1
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Stimulation of GHRH Neuron Axon Growth by Leptin and Impact of Nutrition during Suckling in Mice. Nutrients 2023; 15:nu15051077. [PMID: 36904077 PMCID: PMC10005278 DOI: 10.3390/nu15051077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 02/12/2023] [Accepted: 02/16/2023] [Indexed: 02/24/2023] Open
Abstract
Nutrition during the early postnatal period can program the growth trajectory and adult size. Nutritionally regulated hormones are strongly suspected to be involved in this physiological regulation. Linear growth during the postnatal period is regulated by the neuroendocrine somatotropic axis, whose development is first controlled by GHRH neurons of the hypothalamus. Leptin that is secreted by adipocytes in proportion to fat mass is one of the most widely studied nutritional factors, with a programming effect in the hypothalamus. However, it remains unclear whether leptin stimulates the development of GHRH neurons directly. Using a Ghrh-eGFP mouse model, we show here that leptin can directly stimulate the axonal growth of GHRH neurons in vitro in arcuate explant cultures. Moreover, GHRH neurons in arcuate explants harvested from underfed pups were insensitive to the induction of axonal growth by leptin, whereas AgRP neurons in these explants were responsive to leptin treatment. This insensitivity was associated with altered activating capacities of the three JAK2, AKT and ERK signaling pathways. These results suggest that leptin may be a direct effector of linear growth programming by nutrition, and that the GHRH neuronal subpopulation may display a specific response to leptin in cases of underfeeding.
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2
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Memdouh S, Gavrilović I, Ng K, Cowan D, Abbate V. Advances in the detection of growth hormone releasing hormone synthetic analogs. Drug Test Anal 2021; 13:1871-1887. [PMID: 34665524 DOI: 10.1002/dta.3183] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 10/06/2021] [Accepted: 10/07/2021] [Indexed: 01/26/2023]
Abstract
The administration of growth hormone releasing hormone (GHRH) and its synthetic analogs is prohibited by the World Anti-Doping Agency (WADA). Although there is evidence of their use, based on admissions and intelligence, they do not appear to have been found in anti-doping samples by WADA accredited laboratories. This might be due to their small concentration in urine and limited knowledge about their metabolism, especially for unapproved synthetic analogs. This study investigates the in vitro metabolism and detection of four of the larger GHRH synthetic analogs (sermorelin, tesamorelin, CJC-1295, and CJC-1295 with drug affinity complex) in fortified urine. Nineteen major in vitro metabolites were identified, selected for synthesis, purified, and characterized in house. These were used as reference materials to spike into urine together with commercially available parent peptides and a metabolite of sermorelin (sermorelin(3-29)-NH2 ) to develop a sensitive liquid chromatography-tandem mass spectrometry method for their detection to help prove GHRH administration. Limits of detection of the target peptides were generally 1 ng/ml (WADA required performance limit) or less.
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Affiliation(s)
- Siham Memdouh
- Department of Analytical, Environmental and Forensic Sciences, King's College London, London, UK
| | - Ivana Gavrilović
- Drug Control Centre, King's Forensics, Department of Analytical, Environmental and Forensic Sciences, King's College London, London, UK
| | - Kelsey Ng
- Department of Analytical, Environmental and Forensic Sciences, King's College London, London, UK
| | - David Cowan
- Department of Analytical, Environmental and Forensic Sciences, King's College London, London, UK
| | - Vincenzo Abbate
- Department of Analytical, Environmental and Forensic Sciences, King's College London, London, UK
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3
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Bayne M, Alvarsson A, Devarakonda K, Li R, Jimenez-Gonzalez M, Garibay D, Conner K, Varghese M, Serasinghe MN, Chipuk JE, Hof PR, Stanley SA. Repeated hypoglycemia remodels neural inputs and disrupts mitochondrial function to blunt glucose-inhibited GHRH neuron responsiveness. JCI Insight 2020; 5:133488. [PMID: 33148883 PMCID: PMC7710320 DOI: 10.1172/jci.insight.133488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Accepted: 09/24/2020] [Indexed: 11/29/2022] Open
Abstract
Hypoglycemia is a frequent complication of diabetes, limiting therapy and increasing morbidity and mortality. With recurrent hypoglycemia, the counterregulatory response (CRR) to decreased blood glucose is blunted, resulting in hypoglycemia-associated autonomic failure (HAAF). The mechanisms leading to these blunted effects are only poorly understood. Here, we report, with ISH, IHC, and the tissue-clearing capability of iDISCO+, that growth hormone releasing hormone (GHRH) neurons represent a unique population of arcuate nucleus neurons activated by glucose deprivation in vivo. Repeated glucose deprivation reduces GHRH neuron activation and remodels excitatory and inhibitory inputs to GHRH neurons. We show that low glucose sensing is coupled to GHRH neuron depolarization, decreased ATP production, and mitochondrial fusion. Repeated hypoglycemia attenuates these responses during low glucose. By maintaining mitochondrial length with the small molecule mitochondrial division inhibitor-1, we preserved hypoglycemia sensitivity in vitro and in vivo. Our findings present possible mechanisms for the blunting of the CRR, significantly broaden our understanding of the structure of GHRH neurons, and reveal that mitochondrial dynamics play an important role in HAAF. We conclude that interventions targeting mitochondrial fission in GHRH neurons may offer a new pathway to prevent HAAF in patients with diabetes. GHRH neurons in the arcuate nucleus are activated by glucose deprivation; however, repeated hypoglycemia blunts activation, remodels inputs, and disrupts mitochondrial fusion.
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Affiliation(s)
| | | | | | | | | | | | | | - Merina Varghese
- Nash Family Department of Neuroscience and Friedman Brain Institute, and
| | - Madhavika N Serasinghe
- Tisch Cancer Institute and Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Jerry E Chipuk
- Tisch Cancer Institute and Department of Oncological Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Patrick R Hof
- Nash Family Department of Neuroscience and Friedman Brain Institute, and
| | - Sarah A Stanley
- Diabetes, Obesity and Metabolism Institute.,Nash Family Department of Neuroscience and Friedman Brain Institute, and
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4
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Bednarz K, Alshafie W, Aufmkolk S, Desserteaux T, Markam PS, Storch KF, Stroh T. Ultradian Secretion of Growth Hormone in Mice: Linking Physiology With Changes in Synapse Parameters Using Super-Resolution Microscopy. Front Neural Circuits 2020; 14:21. [PMID: 32523515 PMCID: PMC7261915 DOI: 10.3389/fncir.2020.00021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2020] [Accepted: 04/14/2020] [Indexed: 01/19/2023] Open
Abstract
Neuroendocrine circuits are orchestrated by the pituitary gland in response to hypothalamic hormone-releasing and inhibiting factors to generate an ultradian and/or circadian rhythm of hormone secretion. However, mechanisms that govern this rhythmicity are not fully understood. It has been shown that synaptic transmission in the rodent hypothalamus undergoes cyclical changes in parallel with rhythmic hormone secretion and a growing body of evidence suggests that rapid rewiring of hypothalamic neurons may be the source of these changes. For decades, structural synaptic studies have been utilizing electron microscopy, which provides the resolution suitable for visualizing synapses. However, the small field of view, limited specificity and manual analysis susceptible to bias fuel the search for a more quantitative approach. Here, we apply the fluorescence super-resolution microscopy approach direct Stochastic Optical Reconstruction Microscopy (dSTORM) to quantify and structurally characterize excitatory and inhibitory synapses that contact growth hormone-releasing-hormone (GHRH) neurons during peak and trough values of growth hormone (GH) concentration in mice. This approach relies on a three-color immunofluorescence staining of GHRH and pre- and post-synaptic markers, and a quantitative analysis with a Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm. With this method we confirm our previous findings, using electron microscopy, of increased excitatory synaptic input to GHRH neurons during peak levels of GH. Additionally, we find a shift in synapse numbers during low GH levels, where more inhibitory synaptic inputs are detected. Lastly, we utilize dSTORM to study novel aspects of synaptic structure. We show that more excitatory (but not inhibitory) pre-synaptic clusters associate with excitatory post-synaptic clusters during peaks of GH secretion and that the numbers of post-synaptic clusters increase during high hormone levels. The results presented here provide an opportunity to highlight dSTORM as a valuable quantitative approach to study synaptic structure in the neuroendocrine circuit. Importantly, our analysis of GH circuitry sheds light on the potential mechanism that drives ultradian changes in synaptic transmission and possibly aids in GH pulse generation in mice.
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Affiliation(s)
- Klaudia Bednarz
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada.,Department of Anatomy and Cell Biology, McGill University, Montreal, QC, Canada
| | - Walaa Alshafie
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada.,Integrated Program in Neuroscience, McGill University, Montreal, QC, Canada
| | - Sarah Aufmkolk
- Department of Genetics, Harvard Medical School, Boston, MA, United States
| | - Théotime Desserteaux
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada
| | - Pratap Singh Markam
- Integrated Program in Neuroscience, McGill University, Montreal, QC, Canada.,Douglas Mental Health University Institute, Montreal, QC, Canada
| | - Kai-Florian Storch
- Douglas Mental Health University Institute, Montreal, QC, Canada.,Department of Psychiatry, McGill University, Montreal, QC, Canada
| | - Thomas Stroh
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, QC, Canada.,Department of Anatomy and Cell Biology, McGill University, Montreal, QC, Canada
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5
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Rupp AC, Allison MB, Jones JC, Patterson CM, Faber CL, Bozadjieva N, Heisler LK, Seeley RJ, Olson DP, Myers MG. Specific subpopulations of hypothalamic leptin receptor-expressing neurons mediate the effects of early developmental leptin receptor deletion on energy balance. Mol Metab 2018; 14:130-138. [PMID: 29914853 PMCID: PMC6034096 DOI: 10.1016/j.molmet.2018.06.001] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 05/25/2018] [Accepted: 06/02/2018] [Indexed: 01/29/2023] Open
Abstract
OBJECTIVE To date, early developmental ablation of leptin receptor (LepRb) expression from circumscribed populations of hypothalamic neurons (e.g., arcuate nucleus (ARC) Pomc- or Agrp-expressing cells) has only minimally affected energy balance. In contrast, removal of LepRb from at least two large populations (expressing vGat or Nos1) spanning multiple hypothalamic regions produced profound obesity and metabolic dysfunction. Thus, we tested the notion that the total number of leptin-responsive hypothalamic neurons (rather than specific subsets of cells with a particular molecular or anatomical signature) subjected to early LepRb deletion might determine energy balance. METHODS We generated new mouse lines deleted for LepRb in ARC GhrhCre neurons or in Htr2cCre neurons (representing roughly half of all hypothalamic LepRb neurons, distributed across many nuclei). We compared the phenotypes of these mice to previously-reported models lacking LepRb in Pomc, Agrp, vGat or Nos1 cells. RESULTS The early developmental deletion of LepRb from vGat or Nos1 neurons produced dramatic obesity, but deletion of LepRb from Pomc, Agrp, Ghrh, or Htr2c neurons minimally altered energy balance. CONCLUSIONS Although early developmental deletion of LepRb from known populations of ARC neurons fails to substantially alter body weight, the minimal phenotype of mice lacking LepRb in Htr2c cells suggests that the phenotype that results from early developmental LepRb deficiency depends not simply upon the total number of leptin-responsive hypothalamic LepRb cells. Rather, specific populations of LepRb neurons must play particularly important roles in body energy homeostasis; these as yet unidentified LepRb cells likely reside in the DMH.
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Affiliation(s)
- Alan C Rupp
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Margaret B Allison
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Justin C Jones
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Christa M Patterson
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Chelsea L Faber
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Nadejda Bozadjieva
- Department of Surgery, University of Michigan Medical School, Ann Arbor, MI, USA
| | | | - Randy J Seeley
- Department of Surgery, University of Michigan Medical School, Ann Arbor, MI, USA
| | - David P Olson
- Department of Pediatrics and Communicable Diseases, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Martin G Myers
- Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI, USA.
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6
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Decourtye L, Clemessy M, Mire E, Ledent T, Périn L, Robinson IC, Le Bouc Y, Kappeler L. Impact of insulin on primary arcuate neurons culture is dependent on early-postnatal nutritional status and neuronal subpopulation. PLoS One 2018; 13:e0193196. [PMID: 29466413 PMCID: PMC5821369 DOI: 10.1371/journal.pone.0193196] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 02/06/2018] [Indexed: 12/23/2022] Open
Abstract
Nutrition plays a critical role in programming and shaping linear growth during early postnatal life through direct action on the development of the neuroendocrine somatotropic (GH/IGF-1) axis. IGF-1 is a key factor in modulating the programming of linear growth during this period. Notably, IGF-1 preferentially stimulates axonal growth of GHRH neurons in the arcuate nucleus of the hypothalamus (Arc), which is crucial for the proliferation of somatotroph progenitors in the pituitary, thus influencing later GH secretory capacity. However, other nutrition-related hormones may also be involved. Among them, insulin shares several structural and functional similarities with IGF-1, as well as downstream signaling effectors. We investigated the role of insulin in the control of Arc axonal growth using an in vitro model of arcuate explants culture and a cell-type specific approach (GHRH-eGFP mice) under both physiological conditions (normally fed pups) and those of dietary restriction (underfed pups). Our data suggest that insulin failed to directly control axonal growth of Arc neurons or influence specific IGF-1-mediated effects on GHRH neurons. Insulin may act on neuronal welfare, which appears to be dependent on neuronal sub-populations and is influenced by the nutritional status of pups in which Arc neurons develop.
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Affiliation(s)
- Lyvianne Decourtye
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
| | - Maud Clemessy
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
| | - Erik Mire
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
| | - Tatiana Ledent
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
| | - Laurence Périn
- Sorbonne Université, AP-HP, Hôpital Armand-Trousseau, Paris, France
| | - Iain C. Robinson
- MRC, National Institute for Medical Research, Division of Molecular Neuroendocrinology, London, United Kingdom
| | - Yves Le Bouc
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
| | - Laurent Kappeler
- Sorbonne Université, INSERM, Centre de Recherche St-Antoine, CRSA, Paris, France
- * E-mail:
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7
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Le Tissier P, Campos P, Lafont C, Romanò N, Hodson DJ, Mollard P. An updated view of hypothalamic-vascular-pituitary unit function and plasticity. Nat Rev Endocrinol 2017; 13:257-267. [PMID: 27934864 DOI: 10.1038/nrendo.2016.193] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The discoveries of novel functional adaptations of the hypothalamus and anterior pituitary gland for physiological regulation have transformed our understanding of their interaction. The activity of a small proportion of hypothalamic neurons can control complex hormonal signalling, which is disconnected from a simple stimulus and the subsequent hormone secretion relationship and is dependent on physiological status. The interrelationship of the terminals of hypothalamic neurons and pituitary cells with the vasculature has an important role in determining the pattern of neurohormone exposure. Cells in the pituitary gland form networks with distinct organizational motifs that are related to the duration and pattern of output, and modifications of these networks occur in different physiological states, can persist after cessation of demand and result in enhanced function. Consequently, the hypothalamus and pituitary can no longer be considered as having a simple stratified relationship: with the vasculature they form a tripartite system, which must function in concert for appropriate hypothalamic regulation of physiological processes, such as reproduction. An improved understanding of the mechanisms underlying these regulatory features has implications for current and future therapies that correct defects in hypothalamic-pituitary axes. In addition, recapitulating proper network organization will be an important challenge for regenerative stem cell treatment.
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Affiliation(s)
- Paul Le Tissier
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh, EH8 9XD, UK
| | - Pauline Campos
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique Fonctionnelle, rue de la Cardonille, F-34000 Montpellier, France
- INSERM, U661, rue de la Cardonille, F-34000 Montpellier, France
- Université de Montpellier, rue de la Cardonille, UMR-5203, F-34000 Montpellier, France
| | - Chrystel Lafont
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique Fonctionnelle, rue de la Cardonille, F-34000 Montpellier, France
- INSERM, U661, rue de la Cardonille, F-34000 Montpellier, France
- Université de Montpellier, rue de la Cardonille, UMR-5203, F-34000 Montpellier, France
| | - Nicola Romanò
- Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh, EH8 9XD, UK
| | - David J Hodson
- Institute of Metabolism and Systems Research and Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Edgbaston, B15 2TT, UK
- Centre for Endocrinology, Diabetes and Metabolism, Birmingham Health Partners, Birmingham, B15 2TH, UK
| | - Patrice Mollard
- Centre National de la Recherche Scientifique (CNRS), UMR-5203, Institut de Génomique Fonctionnelle, rue de la Cardonille, F-34000 Montpellier, France
- INSERM, U661, rue de la Cardonille, F-34000 Montpellier, France
- Université de Montpellier, rue de la Cardonille, UMR-5203, F-34000 Montpellier, France
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8
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Clemensson EKH, Clemensson LE, Fabry B, Riess O, Nguyen HP. Further investigation of phenotypes and confounding factors of progressive ratio performance and feeding behavior in the BACHD rat model of Huntington disease. PLoS One 2017; 12:e0173232. [PMID: 28273120 PMCID: PMC5342229 DOI: 10.1371/journal.pone.0173232] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 02/18/2017] [Indexed: 01/29/2023] Open
Abstract
Huntington disease is an inherited neurodegenerative disorder characterized by motor, cognitive, psychiatric and metabolic symptoms. We recently published a study describing that the BACHD rat model of HD shows an obesity phenotype, which might affect their motivation to perform food-based behavioral tests. Further, we argued that using a food restriction protocol based on matching BACHD and wild type rats' food consumption rates might resolve these motivational differences. In the current study, we followed up on these ideas in a longitudinal study of the rats' performance in a progressive ratio test. We also investigated the phenotype of reduced food consumption rate, which is typically seen in food-restricted BACHD rats, in greater detail. In line with our previous study, the BACHD rats were less motivated to perform the progressive ratio test compared to their wild type littermates, although the phenotype was no longer present when the rats' food consumption rates had been matched. However, video analysis of food consumption tests suggested that the reduced consumption rate found in the BACHD rats was not entirely based on differences in hunger, but likely involved motoric impairments. Thus, restriction protocols based on food consumption rates are not appropriate when working with BACHD rats. As an alternative, we suggest that studies where BACHD rats are used should investigate how the readouts of interest are affected by motivational differences, and use appropriate control tests to avoid misleading results. In addition, we show that BACHD rats display distinct behavioral changes in their progressive ratio performance, which might be indicative of striatal dysfunction.
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Affiliation(s)
- Erik Karl Håkan Clemensson
- Institute of Medical Genetics and Applied Genomics, Tuebingen, Tuebingen, Germany
- Centre for Rare Diseases, Tuebingen, Tuebingen, Germany
| | - Laura Emily Clemensson
- Institute of Medical Genetics and Applied Genomics, Tuebingen, Tuebingen, Germany
- Centre for Rare Diseases, Tuebingen, Tuebingen, Germany
- QPS Austria, Grambach, Austria
| | | | - Olaf Riess
- Institute of Medical Genetics and Applied Genomics, Tuebingen, Tuebingen, Germany
- Centre for Rare Diseases, Tuebingen, Tuebingen, Germany
| | - Huu Phuc Nguyen
- Institute of Medical Genetics and Applied Genomics, Tuebingen, Tuebingen, Germany
- Centre for Rare Diseases, Tuebingen, Tuebingen, Germany
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9
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De Magalhaes Filho CD, Kappeler L, Dupont J, Solinc J, Villapol S, Denis C, Nosten-Bertrand M, Billard JM, Blaise A, Tronche F, Giros B, Charriaut-Marlangue C, Aïd S, Le Bouc Y, Holzenberger M. Deleting IGF-1 receptor from forebrain neurons confers neuroprotection during stroke and upregulates endocrine somatotropin. J Cereb Blood Flow Metab 2017; 37:396-412. [PMID: 26762506 PMCID: PMC5381438 DOI: 10.1177/0271678x15626718] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Insulin-like growth factors control numerous processes, namely somatic growth, metabolism and stress resistance, connecting this pathway to aging and age-related diseases. Insulin-like growth factor signaling also impacts on neurogenesis, neuronal survival and structural plasticity. Recent reports demonstrated that diminished insulin-like growth factor signaling confers increased stress resistance in brain and other tissues. To better understand the role of neuronal insulin-like growth factor signaling in neuroprotection, we inactivated insulin-like growth factor type-1-receptor in forebrain neurons using conditional Cre-LoxP-mediated gene targeting. We found that brain structure and function, including memory performance, were preserved in insulin-like growth factor receptor mutants, and that certain characteristics improved, notably synaptic transmission in hippocampal neurons. To reveal stress-related roles of insulin-like growth factor signaling, we challenged the brain using a stroke-like insult. Importantly, when charged with hypoxia-ischemia, mutant brains were broadly protected from cell damage, neuroinflammation and cerebral edema. We also found that in mice with insulin-like growth factor receptor knockout specifically in forebrain neurons, a substantial systemic upregulation of growth hormone and insulin-like growth factor-I occurred, which was associated with significant somatic overgrowth. Collectively, we found strong evidence that blocking neuronal insulin-like growth factor signaling increases peripheral somatotropic tone and simultaneously protects the brain against hypoxic-ischemic injury, findings that may contribute to developing new therapeutic concepts preventing the disabling consequences of stroke.
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Affiliation(s)
- C Daniel De Magalhaes Filho
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
| | - Laurent Kappeler
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
| | | | | | | | - Cécile Denis
- 2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France.,5 INSERM UMR1130, Neurosciences, Institut de Biologie Paris-Seine, Paris, France.,6 CNRS UMR8246, Neurosciences, Institut de Biologie Paris-Seine, Paris, France
| | - Marika Nosten-Bertrand
- 2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France.,5 INSERM UMR1130, Neurosciences, Institut de Biologie Paris-Seine, Paris, France.,6 CNRS UMR8246, Neurosciences, Institut de Biologie Paris-Seine, Paris, France
| | - Jean-Marie Billard
- 7 Centre de Psychiatrie et Neurosciences, UMR894, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Annick Blaise
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
| | - François Tronche
- 2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France.,5 INSERM UMR1130, Neurosciences, Institut de Biologie Paris-Seine, Paris, France.,6 CNRS UMR8246, Neurosciences, Institut de Biologie Paris-Seine, Paris, France
| | - Bruno Giros
- 2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France.,5 INSERM UMR1130, Neurosciences, Institut de Biologie Paris-Seine, Paris, France.,6 CNRS UMR8246, Neurosciences, Institut de Biologie Paris-Seine, Paris, France.,8 Department of Psychiatry, Douglas Mental Health Research Center, McGill University, Montreal, Quebec, Canada
| | | | - Saba Aïd
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
| | - Yves Le Bouc
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
| | - Martin Holzenberger
- 1 INSERM Research Center UMR938, Paris, France.,2 Sorbonne Universités, UPMC - Université Pierre et Marie Curie, Paris, France
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10
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IGF-1 Induces GHRH Neuronal Axon Elongation during Early Postnatal Life in Mice. PLoS One 2017; 12:e0170083. [PMID: 28076448 PMCID: PMC5226784 DOI: 10.1371/journal.pone.0170083] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Accepted: 12/28/2016] [Indexed: 12/21/2022] Open
Abstract
Nutrition during the perinatal period programs body growth. Growth hormone (GH) secretion from the pituitary regulates body growth and is controlled by Growth Hormone Releasing Hormone (GHRH) neurons located in the arcuate nucleus of the hypothalamus. We observed that dietary restriction during the early postnatal period (i.e. lactation) in mice influences postnatal growth by permanently altering the development of the somatotropic axis in the pituitary gland. This alteration may be due to a lack of GHRH signaling during this critical developmental period. Indeed, underfed pups showed decreased insulin-like growth factor I (IGF-I) plasma levels, which are associated with lower innervation of the median eminence by GHRH axons at 10 days of age relative to normally fed pups. IGF-I preferentially stimulated axon elongation of GHRH neurons in in vitro arcuate explant cultures from 7 day-old normally fed pups. This IGF-I stimulating effect was selective since other arcuate neurons visualized concomitantly by neurofilament labeling, or AgRP immunochemistry, did not significantly respond to IGF-I stimulation. Moreover, GHRH neurons in explants from age-matched underfed pups lost the capacity to respond to IGF-I stimulation. Molecular analyses indicated that nutritional restriction was associated with impaired activation of AKT. These results highlight a role for IGF-I in axon elongation that appears to be cell selective and participates in the complex cellular mechanisms that link underfeeding during the early postnatal period with programming of the growth trajectory.
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11
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Tan HY, Steyn FJ, Huang L, Cowley M, Veldhuis JD, Chen C. Hyperphagia in male melanocortin 4 receptor deficient mice promotes growth independently of growth hormone. J Physiol 2016; 594:7309-7326. [PMID: 27558671 DOI: 10.1113/jp272770] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 08/22/2016] [Indexed: 12/13/2022] Open
Abstract
KEY POINTS Loss of function of the melanocortin 4 receptor (MC4R) results in hyperphagia, obesity and increased growth. Despite knowing that MC4Rs control food intake, we are yet to understand why defects in the function of the MC4R receptor contribute to rapid linear growth. We show that hyperphagia following germline loss of MC4R in male mice promotes growth while suppressing the growth hormone-insulin-like growth factor-1 (GH-IGF-1) axis. We propose that hyperinsulinaemia promotes growth while suppressing the GH-IGF-1 axis. It is argued that physiological responses essential to maintain energy flux override conventional mechanisms of pubertal growth to promote the storage of excess energy while ensuring growth. ABSTRACT Defects in melanocortin-4-receptor (MC4R) signalling result in hyperphagia, obesity and increased growth. Clinical observations suggest that loss of MC4R function may enhance growth hormone (GH)-mediated growth, although this remains untested. Using male mice with germline loss of the MC4R, we assessed pulsatile GH release and insulin-like growth factor-1 (IGF-1) production and/or release relative to pubertal growth. We demonstrate early-onset suppression of GH release in rapidly growing MC4R deficient (MC4RKO) mice, confirming that increased linear growth in MC4RKO mice does not occur in response to enhanced activation of the GH-IGF-1 axis. The progressive suppression of GH release in MC4RKO mice occurred alongside increased adiposity and the progressive worsening of hyperphagia-associated hyperinsulinaemia. We next prevented hyperphagia in MC4RKO mice through restricting calorie intake in these mice to match that of wild-type (WT) littermates. Pair feeding of MC4RKO mice did not prevent increased adiposity, but attenuated hyperinsulinaemia, recovered GH release, and normalized linear growth rate to that seen in pair-fed WT littermate controls. We conclude that the suppression of GH release in MC4RKO mice occurs independently of increased adipose mass, and is a consequence of hyperphagia-associated hyperinsulinaemia. It is proposed that physiological responses essential to maintain energy flux (hyperinsulinaemia and the suppression of GH release) override conventional mechanisms of pubertal growth to promote the storage of excess energy while ensuring growth. Implications of these findings are likely to extend beyond individuals with defects in MC4R signalling, encompassing physiological changes central to mechanisms of growth and energy homeostasis universal to hyperphagia-associated childhood-onset obesity.
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Affiliation(s)
- H Y Tan
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
| | - F J Steyn
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.,The University of Queensland Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia
| | - L Huang
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
| | - M Cowley
- Department of Physiology, Monash University, Melbourne, Victoria, Australia
| | - J D Veldhuis
- Department of Medicine, Endocrine Research Unit, Mayo School of Graduate Medical Education, Clinical Translational Science Center, Mayo Clinic, Rochester, MN, USA
| | - C Chen
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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Somatostatin triggers rhythmic electrical firing in hypothalamic GHRH neurons. Sci Rep 2016; 6:24394. [PMID: 27072430 PMCID: PMC4829871 DOI: 10.1038/srep24394] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Accepted: 03/29/2016] [Indexed: 12/12/2022] Open
Abstract
Hypothalamic growth hormone-releasing hormone (GHRH) neurons orchestrate body growth/maturation and have been implicated in feeding responses and ageing. However, the electrical patterns that dictate GHRH neuron functions have remained elusive. Since the inhibitory neuropeptide somatostatin (SST) is considered to be a primary oscillator of the GH axis, we examined its acute effects on GHRH neurons in brain slices from male and female GHRH-GFP mice. At the cellular level, SST irregularly suppressed GHRH neuron electrical activity, leading to slow oscillations at the population level. This resulted from an initial inhibitory action at the GHRH neuron level via K+ channel activation, followed by a delayed, sst1/sst2 receptor-dependent unbalancing of glutamatergic and GABAergic synaptic inputs. The oscillation patterns induced by SST were sexually dimorphic, and could be explained by differential actions of SST on both GABAergic and glutamatergic currents. Thus, a tripartite neuronal circuit involving a fast hyperpolarization and a dual regulation of synaptic inputs appeared sufficient in pacing the activity of the GHRH neuronal population. These “feed-forward loops” may represent basic building blocks involved in the regulation of GHRH release and its downstream sexual specific functions.
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Steyn FJ, Tolle V, Chen C, Epelbaum J. Neuroendocrine Regulation of Growth Hormone Secretion. Compr Physiol 2016; 6:687-735. [PMID: 27065166 DOI: 10.1002/cphy.c150002] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
This article reviews the main findings that emerged in the intervening years since the previous volume on hormonal control of growth in the section on the endocrine system of the Handbook of Physiology concerning the intra- and extrahypothalamic neuronal networks connecting growth hormone releasing hormone (GHRH) and somatostatin hypophysiotropic neurons and the integration between regulators of food intake/metabolism and GH release. Among these findings, the discovery of ghrelin still raises many unanswered questions. One important event was the application of deconvolution analysis to the pulsatile patterns of GH secretion in different mammalian species, including Man, according to gender, hormonal environment and ageing. Concerning this last phenomenon, a great body of evidence now supports the role of an attenuation of the GHRH/GH/Insulin-like growth factor-1 (IGF-1) axis in the control of mammalian aging.
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Affiliation(s)
- Frederik J Steyn
- University of Queensland Centre for Clinical Research and the School of Biomedical Sciences, University of Queensland, St. Lucia, Brisbane, Queensland, Australia
| | - Virginie Tolle
- Unité Mixte de Recherche en Santé 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Chen Chen
- School of Biomedical Sciences, University of Queensland, St. Lucia, Brisbane, Queensland, Australia
| | - Jacques Epelbaum
- University of Queensland Centre for Clinical Research and the School of Biomedical Sciences, University of Queensland, St. Lucia, Brisbane, Queensland, Australia
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14
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Luk HY, Kraemer WJ, Szivak TK, Flanagan SD, Hooper DR, Kupchak BR, Comstock BA, Dunn-Lewis C, Vingren JL, DuPont WH, Hymer WC. Acute resistance exercise stimulates sex-specific dimeric immunoreactive growth hormone responses. Growth Horm IGF Res 2015; 25:136-140. [PMID: 25934139 DOI: 10.1016/j.ghir.2015.02.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 01/30/2015] [Accepted: 02/13/2015] [Indexed: 10/24/2022]
Abstract
PURPOSE We sought to determine if an acute heavy resistance exercise test (AHRET) would elicit sex-specific responses in circulating growth hormone (GH), with untreated serum and serum treated with a reducing agent to break disulfide-bindings between GH dimers. METHODS 19 untrained participants (nine men and ten women) participated in an acute heavy resistance exercise test using the back squat. Blood samples were drawn before exercise (Pre), immediate post (IP), +15 min (+15), and +30 min (+30) afterwards. Serum samples were chemically reduced using glutathione (GSH). ELISAs were then used to compare immunoreactive GH concentrations in reduced (+GSH) and non-reduced (-GSH) samples. Data were analyzed using a three-way (2 sex × 2 treatment × 4 time) mixed methods ANOVA, with significance set at p ≤ 0.05. RESULTS GSH reduction resulted in increased immunoreactive GH concentrations when compared to non-reduced samples at Pre (1.68 ± 0.33 μg/L vs 1.25 ± 0.25 μg/L), IP (7.69 ± 1.08 μg/L vs 5.76 ± 0.80 μg/L), +15 min (4.39 ± 0.58 μg/L vs 3.24 ± 0.43 μg/L), and +30 min (2.35 ± 0.49 μg/L vs 1.45 ± 0.23 μg/L). Also, women demonstrated greater GH responses compared to men, and this was not affected by reduction. CONCLUSIONS Heavy resistance exercise increases immunoreactive GH dimer concentrations in men and women, with larger increases in women and more sustained response in men. The physiological significance of a sexually dimorphic GH response adds to the growing literature on aggregate GH and may be explained by differences in sex hormones and the structure of the GH cell network.
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Affiliation(s)
- Hui Ying Luk
- Department of Kinesiology, Health Promotion and Recreation, University of North Texas, Denton, TX, USA
| | - William J Kraemer
- Department of Human Sciences, The Ohio State University, Columbus, OH, USA.
| | - Tunde K Szivak
- Department of Human Sciences, The Ohio State University, Columbus, OH, USA
| | - Shawn D Flanagan
- Department of Human Sciences, The Ohio State University, Columbus, OH, USA
| | - David R Hooper
- Department of Human Sciences, The Ohio State University, Columbus, OH, USA
| | - Brian R Kupchak
- Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT, USA
| | - Brett A Comstock
- Division of Kinesiology and Sport Science, University of South Dakota, Vermillion, SD, USA
| | - Courtenay Dunn-Lewis
- Department of Health Sciences, School of Science and Engineering, Merrimack College, North Andover, MA, USA
| | - Jakob L Vingren
- Department of Kinesiology, Health Promotion and Recreation, University of North Texas, Denton, TX, USA
| | - William H DuPont
- Department of Human Sciences, The Ohio State University, Columbus, OH, USA
| | - Wesley C Hymer
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, USA
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Alatzoglou KS, Webb EA, Le Tissier P, Dattani MT. Isolated growth hormone deficiency (GHD) in childhood and adolescence: recent advances. Endocr Rev 2014; 35:376-432. [PMID: 24450934 DOI: 10.1210/er.2013-1067] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The diagnosis of GH deficiency (GHD) in childhood is a multistep process involving clinical history, examination with detailed auxology, biochemical testing, and pituitary imaging, with an increasing contribution from genetics in patients with congenital GHD. Our increasing understanding of the factors involved in the development of somatotropes and the dynamic function of the somatotrope network may explain, at least in part, the development and progression of childhood GHD in different age groups. With respect to the genetic etiology of isolated GHD (IGHD), mutations in known genes such as those encoding GH (GH1), GHRH receptor (GHRHR), or transcription factors involved in pituitary development, are identified in a relatively small percentage of patients suggesting the involvement of other, yet unidentified, factors. Genome-wide association studies point toward an increasing number of genes involved in the control of growth, but their role in the etiology of IGHD remains unknown. Despite the many years of research in the area of GHD, there are still controversies on the etiology, diagnosis, and management of IGHD in children. Recent data suggest that childhood IGHD may have a wider impact on the health and neurodevelopment of children, but it is yet unknown to what extent treatment with recombinant human GH can reverse this effect. Finally, the safety of recombinant human GH is currently the subject of much debate and research, and it is clear that long-term controlled studies are needed to clarify the consequences of childhood IGHD and the long-term safety of its treatment.
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Affiliation(s)
- Kyriaki S Alatzoglou
- Developmental Endocrinology Research Group (K.S.A., E.A.W., M.T.D.), Clinical and Molecular Genetics Unit, and Birth Defects Research Centre (P.L.T.), UCL Institute of Child Health, London WC1N 1EH, United Kingdom; and Faculty of Life Sciences (P.L.T.), University of Manchester, Manchester M13 9PT, United Kingdom
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Osterstock G, El Yandouzi T, Romanò N, Carmignac D, Langlet F, Coutry N, Guillou A, Schaeffer M, Chauvet N, Vanacker C, Galibert E, Dehouck B, Robinson ICAF, Prévot V, Mollard P, Plesnila N, Méry PF. Sustained alterations of hypothalamic tanycytes during posttraumatic hypopituitarism in male mice. Endocrinology 2014; 155:1887-98. [PMID: 24601879 DOI: 10.1210/en.2013-1336] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Traumatic brain injury is a leading cause of hypopituitarism, which compromises patients' recovery, quality of life, and life span. To date, there are no means other than standardized animal studies to provide insights into the mechanisms of posttraumatic hypopituitarism. We have found that GH levels were impaired after inducing a controlled cortical impact (CCI) in mice. Furthermore, GHRH stimulation enhanced GH to lower level in injured than in control or sham mice. Because many characteristics were unchanged in the pituitary glands of CCI mice, we looked for changes at the hypothalamic level. Hypertrophied astrocytes were seen both within the arcuate nucleus and the median eminence, two pivotal structures of the GH axis, spatially remote to the injury site. In the arcuate nucleus, GHRH neurons were unaltered. In the median eminence, injured mice exhibited unexpected alterations. First, the distributions of claudin-1 and zonula occludens-1 between tanycytes were disorganized, suggesting tight junction disruptions. Second, endogenous IgG was increased in the vicinity of the third ventricle, suggesting abnormal barrier properties after CCI. Third, intracerebroventricular injection of a fluorescent-dextran derivative highly stained the hypothalamic parenchyma only after CCI, demonstrating an increased permeability of the third ventricle edges. This alteration of the third ventricle might jeopardize the communication between the hypothalamus and the pituitary gland. In conclusion, the phenotype of CCI mice had similarities to the posttraumatic hypopituitarism seen in humans with intact pituitary gland and pituitary stalk. It is the first report of a pathological status in which tanycyte dysfunctions appear as a major acquired syndrome.
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Affiliation(s)
- Guillaume Osterstock
- INSERM Unité 661 (G.O., T.E.Y., N.Co., N.R., A.G., M.S., N.Ch., E.G., P.M., P.-F.M.), Centre National de la Recherche Scientifique Unité Mixte de Recherche 5203 (G.O., T.E.Y., N.R., N.Co., A.G., M.S., N.Ch., E.G., P.M., P.-F.M.), Institut de Génomique Fonctionelle, 34094 Montpellier, France; Université Montpellier 1, 2 (G.O., T.E.Y., N.R., N.Co., A.G., M.S., N.Ch., E.G., P.M., P.-F.M.), 34967 Montpellier, France; Division of Molecular Neuroendocrinology (D.C., I.C.A.F.R.), Medical Research Council National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom; Royal College of Surgeons in Ireland (G.O., T.E.Y., M.S., N.P.), Dublin 2, Ireland; INSERM Unité 837 (F.L., C.V., B.D., V.P.), Department of Development and Plasticity of the Postnatal Brain, Jean-Pierre Aubert Research Center, 59045 Lille, France; and University of Lille 2 (F.L., C.V., B.D., V.P.), 59000 Lille, France
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Aujla PK, Naratadam GT, Xu L, Raetzman LT. Notch/Rbpjκ signaling regulates progenitor maintenance and differentiation of hypothalamic arcuate neurons. Development 2013; 140:3511-21. [PMID: 23884446 DOI: 10.1242/dev.098681] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The hypothalamic arcuate nucleus (Arc), containing pro-opoiomelanocortin (POMC), neuropeptide Y (NPY) and growth hormone releasing hormone (GHRH) neurons, regulates feeding, energy balance and body size. Dysregulation of this homeostatic mediator underlies diseases ranging from growth failure to obesity. Despite considerable investigation regarding the function of Arc neurons, mechanisms governing their development remain unclear. Notch signaling factors such as Hes1 and Mash1 are present in hypothalamic progenitors that give rise to Arc neurons. However, how Notch signaling controls these progenitor populations is unknown. To elucidate the role of Notch signaling in Arc development, we analyzed conditional loss-of-function mice lacking a necessary Notch co-factor, Rbpjκ, in Nkx2.1-cre-expressing cells (Rbpjκ cKO), as well as mice with expression of the constitutively active Notch1 intracellular domain (NICD) in Nkx2.1-cre-expressing cells (NICD Tg). We found that loss of Rbpjκ results in absence of Hes1 but not of Hes5 within the primordial Arc at E13.5. Additionally, Mash1 expression is increased, coincident with increased proliferation and accumulation of Arc neurons at E13.5. At E18.5, Rbpjκ cKO mice have few progenitors and show increased numbers of differentiated Pomc, NPY and Ghrh neurons. By contrast, NICD Tg mice have increased hypothalamic progenitors, show an absence of differentiated Arc neurons and aberrant glial differentiation at E18.5. Subsequently, both Rbpjκ cKO and NICD Tg mice have changes in growth and body size during postnatal development. Taken together, our results demonstrate that Notch/Rbpjκ signaling regulates the generation and differentiation of Arc neurons, which contribute to homeostatic regulation of body size.
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Affiliation(s)
- Paven K Aujla
- University of Illinois at Urbana-Champaign, 407 South Goodwin Avenue, Urbana, IL 61801, USA
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18
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Hassouna R, Zizzari P, Viltart O, Yang SK, Gardette R, Videau C, Badoer E, Epelbaum J, Tolle V. A natural variant of obestatin, Q90L, inhibits ghrelin's action on food intake and GH secretion and targets NPY and GHRH neurons in mice. PLoS One 2012; 7:e51135. [PMID: 23251435 PMCID: PMC3519497 DOI: 10.1371/journal.pone.0051135] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Accepted: 10/29/2012] [Indexed: 01/04/2023] Open
Abstract
Background Ghrelin and obestatin are two gut-derived peptides originating from the same ghrelin/obestatin prepropeptide gene (GHRL). While ghrelin stimulates growth hormone (GH) secretion and food intake and inhibits γ-aminobutyric-acid synaptic transmission onto GHRH (Growth Hormone Releasing Hormone) neurons, obestatin blocks these effects. In Humans, GHRL gene polymorphisms have been associated with pathologies linked to an unbalanced energy homeostasis. We hypothesized that one polymorphism located in the obestatin sequence (Q to L substitution in position 90 of the ghrelin/obestatin prepropeptide, rs4684677) may impact on the function of obestatin. In the present study, we tested the activity of native and Q90L obestatin to modulate ghrelin-induced food intake, GH secretion, cFos activity in GHRH and Neuropeptide Y (NPY) neurons and γ-aminobutyric-acid activity onto GHRH neurons. Methodology/Principal findings Food intake, GH secretion and electrophysiological recordings were assessed in C57BL/6 mice. cFos activity was measured in NPY-Renilla-GFP and GHRH-eGFP mice. Mice received saline, ghrelin or ghrelin combined to native or Q90L obestatin (30 nmol each) in the early light phase. Ghrelin stimulation of food intake and GH secretion varied considerably among individual mice with 59–77% eliciting a robust response. In these high-responders, ghrelin-induced food intake and GH secretion were reduced equally by native and Q90L obestatin. In contrast to in vivo observations, Q90L was slightly more efficient than native obestatin in inhibiting ghrelin-induced cFos activation within the hypothalamic arcuate nucleus and the nucleus tractus solitarius of the brainstem. After ghrelin injection, 26% of NPY neurons in the arcuate nucleus expressed cFos protein and this number was significantly reduced by co-administration of Q90L obestatin. Q90L was also more potent that native obestatin in reducing ghrelin-induced inhibition of γ-aminobutyric-acid synaptic transmission onto GHRH neurons. Conclusions/Significance These data support the hypothesis that Q90L obestatin partially blocks ghrelin-induced food intake and GH secretion by acting through NPY and GHRH neurons.
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Affiliation(s)
- Rim Hassouna
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Philippe Zizzari
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Odile Viltart
- UMR 837 INSERM, Laboratoire “Développement et Plasticité du Cerveau Postnatal”, Centre de Recherches JPARC, Lille and Université Lille Nord de France (USTL- Lille 1), Lille, France
| | - Seung-Kwon Yang
- School of Biomedical Sciences, The University of Queensland, Skerman Building (65), St Lucia, Queensland, Australia
| | - Robert Gardette
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Catherine Videau
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Emilio Badoer
- School of Medical Sciences and Health Innovations Research Institute, RMIT University, Bundoora, Melbourne, Victoria, Australia
| | - Jacques Epelbaum
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Virginie Tolle
- UMR-S 894 INSERM, Centre de Psychiatrie et Neurosciences, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
- * E-mail:
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Sainsbury A, Zhang L. Role of the hypothalamus in the neuroendocrine regulation of body weight and composition during energy deficit. Obes Rev 2012; 13:234-57. [PMID: 22070225 DOI: 10.1111/j.1467-789x.2011.00948.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Energy deficit in lean or obese animals or humans stimulates appetite, reduces energy expenditure and possibly also decreases physical activity, thereby contributing to weight regain. Often overlooked in weight loss trials for obesity, however, is the effect of energy restriction on neuroendocrine status. Negative energy balance in lean animals and humans consistently inhibits activity of the hypothalamo-pituitary-thyroid, -gonadotropic and -somatotropic axes (or reduces circulating insulin-like growth factor-1 levels), while concomitantly activating the hypothalamo-pituitary-adrenal axis, with emerging evidence of similar changes in overweight and obese people during lifestyle interventions for weight loss. These neuroendocrine changes, which animal studies show may result in part from hypothalamic actions of orexigenic (e.g. neuropeptide Y, agouti-related peptide) and anorexigenic peptides (e.g. alpha-melanocyte-stimulating hormone, and cocaine and amphetamine-related transcript), can adversely affect body composition by promoting the accumulation of adipose tissue (particularly central adiposity) and stimulating the loss of lean body mass and bone. As such, current efforts to maximize loss of excess body fat in obese people may inadvertently be promoting long-term complications such as central obesity and associated health risks, as well as sarcopenia and osteoporosis. Future weight loss trials would benefit from assessment of the effects on body composition and key hormonal regulators of body composition using sensitive techniques.
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Affiliation(s)
- A Sainsbury
- Neuroscience Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia.
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Liu X, Zeng J, Zhou A, Theodorsson E, Fahrenkrug J, Reinscheid RK. Molecular fingerprint of neuropeptide S-producing neurons in the mouse brain. J Comp Neurol 2011; 519:1847-66. [PMID: 21452230 DOI: 10.1002/cne.22603] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Neuropeptide S (NPS) has been associated with a number of complex brain functions, including anxiety-like behaviors, arousal, sleep-wakefulness regulation, drug-seeking behaviors, and learning and memory. In order to better understand how NPS influences these functions in a neuronal network context, it is critical to identify transmitter systems that control NPS release and transmitters that are co-released with NPS. For this purpose, we generated several lines of transgenic mice that express enhanced green-fluorescent protein (EGFP) under control of the endogenous NPS precursor promoter. NPS/EGFP-transgenic mice show anatomically correct and overlapping expression of both NPS and EGFP. A total number of ∼500 NPS/EGFP-positive neurons are present in the mouse brain, located in the pericoerulear region and the Kölliker-Fuse nucleus. NPS and transgene expression is first detectable around E14, indicating a potential role for NPS in brain development. EGFP-positive cells were harvested by laser-capture microdissection, and mRNA was extracted for expression profiling by using microarray analysis. NPS was found co-localized with galanin in the Kölliker-Fuse nucleus of the lateral parabrachial area. A dense network of orexin/hypocretin neuronal projections contacting pericoerulear NPS-producing neurons was observed by immunostaining. Expression of a distinct repertoire of metabotropic and ionotropic receptor genes was identified in both NPS neuronal clusters that will allow for detailed investigations of incoming neurotransmission, controlling neuronal activity of NPS-producing neurons. Stress-induced functional activation of NPS-producing neurons was detected by staining for the immediate-early gene c-fos, thus supporting earlier findings that NPS might be part of the brain stress response network.
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Affiliation(s)
- Xiaobin Liu
- Department of Pharmaceutical Sciences, University of California Irvine, Irvine, California 92697, USA
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Feng DD, Yang SK, Loudes C, Simon A, Al-Sarraf T, Culler M, Alvear-Perez R, Llorens-Cortes C, Chen C, Epelbaum J, Gardette R. Ghrelin and obestatin modulate growth hormone-releasing hormone release and synaptic inputs onto growth hormone-releasing hormone neurons. Eur J Neurosci 2011; 34:732-44. [DOI: 10.1111/j.1460-9568.2011.07787.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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He Z, Fernandez-Fuente M, Strom M, Cheung L, Robinson IC, Le Tissier P. Continuous on-line monitoring of secretion from rodent pituitary endocrine cells using fluorescent protein surrogate markers. J Neuroendocrinol 2011; 23:197-207. [PMID: 21166728 DOI: 10.1111/j.1365-2826.2010.02104.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
We have developed a system to use secreted fluorescent proteins (FPs) as surrogate markers for the continuous on-line monitoring of hormone release from perfused tissue slices. We have tested this system using GH-GFP transgenic rats with green fluorescent protein (GFP) targeted to the secretory vesicles (SVs) of pituitary growth hormone (GH) cells. Brief exposures of vibratome slices to GH secretagogues [GH-releasing hormone (GHRH), GH-releasing peptide-6 (GHRP-6)] or somatostatin caused changes in FP output that correlate with hormone secretion, subsequently measured in fractions of perfusate by radioimmunoassay. The temporal resolution of this method was capable of revealing differences in the kinetics of response to GHRH and GHRP-6 between wild-type and dwarf (dw/dw) rats harbouring the GH-GFP transgene. We further tested the utility of the system by generating transgenic mice with red FPs targeted to secretory vesicles (PRL-mRFP(sv)) and to the cytoplasm (PRL-DsRed(cyto)) of lactotrophs. Dopamine had no effect on the FP output from pituitary slices of PRL-DsRed(cyto) mice but inhibited output from those of PRL-mRFP(sv) animals, with a rebound increase of release after removal, which again correlated with hormone output measured in the perfusate by radioimmunoassay. The inhibition of monomeric RFP secretion by dopamine was dose-dependent, as was stimulation by low concentrations of oxytocin. The temporal resolution afforded by this method provides useful insight into the release kinetics from large populations of pituitary cells, and fills a temporo-spatial gap between single vesicle and single cell monitoring of exocytosis in milliseconds, and in vivo sampling studies of release into the bloodstream on a time scale of minutes.
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Affiliation(s)
- Z He
- Division of Molecular Neuroendocrinology, MRC National Institute for Medical Research, London, UK
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McArthur S, Robinson IC, Gillies GE. Novel ontogenetic patterns of sexual differentiation in arcuate nucleus GHRH neurons revealed in GHRH-enhanced green fluorescent protein transgenic mice. Endocrinology 2011; 152:607-17. [PMID: 21159856 DOI: 10.1210/en.2010-0798] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
GH secretion and growth rates are developmentally regulated and sexually dimorphic, but the neuroregulatory mechanisms between birth and puberty are unclear. Using the GHRH-enhanced green fluorescent protein (eGFP) transgenic mouse, in which eGFP provides a strong surrogate signal for identifying GHRH neurons, we showed that numbers in the male arcuate nucleus were double those seen in females at x postnatal day (P)1 and P10, during which time numbers increased 2- to 3-fold. Thereafter (P20, P30, P60, P365) there was a significant trend for numbers to decrease in males and increase in females, such that sex differences were, surprisingly, absent in young and late adulthood. Conversely, we identified the emergence of male-dominant sex differences in the number of processes extended per GHRH perikarya across puberty. Intriguingly, prepubertal gonadectomy (P28), unlike adult gonadectomy, caused a dramatic 40% loss of GHRH cells in both sexes in adulthood and a significant (30%) increase in processes emanating from cell bodies only in females. These findings establish a novel ontogenetic profile for GHRH neurons and suggest previously undiscovered roles for peripubertal gonadal factors in establishing population size in both sexes. They also provide the first demonstration of emergent sex-specific GHRH architecture, which may signal the onset of sex-dependent regulation of activity reported for adult GHRH-eGFP neurons, and its differential regulation by gonadal factors in males and females. This information adds to our knowledge of processes that underpin the emergence of sex-specific GH secretory dynamics and hence biological activity of this pleiotropic hormone.
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Affiliation(s)
- Simon McArthur
- Division of Experimental Medicine, Imperial College, London W12 0NN, United Kingdom
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24
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Gouty-Colomer LA, Méry PF, Storme E, Gavois E, Robinson IC, Guérineau NC, Mollard P, Desarménien MG. Specific involvement of gonadal hormones in the functional maturation of growth hormone releasing hormone (GHRH) neurons. Endocrinology 2010; 151:5762-74. [PMID: 20926590 DOI: 10.1210/en.2010-0298] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Growth hormone (GH) is the key hormone involved in the regulation of growth and metabolism, two functions that are highly modulated during infancy. GH secretion, controlled mainly by GH releasing hormone (GHRH), has a characteristic pattern during postnatal development that results in peaks of blood concentration at birth and puberty. A detailed knowledge of the electrophysiology of the GHRH neurons is necessary to understand the mechanisms regulating postnatal GH secretion. Here, we describe the unique postnatal development of the electrophysiological properties of GHRH neurons and their regulation by gonadal hormones. Using GHRH-eGFP mice, we demonstrate that already at birth, GHRH neurons receive numerous synaptic inputs and fire large and fast action potentials (APs), consistent with effective GH secretion. Concomitant with the GH secretion peak occurring at puberty, these neurons display modifications of synaptic input properties, decrease in AP duration, and increase in a transient voltage-dependant potassium current. Furthermore, the modulation of both the AP duration and voltage-dependent potassium current are specifically controlled by gonadal hormones because gonadectomy prevented the maturation of these active properties and hormonal treatment restored it. Thus, GHRH neurons undergo specific developmental modulations of their electrical properties over the first six postnatal weeks, in accordance with hormonal demand. Our results highlight the importance of the interaction between the somatotrope and gonadotrope axes during the establishment of adapted neuroendocrine functions.
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25
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Mori K, Kim J, Sasaki K. Electrophysiological effect of ghrelin and somatostatin on rat hypothalamic arcuate neurons in vitro. Peptides 2010; 31:1139-45. [PMID: 20338206 DOI: 10.1016/j.peptides.2010.03.025] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Revised: 03/16/2010] [Accepted: 03/16/2010] [Indexed: 10/19/2022]
Abstract
Growth hormone (GH) secretion from the pituitary gland is partly regulated by GH releasing hormone (GHRH)-containing neurons located in the hypothalamic arcuate nucleus (ARC). GHRH-containing neurons express the GH secretagogue (GHS) receptor (GHS-R) and the somatostatin (SRIF) receptor. Recently, an endogenous ligand for the GHS-R named ghrelin was found. Therefore, it seems that both ghrelin and SRIF are involved in the hypothalamic regulation of GH release via GHRH-containing neurons in the ARC. In extracellular single unit recordings from in vitro hypothalamic slice preparations from rats, application of 100 nM ghrelin substantially excited ARC neurons (82.5%), whereas 1 microM SRIF substantially inhibited them (81.8%). The ghrelin-induced excitatory and SRIF-induced inhibitory effects on ARC neurons were dose-dependent and persisted during synaptic blockade using low-Ca(2+)/high-Mg(2+) solution. In addition, the effects were antagonized by [D-Lys(3)]-GHRP-6, a GHS-R antagonist, and CYN154806, a SRIF receptor subtype sst2 antagonist, respectively. When ghrelin and SRIF were sequentially applied to ARC neurons, 95.2% were excited by ghrelin and inhibited by SRIF. Similarly, 85.0% of ARC neuroendocrine cells that project to the median eminence were excited by ghrelin and inhibited by SRIF. These results indicate that ARC neuroendocrine cells projecting to the median eminence are dose-dependently, postsynaptically and oppositely regulated by ghrelin through GHS-R and SRIF via the SRIF sst2 receptor subtype. Our results also suggest that most of these ARC neuroendocrine cells are presumably GHRH-containing neurons and are involved in the cellular processes through which ghrelin and SRIF participate in the hypothalamic regulation of GH release.
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Affiliation(s)
- Kyohei Mori
- Division of Bio-Information Engineering, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama City, Toyama 930-8555, Japan
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26
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Caplan SR, Tannenbaum GS, Johnstone RM. An enzymatic model of the growth hormone-releasing hormone oscillator incorporating neuronal synchronization. J Theor Biol 2010; 264:984-9. [PMID: 20211631 DOI: 10.1016/j.jtbi.2010.02.042] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2009] [Revised: 02/05/2010] [Accepted: 02/24/2010] [Indexed: 10/19/2022]
Abstract
Models of growth hormone (GH) rhythmogenesis which we and others have presented suggest that the GH pulses in the circulation are generated by a GH-releasing hormone (GHRH) oscillator with a 1h periodicity. Here we examine the possibility that this is an intrinsic neuronal rhythm resulting from enzymatic reactions occurring in the axon terminals. A "Baselator" feedback reaction sequence can generate an hourly chemical burst of a primer (presumably a low molecular weight peptide) regulating Ca(2+)-triggered exocytosis of GHRH-loaded vesicles. Accordingly we propose that the priming species is largely immobilized by binding within the terminals. Free unbound primer is able to diffuse and is alternately phosphorylated and dephosphorylated by a kinase and a phosphatase (or undergoes a similar pair of complementary reactions). Under appropriate conditions involving feedback control of one or other of the enzymes the levels of both unreacted and reacted free primer peak sharply at hourly intervals. It is self-evident that synchronization between the packed terminals of the GHRH neurons at the median eminence is necessary to generate highly ordered in vivo pulses of GH release. Gap junctions provide a means of interterminal communication for the primer. Simulations of clusters of 4 adjacent axon terminals in a linear array were performed to assess whether and when synchrony can occur. With gap junctions closed the axons were set to be 90 degrees out of phase, i.e. their chemical bursts were separated by 15 min. Opening the gap junctions, assuming either that only the unphosphorylated species permeates, or that both species permeate, resulted in rapid overall synchronization. The oscillatory systems undergo mutual entrainment and all peaks appeared simultaneously at an intermediate hourly interval. This result was independent of the mode of chemical feedback, whether positive or negative. Closing the gap junctions led to a gradual, but not immediate, loss of synchrony.
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Affiliation(s)
- S Roy Caplan
- Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
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27
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Osterstock G, Escobar P, Mitutsova V, Gouty-Colomer LA, Fontanaud P, Molino F, Fehrentz JA, Carmignac D, Martinez J, Guerineau NC, Robinson ICAF, Mollard P, Méry PF. Ghrelin stimulation of growth hormone-releasing hormone neurons is direct in the arcuate nucleus. PLoS One 2010; 5:e9159. [PMID: 20161791 PMCID: PMC2820089 DOI: 10.1371/journal.pone.0009159] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Accepted: 01/08/2010] [Indexed: 11/26/2022] Open
Abstract
Background Ghrelin targets the arcuate nucleus, from where growth hormone releasing hormone (GHRH) neurones trigger GH secretion. This hypothalamic nucleus also contains neuropeptide Y (NPY) neurons which play a master role in the effect of ghrelin on feeding. Interestingly, connections between NPY and GHRH neurons have been reported, leading to the hypothesis that the GH axis and the feeding circuits might be co-regulated by ghrelin. Principal Findings Here, we show that ghrelin stimulates the firing rate of identified GHRH neurons, in transgenic GHRH-GFP mice. This stimulation is prevented by growth hormone secretagogue receptor-1 antagonism as well as by U-73122, a phospholipase C inhibitor and by calcium channels blockers. The effect of ghrelin does not require synaptic transmission, as it is not antagonized by γ-aminobutyric acid, glutamate and NPY receptor antagonists. In addition, this hypothalamic effect of ghrelin is independent of somatostatin, the inhibitor of the GH axis, since it is also found in somatostatin knockout mice. Indeed, ghrelin does not modify synaptic currents of GHRH neurons. However, ghrelin exerts a strong and direct depolarizing effect on GHRH neurons, which supports their increased firing rate. Conclusion Thus, GHRH neurons are a specific target for ghrelin within the brain, and not activated secondary to altered activity in feeding circuits. These results support the view that ghrelin related therapeutic approaches could be directed separately towards GH deficiency or feeding disorders.
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Affiliation(s)
- Guillaume Osterstock
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Pauline Escobar
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Violeta Mitutsova
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Laurie-Anne Gouty-Colomer
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Pierre Fontanaud
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - François Molino
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Jean-Alain Fehrentz
- Université Montpellier 1, 2, Montpellier, France
- CNRS UMR 5247, Institut des Biomolécules Max Mousseron, Montpellier, France
| | - Danielle Carmignac
- Division of Molecular Neuroendocrinology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
| | - Jean Martinez
- Université Montpellier 1, 2, Montpellier, France
- CNRS UMR 5247, Institut des Biomolécules Max Mousseron, Montpellier, France
| | - Nathalie C. Guerineau
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Iain C. A. F. Robinson
- Division of Molecular Neuroendocrinology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, United Kingdom
| | - Patrice Mollard
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
| | - Pierre-François Méry
- Inserm U-661, Montpellier, France
- CNRS UMR 5203, Institut de Génomique Fonctionnelle, Montpellier, France
- Université Montpellier 1, 2, Montpellier, France
- * E-mail:
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28
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Kumar TR, Larson M, Wang H, McDermott J, Bronshteyn I. Transgenic mouse technology: principles and methods. Methods Mol Biol 2009; 590:335-62. [PMID: 19763515 DOI: 10.1007/978-1-60327-378-7_22] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Introduction of foreign DNA into the mouse germ line is considered a major technical advancement in the fields of developmental biology and genetics. This technology now referred to as transgenic mouse technology has revolutionized virtually all fields of biology and provided new genetic approaches to model many human diseases in a whole animal context. Several hundreds of transgenic lines with expression of foreign genes specifically targeted to desired organelles/cells/tissues have been characterized. Further, the ability to spatio-temporally inactivate or activate gene expression in vivo using the "Cre-lox" technology has recently emerged as a powerful approach to understand various developmental processes including those relevant to molecular endocrinology. In this chapter, we will discuss the principles of transgenic mouse technology, and describe detailed methodology standardized at our institute.
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Affiliation(s)
- T Rajendra Kumar
- Department of Molecular & Integrative Physiology, University of Kansas Medical Center, Kansas City, KS, USA
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29
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Bouyer K, Faivre-Bauman A, Robinson ICAF, Epelbaum J, Loudes C. Sexually dimorphic distribution of sst2A receptors on growth hormone-releasing hormone neurones in mice: modulation by gonadal steroids. J Neuroendocrinol 2008; 20:1278-87. [PMID: 18752655 DOI: 10.1111/j.1365-2826.2008.01780.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ultradian pulsatile pattern of growth hormone (GH) secretion is markedly sexually dimorphic in rodents as in primates, but the neuroanatomical mechanisms of this phenomenon are not clear. In the arcuate nucleus of the hypothalamus, GH-releasing hormone (GHRH) neurones receive somatostatinergic inputs through the sst2A receptor (sst2A-R) and the percentage of GHRH neurones bearing sst2A-R is higher in female than in male GHRH-enhanced green fluorescent protein (eGFP) mice. In the present study, we hypothesised that sst2A-R expression on GHRH neurones is modulated by gonadal steroids and constitutes a mechanism for sexually differentiated GH secretion. The distribution of sst2A-R on GHRH neurones was evaluated by immunohistochemistry in adult GHRH-eGFP mice gonadectomised and treated for 3 weeks with oestradiol or testosterone implants. In gonadectomised females supplemented with testosterone, sst2A-R distribution on GHRH neurones was reduced to the level seen in intact males, whereas oestradiol implants were ineffective. Conversely, orchidectomy induced a female 'sst2A phenotype', which was reversed by testosterone supplementation. Changes in the hepatic expression of GH-dependent genes for major urinary protein-3 and the prolactin receptor reflected the altered steroid influence on GH pulsatile secretion. In the ventromedial-arcuate region, GHRH and sst2-R, as well as GHRH and somatostatin expression as measured by the real-time polymerase chain reaction, were positively correlated in both sexes. By contrast, the positive correlation between ventromedial-arcuate GHRH and periventricular somatostatin expression in males was reversed to a negative one in females. Moreover, the positive correlation between periventricular somatostatin and ventromedial-arcuate sst2-R expressions in males was lost in females. These results suggest that, in the adult mouse, testosterone is a major modulator of sst2A distribution on GHRH neurones. This marked sex difference in sst2A-R distribution may constitute a key element in the genesis of the sexually differentiated pattern of GH secretion, possibly through testosterone-modulated changes in somatostatin inputs from hypophysiotrophic periventricular neurones.
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Affiliation(s)
- K Bouyer
- UMR 894 INSERM, Centre de Psychiatrie et de Neurosciences, 2ter rue d'Alésia, Paris, France
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30
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Abstract
The ability to assess the activity of gonadotropin-releasing hormone (GnRH) neurons has been greatly enhanced by transgenic animal models with targeted expression of green fluorescent protein (GFP). However, it has yet to be demonstrated that the GnRH system continues to exhibit a full range of normal physiological functions in the presence of such genetic manipulation. Accordingly, we have used repetitive blood sampling via indwelling venous catheters to define LH secretory patterns in normal and transgenic mice. Transgenic females proved to be reproductively competent as defined by fecundity, appropriate cyclic changes in vaginal cytology in intact adult females, and spontaneous LH surges as well as surges in response to steroid or mating stimuli. The expression of c-fos following such steroid treatment and mating in ovariectomized transgenics was similar to the expression previously reported in nontransgenic mice. Likewise, the percentage of retrogradely labeled GnRH neurons was similar to that reported in nontransgenic mice. However, episodic LH secretion, an index of GnRH pulse generator activity, was dramatically compromised in ovariectomized female transgenics compared with C57BL6 controls of both sexes and castrated transgenic males. Taken together, these findings suggest that the GnRH pulse generator is selectively impaired in ovariectomized females in which GnRH neurons express GFP.
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Affiliation(s)
- K J Suter
- University of Texas at San Antonio, Department of Biology, One UTSA Circle, San Antonio, TX 78249, USA.
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31
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The effects of cutting solutions on the viability of GABAergic interneurons in cerebral cortical slices of adult mice. J Neurosci Methods 2008; 171:118-25. [DOI: 10.1016/j.jneumeth.2008.02.021] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2007] [Revised: 02/24/2008] [Accepted: 02/28/2008] [Indexed: 11/21/2022]
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32
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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.
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Affiliation(s)
- C B Roberts
- Department of Biology, University of Texas at San Antonio, 6900 North Loop, 1604 West, San Antonio, TX 78249, USA.
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33
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Lin S, Lin EJD, Boey D, Lee NJ, Slack K, During MJ, Sainsbury A, Herzog H. Fasting inhibits the growth and reproductive axes via distinct Y2 and Y4 receptor-mediated pathways. Endocrinology 2007; 148:2056-65. [PMID: 17272395 DOI: 10.1210/en.2006-1408] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Neuropeptide Y, a neuropeptide abundantly expressed in the brain, has been implicated in the regulation of the hypothalamo-pituitary-somatotropic axis and the hypothalamo-pituitary-gonadotropic axis. Elevated hypothalamic neuropeptide Y expression, such as that occurs during fasting, is known to inhibit both of these axes. However, it is not known which Y receptor(s) mediate these effects. Here we demonstrate, using Y receptor knockout mice, that Y2 and Y4 receptors are separately involved in the regulation of these axes. Fasting-induced inhibition of hypothalamic GHRH mRNA expression and reduction of circulating IGF-I levels were observed in wild-type and Y4(-/-) mice but not Y2(-/-) or Y2(-/-)Y4(-/-) mice. In contrast, fasting-induced reduction of GnRH expression in the medial preoptic area and testis testosterone content were abolished in the absence of Y4 receptors. Colocalization of Y2 receptors and GHRH in the arcuate nucleus (Arc) suggests that GHRH mRNA expression in this region might be directly regulated by Y2 receptors. Indeed, hypothalamic-specific deletion of Y2 receptors in conditional knockout mice prevented the fasting-induced reduction in Arc GHRH mRNA expression. On the other hand, fasting-induced decrease in GnRH mRNA expression in the medial preoptic area is more likely indirectly influenced by Y4 receptors because no Y4 receptors could be detected on GnRH neurons in this region. Together these data show that fasting inhibits the somatotropic axis via direct action on Y2 receptors in the Arc and indirectly inhibits the gonadotropic axis via Y4 receptors.
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Affiliation(s)
- Shu Lin
- Neuroscience Research Program, The Garvan Institute of Medical Research, Darlinghurst, New South Wales 2010, Sydney, Australia
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34
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Alonso G, Sanchez-Hormigo A, Loudes C, El Yandouzi T, Carmignac D, Faivre-Bauman A, Recolin B, Epelbaum J, Robinson ICAF, Mollard P, Méry PF. Selective alteration at the growth-hormone- releasing-hormone nerve terminals during aging in GHRH-green fluorescent protein mice. Aging Cell 2007; 6:197-207. [PMID: 17328688 DOI: 10.1111/j.1474-9726.2007.00276.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Growth hormone (GH) secretion decreases spontaneously during lifespan, and the resulting GH deficiency participates in aging-related morbidity. This deficiency appears to involve a defect in the activity of hypothalamic GH-releasing hormone (GHRH) neurons. Here, we investigated this hypothesis, as well as the underlying mechanisms, in identified GHRH neurons from adult ( approximately 13 weeks old) and aged ( approximately 100 weeks old) transgenic GHRH-green fluorescent protein mice, using morphological, biochemical and electrophysiological methods. Surprisingly, the spontaneous action potential frequency was similar in adult and aged GHRH neurons studied in brain slices. This was explained by a lack of change in the intrinsic excitability, and simultaneous increases in both stimulatory glutamatergic- and inhibitory GABAergic-synaptic currents of aged GHRH neurons. Aging did not decrease GHRH and enhanced green fluorescent protein contents, GHRH neuronal number or GHRH-fibre distribution, but we found a striking enlargement of GHRH-positive axons, suggesting neuropeptide accumulation. Unlike in adults, autophagic vacuoles were evident in aged GHRH-axonal profiles using electron microscopy. Thus, GHRH neurons are involved in aging of the GH axis. Aging had a subtle effect at the nerve terminal level in GHRH neurons, contrasting with the view that neuronal aging is accompanied by more widespread damage.
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Affiliation(s)
- Gérard Alonso
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, INSERM U661, CNRS UMR 5203, Université Montpellier 1 et 2, Montpellier, France
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35
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Baccam N, Alonso G, Costecalde T, Fontanaud P, Molino F, Robinson ICAF, Mollard P, Méry PF. Dual-level afferent control of growth hormone-releasing hormone (GHRH) neurons in GHRH-green fluorescent protein transgenic mice. J Neurosci 2007; 27:1631-41. [PMID: 17301171 PMCID: PMC6673740 DOI: 10.1523/jneurosci.2693-06.2007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The organization of the peptidergic neurons of the hypothalamic arcuate nucleus is not fully understood. These include growth hormone-releasing hormone (GHRH) neurons involved in growth and metabolism. We studied identified GHRH neurons of GHRH-green fluorescent protein transgenic mice using patch-clamp methods and focused on gender differences, which govern the physiological patterns of GHRH release. Both the spontaneous firing rates and the intrinsic properties of GHRH neurons were similar in males and females, although higher glutamatergic currents were noticed in females. Surprisingly, marked gender differences in GHRH neuronal activity were observed in response to the muscarinic agonist carbachol (CCh). In females, CCh enhanced action potential firing in all GHRH neurons. In males, CCh enhanced action potential firing in two-thirds of GHRH neurons, whereas it decreased firing in the remainders. M1 agonist McN-A343 (10 microM) mimicked, and M1 antagonist pirenzepine (3 microM) blocked the effects of CCh. In both genders, CCh did not change the intrinsic properties of GHRH neurons, although it strongly increased the frequency of glutamatergic currents, in the presence or absence of tetrodotoxin. In males only, CCh enhanced the frequency of GABAergic currents, and this modulation was antagonized by tetrodotoxin. Thus, the muscarinic regulation involved differential control of afferent inputs at short and long distances in male and female mice. The dual-level control could be a mechanism whereby the selective modulation of the GHRH system (short-distance control) is adjusted to the integrated regulation of arcuate nucleus activity (long-distance control).
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Affiliation(s)
- Nelly Baccam
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - Gérard Alonso
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - Thomas Costecalde
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - Pierre Fontanaud
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - François Molino
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - Iain C. A. F. Robinson
- Division of Molecular Neuroendocrinology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom
| | - Patrice Mollard
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
| | - Pierre-François Méry
- Département d'Endocrinologie, Institut de Génomique Fonctionnelle, Institut National de la Santé et de la Recherche Scientifique U661, Centre National de la Recherche Scientifique UMR 5203, Université Montpellier 1, Université Montpellier 2, 34094 Montpellier, France, and
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Bouyer K, Loudes C, Robinson ICAF, Epelbaum J, Faivre-Bauman A. Multiple co-localizations in arcuate GHRH-eGFP neurons in the mouse hypothalamus. J Chem Neuroanat 2006; 33:1-8. [PMID: 17137749 DOI: 10.1016/j.jchemneu.2006.10.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 10/12/2006] [Accepted: 10/12/2006] [Indexed: 11/22/2022]
Abstract
In the present work, we took advantage of a recently described model of GHRH-enhanced green fluorescent protein (eGFP) transgenic mice to evaluate the extent of co-localization of GHRH neurons with galanin (GAL), neurotensin (NT) and tyrosine hydroxylase (TH) in 3- and 8-month-old male and female mice. The total number of GHRH-eGFP neurons along the rostro-caudal axis of the arcuate nucleus did not differ according to gender or age. GAL-immunoreactivity was present in 40-44% of 3-month-old GHRH-eGFP neurons in male and female arcuate nucleus, respectively, but only 25-22% in 8-month-old mice. TH immunoreactivity occurred in 36-35% of GHRH-eGFP neurons in male and female arcuate nucleus from 3-month-old mice and these proportions increased to 40 and 45% in 8-month-old mice. NT immunoreactivity was present in 14 and 24% of GHRH-eGFP neurons in male and female arcuate nucleus from 3-month-old mice up to 28 and 26% in 8-month-old mice. Thus, co-localization of peptides and enzyme in GHRH-eGFP neurons displays a sexual dimorphism at 3-month of age for NT, and at 8-month for TH, while the total number of GHRH-eGFP neurons does not exhibit gender difference at either age. In summary, it appears that changes in co-localized (and presumably co-released) peptides, rather than GHRH per se, may contribute to the changes in sexually dimorphic GH secretion with aging in the mouse.
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Affiliation(s)
- Karine Bouyer
- UMR 549 INSERM, Faculté de Médecine, Université Paris-René Descartes, IFR Broca Sainte Anne, 2ter rue d'Alésia, 75014 Paris, France
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Carter D. Cellular transcriptomics -- the next phase of endocrine expression profiling. Trends Endocrinol Metab 2006; 17:192-8. [PMID: 16730453 DOI: 10.1016/j.tem.2006.05.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/11/2006] [Revised: 04/24/2006] [Accepted: 05/12/2006] [Indexed: 12/15/2022]
Abstract
Transcriptome analysis, or global gene expression profiling, has become a commonly used and valuable tool in both basic and clinical endocrine research. Novel endocrine regulators have 'surfaced' and greater consideration is now given to understanding function at the level of gene networks. Recent developments have shown that the transcriptome is considerably larger and more divergently expressed than was previously thought. Endocrine cells express a great variety of coding and noncoding RNAs in a highly cell-specific manner. If further value is to be taken from this research area, then steps towards defined cellular transcriptomics must be taken. New sampling techniques that utilize novel genetic models are a key first step.
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Affiliation(s)
- David Carter
- School of Biosciences, Cardiff University, Cardiff, CF10 3US, UK.
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Bouyer K, Loudes C, Robinson ICAF, Epelbaum J, Faivre-Bauman A. Sexually dimorphic distribution of sst2A somatostatin receptors on growth hormone-releasing hormone neurons in mice. Endocrinology 2006; 147:2670-4. [PMID: 16497806 DOI: 10.1210/en.2005-1462] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The pulsatile pattern of GH secretion exhibits sexual dimorphism that is likely to depend on somatostatin (SRIH) effects on somatoliberin (GHRH) neurons in the hypothalamus. Using transgenic GHRH-enhanced green fluorescent protein (eGFP) mice, no difference in the total number of GHRH-eGFP neurons or change in somatostatin receptor sst2 and SRIH mRNA levels in ventromedial hypothalamic nucleus-arcuate nucleus and periventricular nucleus regions and GHRH mRNA levels in the ventromedial hypothalamic-arcuate region were observed between male and female mice. However, the percentage of GHRH-eGFP neurons bearing sst2A receptors reached 78% in female vs. 26% in male GHRH-eGFP mice (P < 0.02). This sex difference in sst2A distribution on GHRH neurons may play an important role in the sexually differentiated pattern of GH secretion.
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Affiliation(s)
- Karine Bouyer
- Unité Mixte de Recherche 549, Institut National de la Santé et de la Recherche Médicale, Faculté de Médecine, Université Paris René Descartes, Institut Fédératif de Recherche Broca Sainte Anne, 75014 Paris, France
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Veldhuis JD, Roemmich JN, Richmond EJ, Bowers CY. Somatotropic and gonadotropic axes linkages in infancy, childhood, and the puberty-adult transition. Endocr Rev 2006; 27:101-40. [PMID: 16434512 DOI: 10.1210/er.2005-0006] [Citation(s) in RCA: 178] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Integrative neuroendocrine control of the gonadotropic and somatotropic axes in childhood, puberty, and young adulthood proceeds via multiple convergent and divergent pathways in the human and experimental animal. Emerging ensemble concepts are required to embody independent, parallel, and interacting mechanisms that subserve physiological adaptations and pathological disruption of reproduction and growth. Significant advances in systems biology will be needed to address these challenges.
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Affiliation(s)
- Johannes D Veldhuis
- Endocrine Research Unit, Department of Internal Medicine, Mayo Medical School, Mayo School of Graduate Medical Education, General Clinical Research Center, Mayo Clinic, Rochester, Minnesota 55905, USA.
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40
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Le Tissier PR, Carmignac DF, Lilley S, Sesay AK, Phelps CJ, Houston P, Mathers K, Magoulas C, Ogden D, Robinson ICAF. Hypothalamic growth hormone-releasing hormone (GHRH) deficiency: targeted ablation of GHRH neurons in mice using a viral ion channel transgene. Mol Endocrinol 2005; 19:1251-62. [PMID: 15661833 DOI: 10.1210/me.2004-0223] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Animal and clinical models of GHRH excess suggest that GHRH provides an important trophic drive to pituitary somatotrophs. We have adopted a novel approach to silence or ablate GHRH neurons, using a modified H37A variant of the influenza virus M2 protein ((H37A)M2). In mammalian cells, (H37A)M2 forms a high conductance monovalent cation channel that can be blocked by the antiviral drug rimantadine. Transgenic mice with (H37A)M2 expression targeted to GHRH neurons developed postweaning dwarfism with hypothalamic GHRH transcripts detectable by RT-PCR but not by in situ hybridization and immunocytochemistry, suggesting that expression of (H37A)M2 had silenced or ablated virtually all the GHRH cells. GHRH-M2 mice showed marked anterior pituitary hypoplasia with GH deficiency, although GH cells were still present. GHRH-M2 mice were also deficient in prolactin but not TSH. Acute iv injections of GHRH in GHRH-M2 mice elicited a significant GH response, whereas injections of GHRP-6 did not. Twice daily injections of GHRH (100 microg/d) for 7 d in GHRH-M2 mice doubled their pituitary GH but not PRL contents. Rimantadine treatment failed to restore growth or pituitary GH contents. Our results show the importance of GHRH neurons for GH and prolactin production and normal growth.
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Affiliation(s)
- Paul R Le Tissier
- Division of Molecular Neuroendocrinology, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom
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Suter KJ. Control of firing by small (S)-alpha-amino-3-hydroxy-5-methyl-isoxazolepropionic acid-like inputs in hypothalamic gonadotropin releasing-hormone (GnRH) neurons. Neuroscience 2004; 128:443-50. [PMID: 15350654 DOI: 10.1016/j.neuroscience.2004.06.044] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/30/2004] [Indexed: 11/21/2022]
Abstract
Episodic release of gonadotropin releasing hormone (GnRH) is obligatory for mammalian reproduction. The contribution of synaptic input to intermittent firing of GnRH neurons is unclear. GnRH neurons have very few synapses and most post-synaptic currents are small. Therefore, the impact of synaptic currents on firing in GnRH neurons was directly examined using simulated (S)-alpha-amino-3-hydroxy-5-methyl-isoxazolepropionic acid (AMPA)-like inputs applied with the method of dynamic current clamping. Tightly synchronized inputs and 50 ms bursts of excitatory input resulted in action potentials that were coincident with the stimulus. Neither input pattern resulted in sustained firing. When ongoing patterns of simulated inputs were applied over a range of parameters, action potentials were associated with clusters of AMPA-like inputs of 250 pS (approximately 15 pA amplitudes), while single inputs of 500 pS (approximately 30 pA amplitudes) resulted in action potentials. Ongoing inputs of 500 pS drove firing at 4-9 Hz. These findings provide evidence that small, simulated glutamatergic inputs can control firing in GnRH neurons and suggest that despite the small amplitudes, endogenous synaptic input mediated by glutamate may contribute to firing in GnRH neurons.
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Affiliation(s)
- K J Suter
- Department of Biology, 1510 Clifton Road, Rollins Research Building, Room 2168, Emory University, Atlanta, GA 30322, USA.
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