1
|
Constantin S, Moenter SM, Piet R. The electrophysiologic properties of gonadotropin-releasing hormone neurons. J Neuroendocrinol 2022; 34:e13073. [PMID: 34939256 PMCID: PMC9163209 DOI: 10.1111/jne.13073] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Revised: 11/10/2021] [Accepted: 11/18/2021] [Indexed: 11/26/2022]
Abstract
For about two decades, recordings of identified gonadotropin-releasing hormone (GnRH) neurons have provided a wealth of information on their properties. We describe areas of consensus and debate the intrinsic electrophysiologic properties of these cells, their response to fast synaptic and neuromodulatory input, Ca2+ imaging correlates of action potential firing, and signaling pathways regulating these aspects. How steroid feedback and development change these properties, functions of GnRH neuron subcompartments and local networks, as revealed by chemo- and optogenetic approaches, are also considered.
Collapse
Affiliation(s)
- Stephanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, Bethesda, MD 20892-3703, USA
- Section on Cellular Signaling, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD 20892, USA
| | - Suzanne M Moenter
- Departments of Molecular & Integrative Physiology, Internal Medicine, Obstetrics & Gynecology, and the Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Richard Piet
- Brain Health Research Institute & Department of Biological Sciences, Kent State University, Kent, OH, 44242, USA
| |
Collapse
|
2
|
Keen KL, Petersen AJ, Figueroa AG, Fordyce BI, Shin J, Yadav R, Erdin S, Pearce RA, Talkowski ME, Bhattacharyya A, Terasawa E. Physiological Characterization and Transcriptomic Properties of GnRH Neurons Derived From Human Stem Cells. Endocrinology 2021; 162:6298609. [PMID: 34125902 PMCID: PMC8294693 DOI: 10.1210/endocr/bqab120] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Indexed: 12/23/2022]
Abstract
Gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus play a key role in the regulation of reproductive function. In this study, we sought an efficient method for generating GnRH neurons from human embryonic and induced pluripotent stem cells (hESC and hiPSC, respectively). First, we found that exposure of primitive neuroepithelial cells, rather than neuroprogenitor cells, to fibroblast growth factor 8 (FGF8), was more effective in generating GnRH neurons. Second, addition of kisspeptin to FGF8 further increased the efficiency rates of GnRH neurogeneration. Third, we generated a fluorescent marker mCherry labeled human embryonic GnRH cell line (mCh-hESC) using a CRISPR-Cas9 targeting approach. Fourth, we examined physiological characteristics of GnRH (mCh-hESC) neurons: similar to GnRH neurons in vivo, they released the GnRH peptide in a pulsatile manner at ~60 min intervals; GnRH release increased in response to high potassium, kisspeptin, estradiol, and neurokinin B challenges; and injection of depolarizing current induced action potentials. Finally, we characterized developmental changes in transcriptomes of GnRH neurons using hESC, hiPSC, and mCh-hESC. The developmental pattern of transcriptomes was remarkably similar among the 3 cell lines. Collectively, human stem cell-derived GnRH neurons will be an important tool for establishing disease models to understand diseases, such as idiopathic hypothalamic hypogonadism, and testing contraceptive drugs.
Collapse
Affiliation(s)
- Kim L Keen
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, WI, USA
| | - Andrew J Petersen
- Waisman Center, Graduate School, University of Wisconsin, Madison, WI, USA
| | - Alexander G Figueroa
- Department of Anesthesiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Benjamin I Fordyce
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, WI, USA
| | - Jaeweon Shin
- Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
| | - Rachita Yadav
- Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Program in Medical and Population Genetics and Stanley Center for Psychiatric Research, Broad Institute, Cambridge, MA, USA
| | - Serkan Erdin
- Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Program in Medical and Population Genetics and Stanley Center for Psychiatric Research, Broad Institute, Cambridge, MA, USA
| | - Robert A Pearce
- Department of Anesthesiology, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
| | - Michael E Talkowski
- Center for Genomic Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
- Program in Medical and Population Genetics and Stanley Center for Psychiatric Research, Broad Institute, Cambridge, MA, USA
| | - Anita Bhattacharyya
- Waisman Center, Graduate School, University of Wisconsin, Madison, WI, USA
- Department of Cell and Regenerative Medicine, University of Wisconsin, Madison, WI, USA
| | - Ei Terasawa
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, WI, USA
- Department of Pediatrics, School of Medicine and Public Health, University of Wisconsin, Madison, WI, USA
- Correspondence: Ei Terasawa, PhD, Wisconsin National Primate Research Center, University of Wisconsin, 1223 Capitol Court, Madison, WI 53715-1299, USA.
| |
Collapse
|
3
|
Lan Z, Zhang W, Xu J, Lu W. GABA A receptor-mediated inhibition of Dahlgren cells electrical activity in the olive flounder, Paralichthys olivaceus. Gen Comp Endocrinol 2021; 306:113753. [PMID: 33711316 DOI: 10.1016/j.ygcen.2021.113753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 02/10/2021] [Accepted: 02/28/2021] [Indexed: 11/24/2022]
Abstract
γ-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system. We investigated its potential role as a neurotransmitter in the neuroendocrine Dahlgren cell population of the caudal neurosecretory system (CNSS) of the flounder Paralichthys olivaceus. The application of GABA in vitro resulted in a decrease in electrical activity of Dahlgren cells, followed by an increase of the number of silent cells, together with a decreased firing frequency of all three activity patterns (tonic, phasic, bursting). GABAA receptor agonist etomidate decreased Dahlgren cell firing activity, in a similar way to GABA. The response to GABA was blocked by the GABAA receptor antagonist bicuculline. GABAA receptor gamma2 subunit (Gabrg2) and chloride channel (Clcn2) mRNA expression were significantly upregulated in the CNSS after GABA superfusion. These data suggest that GABA may modulate CNSS activity in vivo mediated by GABAA receptors.
Collapse
Affiliation(s)
- Zhaohui Lan
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai 201306, China; International Research Center for Marine Biosciences at Shanghai Ocean University, Ministry of Science and Technology, China
| | - Wei Zhang
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai 201306, China; International Research Center for Marine Biosciences at Shanghai Ocean University, Ministry of Science and Technology, China
| | - Jinling Xu
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai 201306, China
| | - Weiqun Lu
- National Demonstration Center for Experimental Fisheries Science Education, Shanghai Ocean University, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai 201306, China; International Research Center for Marine Biosciences at Shanghai Ocean University, Ministry of Science and Technology, China.
| |
Collapse
|
4
|
Lopez-Rodriguez D, Franssen D, Bakker J, Lomniczi A, Parent AS. Cellular and molecular features of EDC exposure: consequences for the GnRH network. Nat Rev Endocrinol 2021; 17:83-96. [PMID: 33288917 DOI: 10.1038/s41574-020-00436-3] [Citation(s) in RCA: 41] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 10/16/2020] [Indexed: 12/12/2022]
Abstract
The onset of puberty and the female ovulatory cycle are important developmental milestones of the reproductive system. These processes are controlled by a tightly organized network of neurotransmitters and neuropeptides, as well as genetic, epigenetic and hormonal factors, which ultimately drive the pulsatile secretion of gonadotropin-releasing hormone. They also strongly depend on organizational processes that take place during fetal and early postnatal life. Therefore, exposure to environmental pollutants such as endocrine-disrupting chemicals (EDCs) during critical periods of development can result in altered brain development, delayed or advanced puberty and long-term reproductive consequences, such as impaired fertility. The gonads and peripheral organs are targets of EDCs, and research from the past few years suggests that the organization of the neuroendocrine control of reproduction is also sensitive to environmental cues and disruption. Among other mechanisms, EDCs interfere with the action of steroidal and non-steroidal receptors, and alter enzymatic, metabolic and epigenetic pathways during development. In this Review, we discuss the cellular and molecular consequences of perinatal exposure (mostly in rodents) to representative EDCs with a focus on the neuroendocrine control of reproduction, pubertal timing and the female ovulatory cycle.
Collapse
Affiliation(s)
| | - Delphine Franssen
- Neuroendocrinology Unit, GIGA Neurosciences, University of Liège, Liège, Belgium
| | - Julie Bakker
- Neuroendocrinology Unit, GIGA Neurosciences, University of Liège, Liège, Belgium
| | - Alejandro Lomniczi
- Division of Neuroscience, Oregon National Primate Research Center (ONPRC), OHSU, OR, USA
| | - Anne-Simone Parent
- Neuroendocrinology Unit, GIGA Neurosciences, University of Liège, Liège, Belgium.
- Department of Pediatrics, University Hospital Liège, Liège, Belgium.
| |
Collapse
|
5
|
Naulé L, Maione L, Kaiser UB. Puberty, A Sensitive Window of Hypothalamic Development and Plasticity. Endocrinology 2021; 162:bqaa209. [PMID: 33175140 PMCID: PMC7733306 DOI: 10.1210/endocr/bqaa209] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Indexed: 12/12/2022]
Abstract
Puberty is a developmental period characterized by a broad range of physiologic changes necessary for the acquisition of adult sexual and reproductive maturity. These changes mirror complex modifications within the central nervous system, including within the hypothalamus. These modifications result in the maturation of a fully active hypothalamic-pituitary-gonadal (HPG) axis, the neuroendocrine cascade ensuring gonadal activation, sex steroid secretion, and gametogenesis. A complex and finely regulated neural network overseeing the HPG axis, particularly the pubertal reactivation of gonadotropin-releasing hormone (GnRH) secretion, has been progressively unveiled in the last 3 decades. This network includes kisspeptin, neurokinin B, GABAergic, and glutamatergic neurons as well as glial cells. In addition to substantial modifications in the expression of key targets, several changes in neuronal morphology, neural connections, and synapse organization occur to establish mature and coordinated neurohormonal secretion, leading to puberty initiation. The aim of this review is to outline the current knowledge of the major changes that neurons secreting GnRH and their neuronal and glial partners undergo before and after puberty. Emerging mediators upstream of GnRH, uncovered in recent years, are also addressed herein. In addition, the effects of sex steroids, particularly estradiol, on changes in hypothalamic neurodevelopment and plasticity are discussed.
Collapse
Affiliation(s)
- Lydie Naulé
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
| | - Luigi Maione
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
- Paris Saclay University, Assistance Publique-Hôpitaux de Paris, Department Endocrinology and Reproductive Diseases, Bicêtre Hospital, Paris, France
| | - Ursula B Kaiser
- Division of Endocrinology, Diabetes and Hypertension, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
| |
Collapse
|
6
|
Spergel DJ. Modulation of Gonadotropin-Releasing Hormone Neuron Activity and Secretion in Mice by Non-peptide Neurotransmitters, Gasotransmitters, and Gliotransmitters. Front Endocrinol (Lausanne) 2019; 10:329. [PMID: 31178828 PMCID: PMC6538683 DOI: 10.3389/fendo.2019.00329] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Accepted: 05/07/2019] [Indexed: 12/18/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) neuron activity and GnRH secretion are essential for fertility in mammals. Here, I review findings from mouse studies on the direct modulation of GnRH neuron activity and GnRH secretion by non-peptide neurotransmitters (GABA, glutamate, dopamine, serotonin, norepinephrine, epinephrine, histamine, ATP, adenosine, and acetylcholine), gasotransmitters (nitric oxide and carbon monoxide), and gliotransmitters (prostaglandin E2 and possibly GABA, glutamate, and ATP). These neurotransmitters, gasotransmitters, and gliotransmitters have been shown to directly modulate activity and/or GnRH secretion in GnRH neurons in vivo or ex vivo (brain slices), from postnatal through adult mice, or in embryonic or immortalized mouse GnRH neurons. However, except for GABA, nitric oxide, and prostaglandin E2, which appear to be essential for normal GnRH neuron activity, GnRH secretion, and fertility in males and/or females, the biological significance of their direct modulation of GnRH neuron activity and/or GnRH secretion in the central regulation of reproduction remains largely unknown and requires further exploration.
Collapse
|
7
|
Song Y, Tao B, Chen J, Jia S, Zhu Z, Trudeau VL, Hu W. GABAergic Neurons and Their Modulatory Effects on GnRH3 in Zebrafish. Endocrinology 2017; 158:874-886. [PMID: 28324056 DOI: 10.1210/en.2016-1776] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 01/17/2017] [Indexed: 01/11/2023]
Abstract
γ-Aminobutyric acid (GABA) is a major amino acid neurotransmitter in the vertebrate brain. To provide detailed information on the distribution of the GABA in zebrafish (Danio rerio), neurons were labeled with mCherry driven by the glutamic acid decarboxylase 67 (gad67) promoter. In the transgenic line Tg(gad67:mCherry), mCherry-positive gad67 cell bodies were predominantly localized to the olfactory bulb, pallial zones, subpallium zones, parvocellular preoptic nucleus, periventricular gray zone of optic tectum, torus semicircularis, posterior tuberculum, medial longitudinal fascicle, caudal zone of periventricular hypothalamus, and oculomotor nucleus. mCherry-positive fibers were widely distributed in the olfactory bulbs, subpallium, thalamus, ventral hypothalamic zone, tectum opticum, mesencephalon, and rhombencephalon. mCherry-positive neurons were also observed in the retina and the spinal cord. The anatomical relationships between GABAergic and gonadotrophin-releasing hormone 3 (GnRH3) neurons were investigated by crossing Tg(gad67:mCherry) fish with the previously established Tg(gnrh3:EGFP) transgenic line. GnRH3 cell bodies and fibers were contacted by GABAergic fibers directly in the ventral telencephalon and anterior tuberal nucleus. A subpopulation of GnRH3 neurons in the ventral telencephalic area was also labeled with mCherry, so some GnRH3 neurons are also GABAergic. GABAB receptor agonist (baclofen) and antagonist (CGP55845) treatments indicated that GABAB receptor signaling inhibited gnrh3 expression in larval fish but was stimulatory in adult fish. The expression of pituitary lhβ and fshβ was stimulated by intraperitoneal injection of baclofen in adult fish. We conclude that GABA via GABAB receptors regulates GnRH3 neurons in a developmentally dependent manner in zebrafish.
Collapse
Affiliation(s)
- Yanlong Song
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Binbin Tao
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Ji Chen
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Shaoting Jia
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | - Zuoyan Zhu
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| | | | - Wei Hu
- State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China
| |
Collapse
|
8
|
Constantin S. Progress and Challenges in the Search for the Mechanisms of Pulsatile Gonadotropin-Releasing Hormone Secretion. Front Endocrinol (Lausanne) 2017; 8:180. [PMID: 28790978 PMCID: PMC5523686 DOI: 10.3389/fendo.2017.00180] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 07/10/2017] [Indexed: 12/05/2022] Open
Abstract
Fertility relies on the proper functioning of the hypothalamic-pituitary-gonadal axis. The hormonal cascade begins with hypothalamic neurons secreting gonadotropin-releasing hormone (GnRH) into the hypophyseal portal system. In turn, the GnRH-activated gonadotrophs in the anterior pituitary release gonadotropins, which then act on the gonads to regulate gametogenesis and sex steroidogenesis. Finally, sex steroids close this axis by feeding back to the hypothalamus. Despite this seeming straightforwardness, the axis is orchestrated by a complex neuronal network in the central nervous system. For reproductive success, GnRH neurons, the final output of this network, must integrate and translate a wide range of cues, both environmental and physiological, to the gonadotrophs via pulsatile GnRH secretion. This secretory profile is critical for gonadotropic function, yet the mechanisms underlying these pulses remain unknown. Literature supports both intrinsically and extrinsically driven GnRH neuronal activity. However, the caveat of the techniques supporting either one of the two hypotheses is the gap between events recorded at a single-cell level and GnRH secretion measured at the population level. This review aims to compile data about GnRH neuronal activity focusing on the physiological output, GnRH secretion.
Collapse
Affiliation(s)
- Stephanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, United States
- *Correspondence: Stephanie Constantin,
| |
Collapse
|
9
|
Woller MJ, Meyer S, Ada-Nguema A, Waechter-Brulla D. Dissecting Autocrine Effects on Pulsatile Release of Gonadotropin-Releasing Hormone in Cultured Rat Hypothalamic Tissue. Exp Biol Med (Maywood) 2016; 229:56-64. [PMID: 14709777 DOI: 10.1177/153537020422900107] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The control of reproductive function is manifested centrally through the control of hypothalamic release of gonadotropin-releasing hormone (GnRH) in episodic events or pulses. For GnRH release to occur in pulses, GnRH neurons must coordinate release events periodically to elicit a bolus of GnRH. We used a perifusion culture system to examine the release of GnRH from both intact hypothalami and enzymatically dispersed hypothalamic cells after challenge with GnRH analogs to evaluate the role of anatomical neuronal connections on autocrine/paracrine signals by GnRH on GnRH neurons. The potent GnRH agonist des-Gly10-D-Ala6-GnRH N-ethylamide, potent GnRH antagonists D-Phe2-D-Ala6-GnRH and D-Phe2,6-Pro3-GnRH or vehicle were infused, whereas GnRH release from hypothalamic tissue and cells were measured. PULSAR analysis of GnRH release profiles was conducted to evaluate parameters of pulsatile GnRH release. Infusion of the GnRH agonist resulted in a decrease in mean GnRH (P < 0.001), pulse nadir (P < 0.01), and pulse frequency (P < 0.05) but no effect on pulse amplitude. Infusion of GnRH antagonists resulted in an increase in mean GnRH (P < 0.001), pulse nadir (P < 0.05), and pulse frequency (P < 0.05) and in GnRH pulse amplitude only in dispersed cells (P < 0.05). These results are consistent with the hypothesis that GnRH inhibits endogenous GnRH release by an ultrashort-loop feedback mechanism and that treatment of hypothalamic tissue or cells with GnRH agonist inhibits ultrashort-loop feedback, whereas treatment with antagonists disrupts normal feedback to GnRH neurons and elicits an increased GnRH signal.
Collapse
Affiliation(s)
- Michael J Woller
- Biological Sciences, University of Wisconsin-Whitewater, Whitewater, Wisconsin 53190, USA.
| | | | | | | |
Collapse
|
10
|
Franssen D, Gérard A, Hennuy B, Donneau AF, Bourguignon JP, Parent AS. Delayed Neuroendocrine Sexual Maturation in Female Rats After a Very Low Dose of Bisphenol A Through Altered GABAergic Neurotransmission and Opposing Effects of a High Dose. Endocrinology 2016; 157:1740-50. [PMID: 26950200 DOI: 10.1210/en.2015-1937] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Rat sexual maturation is preceded by a reduction of the interpulse interval (IPI) of GnRH neurosecretion. This work aims at studying disruption of that neuroendocrine event in females after early exposure to a very low dose of bisphenol A (BPA), a ubiquitous endocrine disrupting chemical. Female rats were exposed to vehicle or BPA 25 ng/kg·d, 25 μg/kg·d, or 5 mg/kg·d from postnatal day (PND)1 to PND5 or PND15. Exposure to 25 ng/kg·d of BPA for 5 or 15 days was followed by a delay in developmental reduction of GnRH IPI studied ex vivo on PND20. After 15 days of exposure to that low dose of BPA, vaginal opening tended to be delayed. In contrast, exposure to BPA 5 mg/kg·d for 15 days resulted in a premature reduction in GnRH IPI and a trend toward early vaginal opening. RNA sequencing analysis on PND20 indicated that exposure to BPA resulted in opposing dose effects on the mRNA expression of hypothalamic genes involved in gamma aminobutyric acid A (GABAA) neurotransmission. The study of GnRH secretion in vitro in the presence of GABAA receptor agonist/antagonist confirmed an increased or a reduced GABAergic tone after in vivo exposure to the very low or the high dose of BPA, respectively. Overall, we show for the first time that neonatal exposure to BPA leads to opposing dose-dependent effects on the neuroendocrine control of puberty in the female rat. A very low and environmentally relevant dose of BPA delays neuroendocrine maturation related to puberty through increased inhibitory GABAergic neurotransmission.
Collapse
Affiliation(s)
- Delphine Franssen
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| | - Arlette Gérard
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| | - Benoit Hennuy
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| | - Anne-Françoise Donneau
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| | - Jean-Pierre Bourguignon
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| | - Anne-Simone Parent
- Neuroendocrinology Unit (D.F., A.G., J.-P.B., A.-S.P.), Interdisciplinary Cluster for Applied Genoproteomics Neurosciences; Interdisciplinary Cluster for Applied Genoproteomics Transcriptomic Platform (B.H.); and Department of Public Health (A.-F.D.), Biostatistics Unit, University of Liège, Sart-Tilman, B-4000 Liège, Belgium; and Department of Pediatrics (A.G., J.-P.B., A.-S.P.), Centre Hospitalier Universitaire de Liège, B-4032 Chênée, Belgium
| |
Collapse
|
11
|
Watanabe M, Fukuda A, Nabekura J. The role of GABA in the regulation of GnRH neurons. Front Neurosci 2014; 8:387. [PMID: 25506316 PMCID: PMC4246667 DOI: 10.3389/fnins.2014.00387] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2014] [Accepted: 11/12/2014] [Indexed: 11/13/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) neurons form the final common pathway for the central regulation of reproduction. Gamma-amino butyric acid (GABA) has long been implicated as one of the major players in the regulation of GnRH neurons. Although GABA is typically an inhibitory neurotransmitter in the mature adult central nervous system, most mature GnRH neurons show the unusual characteristic of being excited by GABA. While many reports have provided much insight into the contribution of GABA to the activity of GnRH neurons, the precise physiological role of the excitatory action of GABA on GnRH neurons remains elusive. This brief review presents the current knowledge of the role of GABA signaling in GnRH neuronal activity. We also discuss the modulation of GABA signaling by neurotransmitters and neuromodulators and the functional consequence of GABAergic inputs to GnRH neurons in both the physiology and pathology of reproduction.
Collapse
Affiliation(s)
- Miho Watanabe
- Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan
| | - Atsuo Fukuda
- Department of Neurophysiology, Hamamatsu University School of Medicine Hamamatsu, Japan
| | - Junichi Nabekura
- Department of Developmental Physiology, National Institute for Physiological Sciences Okazaki, Japan ; Core Research for Evolutionary Science and Technology, Japan Science and Technology Corporation Saitama, Japan ; Department of Physiological Sciences, The Graduate School for Advanced Study Hayama, Japan
| |
Collapse
|
12
|
Ren X, Wang S, Rong P, Zhu B. Activation of hypothalamic gono-like neurons in female rats during estrus. Neural Regen Res 2014; 7:2413-23. [PMID: 25337091 PMCID: PMC4200715 DOI: 10.3969/j.issn.1673-5374.2012.31.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2012] [Accepted: 10/08/2012] [Indexed: 11/18/2022] Open
Abstract
In mammals, gonadal function is controlled by the activity of hypothalamic gonadotropin-releasing hormone neurons, which control the secretion of adenohypophyseal and gonadal hormones. However, there are a number of unanswered questions in relation to gonadal function. It is currently unknown how erotogenic stimulation of the genitals influences the subpopulation of hypothalamic medial preoptic area neurons, antidromically identified as projecting to the median eminence at different periods of the estrous cycle. Additionally, the distinctiveness of hypothalamic medial preoptic area neurons, with respect to methods of feedback control by exogenous hormones, is also unknown. In this study, spontaneous discharges from individual neurons encountered within the medial preoptic area, gono-like neurons, were recorded extracellularly using glass microelectrodes. To confirm the cellular and histochemical properties of the recording units, antidromic stimulation was performed using a side-by-side bipolar stimulating electrode placed into the median eminence, alongside microiontophoretic injections of the conventional tracer, horseradish peroxidase. In addition, further immunohistochemical analyses were performed. Results showed that elevated gono-neuron activity was accompanied by increased background activity and greater responses to erotogenic stimuli during estrus. Application of clitoral traction stimulation resulted in increased activation of the gono-like neurons. This neuronal activity was noticeably inhibited by β-estradiol administration. Immunohistochemical analyses revealed the presence of gonadotropin-releasing hormone-reactive protein in hypothalamic cells in which electrophysiological recordings were taken. Thus, medial preoptic area neurons represent the subset of hypothalamic gonadotropin-releasing hormone neurons described from brain slices in vitro, and might serve as a useful physiological model to form the basis of future in vivo studies.
Collapse
Affiliation(s)
- Xiaoxuan Ren
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China ; School of Acupuncture-Moxibustion and Tuina, Beijing University of Chinese Medicine, Beijing 100029, China
| | - Shaojun Wang
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Peijing Rong
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Bing Zhu
- Institute of Acupuncture and Moxibustion, China Academy of Chinese Medical Sciences, Beijing 100700, China
| |
Collapse
|
13
|
Klenke U, Taylor-Burds C, Wray S. Metabolic influences on reproduction: adiponectin attenuates GnRH neuronal activity in female mice. Endocrinology 2014; 155:1851-63. [PMID: 24564393 PMCID: PMC3990841 DOI: 10.1210/en.2013-1677] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Metabolic dysfunctions are often linked to reproductive abnormalities. Adiponectin (ADP), a peripheral hormone secreted by white adipose tissue, is important in energy homeostasis and appetite regulation. GnRH neurons are integral components of the reproductive axis, controlling synthesis, and release of gonadotropins. This report examined whether ADP can directly act on GnRH neurons. Double-label immunofluorescence on brain sections from adult female revealed that a subpopulation of GnRH neurons express ADP receptor (AdipoR)2. GnRH/AdipoR2+ cells were distributed throughout the forebrain. To determine the influence of ADP on GnRH neuronal activity and the signal transduction pathway of AdipoR2, GnRH neurons maintained in explants were assayed using whole-cell patch clamping and calcium imaging. This mouse model system circumvents the dispersed distribution of GnRH neurons within the forebrain, making analysis of large numbers of GnRH cells possible. Single-cell PCR analysis and immunocytochemistry confirmed the presence of AdipoR2 in GnRH neurons in explants. Functional analysis revealed 20% of the total GnRH population responded to ADP, exhibiting hyperpolarization or decreased calcium oscillations. Perturbation studies revealed that ADP activates AMP kinase via the protein kinase Cζ/liver kinase B1 pathway. The modulation of GnRH neuronal activity by ADP demonstrated in this report directly links energy balance to neurons controlling reproduction.
Collapse
Affiliation(s)
- Ulrike Klenke
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, Maryland 20892-3703
| | | | | |
Collapse
|
14
|
Norberg R, Campbell R, Suter KJ. Ion channels and information processing in GnRH neuron dendrites. Channels (Austin) 2013; 7:135-45. [PMID: 23519241 PMCID: PMC3710340 DOI: 10.4161/chan.24228] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Recent findings indicate that a majority of action potentials originate from dendrites of GnRH neurons. This localization of the dendrite as the principle site of action potential initiation has sparked considerable interest in the nature of ionic channels throughout GnRH neurons. This paper will review the ionic conductances described within GnRH neurons and their implications for physiological output, such as sensitivity to steroids and diurnal state. To date, a majority of information regarding ionic conductances in GnRH neurons pertains to somata and the first 50–100 µm of dendrite length. Thus, unraveling the tapestry created by the nature and distribution of dendritic conductances in GnRH neurons lies at the forefront of understanding the control of reproductive hormone secretion.
Collapse
Affiliation(s)
- Rachael Norberg
- Department of Biology, University of Texas San Antonio, San Antonio, TX, USA
| | | | | |
Collapse
|
15
|
Casoni F, Hutchins BI, Donohue D, Fornaro M, Condie BG, Wray S. SDF and GABA interact to regulate axophilic migration of GnRH neurons. J Cell Sci 2012; 125:5015-25. [PMID: 22976302 DOI: 10.1242/jcs.101675] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Stromal derived growth factor (SDF-1) and gamma-aminobutyric acid (GABA) are two extracellular cues that regulate the rate of neuronal migration during development and may act synergistically. The molecular mechanisms of this interaction are still unclear. Gonadotropin releasing hormone-1 (GnRH) neurons are essential for vertebrate reproduction. During development, these neurons emerge from the nasal placode and migrate through the cribriform plate into the brain. Both SDF-1 and GABA have been shown to regulate the rate of GnRH neuronal migration by accelerating and slowing migration, respectively. As such, this system was used to explore the mechanism by which these molecules act to produce coordinated cell movement during development. In the present study, GABA and SDF-1 are shown to exert opposite effects on the speed of cell movement by activating depolarizing or hyperpolarizing signaling pathways, GABA via changes in chloride and SDF-1 via changes in potassium. GABA and SDF-1 were also found to act synergistically to promote linear rather than random movement. The simultaneous activation of these signaling pathways, therefore, results in tight control of cellular speed and improved directionality along the migratory pathway of GnRH neurons.
Collapse
Affiliation(s)
- Filippo Casoni
- Cellular and Developmental Neurobiology Section, NINDS/NIH, Bethesda, MD 20892, USA
| | | | | | | | | | | |
Collapse
|
16
|
Klenke U, Taylor-Burds C. Culturing embryonic nasal explants for developmental and physiological study. CURRENT PROTOCOLS IN NEUROSCIENCE 2012; Chapter 3:Unit 3.25.1-16. [PMID: 22470149 PMCID: PMC3384499 DOI: 10.1002/0471142301.ns0325s59] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Primary cultures obtained from embryonic nasal placodes can maintain olfactory neurons, olfactory ensheathing cells, and large numbers of gonadotropin releasing hormone-1 (GnRH) neurons. Depending on the age of the starting material, one can examine cell interactions important for placode formation or neuronal migration and axonal outgrowth. When generated at E11.5 in mouse, neuronal migration and axon outgrowth away from the main tissue mass occurs. This area of the explant, the periphery, is only a few cells thick. This characteristic offers the opportunity to image single cells and axons and allows pharmacological and molecular manipulations as well as physiological recordings to be performed. Here, we describe a system for culturing nasal explants used in our laboratory. This model system provides a method for obtaining physiological cellular responses with post hoc immunohistochemistry, or gene expression studies, on cells arising from the nasal placode.
Collapse
Affiliation(s)
- Ulrike Klenke
- Cellular and Developmental Neurobiology Section, NIH/NINDS, Bethesda, Maryland, USA
| | | |
Collapse
|
17
|
Abstract
Gonadotrophin-releasing hormone (GnRH)-secreting neurones are the final output of the central nervous system driving fertility in all mammals. Although it has been known for decades that the efficiency of communication between the hypothalamus and the pituitary depends on the pulsatile profile of GnRH secretion, how GnRH neuronal activity is patterned to generate pulses at the median eminence is unknown. To date, the scattered distribution of the GnRH cell bodies remains the main limitation to assessing the cellular events that could lead to pulsatile GnRH secretion. Taking advantage of the unique developmental feature of GnRH neurones, the nasal explant model allows primary GnRH neurones to be maintained within a micro-network where pulsatile secretion is preserved and where individual cellular activity can be monitored simultaneously across the cell population. This review summarises the data obtained from work using this in vitro model, and brings some insights into GnRH cellular physiology.
Collapse
Affiliation(s)
- S Constantin
- Department of Physiology, Centre for Neuroendocrinology, University of Otago, Dunedin, New Zealand.
| |
Collapse
|
18
|
Campbell RE, Ducret E, Porteous R, Liu X, Herde MK, Wellerhaus K, Sonntag S, Willecke K, Herbison AE. Gap junctions between neuronal inputs but not gonadotropin-releasing hormone neurons control estrous cycles in the mouse. Endocrinology 2011; 152:2290-301. [PMID: 21447638 DOI: 10.1210/en.2010-1311] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The role of gap junctions in the neural control of fertility remains poorly understood. Using acute brain slices from adult GnRH-green fluorescent protein transgenic mice, individual GnRH neurons were filled with a mixture of fluorescent dextran and neurobiotin. No dye transfer was found between any GnRH neurons, although approximately 30% of GnRH neurons exchanged neurobiotin with closely apposed cells. Dual electrophysiological recordings from pairs of GnRH neurons revealed an absence of electrical coupling. Using adult connexin 36 (Cx36)-cyan fluorescent protein transgenic mice, Cx36 was identified in cells within several hypothalamic brain regions, including 64% of preoptic area kisspeptin neurons but not in GnRH neurons. To assess the potential role of Cx36 in non-GnRH neurons within the GnRH neuronal network (i.e. neurons providing afferent inputs to GnRH neurons), a calmodulin kinase IIα-Cre (CKC)-LoxP strategy was used to generate mice with a neuron-specific deletion of Cx36 beginning in the first postnatal week. Mutant female mice exhibited normal puberty onset but disordered estrous cyclicity, although their fecundity was normal as was their estrogen-negative and -positive feedback mechanisms. The effects of adult deletion of Cx36 from neurons were assessed using a tamoxifen-dependent inducible CKC-Cx36 transgenic strategy. Mutant mice exhibited the same reproductive phenotype as the CKC-Cx36 animals. Together these observations demonstrate that there is no gap junctional coupling between GnRH neurons. However, it is apparent that other neurons within the GnRH neuronal network, potentially the preoptic kisspeptin neurons, are dependent on Cx36 gap junctions and that this is critical for normal estrous cyclicity.
Collapse
Affiliation(s)
- Rebecca E Campbell
- Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, Dunedin, New Zealand
| | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Bhattarai JP, Park SA, Park JB, Lee SY, Herbison AE, Ryu PD, Han SK. Tonic extrasynaptic GABA(A) receptor currents control gonadotropin-releasing hormone neuron excitability in the mouse. Endocrinology 2011; 152:1551-61. [PMID: 21285326 DOI: 10.1210/en.2010-1191] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
It is well established that the GABA(A) receptor plays an important role in regulating the electrical excitability of GnRH neurons. Two different modes of GABA(A) receptor signaling exist: one mediated by synaptic receptors generating fast (phasic) postsynaptic currents and the other mediated by extrasynaptic receptors generating a persistent (tonic) current. Using GABA(A) receptor antagonists picrotoxin, bicuculline methiodide, and gabazine, which differentiate between phasic and tonic signaling, we found that ∼50% of GnRH neurons exhibit an approximately 15-pA tonic GABA(A) receptor current in the acute brain slice preparation. The blockade of either neuronal (NO711) or glial (SNAP-5114) GABA transporter activity within the brain slice revealed the presence of tonic GABA signaling in ∼90% of GnRH neurons. The GABA(A) receptor δ subunit is only found in extrasynaptic GABA(A) receptors. Using single-cell RT-PCR, GABA(A) receptor δ subunit mRNA was identified in GnRH neurons and the δ subunit-specific agonist 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridin-3-ol was found to activate inward currents in GnRH neurons. Perforated-patch clamp studies showed that 4,5,6,7-tetrahydroisoxazolo [5,4-c] pyridin-3-ol exerted the same depolarizing or hyperpolarizing effects as GABA on juvenile and adult GnRH neurons and that tonic GABA(A) receptor signaling regulates resting membrane potential. Together, these studies reveal the presence of a tonic GABA(A) receptor current in GnRH neurons that controls their excitability. The level of tonic current is dependent, in part, on neuronal and glial GABA transporter activity and mediated by extrasynaptic δ subunit-containing GABA(A) receptors.
Collapse
Affiliation(s)
- Janardhan P Bhattarai
- Department of Oral Physiology and Institute of Oral Bioscience, School of Dentistry, Chonbuk National University, Jeonju, 561-756, Korea
| | | | | | | | | | | | | |
Collapse
|
20
|
Abstract
Gonadotropin-releasing hormone-1 (GnRH-1) neurons migrate from the nasal placode to the forebrain where they control gonadal function via the hypothalamic-pituitary-gonadal axis. The birth of GnRH-1-expressing neurons is one of the first neurogenic events in the developing nasal placode. By gene expression screening on single GnRH-1 neurons, amyloid precursor binding protein-1 (FE65) was identified in migratory GnRH-1 neurons. FE65 has been shown to modulate β1-integrin dynamics, actin cytoskeleton, cell motility, and FE65/amyloid precursor protein signaling has been described in neuro/glial cell fate determination as well as in modulating neurogenesis. Analysis of two mouse lines, one deficient for the 97 kDa FE65 isoform and a second deficient for the 97 and 60 kDa forms of FE65, showed overlapping phenotypes. In both lines, no migratory defects of the GnRH-1 neurons were observed, but a 25% increase in GnRH-1 neuronal number during embryonic development was found. Bromodeoxyuridine birth tracing and spatiotemporal tracking of GnRH-1 cell precursors demonstrated that the lack of the N-terminal portion of FE65, which includes part of the functional nuclear translocation/gene transcription domain of FE65 (WW domain), extends the timing of GnRH-1 neurogenesis in the developing nasal placode without affecting proliferation of GnRH-1 neuronal progenitors or cell death. The observed changes in the dynamics of GnRH-1 neurogenesis highlight a unique role for the 97 kDa isoform of FE65 and suggest that GnRH-1 cells, which have a short neurogenic window, originate from multipotent progenitors able to generate distinct cell types as GnRH-1 neurogenesis declines in response to environmental changes.
Collapse
|
21
|
Xu Y, Faulkner LD, Hill JW. Cross-Talk between Metabolism and Reproduction: The Role of POMC and SF1 Neurons. Front Endocrinol (Lausanne) 2011; 2:98. [PMID: 22649394 PMCID: PMC3355979 DOI: 10.3389/fendo.2011.00098] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 11/22/2011] [Indexed: 01/22/2023] Open
Abstract
Energy homeostasis and reproduction require tight coordination, but the mechanisms underlying their interaction are not fully understood. Two sets of hypothalamic neurons, namely pro-opiomelanocortin (POMC) neurons in the arcuate nucleus and steroidogenic factor-1 (SF1) neurons in the ventromedial hypothalamic nucleus, are emerging as critical nodes where metabolic and reproductive signals communicate. This view is supported by recent genetic studies showing that disruption of metabolic signals (e.g., leptin and insulin) or reproductive signals (e.g., estradiol) in these neurons leads to impaired regulation of both energy homeostasis and fertility. In this review, we will examine the potential mechanisms of neuronal communication between POMC, SF1, and gonadotropin-releasing hormone neurons in the regulation of metabolism and reproduction.
Collapse
Affiliation(s)
- Yong Xu
- Department of Pediatrics, Children’s Nutrition Research Center, Baylor College of MedicineHouston, TX, USA
- *Correspondence: Yong Xu, Department of Pediatrics, Children’s Nutrition Research Center, Baylor College of Medicine, Houston, TX 77030, USA e-mail: ; Jennifer W. Hill, Department of Physiology and Pharmacology, Center for Diabetes and Endocrine Research, College of Medicine, The University of Toledo, Toledo, OH, USA e-mail:
| | - Latrice D. Faulkner
- Department of Physiology and Pharmacology, Center for Diabetes and Endocrine Research, College of Medicine, The University of ToledoToledo, OH, USA
| | - Jennifer W. Hill
- Department of Physiology and Pharmacology, Center for Diabetes and Endocrine Research, College of Medicine, The University of ToledoToledo, OH, USA
- Department of Obstetrics and Gynecology, College of Medicine, The University of ToledoToledo, OH, USA
- *Correspondence: Yong Xu, Department of Pediatrics, Children’s Nutrition Research Center, Baylor College of Medicine, Houston, TX 77030, USA e-mail: ; Jennifer W. Hill, Department of Physiology and Pharmacology, Center for Diabetes and Endocrine Research, College of Medicine, The University of Toledo, Toledo, OH, USA e-mail:
| |
Collapse
|
22
|
Moenter SM. Identified GnRH neuron electrophysiology: a decade of study. Brain Res 2010; 1364:10-24. [PMID: 20920482 DOI: 10.1016/j.brainres.2010.09.066] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 09/15/2010] [Accepted: 09/17/2010] [Indexed: 12/27/2022]
Abstract
Over the past decade, the existence of transgenic mouse models in which reporter genes are expressed under the control of the gonadotropin-releasing hormone (GnRH) promoter has made possible the electrophysiological study of these cells. Here, we review the intrinsic and synaptic properties of these cells that have been revealed by these approaches, with a particular regard to burst generation. Advances in our understanding of neuromodulation of GnRH neurons and synchronization of this network are also discussed.
Collapse
Affiliation(s)
- Suzanne M Moenter
- Department of Molecular and Integrative Physiology, 7725 Med Sci II, 1301 E Catherine St., Ann Arbor, MI 48109-5622, USA.
| |
Collapse
|
23
|
Hyperpolarization-activated currents in gonadotropin-releasing hormone (GnRH) neurons contribute to intrinsic excitability and are regulated by gonadal steroid feedback. J Neurosci 2010; 30:13373-83. [PMID: 20926664 DOI: 10.1523/jneurosci.1687-10.2010] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Pulsatile release of gonadotropin-releasing hormone (GnRH) is required for fertility and is regulated by steroid feedback. Hyperpolarization-activated currents (I(h)) play a critical role in many rhythmic neurons. We examined the contribution of I(h) to the membrane and firing properties of GnRH neurons and the modulation of this current by steroid milieu. Whole-cell voltage- and current-clamp recordings were made of GFP-identified GnRH neurons in brain slices from male mice that were gonad-intact, castrated, or castrated and treated with estradiol implants. APV, CNQX, and bicuculline were included to block fast synaptic transmission. GnRH neurons (47%) expressed a hyperpolarization-activated current with pharmacological and biophysical characteristics of I(h). The I(h)-specific blocker ZD7288 reduced hyperpolarization-induced sag and rebound potential, decreased GnRH neuron excitability and action potential firing, and hyperpolarized membrane potential in some cells. ZD7288 also altered the pattern of burst firing and reduced the slope of recovery from the after-hyperpolarization potential. Activation of I(h) by hyperpolarization increased spike frequency, whereas inactivation of I(h) by depolarization reduced spike frequency. Castration increased I(h) compared with that in gonad-intact males. This effect was reversed by in vivo estradiol replacement. Together, these data indicate I(h) provides an excitatory drive in GnRH neurons that contributes to action potential burst firing and that estradiol regulates I(h) in these cells. As estradiol is the primary central negative feedback hormone on GnRH neuron firing in males, this provides insight into the mechanisms by which steroid hormones potentially alter the intrinsic properties of GnRH neurons to change their activity.
Collapse
|
24
|
Arroyo A, Kim BS, Biehl A, Yeh J, Bett GCL. Expression of kv4.3 voltage-gated potassium channels in rat gonadotrophin-releasing hormone (GnRH) neurons during the estrous cycle. Reprod Sci 2010; 18:136-44. [PMID: 20861393 DOI: 10.1177/1933719110382306] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Regular and timely electrical activity of gonadotrophin-releasing hormone (GnRH) neurons accompanies the pulsatile release of GnRH that plays a central role in regulating fertility. Although transient outward A-type currents (I(A)) have been electrophysiologically identified in GnRH neurons, the molecular identity of the channels that underlie these currents are unknown. Several families of voltage-gated potassium channels can underlie I(A). However, the biophysical properties of I(A) described in previous electrophysiological studies are strongly characteristic of members of the Kv4 family of voltage-gated channels. We, therefore, sought to determine the presence of Kv4 channels in GnRH neurons. We used reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis to determine whether Kv4 messenger RNA (mRNA) and protein are present in the rat medial preoptic area (MPOA) and median eminence (ME). We used double-label immunohistochemistry to determine whether Kv4 colocalized with GnRH cell bodies in the MPOA and GnRH axons in the ME. Kv4.3 channels co-localized with GnRH in the MPOA but not in the ME. Neither Kv4.2 nor Kv4.1 co-localized with GnRH in either the MPOA or the ME. The electrical activity of GnRH neurons changes dramatically during the estrous cycle. We, therefore, studied the change in Kv4.3 expression in GnRH neurons during the estrous cycle. In the estrus phase, 58.05% of GnRH neurons expressed Kv4.3 compared to 74.48% in diestrus-proestrus rats (P < .05). Our data suggest that Kv4.3 is the major molecular component of I(A) in GnRH neurons, and furthermore that the expression of Kv4.3 changes significantly during the rat estrous cycle.
Collapse
Affiliation(s)
- Armando Arroyo
- Department of Gynecology-Obstetrics, State University of New York, University at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, NY, USA.
| | | | | | | | | |
Collapse
|
25
|
Abstract
Oscillations in intracellular calcium levels have been described in GnRH-1 neurons in both prenatal and adult cells. However, differences have been reported in the mechanisms underlying these [Ca(2+)](i) oscillations, dependent on the model used. The goal of this study was to address whether these changes depend on the maturation status of GnRH-1 neurons by assaying prenatal GnRH-1 cells maintained in explants, at two different developmental stages. This report documents an increase in the frequency of [Ca(2+)](i) oscillations between 1 and 3 wk of in vitro maturation. During the early stage, [Ca(2+)](i) oscillations are blocked by tetrodotoxin and are mainly triggered by excitatory neurotransmitters, gamma-aminobutyric acid (GABA), and glutamate. In contrast, in the later stage, some cells exhibit residual tetrodotoxin-insensitive [Ca(2+)](i) oscillations, which are sustained by action potential-independent GABA and glutamate release. The strength of these two excitatory inputs remained relatively constant during the maturation process, and the increase in frequency of [Ca(2+)](i) oscillations observed at the later stage is due to a novel excitatory input carried by cholecystokinin. Together, these data indicate developmentally regulated release and interactions of neurotransmitters (known regulators of GnRH-1 cells in adults) and point to extrinsic factors regulating GnRH-1 cellular physiology.
Collapse
Affiliation(s)
- Stephanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke/National Institutes of Health, Bethesda, Maryland 20892-3703, USA
| | | | | |
Collapse
|
26
|
Jasoni CL, Romanò N, Constantin S, Lee K, Herbison AE. Calcium dynamics in gonadotropin-releasing hormone neurons. Front Neuroendocrinol 2010; 31:259-69. [PMID: 20594958 DOI: 10.1016/j.yfrne.2010.05.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Revised: 05/25/2010] [Accepted: 05/27/2010] [Indexed: 02/04/2023]
Abstract
The gonadotropin-releasing hormone (GnRH) neurons represent the key output cells of the neuronal network controlling fertility. Intracellular calcium ion concentration ([Ca(2+)](i)) is likely to be a key signaling tool used by GnRH neurons to regulate and co-ordinate multiple cell processes. This review examines the dynamics and control of [Ca(2+)](i) in GT1 cells, embryonic GnRH neurons in the nasal placode culture, and adult GnRH neurons in the acute brain slice preparation. GnRH neurons at all stages of development display spontaneous [Ca(2+)](i) transients driven, primarily, by their burst firing. However, the intracellular mechanisms generating [Ca(2+)](i) transients, and the control of [Ca(2+)](i) by neurotransmitters, varies markedly across the different developmental stages. The functional roles of [Ca(2+)](i) transients are beginning to be unraveled with one key action being that of regulating the dynamics of GnRH neuron burst firing.
Collapse
Affiliation(s)
- Christine L Jasoni
- Centre for Neuroendocrinology, Departments of Physiology, University of Otago, Dunedin 9054, New Zealand
| | | | | | | | | |
Collapse
|
27
|
Csercsik D, Farkas I, Szederkényi G, Hrabovszky E, Liposits Z, Hangos KM. Hodgkin–Huxley type modelling and parameter estimation of GnRH neurons. Biosystems 2010; 100:198-207. [DOI: 10.1016/j.biosystems.2010.03.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 03/01/2010] [Accepted: 03/09/2010] [Indexed: 10/19/2022]
|
28
|
Diurnal in vivo and rapid in vitro effects of estradiol on voltage-gated calcium channels in gonadotropin-releasing hormone neurons. J Neurosci 2010; 30:3912-23. [PMID: 20237262 DOI: 10.1523/jneurosci.6256-09.2010] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A robust surge of gonadotropin-releasing hormone (GnRH) release triggers the luteinizing hormone surge that induces ovulation. The GnRH surge is attributable to estradiol feedback, but the mechanisms are incompletely understood. Voltage-gated calcium channels (VGCCs) regulate hormone release and neuronal excitability, and may be part of the surge-generating mechanism. We examined VGCCs of GnRH neurons in brain slices from a model exhibiting daily luteinizing hormone surges. Mice were ovariectomized (OVX), and a subset was treated with estradiol implants (OVX+E). OVX+E mice exhibit negative feedback in the A.M. and positive feedback in the P.M. GnRH neurons express prominent high-voltage-activated (HVA) and small low-voltage-activated (LVA) macroscopic (whole-cell) Ca currents (I(Ca)). LVA-mediated currents were not altered by estradiol or time of day. In contrast, in OVX+E mice, HVA-mediated currents varied with time of day; HVA currents in cells from OVX+E mice were lower than those in cells from OVX mice in the A.M. but were higher in the P.M. These changes were attributable to diurnal alternations in L- and N-type components. There were no diurnal changes in any aspect of HVA-mediated I(Ca) in OVX mice. Acute in vitro treatment of cells from OVX and OVX+E mice with estradiol rapidly increased HVA currents primarily through L- and R-type VGCCs by activating estrogen receptor beta and GPR30, respectively. These results suggest multiple mechanisms contribute to the overall feedback regulation of HVA-mediated I(Ca) by estradiol. In combination with changes in synaptic inputs to GnRH neurons, these intrinsic changes in GnRH neurons may play critical roles in estradiol feedback.
Collapse
|
29
|
Krsmanovic LZ, Hu L, Leung PK, Feng H, Catt KJ. Pulsatile GnRH secretion: roles of G protein-coupled receptors, second messengers and ion channels. Mol Cell Endocrinol 2010; 314:158-63. [PMID: 19486924 PMCID: PMC2815227 DOI: 10.1016/j.mce.2009.05.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/21/2009] [Accepted: 05/24/2009] [Indexed: 12/31/2022]
Abstract
The pulsatile secretion of GnRH from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to multiple G proteins. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca(2+)- and cAMP-dependent signaling and GnRH neuronal firing. The firing of individual and/or bursts of action potentials (APs) in spontaneously active GnRH neurons is followed by afterhyperpolarization (AHP) that lasts from several milliseconds to several seconds. GnRH-induced activation of GnRH neurons causes a significant increase in medium AHP that is partially sensitive to apamin. GnRH-induced modulation of Ca(2+) influx and the consequent changes in AHP current suggest that the GnRH receptors expressed in hypothalamic GnRH neurons are important modulators of their neuronal excitability. The coexistence of multiple regulatory mechanisms could provide a high degree of redundancy in the maintenance of this crucial component of the reproductive process. It is also conceivable that this multifactorial system could reflect the gradation from simple to more complex neuroendocrine control systems for regulating hypothalamo-pituitary function and gonadal activity during the evolution of the GnRH pulse generator.
Collapse
Affiliation(s)
- Lazar Z Krsmanovic
- Section on Hormonal Regulation, PDEGEN, NICHD, NIH, Bethesda, MD 20892, USA.
| | | | | | | | | |
Collapse
|
30
|
Constantin S, Jasoni CL, Wadas B, Herbison AE. Gamma-aminobutyric acid and glutamate differentially regulate intracellular calcium concentrations in mouse gonadotropin-releasing hormone neurons. Endocrinology 2010; 151:262-70. [PMID: 19864483 DOI: 10.1210/en.2009-0817] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Multiple factors regulate the activity of the GnRH neurons responsible for controlling fertility. Foremost among neuronal inputs to GnRH neurons are those using the amino acids glutamate and gamma-aminobutyric acid (GABA). The present study used a GnRH-Pericam transgenic mouse line, enabling live cell imaging of intracellular calcium concentrations ([Ca(2+)](i)) to evaluate the effects of glutamate and GABA signaling on [Ca(2+)](i) in peripubertal and adult mouse GnRH neurons. Activation of GABA(A), N-methyl-d-aspartate, or alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate acid (AMPA) receptors was found to evoke an increase in [Ca(2+)](i), in subpopulations of GnRH neurons. Approximately 70% of GnRH neurons responded to GABA, regardless of postnatal age or sex. Many fewer (approximately 20%) GnRH neurons responded to N-methyl-d-aspartate, and this was not influenced by postnatal age or sex. In contrast, about 65% of adult male and female GnRH neurons responded to AMPA compared with about 14% of male and female peripubertal mice (P < 0.05). The mechanisms underlying the ability of GABA and AMPA to increase [Ca(2+)](i) in adult GnRH neurons were evaluated pharmacologically. Both GABA and AMPA were found to evoke [Ca(2+)](i) increases through a calcium-induced calcium release mechanism involving internal calcium stores and inositol-1,4,5-trisphosphate receptors. For GABA, the initial increase in [Ca(2+)](i) originated from GABA(A) receptor-mediated activation of L-type voltage-gated calcium channels, whereas for AMPA this appeared to involve direct calcium entry through the AMPA receptor. These observations show that all of the principal amino acid receptors are able to control [Ca(2+)](i) in GnRH neurons but that they do so in a postnatal age- and intracellular pathway-specific manner.
Collapse
Affiliation(s)
- Stephanie Constantin
- Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, Dunedin 9054, New Zealand
| | | | | | | |
Collapse
|
31
|
Zhang C, Bosch MA, Rick EA, Kelly MJ, Rønnekleiv OK. 17Beta-estradiol regulation of T-type calcium channels in gonadotropin-releasing hormone neurons. J Neurosci 2009; 29:10552-62. [PMID: 19710308 PMCID: PMC2774467 DOI: 10.1523/jneurosci.2962-09.2009] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 06/22/2009] [Accepted: 07/20/2009] [Indexed: 11/21/2022] Open
Abstract
T-type calcium channels are responsible for generating low-threshold spikes that facilitate burst firing and neurotransmitter release in neurons. Gonadotropin-releasing hormone (GnRH) neurons exhibit burst firing, but the underlying conductances are not known. Previously, we found that 17beta-estradiol (E2) increases T-type channel expression and excitability of hypothalamic arcuate nucleus neurons. Therefore, we used ovariectomized oil- or E2-treated EGFP (enhanced green fluorescent protein)-GnRH mice to explore the expression and E2 regulation of T-type channels in GnRH neurons. Based on single-cell reverse transcriptase-PCR and real-time PCR quantification of the T-type channel alpha(1) subunits, we found that all three subunits were expressed in GnRH neurons, with expression levels as follows: Cav3.3 > or = Cav3.2 > Cav3.1. The mRNA expression of the three subunits was increased with surge-inducing levels of E2 during the morning. During the afternoon, Cav3.3 mRNA expression remained elevated, whereas Cav3.1 and Cav3.2 were decreased. The membrane estrogen receptor agonist STX increased the expression of Cav3.3 but not Cav3.2 in GnRH neurons. Whole-cell patch recordings in GnRH neurons revealed that E2 treatment significantly augmented T-type current density at both time points and increased the rebound excitation during the afternoon. Although E2 regulated the mRNA expression of all three subunits in GnRH neurons, the increased expression combined with the slower inactivation kinetics of the T-type current indicates that Cav3.3 may be the most important for bursting activity associated with the GnRH/LH (luteinizing hormone) surge. The E2-induced increase in mRNA expression, which depends in part on membrane-initiated signaling, leads to increased channel function and neuronal excitability and could be a mechanism by which E2 facilitates burst firing and cyclic GnRH neurosecretion.
Collapse
Affiliation(s)
| | | | | | | | - Oline K. Rønnekleiv
- Department of Physiology and Pharmacology
- Department of Anesthesiology and Perioperative Medicine, and
- Division of Neuroscience, Oregon National Primate Research Center, Oregon Health & Science University, Portland, Oregon 97239-3098
| |
Collapse
|
32
|
Constantin S, Caligioni CS, Stojilkovic S, Wray S. Kisspeptin-10 facilitates a plasma membrane-driven calcium oscillator in gonadotropin-releasing hormone-1 neurons. Endocrinology 2009; 150:1400-12. [PMID: 18948403 PMCID: PMC2654742 DOI: 10.1210/en.2008-0979] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Kisspeptins, the natural ligands of the G-protein-coupled receptor (GPR)-54, are the most potent stimulators of GnRH-1 secretion and as such are critical to reproductive function. However, the mechanism by which kisspeptins enhance calcium-regulated neuropeptide secretion is not clear. In the present study, we used GnRH-1 neurons maintained in mice nasal explants to examine the expression and signaling of GPR54. Under basal conditions, GnRH-1 cells exhibited spontaneous baseline oscillations in intracellular calcium concentration ([Ca(2+)](i)), which were critically dependent on the operation of voltage-gated, tetrodotoxin (TTX)-sensitive sodium channels and were not coupled to calcium release from intracellular pools. Activation of native GPR54 by kisspeptin-10 initiated [Ca(2+)](i) oscillations in quiescent GnRH-1 cells, increased the frequency of calcium spiking in oscillating cells that led to summation of individual spikes into plateau-bursting type of calcium signals in a subset of active cells. These changes predominantly reflected the stimulatory effect of GPR54 activation on the plasma membrane oscillator activity via coupling of this receptor to phospholipase C signaling pathways. Both components of this pathway, inositol 1,3,4-trisphosphate and protein kinase C, contributed to the receptor-mediated modulation of baseline [Ca(2+)](i) oscillations. TTX and 2-aminoethyl diphenylborinate together abolished agonist-induced elevation in [Ca(2+)](i) in almost all cells, whereas flufenamic acid was less effective. Together these results indicate that a plasma membrane calcium oscillator is spontaneously operative in the majority of prenatal GnRH-1 neurons and is facilitated by kisspeptin-10 through phosphatidyl inositol diphosphate hydrolysis and depolarization of neurons by activating TTX-sensitive sodium channels and nonselective cationic channels.
Collapse
Affiliation(s)
- Stephanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorder and Stroke/National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | | | | |
Collapse
|
33
|
Kato M, Tanaka N, Ishii H, Yin C, Sakuma Y. Ca2+ channels and Ca2+-activated K+ channels in adult rat gonadotrophin-releasing hormone neurones. J Neuroendocrinol 2009; 21:312-5. [PMID: 19187462 DOI: 10.1111/j.1365-2826.2009.01849.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Gonadotrophin-releasing hormone (GnRH) neurones represent the final output neurones in the neuroendocrine system for the control of reproduction. To understand the reproductive neuroendocrine system, an investigation of the intrinsic and extrinsic properties of GnRH neurones is essential. In this review, we focus on the intrinsic properties and summarise our recent findings of ion channels expressed in rat GnRH neurones. Rat GnRH neurones express all four types of high voltage-activated Ca(2+) channel (L, N, P/Q, R) and the low voltage-activated Ca(2+) channel (T). GnRH neurones also express two types of Ca(2+)-activated K(+) [K(Ca)] channel: the small conductance Ca(2+)-activated K(+) (SK) channel and the large conductance Ca(2+)- and voltage-activated K(+) (BK) channel. The activities of these Ca(2+) and K(Ca) channels regulate cell excitability and cellular calcium homeostasis.
Collapse
Affiliation(s)
- M Kato
- Department of Physiology, Nippon Medical School, Tokyo, Japan
| | | | | | | | | |
Collapse
|
34
|
Roberts CB, Suter KJ. Emerging methodologies for the study of hypothalamic gonadotropin-releasing-hormone (GnRH) neurons. Integr Comp Biol 2008; 48:548-59. [PMID: 21669816 DOI: 10.1093/icb/icn039] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Gonadotropin-releasing-hormone (GnRH) neurons form part of a central neural oscillator that controls sexual reproduction through intermittent release of the GnRH peptide. Activity of GnRH neurons, and by extension release of GnRH, has been proposed to reflect intrinsic properties and synaptic input of GnRH neurons. To study GnRH neurons, we used traditional electrophysiology and computational methods. These emerging methodologies enhance the elucidation of processing in GnRH neurons. We used dynamic current-clamping to understand how living GnRH somata process input from glutamate and GABA, two key neurotransmitters in the neuroendocrine hypothalamus. In order to study the impact of synaptic integration in dendrites and neuronal morphology, we have developed full-morphology models of GnRH neurons. Using dynamic clamping, we have demonstrated that small-amplitude glutamatergic currents can drive repetitive firing in GnRH neurons. Furthermore, application of simulated GABAergic synapses with a depolarized reversal potential have revealed two functional subpopulations of GnRH neurons: one population in which GABA chronically depolarizes membrane potential (without inducing action potentials) and a second population in which GABAergic excitation results in slow spiking. Finally, when AMPA-type and GABA-type simulated inputs are applied together, action potentials occur when the AMPA-type conductance occurs during the descending phase of GABAergic excitation and at the nadir of GABAergic inhibition. Compartmental computer models have shown that excitatory synapses at >300 microns from somtata are unable to drive spiking with purely passive dendrites. In models with active dendrites, distal synapses are more efficient at driving spiking than somatic inputs. We then used our models to extend the results from dynamic current clamping at GnRH somata to distribute synaptic inputs along the dendrite. We show that propagation delays for dendritic synapses alter synaptic integration in GnRH neurons by widening the temporal window of interaction for the generation of action potentials. Finally, we have shown that changes in dendrite morphology can modulate the output of GnRH neurons by altering the efficacy of action potential generation in response to after-depolarization potentials (ADPs). Taken together, the methodologies of dynamic current clamping and multi-compartmental modeling can make major contributions to the study of synaptic integration and structure-function relationships in hypothalamic GnRH neurons. Use of these methodological approaches will continue to provide keen insights leading to conceptual advances in our understanding of reproductive hormone secretion in normal and pathological physiology and open the door to understanding whether the mechanisms of pulsatile GnRH release are conserved across species.
Collapse
Affiliation(s)
- Carson B Roberts
- Department of Biology, University of Texas at San Antonio, 1 UTSA Circle, San Antonio TX, 78249; Department of Electrical and Computer Engineering, Boston University, 8 Saint Mary's Street, Boston, MA 02215, USA
| | | |
Collapse
|
35
|
Roberts CB, Campbell RE, Herbison AE, Suter KJ. Dendritic action potential initiation in hypothalamic gonadotropin-releasing hormone neurons. Endocrinology 2008; 149:3355-60. [PMID: 18403488 PMCID: PMC2453095 DOI: 10.1210/en.2008-0152] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
It is dogma that action potentials are initiated at the soma/axon hillock of neurons. However, dendrites often exhibit conductances necessary for spike generation and represent functionally independent processing compartments within neurons. GnRH neurons provide an interesting neuronal phenotype with simple, relatively unbranched, unipolar or bipolar dendrites of extensive lengths (>1000 microm) covered in spines. These neurons control fertility and must integrate a variety of internal homeostatic and external environmental cues. We used imaging, electrophysiological, and modeling studies to understand how they integrate and process information along dendrites. Simultaneous recordings from distal dendrites and somata of individual GnRH neurons indicate distal dendrites are the primary site of spike initiation in these cells. Compartmental modeling indicates that sites of spike initiation depend upon location of excitatory input and dendrite geometry. Together, these studies demonstrate a novel pattern of spike generation in mammalian neurons and indicate that afferent inputs within distal dendritic microdomains directly initiate action potentials.
Collapse
Affiliation(s)
- Carson B Roberts
- Department of Biology, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | | | | | | |
Collapse
|
36
|
Constantin S, Wray S. Gonadotropin-releasing hormone-1 neuronal activity is independent of hyperpolarization-activated cyclic nucleotide-modulated channels but is sensitive to protein kinase a-dependent phosphorylation. Endocrinology 2008; 149:3500-11. [PMID: 18372334 PMCID: PMC2453097 DOI: 10.1210/en.2007-1508] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pulsatile release of GnRH-1 stimulates the anterior pituitary and induces secretion of gonadotropin hormones. GnRH-1 release is modulated by many neurotransmitters that act via G protein-coupled membrane receptors. cAMP is the most ubiquitous effector for these receptors. GnRH-1 neurons express hyperpolarization-activated cyclic nucleotide-modulated (HCN) channel protein in vivo. HCN channels are involved in neuronal pacemaking and can integrate cAMP signals. cAMP-dependent protein kinase (PKA) is also activated by cAMP signals, and PKA-dependent phosphorylation modulates voltage-activated channels. In this report, these two pathways were examined in GnRH-1 neurons as integrators of forskolin (FSK)-induced stimulation. The HCN3 isoform was detected in GnRH-1 neurons obtained from mouse nasal explants. ZD7288, a HCN channel blocker, significantly reduced the efficiency of FSK to stimulate GnRH-1 neurons, whereas blockade of PKA with Rp-adenosine-3',5'-cyclic monophosphorothioate triethylammonium did not attenuate the FSK-induced stimulation. To ensure that disruption of HCN channels on GnRH-1 neurons was responsible for reduction of FSK stimulation, experiments were performed removing gamma-aminobutyric acid (GABA), the major excitatory input to GnRH-1 neurons in nasal explants. Under these conditions, Rp-adenosine-3',5'-cyclic monophosphorothioate triethylammonium, but not ZD7288, altered the FSK-induced response of GnRH-1 neurons. These studies indicate that PKA-dependent phosphorylation is involved in the FSK-induced stimulation of GnRH-1 neurons rather than HCN channels, and HCN channels integrate the FSK-induced stimulation on GABAergic neurons. In addition, blockade of HCN channels did not modify basal GnRH-1 neuronal activity when GABAergic input was intact or removed, negating a role for these channels in basal GABAergic or GnRH-1 neuronal activity.
Collapse
Affiliation(s)
- Stephanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA
| | | |
Collapse
|
37
|
Roberts CB, Hemond P, Suter KJ. Synaptic integration in hypothalamic gonadotropin releasing hormone (GnRH) neurons. Neuroscience 2008; 154:1337-51. [PMID: 18556136 DOI: 10.1016/j.neuroscience.2008.04.067] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2008] [Revised: 04/28/2008] [Accepted: 04/29/2008] [Indexed: 11/29/2022]
Abstract
The impact of the A-type GABA (GABA-A) receptor in gonadotropin releasing hormone (GnRH) neurons is controversial. In adult GnRH neurons, the GABA-A receptor conductance has been reported to either hyperpolarize or depolarize GnRH neurons. Regardless of whether GABA is inhibitory or excitatory in GnRH neurons, GABAergic input would be integrated with post-synaptic potentials generated by other synaptic inputs. We used dynamic current clamping and compartmental computer modeling to examine the integration of AMPA-type glutamatergic input and GABA-mediated input in both the hyperpolarizing (inhibitory) and depolarizing (excitatory) modes in GnRH neurons from transgenic mice (Mus Musculus) generated on a C57BL6 background. In both living and model neurons, action potentials were most likely a few ms after a maximum in AMPA conductance coincided with a minimum in inhibitory GABA. Excitatory GABA interacted differently with AMPA, with spikes most likely, in both dynamic clamping of living neurons and in model neurons, when a maximum in AMPA coincided with the decay from peak of a maximum in GABA. Distributing synapses along the dendrite maximized the temporal relationship between AMPA and GABA conductances and therefore, the potential for spiking. Thus, these two dominant neurotransmitters could interact in multiple frames to generate action potentials in GnRH neurons.
Collapse
Affiliation(s)
- C B Roberts
- Department of Biology, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | | | | |
Collapse
|
38
|
Roberts CB, O'Boyle MP, Suter KJ. Dendrites determine the contribution of after depolarization potentials (ADPs) to generation of repetitive action potentials in hypothalamic gonadotropin releasing-hormone (GnRH) neurons. J Comput Neurosci 2008; 26:39-53. [PMID: 18461432 DOI: 10.1007/s10827-008-0095-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Revised: 02/22/2008] [Accepted: 03/31/2008] [Indexed: 11/25/2022]
Abstract
The impact of structure in modulating synaptic signals originating in dendrites is widely recognized. In this study, we focused on the impact of dendrite morphology on a local spike generating mechanism which has been implicated in hormone secretion, the after depolarization potential (ADP). Using multi-compartmental models of hypothalamic GnRH neurons, we systematically truncated dendrite length and determined the consequence on ADP amplitude and repetitive firing. Decreasing the length of the dendrite significantly increased the amplitude of the ADP and increased repetitive firing. These effects were observed in dendrites both with and without active conductances suggesting they largely reflect passive characteristics of the dendrite. In order to test the findings of the model, we performed whole-cell recordings in GnRH neurons and elicited ADPs using current injection. During recordings, neurons were filled with biocytin so that we could determine dendritic and total projection (dendrite plus axon) length. Neurons exhibited ADPs and increasing ADP amplitude was associated with decreasing dendrite length, in keeping with the predictions of the models. Thus, despite the relatively simple morphology of the GnRH neuron's dendrite, it can still exert a substantial impact on the final neuronal output.
Collapse
Affiliation(s)
- C B Roberts
- Department of Biology, University of Texas at San Antonio, 6900 North Loop, 1604 West, San Antonio, TX 78249, USA.
| | | | | |
Collapse
|
39
|
Kovacic P, Pozos RS, Draskovich CD. Unifying electrostatic mechanism for receptor-ligand activity. J Recept Signal Transduct Res 2008; 27:411-31. [PMID: 18097940 DOI: 10.1080/10799890701699686] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
A prior article in skeletal form proposed an electrostatic mechanism for receptor-ligand activity. The present review provides an elaboration, including supporting evidence. The fundamental aspect entails the presence of molecular electrostatic potential associated with ions and dipoles in the ligand. The ligand can be regarded as an electrical link that joins prevalent electrostatic fields present in the surrounding protein matrix. The exact role of these fields is speculative. One possibility is to function as conduits for electrons and radicals in cell signaling. There is increasing support for important participation of these species in signal transduction. There might also be a favorable influence on energetics involving the electron transfer process. A summary of receptor biology is also provided, including receptors for acetylcholine (nicotinic and muscarinic), GABA, adrenergic, and glutamate.
Collapse
Affiliation(s)
- Peter Kovacic
- Department of Chemistry, San Diego State University, San Diego, California 921812, USA.
| | | | | |
Collapse
|
40
|
Constantin S, Wray S. Gonadotropin-releasing hormone-1 neuronal activity is independent of cyclic nucleotide-gated channels. Endocrinology 2008; 149:279-90. [PMID: 17916627 PMCID: PMC2194613 DOI: 10.1210/en.2007-0955] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Accepted: 09/26/2007] [Indexed: 12/18/2022]
Abstract
Pulsatile release of GnRH-1 is essential for secretion of gonadotropin hormones. The frequency of GnRH-1 pulses is regulated during the reproductive cycle by numerous neurotransmitters. Cyclic nucleotide-gated (CNG) channels have been proposed as a mechanism to integrate the cAMP signal evoked by many neurotransmitters. This study reports the expression of the CNGA2 subunit in GnRH-1 neurons obtained from mouse nasal explants and shows the ability of GnRH-1 neurons to increase their activity in response to forskolin (activator of adenylyl cyclases), or 3-isobutyl-1-methylxanthine (inhibitor of phosphodiesterases) even after removal of gamma-aminobutyric acid (A)-ergic input. Next, the endogenous activity of adenylyl cyclases was evaluated as a component of the oscillatory mechanism of GnRH-1 neurons. Inhibition of endogenous activity of adenylyl cyclases did not alter GnRH-1 activity. The potential involvement of CNGA2 subunit in basal or induced activity was tested on GnRH-1 neurons obtained from CNGA2-deficient mice. Without up-regulation of CNGA1 or CNGA3, the absence of functional CNGA2 did not alter either the endogenous GnRH-1 neuronal activity or the response to forskolin, negating CNG channels from cAMP-sensitive mechanisms leading to changes in GnRH-1 neuronal activity. In addition, the potential role of CNGA2 subunit in the synchronization of calcium oscillations previously described was evaluated in GnRH-1 neurons from CNGA2-deficient explants. Synchronized calcium oscillations persisted in CNGA2-deficient GnRH-1 neurons. Taken together, these results indicate that CNGA2 channels are not necessary for either the response of GnRH-1 neurons to cAMP increases or the basal rhythmic activity of GnRH-1 neurons.
Collapse
Affiliation(s)
- Stéphanie Constantin
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | |
Collapse
|
41
|
Lee JM, Tiong J, Maddox DM, Condie BG, Wray S. Temporal migration of gonadotrophin-releasing hormone-1 neurones is modified in GAD67 knockout mice. J Neuroendocrinol 2008; 20:93-103. [PMID: 18081557 DOI: 10.1111/j.1365-2826.2007.01623.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Gonadotrophin-releasing hormone (GnRH-1) neurones reside in the forebrain and regulate gonadal function via the hypothalamic-pituitary-gonadal axis. Disruption of this axis results in reproductive dysfunction. During embryonic development, GnRH-1 neurones migrate from the nasal pit through the nasal/forebrain junction (NFJ) into the developing brain. Prenatally gamma-aminobutyric acid (GABA) is excitatory and has been shown to play a role in nervous system development. Both in vivo and in vitro experiments suggest that GABA inhibits migration of GnRH-1 neurones. The present study examines the migration of GnRH-1 neurones in GAD67 knockout (KO) mice to further elucidate the role of GABA on GnRH-1 neuronal development. Three stages were examined, embryonic day (E)12.5, E14.5 and E17.5. GnRH-1 cell number and location were analysed by immunocytochemistry and in situ hybridisation histochemistry. The total number of GnRH-1 immunopositive cells was similar between wild-type (WT) and KO mice. However, significant differences were found in the overall distribution of GnRH-1 immunopositive cells in GAD67 KO compared to WT mice at all stages. Subsequent analysis by area revealed differences occurred at the NFJ with an increase in GnRH-1 cells in GAD67 KO at E14.5 and a decrease in GnRH-1 cells in GAD67 KO at E17.5. Comparable counts for cells expressing GnRH-1 transcript and protein were obtained. These data indicate that attenuated levels of GABA accelerate GnRH-1 cell migration in nasal areas as well as movement of GnRH-1 cells into the central nervous system at the NFJ.
Collapse
Affiliation(s)
- J M Lee
- Cellular and Developmental Neurobiology Section, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, MD, USA
| | | | | | | | | |
Collapse
|
42
|
Campbell RE. Defining the gonadotrophin-releasing hormone neuronal network: transgenic approaches to understanding neurocircuitry. J Neuroendocrinol 2007; 19:561-73. [PMID: 17532792 DOI: 10.1111/j.1365-2826.2007.01561.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The gonadotrophin-releasing hormone (GnRH) neurones are the final downstream effector neurones driving the central regulation of reproductive function and fertility in all mammalian species. Although it is abundantly clear that successful fertility relies upon the communication of a variety signals regarding internal and external cues to the GnRH neuronal population, how this is achieved remains poorly understood. A range of technical limitations has posed significant hurdles to defining, with any certainty, the complexities of the synaptic neuronal network regulating GnRH neurones. However, recent advances in transgenic technology have opened up new avenues to reconsider questions aimed at understanding this critical network. This article addresses some of the latest advances that use transgenic mouse models as tools to understand the neuronal circuitry underpinning the regulation of the GnRH neurones. By incorporating standard morphological and viral tract tracing techniques with innovative transgenic tools, recent studies have uncovered previously unappreciated qualities of the GnRH neurone, including extensive dendritic lengths, numerous somal and dendritic spines and plasticity over pubertal development, along with beginning to define the primary and higher-order afferents that make up the GnRH neuronal network.
Collapse
Affiliation(s)
- R E Campbell
- Centre for Neuroendocrinology and Department of Physiology, University of Otago School of Medical Sciences, Dunedin, New Zealand.
| |
Collapse
|
43
|
Spergel DJ. Calcium and small-conductance calcium-activated potassium channels in gonadotropin-releasing hormone neurons before, during, and after puberty. Endocrinology 2007; 148:2383-90. [PMID: 17289846 PMCID: PMC3315592 DOI: 10.1210/en.2006-1693] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The pubertal increase in GnRH secretion resulting in sexual maturation and reproductive competence is a complex process involving kisspeptin stimulation of GnRH neurons and requiring Ca(2+) and possibly other intracellular messengers. To determine whether the expression of Ca(2+) channels, or small-conductance Ca(2+)-activated K(+) (SK) channels, whose activity reflects cytoplasmic free Ca(2+) concentration, changes at puberty in GnRH neurons, Ca(2+) and SK currents in GnRH neurons were recorded in brain slices of juvenile [postnatal day (P) 10-21], pubertal (P28-P42), and adult (> or =P56) male GnRH-green fluorescent protein transgenic mice using perforated-patch and whole-cell techniques. Ca(2+) currents were inhibited by the Ca(2+) channel blocker Cd(2+) and showed marked heterogeneity but were on average similar in juvenile, pubertal, and adult GnRH neurons. SK currents, which were inhibited by the SK channel blocker apamin and enhanced by the SK and intermediate-conductance Ca(2+)-activated K(+) channel activator 1-ethyl-2-benzimidazolinone, were also on average similar in juvenile, pubertal, and adult GnRH neurons. These findings suggest that whereas Ca(2+) and SK channels may participate in the pubertal increase in GnRH secretion and there may be changes in Ca(2+) or SK channel subtypes, overall Ca(2+) and SK channel expression in GnRH neurons remains relatively constant across pubertal development. Hence, the expected increase in GnRH neuron cytoplasmic free Ca(2+) concentration required for increased GnRH secretion at puberty appears to be due to mechanisms other than altered Ca(2+) or SK channel expression, e.g. increased membrane depolarization and subsequent activation of preexisting Ca(2+) channels after increased excitatory synaptic input.
Collapse
Affiliation(s)
- Daniel J Spergel
- Section of Endocrinology, Department of Pediatrics, University of Chicago, Illinois 60637-1470, USA.
| |
Collapse
|
44
|
Christian CA, Moenter SM. Estradiol induces diurnal shifts in GABA transmission to gonadotropin-releasing hormone neurons to provide a neural signal for ovulation. J Neurosci 2007; 27:1913-21. [PMID: 17314287 PMCID: PMC6673555 DOI: 10.1523/jneurosci.4738-06.2007] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ovulation is initiated by a surge of gonadotropin-releasing hormone (GnRH) secretion by the brain. GnRH is normally under negative feedback control by ovarian steroids. During sustained exposure to estradiol in the late follicular phase of the reproductive cycle, however, the feedback action of this steroid switches to positive, inducing the surge. Here, we used an established ovariectomized, estradiol-treated (OVX+E) mouse model exhibiting daily surges to investigate the neurobiological mechanisms underlying this switch. Specifically, we examined changes in GABA transmission to GnRH neurons, which can be excited by GABA(A) receptor activation. Spontaneous GABAergic postsynaptic currents (PSCs) were recorded in GnRH neurons from OVX+E and OVX mice in coronal and sagittal slices. There were no diurnal changes in PSC frequency in cells from OVX mice in either slice orientation. In OVX+E cells in both orientations, PSC frequency was low during negative feedback but increased at surge onset. During the surge peak, this increase subsided in coronal slices but persisted in sagittal slices. Comparison of PSCs before and during tetrodotoxin (TTX) treatment showed TTX decreased PSC frequency in OVX+E cells in sagittal slices, but not coronal slices. This indicates estradiol acts on multiple GABAergic afferent populations to increase transmission through both activity-dependent and -independent mechanisms. Estradiol also increased PSC amplitude during the surge. Estradiol and the diurnal cycle thus interact to induce shifts in both GABA transmission and postsynaptic response that would produce appropriate changes in GnRH neuron firing activity and hormone release.
Collapse
Affiliation(s)
- Catherine A. Christian
- Neuroscience Graduate Program, Departments of Medicine and Cell Biology, University of Virginia, Charlottesville, Virginia 22908
| | - Suzanne M. Moenter
- Neuroscience Graduate Program, Departments of Medicine and Cell Biology, University of Virginia, Charlottesville, Virginia 22908
| |
Collapse
|
45
|
Chu Z, Moenter SM. Physiologic regulation of a tetrodotoxin-sensitive sodium influx that mediates a slow afterdepolarization potential in gonadotropin-releasing hormone neurons: possible implications for the central regulation of fertility. J Neurosci 2006; 26:11961-73. [PMID: 17108170 PMCID: PMC6674881 DOI: 10.1523/jneurosci.3171-06.2006] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The brain controls fertility through release of gonadotropin-releasing hormone (GnRH), but the mechanisms underlying action potential patterning and GnRH release are not understood. We investigated whether GnRH neurons exhibit afterdepolarizing potentials (ADPs) and whether these are modified by reproductive state. Whole-cell current-clamp recordings of GnRH neurons in brain slices from ovariectomized mice revealed a slow ADP (sADP) after action potentials generated by brief current injection. Generating two or four spikes enhanced sADP amplitude and duration. sADP amplitude was not affected by blocking selected neurotransmitter/neuromodulator receptors, delayed-rectifier potassium channels, calcium-dependent cation channels, or hyperpolarization-activated cation channels but was halved by the calcium channel blocker cadmium and abolished by tetrodotoxin. Cadmium also reduced peak latency. Intrinsic mechanisms underlying the sADP were investigated using voltage-clamp protocols simulating action potential waveforms. A single action potential produced an inward current, which increased after double and quadruple stimulation. Cadmium did not affect current amplitude but reduced peak latency. Pretreatment with blockers of calcium-activated potassium currents (I(KCa)) reproduced this shift and blocked subsequent cadmium-induced changes, suggesting cadmium changes latency indirectly by blocking I(KCa). Tetrodotoxin abolished the inward current, suggesting that it is carried by sodium. In contrast, I(KCa) blockers increased the inward current, indicating that I(KCa) may oppose generation of the sADP. Strong sADPs were suprathreshold, generating repetitive spontaneous firing. I(ADP), sADP, and excitability were enhanced by in vivo estradiol, which triggers a preovulatory surge of GnRH release. Physiological feedback modification of this inward current and resulting sADP may modulate action potential firing and subsequent GnRH release.
Collapse
Affiliation(s)
| | - Suzanne M. Moenter
- Departments of Medicine and
- Cell Biology, University of Virginia, Charlottesville, Virginia 22908
| |
Collapse
|
46
|
Fujioka H, Yamanouchi K, Akema T, Nishihara M. The Effects of GABA on embryonic gonadotropin-releasing hormone neurons in rat hypothalamic primary culture. J Reprod Dev 2006; 53:323-31. [PMID: 17179652 DOI: 10.1262/jrd.18103] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) neurons arise in the olfactory placode, migrate into the preoptic area (POA), and then extend axons to the median eminence during embryogenesis. Little information is available concerning the properties of GnRH neurons during the late gestational period when GnRH neurons reach the POA and form neuronal networks, although many studies have examined such properties during earlier developmental stages or the postnatal period. The present study was performed to elucidate the involvement of gamma-aminobutyric acid (GABA), one of the major neurotransmitters modifying GnRH neural activity, in regulation of GnRH gene expression on embryonic day 18.5 (E18.5) using transgenic rats expressing enhanced green fluorescence protein (EGFP) under the control of GnRH promoter. First, using RT-PCR, the mRNA of two isoforms of the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), GAD65 and GAD67 was detected in E18.5 embryonic POA-containing tissues. GAD67-positive cells were also demonstrated in close vicinity to GnRH-positive cells by immunohistochemistry, and immunoreactivity for both the GABA-A and GABA-B receptor subunits was detected in GnRH neurons. Next, primary cultures derived from anterior hypothalamic tissue of E18.5 embryos were prepared, and the effects of GABA and its agonists on GnRH promoter activity were evaluated using EGFP expression as a marker. GABA and the GABA-A receptor agonist muscimol, but not the GABA-B receptor agonist baclofen, significantly increased the EGFP-positive/GnRH-positive cell ratio. These results suggest that GABA plays a role in stimulating GnRH gene expression through GABA-A receptors in embryonic GnRH neurons in late gestational stages.
Collapse
Affiliation(s)
- Hitomi Fujioka
- Department of Veterinary Physiology, Veterinary Medical Science, The University of Tokyo, Tokyo, Japan
| | | | | | | |
Collapse
|
47
|
Cottrell EC, Campbell RE, Han SK, Herbison AE. Postnatal remodeling of dendritic structure and spine density in gonadotropin-releasing hormone neurons. Endocrinology 2006; 147:3652-61. [PMID: 16644918 DOI: 10.1210/en.2006-0296] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The GnRH neurons represent the output cells of the neuronal network controlling gonadal function. Their activation initiates the onset of puberty, but the underlying mechanisms remain unclear. Using a GnRH-green fluorescent protein mouse model, we have been able to fill individual GnRH neurons with biocytin in the acute brain slice preparation to examine their morphological characteristics across puberty. GnRH neurons in prepubertal male mice [postnatal d 10-15 (PND10-15)] exhibited half as many dendritic and somal spines as adult male mice (>PND60; P < 0.05) but, surprisingly, a much more complex dendritic tree with 5-fold greater branch points (P < 0.05). Experiments examining somal and proximal dendritic spine numbers in vivo, in perfusion-fixed tissue from GnRH-green fluorescent protein mice, revealed the same pattern of approximately twice as many spines on adult GnRH neurons compared with PND10 male mice (P < 0.01). In contrast to the spine density alterations, reflecting changing excitatory input, confocal immunofluorescence studies revealed no differences in the numbers of vesicular gamma-aminobutyric acid transporter-immunoreactive elements adjacent to GnRH soma or proximal dendrites in prepubertal and adult male mice. Experiments evaluating dendritic tree structure in vivo (PND3, -10, and -35 and adult) revealed that GnRH neurons located in the rostral preoptic area, but not the medial septum, exhibited a more complex branching pattern at PND10, but that this was adult-like by PND35. These studies demonstrate unexpected dendritic tree remodeling in the GnRH neurons and provide evidence for an increase in direct excitatory inputs to GnRH neurons across the time of puberty.
Collapse
Affiliation(s)
- Elizabeth C Cottrell
- Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, P.O. Box 913, Dunedin 9001, New Zealand
| | | | | | | |
Collapse
|
48
|
Arroyo A, Kim B, Rasmusson RL, Bett G, Yeh J. Hyperpolarization-activated cation channels are expressed in rat hypothalamic gonadotropin-releasing hormone (GnRH) neurons and immortalized GnRH neurons. ACTA ACUST UNITED AC 2006; 13:442-50. [PMID: 16879992 DOI: 10.1016/j.jsgi.2006.05.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Indexed: 10/24/2022]
Abstract
OBJECTIVES The current research was conducted to determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN1-4) channels are expressed in gonadotropin-releasing hormone (GnRH) neurons in the female rat hypothalamus and immortalized GnRH neurons (GT1-7 cells). METHODS Double-label fluorescence immunohistochemistry was used to colocalize HCN1-4 channels and GnRH in GnRH neurons in the female rat hypothalamus. Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting, and immunocytochemistry were used to analyze HCN channel gene expression in GT1-7 cells. RESULTS Double-label fluorescence immunohistochemistry showed that 43% of hypothalamic GnRH neurons immunostained for HCN2 and 90% of GnRH neurons immunostained for HCN3. RT-PCR and Western blot showed expression of all four HCN channel subunits in GT1-7 cells. Double-label immunocytochemistry showed cytoplasmic immunostaining of HCN2 and HCN3 in GT1-7 cells. CONCLUSIONS This study demonstrates for the first time that HCN channels are expressed in GnRH neurons in the rat hypothalamus and GT1-7 cells. Our research supports the hypothesis that HCN channels may be involved in electrical bursting activity and pulsatile GnRH secretion in endogenous GnRH neurons and GT1-7 cells.
Collapse
Affiliation(s)
- Armando Arroyo
- Department of Gynecology-Obstetrics, University at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York 14222, USA.
| | | | | | | | | |
Collapse
|
49
|
Clarkson J, Herbison AE. Development of GABA and glutamate signaling at the GnRH neuron in relation to puberty. Mol Cell Endocrinol 2006; 254-255:32-8. [PMID: 16781054 DOI: 10.1016/j.mce.2006.04.036] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The gonadotropin-releasing hormone (GnRH) neurons represent the critical cell type activated to induce puberty in mammals. However, the mechanisms underlying their activation remain unclear. As the principal amino acid neurotransmitters in the brain, GABA and glutamate are known to have critical roles in the development of neuronal networks. This review provides an update on what is known about GABA and glutamate signaling at the GnRH neuron across development. An examination of morphological, receptor subunit expression, and electrophysiological data suggest that GABAA receptor signaling develops in advance of glutamatergic signaling. However, compared with other networks, the switch from GABAA receptor depolarization to hyperpolarization of GnRH neurons is delayed until the time of puberty. These observations suggest that developing GnRH neurons exhibit a sequence of GABA-->glutamate signaling similar to that of other neuronal networks but that it is significantly elongated so as to only be complete by the time of puberty onset.
Collapse
Affiliation(s)
- Jenny Clarkson
- Centre for Neuroendocrinology, Department of Physiology, University of Otago School of Medical Sciences, P.O. Box 913, Dunedin, New Zealand
| | | |
Collapse
|
50
|
Roberts CB, Best JA, Suter KJ. Dendritic processing of excitatory synaptic input in hypothalamic gonadotropin releasing-hormone neurons. Endocrinology 2006; 147:1545-55. [PMID: 16373415 DOI: 10.1210/en.2005-1350] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The activity of hypothalamic GnRH neurons results in the intermittent release of GnRH required for reproductive function. This intermittent neurosecretory activity has been proposed to reflect integration of intrinsic properties of and synaptic input to GnRH neurons. Determining the relative impact of synaptic inputs at different locations on the GnRH neuron is difficult, if not impossible, using only experimental approaches. Thus, we used electrophysiological recordings and neuronal reconstructions to generate computer models of GnRH neurons to examine the effects of synaptic inputs at varying distances from the soma along dendrites. The parameters of the models were adjusted to duplicate measured passive and active electrophysiology of cells from mouse brain slices. Our morphological findings reinforce the emerging picture of a complex dendritic structure of GnRH neurons. Furthermore, analysis of reduced morphology models indicated that this population of cells is unlikely to exhibit low-frequency tonic spiking in the absence of synaptic input. Finally, applying realistic patterns of synaptic input to modeled GnRH neurons indicates that synapses located more than about 30% of the average dendrite length from the soma cannot drive firing at frequencies consistent with neuropeptide release. Thus, processing of synaptic input to dendrites of GnRH neurons is probably more complex than simple summation.
Collapse
Affiliation(s)
- C B Roberts
- Department of Physiology, Emory University, School of Medicine, 615 Michael Street, Atlanta, Georgia 30322, USA
| | | | | |
Collapse
|