primates, and rodents. They include radial glial cells, microglia, astrocytes, tanycytes, oligodendrocytes, and oligodendrocyte precursor cells. Many of these cells influence the hypothalamic neuroendocrine system controlling fertility. Indeed, glia regulate GnRH neuronal activity and secretion, acting both at their cell bodies and their nerve endings. Recent work has also made clear that these interactions are an essential aspect of how the HPG axis integrates endocrine, metabolic, and environmental signals to control fertility. Recognition of the clinical importance of interactions between glia and the GnRH network may pave the way for the development of new treatment strategies for dysfunctions of puberty and adult fertility.

Firing patterns of gonadotropin-releasing hormone neurons are sculpted by their biologic state

Gonadotropin-releasing hormone (GnRH) neurons form the final pathway for the central neuronal control of fertility. GnRH is released in pulses that vary in frequency in females, helping drive hormonal changes of the reproductive cycle. In the common fertility disorder polycystic ovary syndrome (PCOS), persistent high-frequency hormone release is associated with disrupted cycles. We investigated long- and short-term action potential patterns of GnRH neurons in brain slices before and after puberty in female control and prenatally androgenized (PNA) mice, which mimic aspects of PCOS. A Monte Carlo (MC) approach was used to randomize action potential interval order. Dataset distributions were analysed to assess (i) if organization persists in GnRH neuron activity in vitro, and (ii) to determine if any organization changes with development and/or PNA treatment. GnRH neurons in adult control, but not PNA, mice produce long-term patterns different from MC distributions. Short-term patterns differ from MC distributions before puberty but become absorbed into the distributions with maturation, and the distributions narrow. These maturational changes are blunted by PNA treatment. Firing patterns of GnRH neurons in brain slices thus maintain organization dictated at least in part by the biologic status of the source and are disrupted in models of disease.

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.

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.

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.

Modulation of Gonadotropin-Releasing Hormone Neuron Activity and Secretion in Mice by Non-peptide Neurotransmitters, Gasotransmitters, and Gliotransmitters

Gonadotropin-releasing hormone (GnRH) neuron activity and GnRH secretion are essential for fertility in mammals. Here, I review findings from mouse studies on the direct modulation of GnRH neuron activity and GnRH secretion by non-peptide neurotransmitters (GABA, glutamate, dopamine, serotonin, norepinephrine, epinephrine, histamine, ATP, adenosine, and acetylcholine), gasotransmitters (nitric oxide and carbon monoxide), and gliotransmitters (prostaglandin E2 and possibly GABA, glutamate, and ATP). These neurotransmitters, gasotransmitters, and gliotransmitters have been shown to directly modulate activity and/or GnRH secretion in GnRH neurons in vivo or ex vivo (brain slices), from postnatal through adult mice, or in embryonic or immortalized mouse GnRH neurons. However, except for GABA, nitric oxide, and prostaglandin E2, which appear to be essential for normal GnRH neuron activity, GnRH secretion, and fertility in males and/or females, the biological significance of their direct modulation of GnRH neuron activity and/or GnRH secretion in the central regulation of reproduction remains largely unknown and requires further exploration.

Changes in GABAergic Transmission to and Intrinsic Excitability of Gonadotropin-Releasing Hormone (GnRH) Neurons during the Estrous Cycle in Mice

Gonadotropin-releasing hormone (GnRH) neurons form the final common central output pathway controlling fertility and are regulated by steroid feedback. In females, estradiol feedback action varies between negative and positive; negative feedback typically regulates episodic GnRH release whereas positive feedback initiates a surge of GnRH, and subsequently luteinizing hormone (LH) release ultimately triggering ovulation. During the estrous cycle, changes between estradiol negative and positive feedback occur with cycle stage and time of day, with positive feedback in the late afternoon of proestrus in nocturnal species. To test the hypotheses that synaptic and intrinsic properties of GnRH neurons are regulated by cycle stage and time of day, we performed whole-cell patch-clamp studies of GnRH neurons in brain slices from mice at two times considered negative feedback (diestrous PM and proestrous AM) and during positive feedback (proestrous PM). GABAergic transmission can excite GnRH neurons and was higher in cells from proestrous PM mice than cells from proestrous AM mice and approached traditional significance levels relative to cells from diestrous PM mice. Action potential response to current injection was also greater in cells from proestrous PM mice than the other two groups. Interestingly, the hormonal milieu of proestrous AM provided stronger negative feedback on both GnRH neuron excitability and GABAergic postsynaptic current (PSC) amplitude than diestrous PM. These observations demonstrate elements of both synaptic and intrinsic properties of GnRH neurons are regulated in a cycle-dependent manner and provide insight into the neurobiological mechanisms underlying cyclic changes in neuroendocrine function among states of estradiol negative and positive feedback.

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.

Progesterone administration does not acutely alter LH pulse secretion in the mid-follicular phase in women

It remains unclear how rapidly progesterone suppresses luteinizing hormone (LH) pulse frequency in women. Previous studies suggested that progesterone markedly increases LH pulse amplitude but does not slow LH pulse frequency within 10 h in estradiol‐pretreated women studied during the late follicular phase. However, this experimental paradigm may be a model of preovulatory physiology, and progesterone may have different effects at other times of the cycle. We studied regularly cycling, nonobese women without hyperandrogenism to assess the acute effect of progesterone during the midfollicular phase and in the absence of estradiol pretreatment. The study involved two admissions in separate cycles (cycle days 5–9). For each admission, either oral micronized progesterone (100 mg) or placebo was administered at 0900 h in a randomized, double‐blind fashion. Frequent blood sampling was performed between 0900 and 1900 h to define 10‐h LH pulsatility. Treatment crossover (placebo exchanged for progesterone and vice versa) occurred in a subsequent cycle. After an interim futility analysis, the study was halted after 7 women completed study. Mean progesterone concentrations after placebo and progesterone administration were 0.5 ± 0.1 (mean ± SD) and 6.7 ± 1.6 ng/mL, respectively. Compared to placebo, progesterone was not associated with a significant difference in 10‐h LH pulse frequency (0.79 ± 0.35 vs. 0.77 ± 0.28 pulses/h, P = 1.0) or amplitude (3.6 ± 2.8 vs. 4.3 ± 2.8 IU/L, P = 0.30). This study suggests that LH pulse frequency is not rapidly influenced by progesterone administration during the midfollicular phase.

Identification of Genes Enriched in GnRH Neurons by Translating Ribosome Affinity Purification and RNAseq in Mice

Gonadotropin-releasing hormone (GnRH) neurons are a nexus of fertility regulation. We used translating ribosome affinity purification coupled with RNA sequencing to examine messenger RNAs of GnRH neurons in adult intact and gonadectomized (GDX) male and female mice. GnRH neuron ribosomes were tagged with green fluorescent protein (GFP) and GFP-labeled polysomes isolated by immunoprecipitation, producing one RNA fraction enhanced for GnRH neuron transcripts and one RNA fraction depleted. Complementary DNA libraries were created from each fraction and 50-base, paired-end sequencing done and differential expression (enhanced fraction/depleted fraction) determined with a threshold of >1.5- or <0.66-fold (false discovery rate P ≤ 0.05). A core of ∼840 genes was differentially expressed in GnRH neurons in all treatments, including enrichment for Gnrh1 (∼40-fold), and genes critical for GnRH neuron and/or gonadotrope development. In contrast, non-neuronal transcripts were not enriched or were de-enriched. Several epithelial markers were also enriched, consistent with the olfactory epithelial origins of GnRH neurons. Interestingly, many synaptic transmission pathways were de-enriched, in accordance with relatively low innervation of GnRH neurons. The most striking difference between intact and GDX mice of both sexes was a marked downregulation of genes associated with oxidative phosphorylation and upregulation of glucose transporters in GnRH neurons from GDX mice. This may suggest that GnRH neurons switch to an alternate fuel to increase adenosine triphosphate production in the absence of negative feedback when GnRH release is elevated. Knowledge of the GnRH neuron translatome and its regulation can guide functional studies and can be extended to disease states, such as polycystic ovary syndrome.

Regulation of reproduction via tight control of gonadotropin hormone levels

Mammalian reproduction is controlled by the hypothalamic-pituitary-gonadal axis. GnRH from the hypothalamus regulates synthesis and secretion of gonadotropins, LH and FSH, which then control steroidogenesis and gametogenesis. In females, serum LH and FSH levels exhibit rhythmic changes throughout the menstrual or estrous cycle that are correlated with pulse frequency of GnRH. Lack of gonadotropins leads to infertility or amenorrhea. Dysfunctions in the tightly controlled ratio due to levels slightly outside the normal range occur in a larger number of women and are correlated with polycystic ovaries and premature ovarian failure. Since the etiology of these disorders is largely unknown, studies in cell and mouse models may provide novel candidates for investigations in human population. Hence, understanding the mechanisms whereby GnRH regulates gonadotropin hormone levels will provide insight into the physiology and pathophysiology of the reproductive system. This review discusses recent advances in our understanding of GnRH regulation of gonadotropin synthesis.

Progesterone-Mediated Inhibition of the GnRH Pulse Generator: Differential Sensitivity as a Function of Sleep Status

CONTEXT

During normal, early puberty, luteinizing hormone (LH) pulse frequency is low while awake but increases during sleep. Mechanisms underlying such changes are unclear, but a small study in early pubertal girls suggested that differential wake-sleep sensitivity to progesterone negative feedback plays a role.

OBJECTIVE

To test the hypothesis that progesterone acutely reduces waking LH pulse frequency more than sleep-associated pulse frequency in late pubertal girls.

DESIGN

Randomized, placebo-controlled, double-blinded crossover study.

SETTING

Academic clinical research unit.

PARTICIPANTS

Eleven normal, postmenarcheal girls, ages 12 to 15 years.

INTERVENTION

Subjects completed two 18-hour admissions in separate menstrual cycles (cycle days 6 to 11). Frequent blood sampling for LH assessment was performed at 1800 to 1200 hours; sleep was encouraged at 2300 to 0700 hours. Either oral micronized progesterone (0.8 mg/kg/dose) or placebo was given at 0700, 1500, 2300, and 0700 hours, before and during the first admission. A second admission, performed at least 2 months later, was identical to the first except that placebo was exchanged for progesterone or vice versa (treatment crossover).

MAIN OUTCOME MEASURES

LH pulse frequency during waking and sleeping hours.

RESULTS

Progesterone reduced waking LH pulse frequency by 26% (P = 0.019), with no change observed during sleep (P = 0.314). The interaction between treatment condition (progesterone vs placebo) and sleep status (wake vs sleep) was highly significant (P = 0.007).

CONCLUSIONS

In late pubertal girls, progesterone acutely reduced waking LH pulse frequency more than sleep-associated pulse frequency. Differential wake-sleep sensitivity to progesterone negative feedback may direct sleep-wake LH pulse frequency changes across puberty.

Influence of Sleep Stage on LH Pulse Initiation in the Normal Late Follicular Phase and in Polycystic Ovary Syndrome

OBJECTIVE

During the early follicular phase, sleep-related luteinizing hormone (LH) pulse initiation is positively associated with brief awakenings but negatively associated with rapid eye movement (REM) sleep. The relationship between sleep architecture and LH pulse initiation has not been assessed in other cycle stages or in women with polycystic ovary syndrome (PCOS).

DESIGN AND METHODS

We performed concomitant frequent blood sampling (LH pulse analysis) and polysomnography on 8 normal women (cycle day 7-11) and 7 women with PCOS (at least cycle day 7).

RESULTS

In the normal women, the 5 min preceding LH pulses contained more wake epochs and fewer REM epochs than the 5 min preceding randomly determined time points (wake: 22.3 vs. 9.1%, p = 0.0111; REM: 4.4 vs. 18.8%, p = 0.0162). However, LH pulse initiation was not related to wake or REM epochs in PCOS; instead, the 5 min preceding LH pulses contained more slow-wave sleep (SWS) than the 5 min before random time points (20.9 vs. 6.7%, p = 0.0089). Compared to the normal subjects, the women with PCOS exhibited a higher REM-associated LH pulse frequency (p = 0.0443) and a lower proportion of wake epochs 0-5 min before LH pulses (p = 0.0205).

CONCLUSIONS

Sleep-related inhibition of LH pulse generation during the later follicular phase is normally weakened by brief awakenings and strengthened by REM sleep. In women with PCOS, LH pulse initiation is not appropriately discouraged by REM sleep and may be encouraged by SWS; these abnormalities may contribute to a high sleep-related LH pulse frequency in PCOS.

GnRH Neurons on LSD: A Year of Rejecting Hypotheses That May Have Made Karl Popper Proud

Gonadotropin-releasing hormone (GnRH) neurons are critical to many aspects of fertility regulation, from producing episodic release critical to both sexes, to providing a central signal to induce the ovulatory cascade in females. This year saw progress through the rejection, and occasional support, of hypotheses in understanding how GnRH neurons contribute to these processes. This brief review provides one laboratory's view of new insights into possible roles for these cells in development, adult reproductive function, and what may go wrong with GnRH neurons in some cases of infertility.

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.

Progesterone has rapid positive feedback actions on LH release but fails to reduce LH pulse frequency within 12 h in estradiol-pretreated women

In women, progesterone suppresses luteinizing hormone (LH) (gonadotropin‐releasing hormone) pulse frequency, but how rapidly this occurs is unknown. In estradiol‐pretreated women in the late follicular phase, progesterone administration at 1800 did not slow sleep‐associated LH pulse frequency. However, mechanisms controlling LH pulse frequency may differ according to sleep status; and we thus hypothesized that progesterone acutely suppresses waking LH pulse frequency. This was a randomized, double‐blind, crossover study of LH secretory responses to progesterone versus placebo administered at 0600. We studied 12 normal women in the late follicular phase (cycle days 7–11), pretreated with 3 days of transdermal estradiol (0.2 mg/day). Subjects underwent a 24‐h blood sampling protocol (starting at 2000) and received either 100 mg oral micronized progesterone or placebo at 0600. In a subsequent menstrual cycle, subjects underwent an identical protocol except that oral progesterone was exchanged for placebo or vice versa. Changes in 10‐h LH pulse frequency were similar between progesterone and placebo. However, mean LH, LH pulse amplitude, and mean follicle‐stimulating hormone exhibited significantly greater increases with progesterone. Compared to our previous study (progesterone administered at 1800), progesterone administration at 0600 was associated with a similar increase in mean LH, but a less pronounced increase in LH pulse amplitude. We conclude that, in estradiol‐pretreated women in the late follicular phase, a single dose of progesterone does not suppress waking LH pulse frequency within 12 h, but it acutely amplifies mean LH and LH pulse amplitude – an effect that may be influenced by sleep status and/or time of day.

Independent relationship between body mass index and LH peak value of GnRH stimulation test in ICPP girls: A cross-sectional study

The effect of obesity on idiopathic central precocious puberty (ICPP) girls is still under discussion. The relationship between body mass index (BMI) and sexual hormone levels of gonadotropin-releasing hormone (GnRH) stimulation test in ICPP girls is controversial and the underlying mechanism is unclear. This study aims to further explore the independent effect of excess adiposity on peak luteinizing hormone (LH) level of stimulation test in ICPP girls and the role of other related factors. A retrospective cross-sectional study was performed on 618 girls diagnosed as having ICPP, including 355 cases of normal weight, 99 cases of overweight and 164 cases of obese. The results showed that obese group had more progressed Tanner stage and no significant difference (P=0.28) in LH peak was found as basal LH value was used as a covariate. The obese group had higher total testosterone (TT), adrenocorticotrophic hormone (ACTH), 17-α hydroxyprogesterone (17-αOHP) and androstendione (AN), with significantly increased fasting insulin (FIN) and homeostasis model of assessment for insulin resistance index (HOMA-IR). Stratified analysis showed inconsistency of the relationship between BMI-standard deviation score (BMI-SDS) and LH peak in different Tanner stages (P for interaction=0.017). Further smoothing plot showed linear and non-linear relationship between BMI-SDS and LH peak in three Tanner stages. Then linear regression model was used to analyze the relationship between BMI-SDS and LH peak in different Tanner stages, with and without different confounding factors being adjusted. In B2 stage, BMI-SDS was negatively associated with LH peak. In B3 stage, when BMI-SDS <1.5, as BMI-SDS increased, the level of LH peak decreased (model I: β=-1.8, 95% CI=-4.7 to 1.1, P=0.214). When BMI-SDS ≥1.5, BMI-SDS was significantly positively associated with LH peak (model I: β=4.5, 95% CI=1.7 to 7.4, P=0.002). In B4 stage, when BMI-SDS <1.5, BMI-SDS was negatively associated with LH peak (model I: β=-11.6, 95% CI=-22.7 to-0.5, P=0.049). When BMI-SDS ≥1.5, BMI-SDS was positively associated with LH peak (model I: β=-4.2, 95% CI=-3.3 to 11.7, P=0.28). It is concluded that there is an independent correlation between BMI-SDS and LH peak of stimulation test in ICPP girls, their relationships are different in different Tanner stages, and the effect of BMI-SDS can be affected by adrenal androgens, estradiol and glucose metabolism parameters.

Hypothalamic transcriptional expression of the kisspeptin system and sex steroid receptors differs among polycystic ovary syndrome rat models with different endocrine phenotypes

OBJECTIVES:

Polycystic ovary syndrome is a heterogeneous endocrine disorder that affects reproductive-age women. The mechanisms underlying the endocrine heterogeneity and neuroendocrinology of polycystic ovary syndrome are still unclear. In this study, we investigated the expression of the kisspeptin system and gonadotropin-releasing hormone pulse regulators in the hypothalamus as well as factors related to luteinizing hormone secretion in the pituitary of polycystic ovary syndrome rat models induced by testosterone or estradiol.

METHODS:

A single injection of testosterone propionate (1.25 mg) (n=10) or estradiol benzoate (0.5 mg) (n=10) was administered to female rats at 2 days of age to induce experimental polycystic ovary syndrome. Controls were injected with a vehicle (n=10). Animals were euthanized at 90-94 days of age, and the hypothalamus and pituitary gland were used for gene expression analysis.

RESULTS:

Rats exposed to testosterone exhibited increased transcriptional expression of the androgen receptor and estrogen receptor-β and reduced expression of kisspeptin in the hypothalamus. However, rats exposed to estradiol did not show any significant changes in hormone levels relative to controls but exhibited hypothalamic downregulation of kisspeptin, tachykinin 3 and estrogen receptor-α genes and upregulation of the gene that encodes the kisspeptin receptor.

CONCLUSIONS:

Testosterone- and estradiol-exposed rats with different endocrine phenotypes showed differential transcriptional expression of members of the kisspeptin system and sex steroid receptors in the hypothalamus. These differences might account for the different endocrine phenotypes found in testosterone- and estradiol-induced polycystic ovary syndrome rats.

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.

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.

High-fat diets exaggerate endocrine and metabolic phenotypes in a rat model of DHEA-induced PCOS

Polycystic ovary syndrome (PCOS) is a complex endocrine and metabolic disorder with unclear etiology and unsatisfactory management. Effects of diets on the phenotype of PCOS were not fully understood. In the present study, we applied 45 and 60% high-fat diets (HFDs) on a rat model of PCOS induced by postnatal DHEA injection. We found that both DHEA and DHEA+HFDs rats exhibited reproductive abnormalities, including hyperandrogenism, irregular cycles and polycystic ovaries. The addition of HFDs, especially 60% HFDs, exaggerated morphological changes of ovaries and a number of metabolic changes, including increased body weight and body fat content, impaired glucose tolerance and increased serum insulin levels. Results from qPCR showed that DHEA-induced increased expression of hypothalamic androgen receptor and LH receptor were reversed by the addition of 60% HFDs. In contrast, the ovarian expression of LH receptor and insulin receptor mRNA was upregulated only with the addition of 60% HFDs. These findings indicated that DHEA and DHEA+HFDs might influence PCOS phenotypes through distinct mechanisms: DHEA affects the normal function of hypothalamus-pituitary-ovarian axis through LH, whereas the addition of HFDs exaggerated endocrine and metabolic dysfunction through ovarian responses to insulin-related mechanisms. We concluded that the addition of HFDs yielded distinct phenotypes of DHEA-induced PCOS and could be used for studies on both reproductive and metabolic features of the syndrome.

A Novel Letrozole Model Recapitulates Both the Reproductive and Metabolic Phenotypes of Polycystic Ovary Syndrome in Female Mice

Polycystic ovary syndrome (PCOS) pathophysiology is poorly understood, due partly to lack of PCOS animal models fully recapitulating this complex disorder. Recently, a PCOS rat model using letrozole (LET), a nonsteroidal aromatase inhibitor, mimicked multiple PCOS phenotypes, including metabolic features absent in other models. Given the advantages of using genetic and transgenic mouse models, we investigated whether LET produces a similar PCOS phenotype in mice. Pubertal female C57BL/6N mice were treated for 5 wk with LET, which resulted in increased serum testosterone and normal diestrus levels of estradiol, similar to the hyperandrogenemia and follicular phase estrogen levels of PCOS women. As in PCOS, ovaries from LET mice were larger, polycystic, and lacked corpora lutea versus controls. Most LET females were acyclic, and all were infertile. LET females displayed elevated serum LH levels and higher Lhb mRNA in the pituitary. In contrast, serum FSH and Fshb were significantly reduced in LET females, demonstrating differential effects on gonadotropins, as in PCOS. Within the ovary, LET females had higher Cyp17, Cyp19, and Fsh receptor mRNA expression. In the hypothalamus, LET females had higher kisspeptin receptor mRNA expression but lower progesterone receptor mRNA levels. LET females also gained more weight than controls, had increased abdominal adiposity and adipocyte size, elevated adipose inflammatory mRNA levels, and impaired glucose tolerance, mirroring the metabolic phenotype in PCOS women. This is the first report of a LET paradigm in mice that recapitulates both reproductive and metabolic PCOS phenotypes and will be useful to genetically probe the PCOS condition.