scholarly journals The Gonadotropin-Releasing Hormone (GnRH) Neuronal Population Is Normal in Size and Distribution in GnRH-Deficient and GnRH Receptor-Mutant Hypogonadal Mice

Endocrinology ◽  
2008 ◽  
Vol 149 (9) ◽  
pp. 4596-4604 ◽  
Author(s):  
John C. Gill ◽  
Brandon Wadas ◽  
Peilin Chen ◽  
Wendy Portillo ◽  
Andrea Reyna ◽  
...  
Keyword(s):  
Fluorescent Protein ◽  
Gene Dosage ◽  
Normal Population ◽  
Reproductive Function ◽  
Neuronal Population ◽  
Mouse Strains ◽  
Gnrh Neuron ◽  
Action Potential Firing ◽  
Adult Mice ◽  
Gnrh Neurons

Hypothalamic GnRH neurons are essential for initiation and regulation of reproductive function. In addition to pituitary gonadotrope stimulation, activity of GnRH through its receptor (GnRHR) has been suggested to include autocrine regulation of the GnRH neuron. Two hypogonadal mouse strains, the Gnrh1 mutant (hpg) mice and Gnrhr mutant mice were used to investigate the potential role of GnRH signaling in the proper development and maintenance of GnRH neurons. Immunocytochemical analysis of heterozygous hpg mice revealed a GnRH neuron population that was normal in size and distribution, indicating no effect from reduced Gnrh1 gene dosage on the neurons themselves. To visualize GnRH neurons in homozygous GnRH-deficient hpg mice, heterozygous hpg mice were crossed with GnRH-green fluorescent protein (GFP) transgenic mice with targeted expression of the GFP reporter gene in GnRH neurons. Analysis of forebrains of homozygous hpg/GFP-positive mice immunostained for GFP revealed a normal population size and appropriate distribution of GnRH neurons in hpg mice, with immunoreactive neuronal processes present at the median eminence. Similarly, adult mice deficient in functional GnRHR possessed a full complement of GnRH neurons in the basal forebrain that was indistinguishable from the distribution of GnRH neurons in their wild-type counterparts. Moreover, hpg/GFP neurons retained the ability to generate spontaneous bursts of action potential firing activity, suggesting that GnRH peptide is not required for this function. These data establish that autocrine-paracrine GnRH-signaling is not a prerequisite for the developmental migration of GnRH neurons into the brain or for the projection of GnRH neurosecretory axons.

scholarly journals Impairments in the reproductive axis of female mice lacking estrogen receptor β in GnRH neurons

2018 ◽  
Vol 315 (5) ◽  
pp. E1019-E1033 ◽  
Author(s):  
Horacio J. Novaira ◽  
Ariel L. Negron ◽  
Jones B. Graceli ◽  
Silvia Capellino ◽  
Andrew Schoeffield ◽  
...  
Keyword(s):  
Mouse Models ◽  
Reproductive Function ◽  
Stimulation Test ◽  
Abnormal Development ◽  
Gnrh Neuron ◽  
Serum Luteinizing Hormone ◽  
Reproductive Axis ◽  
Gnrh Neurons ◽  
Serum Gonadotropin

The effect of estrogen on the differentiation and maintenance of reproductive tissues is mediated by two nuclear estrogen receptors (ERs), ERα, and ERβ. Lack of functional ERα and ERβ genes in vivo significantly affects reproductive function; however, the target tissues and signaling pathways in the hypothalamus are not clearly defined. Here, we describe the generation and reproductive characterization of a complete-ERβ KO (CERβKO) and a GnRH neuron-specific ERβKO (GERβKO) mouse models. Both ERβKO mouse models displayed a delay in vaginal opening and first estrus. Hypothalamic gonadotropin-releasing hormone (GnRH) mRNA expression levels in both ERβKO mice were similar to control mice; however female CERβKO and GERβKO mice had lower basal and surge serum gonadotropin levels. Although a GnRH stimulation test in both female ERβKO models showed preserved gonadotropic function in the same animals, a kisspeptin stimulation test revealed an attenuated response by GnRH neurons, suggesting a role for ERβ in normal GnRH neuron function. No alteration in estrogen-negative feedback was observed in either ERβKO mouse models after ovariectomy and estrogen replacement. Further, abnormal development of ovarian follicles with low serum estradiol levels and impairment of fertility were observed in both ERβKO mouse models. In male ERβKO mice, no differences in the timing of pubertal onset or serum luteinizing hormone and follicle-stimulating hormone levels were observed as compared with controls. Taken together, these data provide in vivo evidence for a role of ERβ in GnRH neurons in modulating puberty and reproduction, specifically through kisspeptin responsiveness in the female hypothalamic-pituitary-gonadal axis.

scholarly journals Effects of Leptin and Melanocortin Signaling Interactions on Pubertal Development and Reproduction

Endocrinology ◽  
2012 ◽  
Vol 153 (5) ◽  
pp. 2408-2419 ◽  
Author(s):  
Davelene D. Israel ◽  
Sharone Sheffer-Babila ◽  
Carl de Luca ◽  
Young-Hwan Jo ◽  
Shun Mei Liu ◽  
...  
Keyword(s):  
Pubertal Development ◽  
Receptor Activation ◽  
Ingestive Behavior ◽  
Neuron Activity ◽  
Gnrh Neuron ◽  
Action Potential Firing ◽  
Related Peptide ◽  
Melanocortin 4 Receptor ◽  
Gnrh Neurons ◽  
Melanocortin Signaling

Leptin and melanocortin signaling control ingestive behavior, energy balance, and substrate utilization, but only leptin signaling defects cause hypothalamic hypogonadism and infertility. Although GnRH neurons do not express leptin receptors, leptin influences GnRH neuron activity via regulation of immediate downstream mediators including the neuropeptides neuropeptide Y and the melanocortin agonist and antagonist, α-MSH, agouti-related peptide, respectively. Here we show that modulation of melanocortin signaling in female db/db mice through ablation of agouti-related peptide, or heterozygosity of melanocortin 4 receptor, restores the timing of pubertal onset, fertility, and lactation. Additionally, melanocortin 4 receptor activation increases action potential firing and induces c-Fos expression in GnRH neurons, providing further evidence that melanocortin signaling influences GnRH neuron activity. These studies thus establish melanocortin signaling as an important component in the leptin-mediated regulation of GnRH neuron activity, initiation of puberty and fertility.

scholarly journals Gonadotropin-Releasing Hormone Neuron Requirements for Puberty, Ovulation, and Fertility

Endocrinology ◽  
2007 ◽  
Vol 149 (2) ◽  
pp. 597-604 ◽  
Author(s):  
Allan E. Herbison ◽  
Robert Porteous ◽  
Jean-Rémi Pape ◽  
Jocelyn M. Mora ◽  
Peter R. Hurst
Keyword(s):  
Great Majority ◽  
Neuronal Population ◽  
The Body ◽  
Gnrh Neuron ◽  
Neuron Population ◽  
Gonadotropin Secretion ◽  
Estrous Cycles ◽  
Absolute Requirement ◽  
Gnrh Neurons ◽  
Puberty Onset

The absolute requirement for reproduction implies that the hypothalamo-pituitary-gonadal axis, controlling fertility, is an evolutionary robust mechanism. The GnRH neurons of the hypothalamus represent the key cell type within the body dictating fertility. However, the level of functional redundancy within the GnRH neuron population is unknown. As a result of a fortuitous transgene insertion event, GNR23 mice exhibit a marked allele-dependent reduction in GnRH neuron number within their brain. Wild-type mice have approximately 600 GnRH neurons, compared with approximately 200 (34%) and approximately 70 (12%) in GNR23+/− and GNR23−/− mice, respectively. Using these mice, we examined the minimal GnRH neuron requirements for fertility. Male GNR23−/− mice exhibited normal fertility. In contrast, female GNR23−/− mice were markedly subfertile, failing to produce normal litters, have estrous cycles, or ovulate. The failure of ovulation resulted from an inability of the few existing GnRH neurons to generate the LH surge. This was not the case, however, for the first cycle at puberty that appeared normal. Together, these observations demonstrate that 12% of the GnRH neuron population is sufficient for pulsatile gonadotropin secretion and puberty onset, whereas between 12 and 34% are required for cyclical control in adult female mice. This indicates that substantial redundancy exists within the GnRH neuronal population and suggests that the great majority of GnRH neurons must be dysfunctional before fertility is affected.

scholarly journals Estradiol Negative and Positive Feedback in a Prenatal Androgen-Induced Mouse Model of Polycystic Ovarian Syndrome

Endocrinology ◽  
2012 ◽  
Vol 154 (2) ◽  
pp. 796-806 ◽  
Author(s):  
Aleisha M. Moore ◽  
Melanie Prescott ◽  
Rebecca E. Campbell
Keyword(s):  
Positive Feedback ◽  
Polycystic Ovarian Syndrome ◽  
Fluorescent Protein ◽  
Spine Density ◽  
Gnrh Neuron ◽  
Feedback Effects ◽  
Gnrh Neurons ◽  
Green Fluorescent ◽  
Prenatal Androgen ◽  
Ovarian Syndrome

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

scholarly journals Estradiol-Sensitive Afferents Modulate Long-Term Episodic Firing Patterns of GnRH Neurons

Endocrinology ◽  
2002 ◽  
Vol 143 (6) ◽  
pp. 2284-2292 ◽  
Author(s):  
Craig S. Nunemaker ◽  
R. Anthony DeFazio ◽  
Suzanne M. Moenter
Keyword(s):  
Green Fluorescent Protein Expression ◽  
Fluorescent Protein ◽  
Gnrh Neuron ◽  
Action Current ◽  
Neuron Firing ◽  
Firing Patterns ◽  
Gnrh Neurons ◽  
Episode Frequency ◽  
Green Fluorescent

Abstract GnRH neurons comprise the final common pathway of an estrogen-sensitive pattern generator controlling fertility. To determine estradiol effects on GnRH neuron firing patterns, adult transgenic mice were ovariectomized (OVX), and half were treated with estradiol (OVX+E). One week later targeted single-unit extracellular recordings were made from GnRH neurons identified by green fluorescent protein expression. Estradiol markedly affected GnRH neuron firing patterns, increasing the percentage and duration of time these cells were quiescent (≤1 action current/min). Estradiol increased the interval between episodes of increased firing rate determined by Cluster analysis of recordings more than 45 min (OVX+E 38.8 ± 7.2 min, OVX 16.7 ± 2.1 min, n = 6 each). Possible mechanisms of estradiol modulation were examined by simultaneously blocking ionotropic secretion of γ-aminobutyric acid and glutamatergic receptors. This treatment had no effect on cells from OVX mice (n = 10), indicating episodic firing of GnRH neurons is not driven by activation of these receptors. Receptor blockade eliminated estradiol effects on GnRH neurons in the midventral preoptic area (n = 7) but not elsewhere (n = 7). Individual GnRH neurons thus display episodic firing patterns at intervals previously reported for secretory pulses. Estradiol modulates episode frequency to exert feedback control; in a substantial subset of GnRH neurons, estradiol feedback is enforced via GABAergic and/or glutamatergic afferents.

scholarly journals Conditional Viral Tract Tracing Delineates the Projections of the Distinct Kisspeptin Neuron Populations to Gonadotropin-Releasing Hormone (GnRH) Neurons in the Mouse

Endocrinology ◽  
2015 ◽  
Vol 156 (7) ◽  
pp. 2582-2594 ◽  
Author(s):  
Siew Hoong Yip ◽  
Ulrich Boehm ◽  
Allan E. Herbison ◽  
Rebecca E. Campbell
Keyword(s):  
Fluorescent Protein ◽  
Recombinant Adenovirus ◽  
Close Contact ◽  
Third Ventricle ◽  
Gnrh Neuron ◽  
Tract Tracing ◽  
Neuron Populations ◽  
Gnrh Neurons ◽  
A Cell ◽  
Green Fluorescent

Kisspeptin neurons play an essential role in the regulation of fertility through direct regulation of the GnRH neurons. However, the relative contributions of the two functionally distinct kisspeptin neuron subpopulations to this critical regulation are not fully understood. Here we analyzed the specific projection patterns of kisspeptin neurons originating from either the rostral periventricular nucleus of the third ventricle (RP3V) or the arcuate nucleus (ARN) using a cell-specific, viral-mediated tract-tracing approach. We stereotaxically injected a Cre-dependent recombinant adenovirus encoding farnesylated enhanced green fluorescent protein into the ARN or RP3V of adult male and female mice expressing Cre recombinase in kisspeptin neurons. Fibers from ARN kisspeptin neurons projected widely; however, we did not find any evidence for direct contact with GnRH neuron somata or proximal dendrites in either sex. In contrast, we identified RP3V kisspeptin fibers in close contact with GnRH neuron somata and dendrites in both sexes. Fibers originating from both the RP3V and ARN were observed in close contact with distal GnRH neuron processes in the ARN and in the lateral and internal aspects of the median eminence. Furthermore, GnRH nerve terminals were found in close contact with the proximal dendrites of ARN kisspeptin neurons in the ARN, and ARN kisspeptin fibers were found contacting RP3V kisspeptin neurons in both sexes. Together these data delineate selective zones of kisspeptin neuron inputs to GnRH neurons and demonstrate complex interconnections between the distinct kisspeptin populations and GnRH neurons.

scholarly journals Investigating the NPY/AgRP/GABA to GnRH Neuron Circuit in Prenatally Androgenized PCOS-Like Mice

2020 ◽  
Vol 4 (11) ◽  
Author(s):  
Christopher J Marshall ◽  
Melanie Prescott ◽  
Rebecca E Campbell
Keyword(s):  
Polycystic Ovary ◽  
Reproductive Function ◽  
Receptor Expression ◽  
Late Gestation ◽  
Gnrh Neuron ◽  
Androgen Excess ◽  
Neuron Circuit ◽  
Gaba Neurons ◽  
Gnrh Neurons ◽  
Prenatal Androgen

Abstract Polycystic ovary syndrome (PCOS), the most common form of anovulatory infertility, is associated with altered signaling within the hormone-sensitive neuronal network that regulates gonadotropin-releasing hormone (GnRH) neurons, leading to a pathological increase in GnRH secretion. Circuit remodeling is evident between GABAergic neurons in the arcuate nucleus (ARN) and GnRH neurons in a murine model of PCOS. One-third of ARN GABA neurons co-express neuropeptide Y (NPY), which has a known yet complex role in regulating GnRH neurons and reproductive function. Here, we investigated whether the NPY-expressing subpopulation (NPYARN) of ARN GABA neurons (GABAARN) is also affected in prenatally androgenized (PNA) PCOS-like NPYARN reporter mice [Agouti-related protein (AgRP)-Cre;τGFP]. PCOS-like mice and controls were generated by exposure to di-hydrotestosterone or vehicle (VEH) in late gestation. τGFP-expressing NPYARN neuron fiber appositions with GnRH neurons and gonadal steroid hormone receptor expression in τGFP-expressing NPYARN neurons were assessed using confocal microscopy. Although GnRH neurons received abundant close contacts from τGFP-expressing NPYARN neuron fibers, the number and density of putative inputs was not affected by prenatal androgen excess. NPYARN neurons did not co-express progesterone receptor or estrogen receptor α in either PNA or VEH mice. However, the proportion of NPYARN neurons co-expressing the androgen receptor was significantly elevated in PNA mice. Therefore, NPYARN neurons are not remodeled by prenatal androgen excess like the wider GABAARN population, indicating GABA-to-GnRH neuron circuit remodeling occurs in a presently unidentified non-NPY/AgRP population of GABAARN neurons. NPYARN neurons do, however, show independent changes in the form of elevated androgen sensitivity.

scholarly journals Retrograde Endocannabinoid Signaling Reduces GABAergic Synaptic Transmission to Gonadotropin-Releasing Hormone Neurons

Endocrinology ◽  
2010 ◽  
Vol 151 (12) ◽  
pp. 5818-5829 ◽  
Author(s):  
Imre Farkas ◽  
Imre Kalló ◽  
Levente Deli ◽  
Barbara Vida ◽  
Erik Hrabovszky ◽  
...  
Keyword(s):  
Fluorescent Protein ◽  
Cannabinoid Receptor ◽  
Gaba Release ◽  
Vesicle Fusion ◽  
Gnrh Neuron ◽  
Neuron Firing ◽  
Gabaergic Neurotransmission ◽  
Functional Studies ◽  
Gnrh Neurons ◽  
Green Fluorescent

Cannabinoids suppress fertility via reducing hypothalamic GnRH output. γ-Aminobutyric acid (GABA)A receptor (GABAA-R)-mediated transmission is a major input to GnRH cells that can be excitatory. We hypothesized that cannabinoids act via inhibiting GABAergic input. We performed loose-patch electrophysiological studies of acute slices from adult male GnRH-green fluorescent protein transgenic mice. Bath application of type 1 cannabinoid receptor (CB1) agonist WIN55,212 decreased GnRH neuron firing rate. This action was detectable in presence of the glutamate receptor antagonist kynurenic acid but disappeared when bicuculline was also present, indicating GABAA-R involvement. In immunocytochemical experiments, CB1-immunoreactive axons formed contacts with GnRH neurons and a subset established symmetric synapses characteristic of GABAergic neurotransmission. Functional studies were continued with whole-cell patch-clamp electrophysiology in presence of tetrodotoxin. WIN55,212 decreased the frequency of GABAA-R-mediated miniature postsynaptic currents (mPSCs) (reflecting spontaneous vesicle fusion), which was prevented with the CB1 antagonist AM251, indicating collectively that activation of presynaptic CB1 inhibits GABA release. AM251 alone increased mPSC frequency, providing evidence that endocannabinoids tonically inhibit GABAA-R drive onto GnRH neurons. Increased mPSC frequency was absent when diacylglycerol lipase was blocked intracellularly with tetrahydrolipstatin, showing that tonic inhibition is caused by 2-arachidonoylglycerol production of GnRH neurons. CdCl2 in extracellular solution can maintain both action potentials and spontaneous vesicle fusion. Under these conditions, when endocannabinoid-mediated blockade of spontaneous vesicle fusion was blocked with AM251, GnRH neuron firing increased, revealing an endogenous endocannabinoid brake on GnRH neuron firing. Retrograde endocannabinoid signaling may represent an important mechanism under physiological and pathological conditions whereby GnRH neurons regulate their excitatory GABAergic inputs.

scholarly journals Targeted Expression of a Dominant-Negative Fibroblast Growth Factor (FGF) Receptor in Gonadotropin-Releasing Hormone (GnRH) Neurons Reduces FGF Responsiveness and the Size of GnRH Neuronal Population

2005 ◽  
Vol 19 (1) ◽  
pp. 225-236 ◽  
Author(s):  
Pei-San Tsai ◽  
Suzanne M. Moenter ◽  
Hector R. Postigo ◽  
Mohammed El Majdoubi ◽  
Toni R. Pak ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Neuronal Cell ◽  
Neuronal Population ◽  
Dominant Negative ◽  
Delayed Puberty ◽  
Fibroblast Growth ◽  
Gnrh Neuron ◽  
Fgf Receptor ◽  
Gnrh Neurons ◽  
A Cell

Abstract Increasing evidence suggests that fibroblast growth factors (FGFs) are neurotrophic in GnRH neurons. However, the extent to which FGFs are involved in establishing a functional GnRH system in the whole organism has not been investigated. In this study, transgenic mice with the expression of a dominant-negative FGF receptor mutant (FGFRm) targeted to GnRH neurons were generated to examine the consequence of disrupted FGF signaling on the formation of the GnRH system. To first test the effectiveness of this strategy, GT1 cells, a GnRH neuronal cell line, were stably transfected with FGFRm. The transfected cells showed attenuated neurite outgrowth, diminished FGF-2 responsiveness in a cell survival assay, and blunted activation of the signaling pathway in response to FGF-2. Transgenic mice expressing FGFRm in a GnRH neuron-specific manner exhibited a 30% reduction in GnRH neuron number, but the anatomical distribution of GnRH neurons was unaltered. Although these mice were initially fertile, they displayed several reproductive defects, including delayed puberty, reduced litter size, and early reproductive senescence. Overall, our results are the first to show, at the level of the organism, that FGFs are one of the important components involved in the formation and maintenance of the GnRH system.

scholarly journals Vasoactive Intestinal Peptide Excites GnRH Neurons in Male and Female Mice

Endocrinology ◽  
2016 ◽  
Vol 157 (9) ◽  
pp. 3621-3630 ◽  
Author(s):  
Richard Piet ◽  
Henry Dunckley ◽  
Kiho Lee ◽  
Allan E. Herbison
Keyword(s):  
Vasoactive Intestinal Peptide ◽  
Estrous Cycle ◽  
Suprachiasmatic Nucleus ◽  
Fluorescent Protein ◽  
Neuron Activity ◽  
Gnrh Neuron ◽  
Male And Female ◽  
Vip Receptors ◽  
Female Mice ◽  
Gnrh Neurons

A variety of external and internal factors modulate the activity of GnRH neurons to control fertility in mammals. A direct, vasoactive intestinal peptide (VIP)-mediated input to GnRH neurons originating from the suprachiasmatic nucleus is thought to relay circadian information within this network. In the present study, we examined the effects of VIP on GnRH neuron activity in male and female mice at different stages of the estrous cycle. We carried out cell-attached recordings in slices from GnRH-green fluorescent protein mice and calcium imaging in slices from a mouse line expressing the genetically encoded calcium indicator GCaMP3 selectively in GnRH neurons. We show that 50%–80% of GnRH neurons increase their firing rate in response to bath-applied VIP (1nM–1000nM) in both male and female mice and that this is accompanied by a robust increase in intracellular calcium concentrations. This effect is mediated directly at the GnRH neuron likely through activation of high-affinity VIP receptors. Because suprachiasmatic nucleus-derived timing cues trigger the preovulatory surge only on the afternoon of proestrus in female mice, we examined the effects of VIP during the estrous cycle at different times of day. VIP responsiveness in GnRH neurons did not vary significantly in diestrous and proestrous mice before or around the time of the expected preovulatory surge. These results indicate that the majority of GnRH neurons in male and female mice express functional VIP receptors and that the effects of VIP on GnRH neurons do not alter across the estrous cycle.

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