Development of a methodology for and assessment of pulsatile luteinizing hormone secretion in juvenile and adult male mice

POMC neurons control fertility through differential signaling of MC4R in Kisspeptin neurons

Inactivating mutations in the melanocortin 4 receptor ( MC4R ) gene cause monogenic obesity. Interestingly, female patients also display various degrees of reproductive disorders, in line with the subfertile phenotype of MC4RKO female mice. However, the cellular mechanisms by which MC4R regulates reproduction are unknown. Kiss1 neurons directly stimulate gonadotropin-releasing hormone (GnRH) release through two distinct populations; the Kiss1 ARH neurons, controlling GnRH pulses, and the sexually dimorphic Kiss1 AVPV/PeN neurons controlling the preovulatory LH surge. Here, we show that Mc4r expressed in Kiss1 neurons is required for fertility in females. In vivo , deletion of Mc4r from Kiss1 neurons in female mice replicates the reproductive impairments of MC4RKO mice without inducing obesity. Conversely, reinsertion of Mc4r in Kiss1 neurons of MC4R null mice restores estrous cyclicity and LH pulsatility without reducing their obese phenotype. In vitro , we dissect the specific action of MC4R on Kiss1 ARH vs Kiss1 AVPV/PeN neurons and show that MC4R activation excites Kiss1 ARH neurons through direct synaptic actions. In contrast, Kiss1 AVPV/PeN neurons are normally inhibited by MC4R activation except under elevated estradiol levels, thus facilitating the activation of Kiss1 AVPV/PeN neurons to induce the LH surge driving ovulation in females. Our findings demonstrate that POMC ARH neurons acting through MC4R, directly regulate reproductive function in females by stimulating the "pulse generator" activity of Kiss1 ARH neurons and restricting the activation of Kiss1 AVPV/PeN neurons to the time of the estradiol-dependent LH surge, and thus unveil a novel pathway of the metabolic regulation of fertility by the melanocortin system.

NK3R signalling in the posterodorsal medial amygdala is involved in stress-induced suppression of pulsatile LH secretion in female mice

Psychosocial stress negatively impacts reproductive function by inhibiting pulsatile luteinizing hormone (LH) secretion. The posterodorsal medial amygdala (MePD) is responsible in part for processing stress and modulating the reproductive axis. Activation of the neurokinin 3 receptor (NK3R) suppresses the gonadotropin-releasing hormone (GnRH) pulse generator, under hypoestrogenic conditions, and NK3R activity in the amygdala has been documented to play a role in stress and anxiety. We investigate whether NK3R activation in the MePD is involved in mediating the inhibitory effect of psychosocial stress on LH pulsatility in ovariectomised female mice. First, we administered senktide, an NK3R agonist, into the MePD and monitored the effect on pulsatile LH secretion. We then delivered SB222200, a selective NK3R antagonist, intra-MePD in the presence of predator odour, 2,4,5-trimethylthiazole (TMT) and examined the effect on LH pulses. Senktide administration into the MePD dose-dependently suppresses pulsatile LH secretion. Moreover, NK3R signalling in the MePD mediates TMT-induced suppression of the GnRH pulse generator, which we verified using a mathematical model. The model verifies our experimental findings: (i) predator odour exposure inhibits LH pulses, (ii) activation of NK3R in the MePD inhibits LH pulses and (iii) NK3R antagonism in the MePD blocks stressor-induced inhibition of LH pulse frequency in the absence of ovarian steroids. These results demonstrate for the first time that NK3R neurons in the MePD mediate psychosocial stress-induced suppression of the GnRH pulse generator.

Glutamate neurotransmission from leptin receptor cells is required for typical puberty and reproductive function in female mice

The hypothalamic ventral premammillary nucleus (PMv) is a glutamatergic nucleus essential for the metabolic control of reproduction. However, conditional deletion of leptin receptor (LepRb) in vesicular glutamate transporter 2 (Vglut2) expressing neurons results in virtually no reproductive deficits. In this study, we determine the role of glutamatergic signaling from leptin responsive PMv neurons on puberty and fertility. We first assessed if stimulation of PMv neurons induces LH release in fed adult females. We used the stimulatory form of designer receptor exclusively activated by designer drugs (DREADDs) in LepRb-Cre mice. We collected blood sequentially before and for 1h after iv. clozapine-N-oxide injection. LH level increased in animals correctly targeted to the PMv, and LH level was correlated to the number of cFos immunoreactive neurons in the PMv. Next, females with deletion of Vglut2 in LepRb neurons (LepR∆VGlut2) showed delayed age of puberty, disrupted estrous cycles, increased GnRH concentration in the axon terminals and disrupted LH responses, suggesting impaired GnRH release. To assess if glutamate is required for PMv actions in pubertal development, we generated a Cre-induced reexpression of endogenous LepRb (LepRloxTB) with concomitant deletion of Vglut2 (Vglut2-floxed) mice. Rescue of Lepr and deletion of Vglut2 in the PMv was obtained by stereotaxic injection of an adeno-associated virus vector expressing Cre recombinase. Control LepRloxTB mice with PMv LepRb rescue showed vaginal opening, follicle maturation and became pregnant, while LepRloxTB;Vglut2flox mice showed no pubertal development. Our results indicate that glutamatergic signaling from leptin sensitive neurons regulates the reproductive axis, and that leptin action on pubertal development via PMv neurons requires Vglut2.

Cholinergic Control of GnRH Neuron Physiology and Luteinizing Hormone Secretion in Male Mice: Involvement of ACh/GABA Cotransmission

Gonadotropin-releasing hormone (GnRH)-synthesizing neurons orchestrate reproduction centrally. Early studies have proposed the contribution of acetylcholine (ACh) to hypothalamic control of reproduction, although the causal mechanisms have not been clarified. Here, we report that in vivo pharmacogenetic activation of the cholinergic system increased the secretion of luteinizing hormone (LH) in orchidectomized mice. 3DISCO immunocytochemistry and electron microscopy revealed the innervation of GnRH neurons by cholinergic axons. Retrograde viral labeling initiated from GnRH-Cre neurons identified the medial septum and the diagonal band of Broca as exclusive sites of origin for cholinergic afferents of GnRH neurons. In acute brain slices, ACh and carbachol evoked a biphasic effect on the firing rate in GnRH neurons, first increasing and then diminishing it. In the presence of tetrodotoxin, carbachol induced an inward current, followed by a decline in the frequency of miniature postsynaptic currents (mPSCs), indicating a direct influence on GnRH cells. RT-PCR and whole-cell patch-clamp studies revealed that GnRH neurons expressed both nicotinic (α4β2, α3β4, and α7) and muscarinic (M1-M5) AChRs. The nicotinic AChRs contributed to the nicotine-elicited inward current and the rise in firing rate. Muscarine via M1 and M3 receptors increased, while via M2 and M4 reduced the frequency of both mPSCs and firing. Optogenetic activation of channelrhodopsin-2-tagged cholinergic axons modified GnRH neuronal activity and evoked cotransmission of ACh and GABA from a subpopulation of boutons. These findings confirm that the central cholinergic system regulates GnRH neurons and activates the pituitary-gonadal axis via ACh and ACh/GABA neurotransmissions in male mice.

Male reproductive phenotypes of genetically altered laboratory mice (Mus musculus): a review based on pertinent literature from the last three decades

Laboratory mice (Mus musculus) are preferred animals for biomedical research due to the close relationship with humans in several aspects. Therefore, mice with diverse genetic traits have been generated to mimic human characteristics of interest. Some genetically altered mouse strains, on purpose or by accident, have reproductive phenotypes and/or fertility deviating from wild-type mice. The distinct reproductive phenotypes of genetically altered male mice mentioned in this paper are grouped based on reproductive organs, beginning with the brain (i.e., the hypothalamus and anterior pituitary) that regulates sexual maturity and development, the testis where male gametes and sex steroid hormones are produced, the epididymis, the accessory sex glands, and the penis which involve in sperm maturation, storage, and ejaculation. Also, distinct characteristics of mature sperm from genetically altered mice are described here. This repository will hopefully be a valuable resource for both humans, in terms of future biomedical research, and mice, in the aspect of the establishment of optimal sperm preservation protocols for individual mouse strains.

Development of a reporter gene-based assay for the bioactivity determination of rhLH pharmaceutical products

To establish an in vitro biological activity detection method for luteinizing hormone (LH), the hLHCGR-CREB-HEK293 cell line was constructed to stably express human luteinizing hormone/chorionic gonadotropin receptor (hLHCGR). After optimization, the rhLH starting working concentration was 800 mIU/mL with 4-fold serial dilutions, 10 concentrations and an incubation time of 5 h. The method was confirmed to be highly specific, with good accuracy, precision and linearity, meeting the needs of process research and release testing, and can be used as a routine detection method for LH biological activity. With the increasing demand for research and development of rhLH biologically similar drugs, establishing a stable and simple activity assay method to evaluate the biological activity of rhLH can provide technical support for quality control of rhLH products and powerful tools for comparability research of similar products.

Neuroendocrine effects of the duper mutation in Syrian hamsters: a role for Cryptochrome 1

Molecular and physiological determinants of the timing of reproductive events, including the pre-ovulatory LH surge and seasonal fluctuations in fertility, are incompletely understood. We used the Cryptochrome 1-deficient duper mutant to examine the role of this core circadian clock gene in Syrian hamsters. We find that the phase of the LH surge and its stability upon shifts of the light: dark cycle are altered in duper mutants. The intensity of immunoreactive PER1 in GnRH cells of the preoptic area peaks earlier in the day in duper than wild type hamsters. We note that GnRH fibers coursing through the suprachiasmatic nucleus (SCN) contact vasopressin- and VIP-immunoreactive cells, suggesting a possible locus of circadian control of the LH surge. Unlike wild types, duper hamsters do not regress their gonads within 8 weeks of constant darkness, despite evidence of melatonin secretion during the subjective night. In light of the finding that the duper allele is a stop codon in Cryptochrome 1, our results suggest important neuroendocrine functions of this core circadian clock gene.

Social isolation and aggression training lead to escalated aggression and hypothalamus-pituitary-gonad axis hyperfunction in mice

Although the participation of sex hormones and sex hormone-responsive neurons in aggressive behavior has been extensively studied, the role of other systems within the hypothalamus-pituitary-gonadal (HPG) axis remains elusive. Here we assessed how the gonadotropin-releasing hormone (GnRH) and kisspeptin systems are impacted by escalated aggression in male mice. We used a combination of social isolation and aggression training (IST) to exacerbate mice's aggressive behavior. Next, low-aggressive (group-housed, GH) and highly aggressive (IST) mice were compared regarding neuronal activity in the target populations and hormonal levels, using immunohistochemistry and ELISA, respectively. Finally, we used pharmacological and viral approaches to manipulate neuropeptide signaling and expression, subsequently evaluating its effects on behavior. IST mice exhibited enhanced aggressive behavior compared to GH controls, which was accompanied by elevated neuronal activity in GnRH neurons and arcuate nucleus kisspeptin neurons. Remarkably, IST mice presented an increased number of kisspeptin neurons in the anteroventral periventricular nucleus (AVPV). In addition, IST mice exhibited elevated levels of luteinizing hormone (LH) in serum. Accordingly, activation and blockade of GnRH receptors (GnRHR) exacerbated and reduced aggression, respectively. Surprisingly, kisspeptin had intricate effects on aggression, i.e., viral ablation of AVPV-kisspeptin neurons impaired the training-induced rise in aggressive behavior whereas kisspeptin itself strongly reduced aggression in IST mice. Our results indicate that IST enhances aggressive behavior in male mice by exacerbating HPG-axis activity. Particularly, increased GnRH neuron activity and GnRHR signaling were found to underlie aggression whereas the relationship with kisspeptin remains puzzling.

Single-Cell Transcriptomics Identifies Pituitary Gland Changes in Diet-Induced Obesity in Male Mice

Obesity is a chronic disease with increasing prevalence worldwide. Obesity leads to an increased risk of heart disease, stroke, and diabetes, as well as endocrine alterations, reproductive disorders, changes in basal metabolism, and stress hormone production, all of which are regulated by the pituitary. In this study, we performed single-cell RNA sequencing of pituitary glands from male mice fed control and high-fat diet (HFD) to determine obesity-mediated changes in pituitary cell populations and gene expression. We determined that HFD exposure is associated with dramatic changes in somatotrope and lactotrope populations, by increasing the proportion of somatotropes and decreasing the proportion of lactotropes. Fractions of other hormone-producing cell populations remained unaffected. Gene expression changes demonstrated that in HFD, somatotropes became more metabolically active, with increased expression of genes associated with cellular respiration, and downregulation of genes and pathways associated with cholesterol biosynthesis. Despite a lack of changes in gonadotrope fraction, genes important in the regulation of gonadotropin hormone production were significantly downregulated. Corticotropes and thyrotropes were the least affected in HFD, while melanotropes exhibited reduced proportion. Lastly, we determined that changes in plasticity and gene expression were associated with changes in hormone levels. Serum prolactin was decreased corresponding to reduced lactotrope fraction, while lower luteinizing hormone and follicle-stimulating hormone in the serum corresponded to a decrease in transcription and translation. Taken together, our study highlights diet-mediated changes in pituitary gland populations and gene expression that play a role in altered hormone levels in obesity.

Chemogenetic activation of PVN CRH neurons disrupts the estrous cycle and LH dynamics in female mice

Introduction

The impact of stress on reproductive function is significant. Hypothalamic paraventricular nucleus (PVN) corticotrophin-releasing hormone (CRH) plays a major role in regulating the stress response. Understanding how the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-gonadal (HPG) axis interact is crucial for comprehending how stress can lead to reproductive dysfunction. However, whether stress influences reproductive function via modulating PVN CRH or HPA sequelae is not fully elucidated.

Methods

In this study, we investigated the impact of chemogenetic activation of PVN CRH neurons on reproductive function. We chronically and selectively stimulated PVN CRH neurons in female CRH-Cre mice using excitatory designer receptor exclusively activated by designer drugs (DREADDs) viral constructs, which were bilaterally injected into the PVN. The agonist compound-21 (C21) was delivered through the drinking water. We determined the effects of DREADDs activation of PVN CRH neurons on the estrous cycles, LH pulse frequency in diestrus and metestrus and LH surge in proestrus mice. The effect of long-term C21 administration on basal corticosterone secretion and the response to acute restraint stress during metestrus was also examined. Additionally, computer simulations of a mathematical model were used to determine the effects of DREADDs activation of PVN CRH neurons, simulating chronic stress, on the physiological parameters examined experimentally.

Results

As a result, and consistent with our mathematical model predictions, the length of the estrous cycle was extended, with an increase in the time spent in estrus and metestrus, and a decrease in proestrus and diestrus. Additionally, the frequency of LH pulses during metestrus was decreased, but unaffected during diestrus. The occurrence of the preovulatory LH surge during proestrus was disrupted. The basal level of corticosterone during metestrus was not affected, but the response to acute restraint stress was diminished after long-term C21 application.

Discussion

These data suggest that PVN CRH neurons play a functional role in disrupting ovarian cyclicity and the preovulatory LH surge, and that the activity of the GnRH pulse generator remains relatively robust during diestrus but not during metestrus under chronic stress exposure in accordance with our mathematical model predictions.

CRISPR-Cas9 knockdown of ESR1 in preoptic GABA-kisspeptin neurons suppresses the preovulatory surge and estrous cycles in female mice

Evidence suggests that estradiol-sensing preoptic area GABA neurons are involved in the preovulatory surge mechanism necessary for ovulation. In vivo CRISPR-Cas9 editing was used to achieve a 60-70% knockdown in estrogen receptor alpha (ESR1) expression by GABA neurons located within the regions of the rostral periventricular area of the third ventricle (RP3V) and medial preoptic nuclei (MPN) in adult female mice. Mice exhibited variable reproductive phenotypes with the only significant finding being mice with bilateral ESR1 deletion in RP3V GABA neurons having reduced cFos expression in gonadotropin-releasing hormone (GnRH) neurons at the time of the surge. One sub-population of RP3V GABA neurons expresses kisspeptin. Re-grouping ESR1-edited mice on the basis of their RP3V kisspeptin expression revealed a highly consistent phenotype; mice with a near-complete loss of kisspeptin immunoreactivity displayed constant estrus and failed to exhibit surge activation but retained pulsatile luteinizing hormone (LH) secretion. These observations demonstrate that ESR1-expressing GABA-kisspeptin neurons in the RP3V are essential for the murine preovulatory LH surge mechanism.

Genetic and immune determinants of E. coli liver abscess formation

Systemic infections can yield distinct outcomes in different tissues. In mice, intravenous inoculation of Escherichia coli leads to bacterial replication within liver abscesses, while other organs such as the spleen clear the pathogen. Abscesses are macroscopic necrotic regions that comprise the vast majority of the bacterial burden in the animal, yet little is known about the processes underlying their formation. Here, we characterize E. coli liver abscesses and identify host determinants of abscess susceptibility. Spatial transcriptomics revealed that liver abscesses are associated with heterogenous immune cell clusters comprised of macrophages, neutrophils, dendritic cells, innate lymphoid cells, and T-cells that surround necrotic regions of the liver. Abscess susceptibility is heightened in the C57BL lineage, particularly in C57BL/6N females. Backcross analyses demonstrated that abscess susceptibility is a polygenic trait inherited in a sex-dependent manner without direct linkage to sex chromosomes. As early as 1 d post infection, the magnitude of E. coli replication in the liver distinguishes abscess-susceptible and abscess-resistant strains of mice, suggesting that the immune pathways that regulate abscess formation are induced within hours. We characterized the early hepatic response with single-cell RNA sequencing and found that mice with reduced activation of early inflammatory responses, such as those lacking the LPS receptor TLR4 (Toll-like receptor 4), are resistant to abscess formation. Experiments with barcoded E. coli revealed that TLR4 mediates a tradeoff between abscess formation and bacterial clearance. Together, our findings define hallmarks of E. coli liver abscess formation and suggest that hyperactivation of the hepatic innate immune response drives liver abscess susceptibility.

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).

New Horizons: Gonadotropin-Releasing Hormone and Cognition

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for activating and maintaining the function of the hypothalamic-pituitary-gonadal axis, which controls the onset of puberty and fertility. Two recent studies suggest that, in addition to controlling reproduction, the neurons in the brain that produce GnRH are also involved in the control of postnatal brain maturation, odor discrimination, and adult cognition. This review will summarize the development and establishment of the GnRH system, with particular attention to the importance of its first postnatal activation, a phenomenon known as minipuberty, for later reproductive and nonreproductive functions. In addition, we will discuss the beneficial effects of restoring physiological (ie, pulsatile) GnRH levels on olfactory and cognitive alterations in preclinical Down syndrome and Alzheimer disease models, as well as the potential risks associated with long-term continuous (ie, nonphysiological) GnRH administration in certain disorders. Finally, this review addresses the intriguing possibility that pulsatile GnRH therapy may hold therapeutic potential for the management of some neurodevelopmental cognitive disorders and pathological aging in elderly people.

A role for GnRH in olfaction and cognition: Implications for veterinary medicine

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) is essential for the activation and maintenance of the function of the hypothalamic-pituitary-gonadal (HPG) axis, which controls the onset of puberty and fertility. Two provocative recent studies suggest that, in addition to control reproduction, the neurons in the brain that produce GnRH are also involved in the control postnatal brain maturation, odour discrimination and adult cognition. Long-acting GnRH antagonists and agonists are commonly used to control fertility and behaviour in veterinary medicine, primarily in males. This review puts into perspective the potential risks of these androgen deprivation therapies and immunization on olfactory and cognitive performances and well-aging in domestic animals, including pets. We will also discuss the results reporting beneficial effects of pharmacological interventions restoring physiological GnRH levels on olfactory and cognitive alterations in preclinical models of Alzheimer's disease, which shares many pathophysiological and behavioural hallmarks with canine cognitive dysfunction. These novel findings raise the intriguing possibility that pulsatile GnRH therapy holds therapeutic potential for the management of this behavioural syndrome affecting older dogs.

Remote Neuronal Activation Coupled with Automated Blood Sampling to Induce and Measure Circulating Luteinizing Hormone in Mice

Circulating luteinizing hormone (LH) levels are an essential index of the functioning of the hypothalamic-pituitary control of reproduction. The role of numerous inputs and neuronal populations in the modulation of LH release is still unknown. Measuring changes in LH levels in mice is often a challenge since they are easily disrupted by environmental stress. Current techniques to measure LH release and pulsatility require long-term training for mice to adapt to manipulation stress, certain restraint, the presence of the investigator, and working on individual animals, reducing its usefulness for many research questions. This paper presents a technique to remotely activate specific neuronal populations using Designer Receptor Exclusively Activated by Designer Drugs (DREADDs) technology coupled with automated sequential blood sampling in conscious, freely moving, and undisturbed mice. We first describe the stereotaxic surgery protocol to deliver adeno-associated virus (AAV) vectors expressing DREADDs to specific neuronal populations. Next, we describe the protocol for carotid artery and jugular vein cannulation and postsurgical connection to the CULEX automated blood sampling system. Finally, we describe the protocol for clozapine-N-oxide intravenous injection for remote neuronal activation and automated blood collection. This technique allows for programmed automated sampling every 5 min or longer for a given period, coupled with intravenous substance injection at a desired time point or duration. Overall, we found this technique to be a powerful approach for research on neuroendocrine control.

A delayed ovulation of progestin-primed ovarian stimulation (PPOS) by downregulating the LHCGR/PGR pathway

Progestin-primed ovarian stimulation (PPOS) is a new ovulation stimulation protocol, and its role in ovulation and regulatory mechanism is unclear. The clinical PPOS protocol was simulated in mice. The ovulated oocytes, estradiol, progesterone, and luteinizing hormone (LH) levels were analyzed at different hours after trigger. mRNA extraction and real-time PCR, hematoxylin and eosin staining, and immunofluorescence of ovaries were used to explore the involved signaling pathways. The PPOS group had a delayed ovulation at 12.5 h after trigger. Its suppressed LH level reduced the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) on the preovulatory follicles before trigger and significantly decreased the following progesterone synthesis, blood progesterone level, and progesterone receptor (PGR) expression within 4-6 h after trigger. Furthermore, the important ovulatory genes regulated by PGR including ADAMTS-1, VEGF-A, and EDN2 were downregulated, ultimately delaying the ovulation. PPOS suppresses the LH level before trigger and decreases the synthesis of progesterone after trigger, thus delaying the ovulation by downregulating the LHCGR-PGR pathway.

Female-specific pituitary gonadotrope dysregulation in mice with chronic focal epilepsy

Gonadotropin hormone release from the anterior pituitary is critical to regulating reproductive endocrine function. Clinical evidence has documented that people with epilepsy display altered levels of gonadotropin hormones, both acutely following seizures and chronically. Despite this relationship, pituitary function remains a largely understudied avenue in preclinical epilepsy research. Recently, we showed that females in the intrahippocampal kainic acid (IHKA) mouse model of temporal lobe epilepsy displayed changes in pituitary expression of gonadotropin hormone and gonadotropin-releasing hormone (GnRH) receptor genes. Circulating gonadotropin hormone levels, however, have yet to be measured in an animal model of epilepsy. Here, we evaluated the circulating levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), GnRH receptor (Gnrhr) gene expression, and sensitivity to exogenous GnRH in IHKA males and females. Although no changes in overall dynamics of pulsatile patterns of LH release were found in IHKA mice of either sex, estrus vs. diestrus changes in basal and mean LH levels were larger in IHKA females with prolonged, disrupted estrous cycles. In addition, IHKA females displayed increased pituitary sensitivity to GnRH and higher Gnrhr expression. The hypersensitivity to GnRH was observed on diestrus, but not estrus. Chronic seizure severity was not found to be correlated with LH parameters, and FSH levels were unchanged in IHKA mice. These results indicate that although there are changes in pituitary gene expression and sensitivity to GnRH in IHKA females, there may also be compensatory mechanisms that aid in maintaining gonadotropin release in the state of chronic epilepsy in this model.

Dax1 modulates ERα-dependent hypothalamic estrogen sensing in female mice

Coupling the release of pituitary hormones to the developmental stage of the oocyte is essential for female fertility. It requires estrogen to restrain kisspeptin (KISS1)-neuron pulsatility in the arcuate hypothalamic nucleus, while also exerting a surge-like effect on KISS1-neuron activity in the AVPV hypothalamic nucleus. However, a mechanistic basis for this region-specific effect has remained elusive. Our genomic analysis in female mice demonstrate that some processes, such as restraint of KISS1-neuron activity in the arcuate nucleus, may be explained by region-specific estrogen receptor alpha (ERα) DNA binding at gene regulatory regions. Furthermore, we find that the Kiss1-locus is uniquely regulated in these hypothalamic nuclei, and that the nuclear receptor co-repressor NR0B1 (DAX1) restrains its transcription specifically in the arcuate nucleus. These studies provide mechanistic insight into how ERα may control the KISS1-neuron, and Kiss1 gene expression, to couple gonadotropin release to the developmental stage of the oocyte.

Dynamics of pulsatile activities of arcuate kisspeptin neurons in aging female mice

Reproductive senescence is broadly observed across mammalian females, including humans, eventually leading to a loss of fertility. The pulsatile secretion of gonadotropin-releasing hormone (GnRH), which is essential for gonad function, is primarily controlled by kisspeptin neurons in the hypothalamic arcuate nucleus (ARC^kiss), the pulse generator of GnRH. The pulsatility of GnRH release, as assessed by the amount of circulating gonadotropin, is markedly reduced in aged animals, suggesting that the malfunctions of ARC^kiss may be responsible for reproductive aging and menopause-related disorders. However, the activity dynamics of ARC^kiss during the natural transition to reproductive senescence remain unclear. Herein, we introduce chronic in vivo Ca²⁺ imaging of ARC^kiss in female mice by fiber photometry to monitor the synchronous episodes of ARC^kiss (SEs^kiss), a known hallmark of GnRH pulse generator activity, from the fully reproductive to acyclic phase over 1 year. During the reproductive phase, we find that not only the frequency, but also the intensities and waveforms of individual SEs^kiss, vary depending on the stage of the estrus cycle. During the transition to reproductive senescence, the integrity of SEs^kiss patterns, including the frequency and waveforms, remains mostly unchanged, whereas the intensities tend to decline. These data illuminate the temporal dynamics of ARC^kiss activities in aging female mice. More generally, our findings demonstrate the utility of fiber-photometry-based chronic imaging of neuroendocrine regulators in the brain to characterize aging-associated malfunction.

Female scent accelerates growth of juvenile male mice

Exposing female house mice (Mus musculus) to male urinary scent accelerates their sexual development (Vandenbergh effect). Here, we tested whether exposing juvenile male mice to females' urine similarly influences male growth and size of their sexual organs. We exposed three-week old male house mice to female urine or water (control) for ca. three months. We found that female-exposed males grew significantly faster and gained more body mass than controls, despite all males being reared on a controlled diet, but we detected no differences in males' muscle mass or sexual organs. In contrast, exposing juvenile males to male urine had no effect their growth. We tested whether the males' accelerated growth imposed functional trade-offs on males' immune resistance to an experimental infection. We challenged the same male subjects with an avirulent bacterial pathogen (Salmonella enterica), but found no evidence that faster growth impacted their bacterial clearance, body mass or survival during infection compared to controls. Our results provide the first evidence to our knowledge that juvenile male mice accelerate their growth when exposed to the urine of adult females, though we found no evidence that increased growth had negative trade-offs on immune resistance to infectious disease.

Gold nanoparticle intratesticular injections as a potential animal sterilization tool: Long-term reproductive and toxicological implications

This study aimed to evaluate the gold nanoparticles (AuNPs) animal sterilizing potential after intratesticular injections and long-term adverse reproductive and systemic effects. Adult male Wistar rats were divided into control and gold nanoparticle (AuNPs) groups. The rats received 200µL of saline or AuNPs solution (16µg/mL) on experimental days 1 and 7 (ED1 and ED7). After 150 days, the testicular blood flow was measured, and the rats were mated with females. After mating, male animals were euthanized for histological, cellular, and molecular evaluations. The female fertility indices and fetal development were also recorded. The results indicated increased blood flow in the testes of treated animals. Testes from treated rats had histological abnormalities, shorter seminiferous epithelia, and oxidative stress. Although the sperm concentration was lower in the AuNP-treated rats, there were no alterations in sperm morphology. Animals exposed to AuNPs had decreased male fertility indices, and their offspring had lighter and less efficient placentas. Additionally, the anogenital distance was longer in female fetuses. There were no changes in the histology of the kidney and liver, the lipid profile, and the serum levels of LH, testosterone, AST, ALT, ALP, albumin, and creatinine. The primary systemic effect was an increase in MDA levels in the liver and kidney, with only the liver experiencing an increase in CAT activity. In conclusion, AuNPs have a long-term impact on reproduction with very slight alterations in animal health. The development of reproductive biotechnologies that eliminate germ cells or treat local cancers can benefit from using AuNPs.

Dissecting the KNDy hypothesis: KNDy neuron-derived kisspeptins are dispensable for puberty but essential for preserved female fertility and gonadotropin pulsatility

BACKGROUND

Kiss1 neurons in the hypothalamic arcuate-nucleus (ARC) play key roles in the control of GnRH pulsatility and fertility. A fraction of ARC Kiss1 neurons, termed KNDy, co-express neurokinin B (NKB; encoded by Tac2). Yet, NKB- and Kiss1-only neurons are also found in the ARC, while a second major Kiss1-neuronal population is present in the rostral hypothalamus. The specific contribution of different Kiss1 neuron sub-sets and kisspeptins originating from them to the control of reproduction and eventually other bodily functions remains to be fully determined.

METHODS

To tease apart the physiological roles of KNDy-born kisspeptins, conditional ablation of Kiss1 in Tac2-expressing cells was implemented in vivo. To this end, mice with Tac2 cell-specific Kiss1 KO (TaKKO) were generated and subjected to extensive reproductive and metabolic characterization.

RESULTS

TaKKO mice displayed reduced ARC kisspeptin content and Kiss1 expression, with greater suppression in females, which was detectable at infantile-pubertal age. In contrast, Tac2/NKB levels were fully preserved. Despite the drop of ARC Kiss1/kisspeptin, pubertal timing was normal in TaKKO mice of both sexes. However, young-adult TaKKO females displayed disturbed LH pulsatility and sex steroid levels, with suppressed basal LH and pre-ovulatory LH surges, early-onset subfertility and premature ovarian insufficiency. Conversely, testicular histology and fertility were grossly conserved in TaKKO males. Ablation of Kiss1 in Tac2-cells led also to sex-dependent alterations in body composition, glucose homeostasis, especially in males, and locomotor activity, specifically in females.

CONCLUSIONS

Our data document that KNDy-born kisspeptins are dispensable/compensable for puberty in both sexes, but required for maintenance of female gonadotropin pulsatility and fertility, as well as for adult metabolic homeostasis.

SIGNIFICANCE STATEMENT

Neurons in the hypothalamic arcuate nucleus (ARC) co-expressing kisspeptins and NKB, named KNDy, have been recently suggested to play a key role in pulsatile secretion of gonadotropins, and hence reproduction. However, the relative contribution of this Kiss1 neuronal-subset, vs. ARC Kiss1-only and NKB-only neurons, as well as other Kiss1 neuronal populations, has not been assessed in physiological settings. We report here findings in a novel mouse-model with elimination of KNDy-born kisspeptins, without altering other kisspeptin compartments. Our data highlights the heterogeneity of ARC Kiss1 populations and document that, while dispensable/compensable for puberty, KNDy-born kisspeptins are required for proper gonadotropin pulsatility and fertility, specifically in females, and adult metabolic homeostasis. Characterization of this functional diversity is especially relevant, considering the potential of kisspeptin-based therapies for management of human reproductive disorders.

Activating Transcription Factor 3 Stimulates Follicle-Stimulating Hormone-β Expression In Vitro But Is Dispensable for Follicle-Stimulating Hormone Production in Murine Gonadotropes In Vivo

Follicle-stimulating hormone (FSH), a dimeric glycoprotein produced by pituitary gonadotrope cells, regulates spermatogenesis in males and ovarian follicle growth in females. Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates FSHβ subunit gene (Fshb) transcription, though the underlying mechanisms are poorly understood. To address this gap in knowledge, we examined changes in pituitary gene expression in GnRH-deficient mice (hpg) treated with a regimen of exogenous GnRH that increases pituitary Fshb but not luteinizing hormone β (Lhb) messenger RNA levels. Activating transcription factor 3 (Atf3) was among the most upregulated genes. Activating transcription factor 3 (ATF3) can heterodimerize with members of the activator protein 1 family to regulate gene transcription. Co-expression of ATF3 with JunB stimulated murine Fshb, but not Lhb, promoter-reporter activity in homologous LβT2b cells. ATF3 also synergized with a constitutively active activin type I receptor to increase endogenous Fshb expression in these cells. Nevertheless, FSH production was intact in gonadotrope-specific Atf3 knockout [conditional knockout (cKO)] mice. Ovarian follicle development, ovulation, and litter sizes were equivalent between cKOs and controls. Testis weights and sperm counts did not differ between genotypes. Following gonadectomy, increases in LH secretion were enhanced in cKO animals. Though FSH levels did not differ between genotypes, post-gonadectomy increases in pituitary Fshb and gonadotropin α subunit expression were more pronounced in cKO than control mice. These data indicate that ATF3 can selectively stimulate Fshb expression in vitro but is not required for FSH production in vivo.

Altered GnRH neuron and ovarian innervation characterize reproductive dysfunction linked to the Fragile X messenger ribonucleoprotein (Fmr1) gene mutation

Introduction

Mutations in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene cause Fragile X Syndrome, the most common monogenic cause of intellectual disability. Mutations of FMR1 are also associated with reproductive disorders, such as early cessation of reproductive function in females. While progress has been made in understanding the mechanisms of mental impairment, the causes of reproductive disorders are not clear. FMR1-associated reproductive disorders were studied exclusively from the endocrine perspective, while the FMR1 role in neurons that control reproduction was not addressed.

Results

Here, we demonstrate that similar to women with FMR1 mutations, female Fmr1 null mice stop reproducing early. However, young null females display larger litters, more corpora lutea in the ovaries, increased inhibin, progesterone, testosterone, and gonadotropin hormones in the circulation. Ovariectomy reveals both hypothalamic and ovarian contribution to elevated gonadotropins. Altered mRNA and protein levels of several synaptic molecules in the hypothalamus are identified, indicating reasons for hypothalamic dysregulation. Increased vascularization of corpora lutea, higher sympathetic innervation of growing follicles in the ovaries of Fmr1 nulls, and higher numbers of synaptic GABAA receptors in GnRH neurons, which are excitatory for GnRH neurons, contribute to increased FSH and LH, respectively. Unmodified and ovariectomized Fmr1 nulls have increased LH pulse frequency, suggesting that Fmr1 nulls exhibit hyperactive GnRH neurons, regardless of the ovarian feedback.

Conclusion

These results reveal Fmr1 function in the regulation of GnRH neuron secretion, and point to the role of GnRH neurons, in addition to the ovarian innervation, in the etiology of Fmr1-mediated reproductive disorders.

Deletion of Androgen Receptor in LepRb Cells Improves Estrous Cycles in Prenatally Androgenized Mice

Androgens are steroid hormones crucial for sexual differentiation of the brain and reproductive function. In excess, however, androgens may decrease fertility as observed in polycystic ovary syndrome, a common endocrine disorder characterized by oligo/anovulation and/or polycystic ovaries. Hyperandrogenism may also disrupt energy homeostasis, inducing higher central adiposity, insulin resistance, and glucose intolerance, which may exacerbate reproductive dysfunction. Androgens bind to androgen receptors (ARs), which are expressed in many reproductive and metabolic tissues, including brain sites that regulate the hypothalamo-pituitary-gonadal axis and energy homeostasis. The neuronal populations affected by androgen excess, however, have not been defined. We and others have shown that, in mice, AR is highly expressed in leptin receptor (LepRb) neurons, particularly in the arcuate (ARH) and the ventral premammillary nuclei (PMv). Here, we assessed if LepRb neurons, which are critical in the central regulation of energy homeostasis and exert permissive actions on puberty and fertility, have a role in the pathogenesis of female hyperandrogenism. Prenatally androgenized (PNA) mice lacking AR in LepRb cells (LepRbΔAR) show no changes in body mass, body composition, glucose homeostasis, or sexual maturation. They do show, however, a remarkable improvement of estrous cycles combined with normalization of ovary morphology compared to PNA controls. Our findings indicate that the prenatal androgenization effects on adult reproductive physiology (ie, anestrus and anovulation) are mediated by a subpopulation of LepRb neurons directly sensitive to androgens. They also suggest that the effects of hyperandrogenism on sexual maturation and reproductive function in adult females are controlled by distinct neural circuits.

Long-term effects of prenatal undernutrition on female rat hypothalamic KNDy neurons

The nutritional environment during development periods induces metabolic programming, leading to metabolic disorders and detrimental influences on human reproductive health. This study aimed to determine the long-term adverse effect of intrauterine malnutrition on the reproductive center kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus (ARC) of female offspring. Twelve pregnant rats were divided into ad-lib-fed (control, n = 6) and 50% undernutrition (UN, n = 6) groups. The UN group was restricted to 50% daily food intake of the control dams from gestation day 9 until term delivery. Differences between the two groups in terms of various maternal parameters, including body weight (BW), pregnancy duration, and litter size, as well as birth weight, puberty onset, estrous cyclicity, pulsatile luteinizing hormone (LH) secretion, and hypothalamic gene expression of offspring, were determined. Female offspring of UN dams exhibited low BW from birth to 3 weeks, whereas UN offspring showed signs of precocious puberty; hypothalamic Tac3 (a neurokinin B gene) expression was increased in prepubertal UN offspring, and the BW at the virginal opening was lower in UN offspring than that in the control group. Interestingly, the UN offspring showed significant decreases in the number of KNDy gene-expressing cells after 29 weeks of age, but the number of ARC kisspeptin-immunoreactive cells, pulsatile LH secretions, and estrous cyclicity were comparable between the groups. In conclusion, intrauterine undernutrition induced various changes in KNDy gene expression depending on the life stage. Thus, intrauterine undernutrition affected hypothalamic developmental programming in female rats.

Male minipuberty involves the gonad-independent activation of preoptic nNOS neurons

BACKGROUND

The maturation of the hypothalamic-pituitary-gonadal (HPG) axis is crucial for the establishment of reproductive function. In female mice, neuronal nitric oxide synthase (nNOS) activity appears to be key for the first postnatal activation of the neural network promoting the release of gonadotropin-releasing hormone (GnRH), i.e. minipuberty. However, in males, the profile of minipuberty as well as the role of nNOS-expressing neurons remain unexplored.

METHODS

nNOS-deficient and wild-type mice were studied during postnatal development. The expression of androgen (AR) and estrogen receptor alpha (ERα) as well as nNOS phosphorylation were evaluated by immunohistochemistry in nNOS neurons in the median preoptic nucleus (MePO), where most GnRH neuronal cell bodies reside, and the hormonal profile of nNOS-deficient male mice was assessed using previously established radioimmunoassay and ELISA methods. Gonadectomy and pharmacological manipulation of ERα were used to elucidate the mechanism of minipubertal nNOS activation and the maturation of the HPG axis.

RESULTS

In male mice, minipubertal FSH release occurred at P23, preceding the LH surge at P30, when balanopreputial separation occurs. Progesterone and testosterone remained low during minipuberty, increasing around puberty, whereas estrogen levels were high throughout postnatal development. nNOS neurons showed a sharp increase in Ser¹⁴¹² phosphorylation of nNOS at P23, a phenomenon that occurred even in the absence of the gonads. In male mice, nNOS neurons did not appear to express AR, but abundantly expressed ERα throughout postnatal development. Selective pharmacological blockade of ERα during the infantile period blunted Ser¹⁴¹² phosphorylation of nNOS at P23.

CONCLUSIONS

Our results show that the timing of minipuberty differs in male mice when compared to females, but as in the latter, nNOS activity in the preoptic region plays a role in this process. Additionally, akin to male non-human primates, the profile of minipuberty in male mice is shaped by sex-independent mechanisms, and possibly involves extragonadal estrogen sources.

Central Irisin Signaling Is Required for Normal Timing of Puberty in Female Mice

Timing of puberty requires exquisite coordination of genes, hormones, and brain circuitry. An increasing level of body adiposity, signaled to the brain via the fat-derived hormone leptin, is recognized as a major factor controlling puberty onset. However, it is clear that leptin is not the only metabolic cue regulating puberty, and that developmental regulation of this process also involves tissues other than adipose, with muscle development potentially playing a role in the timing of puberty. The proteolytic processing of fibronectin type 3 domain-containing protein 5 (FNDC5) releases a hormone, irisin. Irisin is primarily produced by muscle and is released into circulation, where levels increase dramatically as puberty approaches. We investigated the effects of a global deletion of the Fndc5 gene on pubertal timing. The absence of irisin induced a delay in puberty onset in female knockout mice compared with controls, without affecting body weight or gonadotropin-releasing hormone (GnRH) neuronal density. We next treated pre-pubertal wild-type male and female mice with an irisin receptor antagonist, cilengitide, for 7 days and observed a delay in first estrus occurrence compared to vehicle-treated control mice. Male puberty timing was unaffected. Next, we deleted the irisin receptor (integrin subunit alpha V) in all forebrain neurons and found a delay in the occurrence of first estrus in knockout females compared to controls. Taken together, these data suggest irisin plays a role in the timing of puberty onset in female mice via a centrally mediated mechanism.

Definition of the estrogen negative feedback pathway controlling the GnRH pulse generator in female mice

The mechanisms underlying the homeostatic estrogen negative feedback pathway central to mammalian fertility have remained unresolved. Direct measurement of gonadotropin-releasing hormone (GnRH) pulse generator activity in freely behaving mice with GCaMP photometry demonstrated striking estradiol-dependent plasticity in the frequency, duration, amplitude, and profile of pulse generator synchronization events. Mice with Cre-dependent deletion of ESR1 from all kisspeptin neurons exhibited pulse generator activity identical to that of ovariectomized wild-type mice. An in vivo CRISPR-Cas9 approach was used to knockdown ESR1 expression selectively in arcuate nucleus (ARN) kisspeptin neurons. Mice with >80% deletion of ESR1 in ARN kisspeptin neurons exhibited the ovariectomized pattern of GnRH pulse generator activity and high frequency LH pulses but with very low amplitude due to reduced responsiveness of the pituitary. Together, these studies demonstrate that estrogen utilizes ESR1 in ARN kisspeptin neurons to achieve estrogen negative feedback of the GnRH pulse generator in mice.

Provocative tests with Kisspeptin-10 and GnRH set the scene for determining social status and environmental impacts on reproductive capacity in male African lions (Panthera leo)

Understanding the hypothalamic factors regulating reproduction facilitates maximising the reproductive success of breeding programmes and in the management and conservation of threatened species, including African lions. To provide insight into the physiology and pathophysiology of the hypothalamic-pituitary-gonadal reproductive axis in lions, we studied the luteinising hormone (LH) and steroid hormone responses to gonadotropin-releasing hormone (GnRH) and its upstream regulator, kisspeptin. Six young (13.3 ± 1.7 months, 56.2 ± 4.3 kg) and four adult (40.2 ± 1.4 months, 174 ± 6 kg) male lions (Ukutula Conservation Centre, South Africa) were used in this study. Lions were immobilised with a combination of medetomidine and ketamine and an intravenous catheter was placed in a jugular, cephalic or medial saphenous vein for blood sampling at 10-min intervals for 220 min. The ten-amino acid kisspeptin which has full intrinsic activity (KP-10, 1 µg/kg) and GnRH (1 µg/kg) were administered intravenously to study their effects on LH and steroid hormone plasma concentrations, measured subsequently by ELISA and liquid chromatography tandem mass spectrometry (LC-MS/MS), respectively. Basal LH levels were similarly low between the age groups, but testosterone and its precursor levels were higher in the adult animals. Adult lions showed a significant LH response to KP-10 (10-fold) and GnRH (11-fold) administration (p < 0.05 and P < 0.001, respectively) whereas in young lions LH increased significantly only in response to GnRH. In adults alone, testosterone and its precursors steadily increased in response to KP-10, with no significant further increase in response to GnRH. Plasma levels of glucocorticoids in response to KP-10 remained unchanged. We suggest that provocative testing of LH and steroid stimulation with kisspeptin provides a new and sensitive tool for determining reproductive status and possibly an index of exposure to stress, environmental insults such as disease, endocrine disruptors and nutritional status. 272 words.

Exposure to the pesticides linuron, dimethomorph and imazalil alters steroid hormone profiles and gene expression in developing rat ovaries

Inhibition of androgen signaling during critical stages of ovary development can disrupt folliculogenesis with potential consequences for reproductive function later in life. Many environmental chemicals can inhibit the androgen signaling pathway, which raises the question if developmental exposure to anti-androgenic chemicals can negatively impact female fertility. Here, we report on altered reproductive hormone profiles in prepubertal female rats following developmental exposure to three pesticides with anti-androgenic potential: linuron (25 and 50 mg/kg bw/d), dimethomorph (60 and 180 mg/kg bw/d) and imazalil (8 and 24 mg/kg bw/d). Dams were orally exposed from gestational day 7 (dimethomorph and imazalil) or 13 (linuron) until birth, then until end of dosing at early postnatal life. Linuron and dimethomorph induced dose-related reductions to plasma corticosterone levels, whereas imazalil mainly suppressed gonadotropin levels. In the ovaries, expression levels of target genes were affected by linuron and dimethomorph, suggesting impaired follicle growth. Based on our results, we propose that anti-androgenic chemicals can negatively impact female reproductive development. This highlights a need to integrate data from all levels of the hypothalamic-pituitary-gonadal axis, as well as the hypothalamic-pituitary-adrenal axis, when investigating the potential impact of endocrine disruptors on female reproductive development and function.

GABA Signaling in the Posterodorsal Medial Amygdala Mediates Stress-induced Suppression of LH Pulsatility in Female Mice

Psychological stress is linked to infertility by suppressing the hypothalamic GnRH pulse generator. The posterodorsal subnucleus of the medial amygdala (MePD) is an upstream regulator of GnRH pulse generator activity and displays increased neuronal activation during psychological stress. The MePD is primarily a GABAergic nucleus with a strong GABAergic projection to hypothalamic reproductive centers; however, their functional significance has not been determined. We hypothesize that MePD GABAergic signalling mediates psychological stress-induced suppression of pulsatile LH secretion. We selectively inhibited MePD GABA neurons during psychological stress in ovariectomized (OVX) Vgat-cre-tdTomato mice to determine the effect on stress-induced suppression of pulsatile LH secretion. MePD GABA neurons were virally infected with inhibitory hM4DGi-designer receptor exclusively activated by designer drugs (DREADDs) to selectively inhibit MePD GABA neurons. Furthermore, we optogenetically stimulated potential MePD GABAergic projection terminals in the hypothalamic arcuate nucleus (ARC) and determined the effect on pulsatile LH secretion. MePD GABA neurons in OVX female Vgat-cre-tdTomato mice were virally infected to express channelrhodopsin-2 and MePD GABAergic terminals in the ARC were selectively stimulated by blue light via an optic fiber implanted in the ARC. DREADD-mediated inhibition of MePD GABA neurons blocked predator odor and restraint stress-induced suppression of LH pulse frequency. Furthermore, sustained optogenetic stimulation at 10 and 20 Hz of MePD GABAergic terminals in the ARC suppressed pulsatile LH secretion. These results show for the first time that GABAergic signalling in the MePD mediates psychological stress-induced suppression of pulsatile LH secretion and suggest a functionally significant MePD GABAergic projection to the hypothalamic GnRH pulse generator.

GnRH pulse generator frequency is modulated by kisspeptin and GABA-glutamate interactions in the posterodorsal medial amygdala in female mice

Kisspeptin neurons in the arcuate nucleus of the hypothalamus generate gonadotrophin-releasing hormone (GnRH) pulses, and act as critical initiators of functional gonadotrophin secretion and reproductive competency. However, kisspeptin in other brain regions, most notably the posterodorsal subnucleus of the medial amygdala (MePD), plays a significant modulatory role over the hypothalamic kisspeptin population; our recent studies using optogenetics have shown that low-frequency light stimulation of MePD kisspeptin results in increased luteinsing hormone pulse frequency. Nonetheless, the neurochemical pathways that underpin this regulatory function remain unknown. To study this, we have utilised an optofluid technology, precisely combining optogenetic stimulation with intra-nuclear pharmacological receptor antagonism, to investigate the neurotransmission involved in this circuitry. We have shown experimentally and verified using a mathematical model that functional neurotransmission of both GABA and glutamate is a requirement for effective modulation of the GnRH pulse generator by amygdala kisspeptin neurons.

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

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

Steroidogenic Factor 1 Regulates Transcription of the Inhibin B Coreceptor in Pituitary Gonadotrope Cells

The inhibins control reproduction by suppressing follicle-stimulating hormone synthesis in pituitary gonadotrope cells. The newly discovered inhibin B coreceptor, TGFBR3L, is selectively and highly expressed in gonadotropes in both mice and humans. Here, we describe our initial characterization of mechanisms controlling cell-specific Tgfbr3l/TGFBR3L transcription. We identified two steroidogenic factor 1 (SF-1 or NR5A1) cis-elements in the proximal Tgfbr3l promoter in mice. SF-1 induction of murine Tgfbr3l promoter-reporter activity was inhibited by mutations in one or both sites in heterologous cells. In homologous cells, mutation of these cis-elements or depletion of endogenous SF-1 similarly decreased reporter activity. We observed nearly identical results when using a human TGFBR3L promoter-reporter. The Tgfbr3l gene was tightly compacted and Tgfbr3l mRNA expression was essentially absent in gonadotropes of SF-1 (Nr5a1) conditional knockout mice. During murine embryonic development, Tgfbr3l precedes Nr5a1 expression, though the two transcripts are fully colocalized by embryonic day 18.5 and thereafter. Collectively, these data indicate that SF-1 directly regulates Tgfbr3l/TGFBR3L transcription and is required for postnatal expression of the gene in gonadotropes.

Hypothalamic Overexpression of Makorin Ring Finger Protein 3 Results in Delayed Puberty in Female Mice

Makorin ring finger protein 3 (MKRN3) is an important neuroendocrine player in the control of pubertal timing and upstream inhibitor of gonadotropin-releasing hormone secretion. In mice, expression of Mkrn3 in the hypothalamic arcuate and anteroventral periventricular nucleus is high early in life and declines before the onset of puberty. Therefore, we aimed to explore if the persistence of hypothalamic Mkrn3 expression peripubertally would result in delayed puberty. Female mice that received neonatal bilateral intracerebroventricular injections of a recombinant adeno-associated virus expressing Mkrn3 had delayed vaginal opening and first estrus compared with animals injected with control virus. Subsequent estrous cycles and fertility were normal. Interestingly, male mice treated similarly did not exhibit delayed puberty onset. Kiss1, Tac2, and Pdyn mRNA levels were increased in the mediobasal hypothalamus in females at postnatal day 28, whereas kisspeptin and neurokinin B protein levels in the arcuate nucleus were decreased, following Mkrn3 overexpression, compared to controls. Cumulatively, these data suggest that Mkrn3 may directly or indirectly target neuropeptides of Kiss1 neurons to degradation pathways. This mouse model suggests that MKRN3 may be a potential contributor to delayed onset of puberty, in addition to its well-established roles in central precocious puberty and the timing of menarche.

NOS1 mutations cause hypogonadotropic hypogonadism with sensory and cognitive deficits that can be reversed in infantile mice

The nitric oxide (NO) signaling pathway in hypothalamic neurons plays a key role in the regulation of the secretion of gonadotropin-releasing hormone (GnRH), which is crucial for reproduction. We hypothesized that a disruption of neuronal NO synthase (NOS1) activity underlies some forms of hypogonadotropic hypogonadism. Whole-exome sequencing was performed on a cohort of 341 probands with congenital hypogonadotropic hypogonadism to identify ultrarare variants in NOS1. The activity of the identified NOS1 mutant proteins was assessed by their ability to promote nitrite and cGMP production in vitro. In addition, physiological and pharmacological characterization was carried out in a Nos1-deficient mouse model. We identified five heterozygous NOS1 loss-of-function mutations in six probands with congenital hypogonadotropic hypogonadism (2%), who displayed additional phenotypes including anosmia, hearing loss, and intellectual disability. NOS1 was found to be transiently expressed by GnRH neurons in the nose of both humans and mice, and Nos1 deficiency in mice resulted in dose-dependent defects in sexual maturation as well as in olfaction, hearing, and cognition. The pharmacological inhibition of NO production in postnatal mice revealed a critical time window during which Nos1 activity shaped minipuberty and sexual maturation. Inhaled NO treatment at minipuberty rescued both reproductive and behavioral phenotypes in Nos1-deficient mice. In summary, lack of NOS1 activity led to GnRH deficiency associated with sensory and intellectual comorbidities in humans and mice. NO treatment during minipuberty reversed deficits in sexual maturation, olfaction, and cognition in Nos1 mutant mice, suggesting a potential therapy for humans with NO deficiency.

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

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

Follicle isolation methods reveal plasticity of granulosa cell steroidogenic capacity during mouse in vitro follicle growth

Follicles are the functional unit of the ovary and several methods have been developed to grow follicles ex vivo, which recapitulate key events of oogenesis and folliculogenesis. Enzymatic digestion protocols are often used to increase the yield of follicles from the ovary. However, the impact of these protocols on the outermost theca and granulosa cells, and thereby follicle function, is not well defined. To investigate the impact of enzymatic digestion on follicle function, we collected preantral follicles from CD1 mice either by enzymatic digestion (Enzy-FL) or mechanical isolation (Mech-FL) and compared follicle growth, steroidogenesis and cell differentiation within an encapsulated in vitro follicle growth system which maintains the 3D architecture of the oocyte and its surrounding somatic cells. Follicles were encapsulated in 0.5% alginate and cultured for 8 days. Compared with Enzy-FL, Mech-FL grew more rapidly and produced significantly higher levels of androstenedione, estradiol and progesterone. The expression of theca-interstitial cell marker genes, Cyp17a1, which encodes 17-hydroxylase/17, 20-lyase and catalyzes the hydroxylation of pregnenolone and progesterone to 17-hydroxypregnenolone and 17-hydroxyprogesterone, and the conversion of these products into dehydroepiandrosterone and androstenedione, and Star, which encodes a transport protein essential for cholesterol entry into mitochondria, were also higher in Mech-FL than in Enzy-FL. Mech-FL maintained an intact theca-interstitial layer on the outer edge of the follicle that phenocopied in vivo patterns as confirmed by alkaline phosphatase staining, whereas theca-interstitial cells were absent from Enzy-FL from the onset of culture. Therefore, preservation of the theca cell layer at the onset of culture better supports follicle growth and function. Interestingly, granulosa cells in the outermost layers of Enzy-FL expressed CYP17A1 by Day 4 of culture while maintaining inhibin α-subunit expression and a cuboidal nucleus. Thus, in the absence of theca-interstitial cells, granulosa cells have the potential to differentiate into androgen-producing cells. This work may have implications for human follicle culture, where enzymatic isolation is required owing to the density of the ovarian cortex.

GnRH replacement rescues cognition in Down syndrome

At the present time, no viable treatment exists for cognitive and olfactory deficits in Down syndrome (DS). We show in a DS model (Ts65Dn mice) that these progressive nonreproductive neurological symptoms closely parallel a postpubertal decrease in hypothalamic as well as extrahypothalamic expression of a master molecule that controls reproduction-gonadotropin-releasing hormone (GnRH)-and appear related to an imbalance in a microRNA-gene network known to regulate GnRH neuron maturation together with altered hippocampal synaptic transmission. Epigenetic, cellular, chemogenetic, and pharmacological interventions that restore physiological GnRH levels abolish olfactory and cognitive defects in Ts65Dn mice, whereas pulsatile GnRH therapy improves cognition and brain connectivity in adult DS patients. GnRH thus plays a crucial role in olfaction and cognition, and pulsatile GnRH therapy holds promise to improve cognitive deficits in DS.

A Modified Ultra-Sensitive ELISA for Measurement of LH in Mice

A major obstacle to monitoring pulsatile luteinizing hormone (LH) secretion in mice has been an assay with sufficient sensitivity in small blood volumes. In 2013, Steyn and colleagues published a highly sensitive enzyme-linked immunosorbent assay (ELISA) that overcame this barrier by coupling a duo of LH antibodies effective in accurately measuring LH in 4-µL whole-blood aliquots. To address the unavailability of the original detection antibody, AFP240580Rb, we validated a replacement detection antibody, biotinylated-5303 SPRN-5, to be used within the established ELISA. This modified LH ELISA demonstrated a minimum detection limit of 0.0028 ng/mL and a limit of quantification of 0.0333 ng/mL or 0.0666 ng/mL in diluted whole-blood samples of volume 6.4 µL (1:10) or 3.2 µL (1:20), respectively. Detection antibody 5303 SPRN-5 demonstrated parallelism, high precision, and accuracy across the standard curve. LH concentrations in comparison assays, using either 5303 SPRN-5 or AFP240580Rb, were highly correlated (R2 = 0.9829) and demonstrated LH pulse profiles from gonadectomized mice that were nearly superimposable. Pulsatile LH secretion was demonstrated in gonad-intact males and diestrous females and basal LH levels measured with 5303 SPRN-5 were approximately 5-fold higher than the limit of quantification. In addition, we document utility of this new LH ELISA to accurately measure LH in whole blood or serum across multiple sampling sites, as well as in pituitary extracts, LβT2 cells, or media. In summary, the modified LH ELISA described here is highly effective in measuring LH across a range of sample types and small volumes in mice.

Dicer ablation in Kiss1 neurons impairs puberty and fertility preferentially in female mice

Kiss1 neurons, producing kisspeptins, are essential for puberty and fertility, but their molecular regulatory mechanisms remain unfolded. Here, we report that congenital ablation of the microRNA-synthesizing enzyme, Dicer, in Kiss1 cells, causes late-onset hypogonadotropic hypogonadism in both sexes, but is compatible with pubertal initiation and preserved Kiss1 neuronal populations at the infantile/juvenile period. Yet, failure to complete puberty and attain fertility is observed only in females. Kiss1-specific ablation of Dicer evokes disparate changes of Kiss1-cell numbers and Kiss1/kisspeptin expression between hypothalamic subpopulations during the pubertal-transition, with a predominant decline in arcuate-nucleus Kiss1 levels, linked to enhanced expression of its repressors, Mkrn3, Cbx7 and Eap1. Our data unveil that miRNA-biosynthesis in Kiss1 neurons is essential for pubertal completion and fertility, especially in females, but dispensable for initial reproductive maturation and neuronal survival in both sexes. Our results disclose a predominant miRNA-mediated inhibitory program of repressive signals that is key for precise regulation of Kiss1 expression and, thereby, reproductive function.

Female sexual behavior is disrupted in a preclinical mouse model of PCOS via an attenuated hypothalamic nitric oxide pathway

Polycystic ovary syndrome (PCOS) is a major endocrine disorder leading to female infertility worldwide. Patients with PCOS also often experience sexual dysfunction; however, the developmental and central mechanisms mediating this behavioral derangement are unclear. Here, we show that prenatal excess of anti-Müllerian hormone triggers PCOS-like impairment in female sexual behavior in mice. Sexual dysfunction in PCOS-like mice is associated with decreased expression of progesterone-sensitive neuronal nitric oxide synthase (nNOS) neurons in the hypothalamus. Chemogenetic inhibition of nNOS neuronal activity in the ventromedial nucleus of the hypothalamus recapitulates PCOS-like sexual dysfunction. Of clinical relevance, administration of nitric oxide donor rescues normal sexual behavior in PCOS-like mice.

Women with polycystic ovary syndrome (PCOS) frequently experience decreased sexual arousal, desire, and sexual satisfaction. While the hypothalamus is known to regulate sexual behavior, the specific neuronal pathways affected in patients with PCOS are not known. To dissect the underlying neural circuitry, we capitalized on a robust preclinical animal model that reliably recapitulates all cardinal PCOS features. We discovered that female mice prenatally treated with anti-Müllerian hormone (PAMH) display impaired sexual behavior and sexual partner preference over the reproductive age. Blunted female sexual behavior was associated with increased sexual rejection and independent of sex steroid hormone status. Structurally, sexual dysfunction was associated with a substantial loss of neuronal nitric oxide synthase (nNOS)-expressing neurons in the ventromedial nucleus of the hypothalamus (VMH) and other areas of hypothalamic nuclei involved in social behaviors. Using in vivo chemogenetic manipulation, we show that nNOS^VMH neurons are required for the display of normal sexual behavior in female mice and that pharmacological replenishment of nitric oxide restores normal sexual performance in PAMH mice. Our data provide a framework to investigate facets of hypothalamic nNOS neuron biology with implications for sexual disturbances in PCOS.

Dapagliflozin partially restores reproductive function in MC4R KO obese female mice

Obese women often have certain degree of reproductive dysfunction with infertility. Although the clinical impact of obesity on female infertility has been extensively studied, the effective and targeted treatment is still lacking. Melanocortin-4-receptor knock-out (MC4R KO) mouse is an over-eating obese model with hyperphagia, hyperinsulinemia, reduced growth hormone (GH), and insulin resistance. Dapagliflozin improved the metabolic and hormonal parameters in MC4R KO mice. MC4R KO female mice were treated with dapagliflozin for 14 weeks from 14-week age. Age-matched WT littermates and non-treated MC4R KO mice were used as control groups. Food intake was measured daily. Body weight was measured twice a week. Estrous cycles, GH, and luteinizing hormone (LH) profiles were measured. Selected tissues were collected at the end of experiments for gene expression profiles and hematoxylin-eosin staining. Regularity and mode of hormonal profiles were restored by the dapagliflozin treatment. Estrous cycle was partially normalized, number of CL was significantly increased, and the expression of Kiss1 and Gnrh1 in the hypothalamus and LH in the pituitary was markedly increased by the dapagliflozin treatment. It is conclsuded that dapagliflozin may recover LH and GH profiles partially through modification of relevant gene expression in the hypothalamus and pituitary, and result in an improved ovulation rate in obese mouse model. Dapagliflozin may therefore improve fertility in obese patients.

Elevated prolactin secretion during proestrus in mice: Absence of a defined surge

Throughout the reproductive cycle in rodents, prolactin levels are generally low. In some species, including rats, a prolactin surge occurs on proestrus with peak concentrations coinciding with the preovulatory luteinizing hormone (LH) surge. In mice, however, there are conflicting reports relating to the occurrence and timing of a proestrous prolactin surge. To gain further insight into the incidence and characteristics of this surge in mice, we have used serial tail tip blood sampling and trunk blood collection from both C57BL/6J (inbred) and Swiss Webster (outbred) mouse strains to build a profile of prolactin secretion during proestrus in individual mice. A clearly defined LH surge was detected in most animals, suggesting the blood sampling approach was suitable for detecting patterns of hormone secretion on proestrus. Despite this, levels of prolactin were quite variable between individuals. Overall both mouse strains showed a generalized rise in prolactin levels on the day of proestrus compared with levels seen in diestrus. This pattern is quite distinct from the discreet, circadian-entrained surge observed in rats.

Role of Posterodorsal Medial Amygdala Urocortin-3 in Pubertal Timing in Female Mice

Post-traumatic stress disorder impedes pubertal development and disrupts pulsatile LH secretion in humans and rodents. The posterodorsal sub-nucleus of the medial amygdala (MePD) is an upstream modulator of the hypothalamic gonadotropin-releasing hormone (GnRH) pulse generator, pubertal timing, as well as emotional processing and anxiety. Psychosocial stress exposure alters neuronal activity within the MePD increasing the expression of Urocortin3 (Ucn3) and its receptor corticotropin-releasing factor type-2 receptor (CRFR2) while enhancing the inhibitory output from the MePD to key hypothalamic reproductive centres. We test the hypothesis that psychosocial stress, processed by the MePD, is relayed to the hypothalamic GnRH pulse generator to delay puberty in female mice. We exposed C57Bl6/J female mice to the predator odor, 2,4,5-Trimethylthiazole (TMT), during pubertal transition and examined the effect on pubertal timing, pre-pubertal LH pulses and anxiety-like behaviour. Subsequently, we virally infected Ucn3-cre-tdTomato female mice with stimulatory DREADDs targeting MePD Ucn3 neurons and determined the effect on pubertal timing and pre-pubertal LH pulse frequency. Exposure to TMT during pubertal development delayed puberty, suppressed pre-pubertal LH pulsatility and enhanced anxiety-like behaviour, while activation of MePD Ucn3 neurons reduced LH pulse frequency and delayed puberty. Early psychosocial stress exposure decreases GnRH pulse generator frequency delaying puberty while inducing anxiety-behaviour in female mice, an effect potentially involving Ucn3 neurons in the MePD.

Gonadotropin-releasing hormone (GnRH) measurements in pituitary portal blood: A history

Much about the neuroendocrine control of reproduction is inferred from changes in the episodic release of luteinizing hormone (LH), as measured in samples of peripheral blood. This, however, assumes that LH precisely mirrors gonadotropin-releasing hormone (GnRH) release from the hypothalamus. Because GnRH is not measurable in peripheral blood, characterization of the relationship between these two hormones required the simultaneous measurement of GnRH and LH in pituitary portal and peripheral blood, respectively. Here, we review the history of why and how portal blood collection was developed, the aspects of the true output of the central component of the hypothalamic-pituitary-gonadal axis that this methodology helped clarify, and conditions under which the pituitary fails to serve as an adequate bioassay for the release pattern of GnRH.

Steroidogenic Factor 1 Regulation of the Hypothalamic-Pituitary-Ovarian Axis of Adult Female Mice

The orphan nuclear receptor steroidogenic factor-1 (SF-1 or NR5A1) is an indispensable regulator of adrenal and gonadal formation, playing roles in sex determination, hypothalamic development, and pituitary function. This study aimed to identify the roles of SF-1 in postnatal female reproductive function. Using a progesterone receptor-driven Cre recombinase, we developed a novel murine model, characterized by conditional depletion of SF-1 [PR-Cre;Nr5a1f/f; conditional knockout (cKO)] in the hypothalamic-pituitary-gonadal axis. Mature female cKO were infertile due to the absence of ovulation. Reduced gonadotropin concentrations in the pituitary gland that were nevertheless sufficient to maintain regular estrous cycles were observed in mature cKO females. The cKO ovaries showed abnormal lipid accumulation in the stroma, associated with an irregular expression of cholesterol homeostatic genes such as Star, Scp2, and Acat1. The depletion of SF-1 in granulosa cells prevented appropriate cumulus oöphorus expansion, characterized by reduced expression of Areg, Ereg, and Ptgs2. Exogenous delivery of gonadotropins to cKO females to induce ovulation did not restore fertility and was associated with impaired formation and function of corpora lutea accompanied by reduced expression of the steroidogenic genes Cyp11a1 and Cyp19a1 and attenuated progesterone production. Surgical transplantation of cKO ovaries to ovariectomized control animals (Nr5a1f/f) resulted in 2 separate phenotypes, either sterility or apparently normal fertility. The deletion of SF-1 in the pituitary and in granulosa cells near the moment of ovulation demonstrated that this nuclear receptor functions across the pituitary-gonadal axis and plays essential roles in gonadotropin synthesis, cumulus expansion, and luteinization.