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Kolaj M, Zhang L, Renaud LP. L-type calcium channels and MAP kinase contribute to thyrotropin-releasing hormone-induced depolarization in thalamic paraventricular nucleus neurons. Am J Physiol Regul Integr Comp Physiol 2016; 310:R1120-7. [PMID: 27009047 PMCID: PMC4935505 DOI: 10.1152/ajpregu.00082.2016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2016] [Accepted: 03/18/2016] [Indexed: 12/11/2022]
Abstract
In rat paraventricular thalamic nucleus (PVT) neurons, activation of thyrotropin-releasing hormone (TRH) receptors enhances neuronal excitability via concurrent decrease in a G protein-coupled inwardly rectifying K (GIRK)-like conductance and opening of a cannabinoid receptor-sensitive transient receptor potential canonical (TRPC)-like conductance. Here, we investigated the calcium (Ca(2+)) contribution to the components of this TRH-induced response. TRH-induced membrane depolarization was reduced in the presence of intracellular BAPTA, also in media containing nominally zero [Ca(2+)]o, suggesting a critical role for both intracellular Ca(2+) release and Ca(2+) influx. TRH-induced inward current was unchanged by T-type Ca(2+) channel blockade, but was decreased by blockade of high-voltage-activated Ca(2+) channels (HVACCs). Both the pharmacologically isolated GIRK-like and the TRPC-like components of the TRH-induced response were decreased by nifedipine and increased by BayK8644, implying Ca(2+) influx via L-type Ca(2+) channels. Only the TRPC-like conductance was reduced by either thapsigargin or dantrolene, suggesting a role for ryanodine receptors and Ca(2+)-induced Ca(2+) release in this component of the TRH-induced response. In pituitary and other cell lines, TRH stimulates MAPK. In PVT neurons, only the GIRK-like component of the TRH-induced current was selectively decreased in the presence of PD98059, a MAPK inhibitor. Collectively, the data imply that TRH-induced depolarization and inward current in PVT neurons involve both a dependency on extracellular Ca(2+) influx via opening of L-type Ca(2+) channels, a sensitivity of a TRPC-like component to intracellular Ca(2+) release via ryanodine channels, and a modulation by MAPK of a GIRK-like conductance component.
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Affiliation(s)
- Miloslav Kolaj
- Ottawa Hospital Research Institute, Neuroscience Program and University of Ottawa, Department of Medicine, Ottawa, Ontario, Canada
| | - Li Zhang
- Ottawa Hospital Research Institute, Neuroscience Program and University of Ottawa, Department of Medicine, Ottawa, Ontario, Canada
| | - Leo P Renaud
- Ottawa Hospital Research Institute, Neuroscience Program and University of Ottawa, Department of Medicine, Ottawa, Ontario, Canada
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Haslam IS, Roubos EW, Mangoni ML, Yoshizato K, Vaudry H, Kloepper JE, Pattwell DM, Maderson PFA, Paus R. From frog integument to human skin: dermatological perspectives from frog skin biology. Biol Rev Camb Philos Soc 2013; 89:618-55. [DOI: 10.1111/brv.12072] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2012] [Revised: 10/03/2013] [Accepted: 10/22/2013] [Indexed: 12/15/2022]
Affiliation(s)
- Iain S. Haslam
- The Dermatology Centre, Salford Royal NHS Foundation Trust, Institute of Inflammation and Repair; University of Manchester; Oxford Road Manchester M13 9PT U.K
| | - Eric W. Roubos
- Department of Anatomy; Radboud University Medical Centre; Geert Grooteplein Noord 2, 6525 EZ, Nijmegen P.O. Box 9101, 6500 HB Nijmegen The Netherlands
| | - Maria Luisa Mangoni
- Department of Biochemical Sciences, Istituto Pasteur-Fondazione Cenci Bolognetti; La Sapienza University of Rome, Piazzale Aldo Moro, 5-00185; Rome Italy
| | - Katsutoshi Yoshizato
- Academic Advisors Office, Synthetic Biology Research Center; Osaka City University Graduate School of Medicine; Osaka Japan
- Phoenixbio Co. Ltd; 3-4-1, Kagamiyama; Higashihiroshima Hiroshima 739-0046 Japan
| | - Hubert Vaudry
- European Institute for Peptide Research; University of Rouen; Mont-Saint-Aignan Place Emile Blondel 76821 France
- INSERM U-982, CNRS; University of Rouen; Mont-Saint-Aignan Place Emile Blondel 76821 France
| | - Jennifer E. Kloepper
- Klinik für Dermatologie, Allergologie und Venerologie; Universitätsklinikum Schleswig-Holstein, Ratzeburger Allee 160; 23538 Lübeck Germany
| | - David M. Pattwell
- Leahurst Campus, Institute of Learning & Teaching; School of Veterinary Science, University of Liverpool; Neston CH64 7TE U.K
| | | | - Ralf Paus
- The Dermatology Centre, Salford Royal NHS Foundation Trust, Institute of Inflammation and Repair; University of Manchester; Oxford Road Manchester M13 9PT U.K
- Klinik für Dermatologie, Allergologie und Venerologie; Universitätsklinikum Schleswig-Holstein, Ratzeburger Allee 160; 23538 Lübeck Germany
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3
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Jenks BG, Galas L, Kuribara M, Desrues L, Kidane AH, Vaudry H, Scheenen WJJM, Roubos EW, Tonon MC. Analysis of the melanotrope cell neuroendocrine interface in two amphibian species, Rana ridibunda and Xenopus laevis: a celebration of 35 years of collaborative research. Gen Comp Endocrinol 2011; 170:57-67. [PMID: 20888821 DOI: 10.1016/j.ygcen.2010.09.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 09/17/2010] [Accepted: 09/27/2010] [Indexed: 01/19/2023]
Abstract
This review gives an overview of the functioning of the hypothalamo-hypophyseal neuroendocrine interface in the pituitary neurointermediate lobe, as it relates to melanotrope cell function in two amphibian species, Rana ridibunda and Xenopus laevis. It primarily but not exclusively concerns the work of two collaborating laboratories, the Laboratory for Molecular and Cellular Neuroendocrinology (University of Rouen, France) and the Department of Cellular Animal Physiology (Radboud University Nijmegen, The Netherlands). In the course of this review it will become apparent that Rana and Xenopus have, for the most part, developed the same or similar strategies to regulate the release of α-melanophore-stimulating hormone (α-MSH). The review concludes by highlighting the molecular and cellular mechanisms utilized by thyrotropin-releasing hormone (TRH) to activate Rana melanotrope cells and the function of autocrine brain-derived neurotrophic factor (BDNF) in the regulation of Xenopus melanotrope cell function.
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Affiliation(s)
- Bruce G Jenks
- Department of Cellular Animal Physiology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands.
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4
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Kuribara M, Eijsink VD, Roubos EW, Jenks BG, Scheenen WJJM. BDNF stimulates Ca2+ oscillation frequency in melanotrope cells of Xenopus laevis: contribution of IP3-receptor-mediated release of intracellular Ca2+ to gene expression. Gen Comp Endocrinol 2010; 169:123-9. [PMID: 20736010 DOI: 10.1016/j.ygcen.2010.08.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 08/06/2010] [Accepted: 08/16/2010] [Indexed: 10/19/2022]
Abstract
Pituitary melanotrope cells of the amphibian Xenopus laevis are neuroendocrine cells regulating the animal's skin color adaptation through secretion of α-melanophore-stimulating hormone (α-MSH). To fulfill this function optimally, the melanotrope cell undergoes plastic changes in structure and secretory activity in response to changed background light conditions. Xenopus melanotrope cells display Ca(2+) oscillations that are thought to drive α-MSH secretion and gene expression. They also produce brain-derived neurotrophic factor (BDNF), which stimulates in an autocrine way the biosynthesis of the α-MSH precursor, pro-opiomelanocortin (POMC). We have used this physiological adaptation mechanism as a model to investigate the role of BDNF in the regulation of Ca(2+) kinetics and Ca(2+)-dependent gene expression. By dynamic video imaging of isolated cultured melanotropes we demonstrated that BDNF caused a dose-dependent increase in Ca(2+) oscillation frequency up to 64.7±2.3% of control level. BDNF also induced a transient Ca(2+) peak in Ca(2+)-free medium, which was absent when calcium stores were blocked by thapsigargin and 2-aminoethoxydiphenyl borate, indicating that BDNF stimulates acute release of Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores. Moreover, we show that thapsigargin inhibits the expression of BDNF transcript IV (by 61.1±28.8%) but does not affect POMC transcript. We conclude that BDNF mobilizes Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores and propose the possibility that the resulting Ca(2+) oscillations selectively stimulate expression of the BDNF gene.
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Affiliation(s)
- Miyuki Kuribara
- Department of Cellular Animal Physiology, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, Nijmegen, The Netherlands
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Nakano M, Minagawa A, Hasunuma I, Okada R, Tonon MC, Vaudry H, Yamamoto K, Kikuyama S, Machida T, Kobayashi T. D2 Dopamine receptor subtype mediates the inhibitory effect of dopamine on TRH-induced prolactin release from the bullfrog pituitary. Gen Comp Endocrinol 2010; 168:287-92. [PMID: 20553721 DOI: 10.1016/j.ygcen.2010.05.008] [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: 11/27/2009] [Revised: 05/13/2010] [Accepted: 05/24/2010] [Indexed: 11/23/2022]
Abstract
Dopamine receptors in mammals are known to consist of two D1-like receptors (D1 and D5) and three D2-like receptors (D2, D3 and D4). The aim of this study was to determine the dopamine receptor subtype that mediates the inhibitory action of dopamine on the release of prolactin (PRL) from the amphibian pituitary. Distal lobes of the bullfrog (Rana catesbeiana) were perifused and the amount of PRL released in the effluent medium was measured by means of a homologous enzyme-immunoassay. TRH stimulated the release of PRL from perifused pituitaries. Dopamine suppressed TRH-induced elevation of PRL release. Quinpirole (a D2 receptor agonist) also suppressed the stimulatory effect of TRH on the release of PRL, whereas SKF-38393 (a D1 receptor agonist) exhibited no such an effect. The inhibitory action of dopamine on TRH-induced PRL release from the pituitary was nullified by the addition of L-741,626 (a selective D2 receptor antagonist) to the medium, but not by the addition of SCH-23390 (a selective D1 receptor antagonist). These data indicate that the inhibitory effect of dopamine on TRH-evoked PRL release from the bullfrog pituitary gland is mediated through D2 dopamine receptors.
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Affiliation(s)
- Masaki Nakano
- Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
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Galas L, Raoult E, Tonon MC, Okada R, Jenks BG, Castaño JP, Kikuyama S, Malagon M, Roubos EW, Vaudry H. TRH acts as a multifunctional hypophysiotropic factor in vertebrates. Gen Comp Endocrinol 2009; 164:40-50. [PMID: 19435597 DOI: 10.1016/j.ygcen.2009.05.003] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 04/28/2009] [Accepted: 05/05/2009] [Indexed: 11/17/2022]
Abstract
Thyrotropin-releasing hormone (TRH) is the first hypothalamic hypophysiotropic neuropeptide whose sequence has been chemically characterized. The primary structure of TRH (pGlu-His-Pro-NH(2)) has been fully conserved across the vertebrate phylum. TRH is generated from a large precursor protein that contains multiple repeats of the TRH progenitor tetrapeptide Gln-His-Pro-Gly. In all tetrapods, TRH-expressing neurons located in the hypothalamus project towards the external zone of the median eminence while in teleosts they directly innervate the pars distalis of the pituitary. In addition, in frogs and teleosts, a bundle of TRH-containing fibers terminate in the neurointermediate lobe of the pituitary gland. Although TRH was originally named for its ability to trigger the release of thyroid-stimulating hormone (TSH) in mammals, it later became apparent that it exerts multiple, species-dependent hypophysiotropic activities. Thus, in fish TRH stimulates growth hormone (GH) and prolactin (PRL) release but does not affect TSH secretion. In amphibians, TRH is a marginal stimulator of TSH release in adult frogs, not in tadpoles, and a major releasing factor for GH and PRL. In birds, TRH triggers TSH and GH secretion. In mammals, TRH stimulates TSH, GH and PRL release. In fish and amphibians, TRH is also a very potent stimulator of alpha-melanocyte-stimulating hormone release. Because the intermediate lobe of the pituitary of amphibians is composed by a single type of hormone-producing cells, the melanotrope cells, it is a suitable model in which to investigate the mechanism of action of TRH at the cellular and molecular level. The occurrence of large amounts of TRH in the frog skin and high concentrations of TRH in frog plasma suggests that, in amphibians, skin-derived TRH may exert hypophysiotropic functions.
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Affiliation(s)
- Ludovic Galas
- Regional Platform for Cell Imaging (PRIMACEN), European Institute for Peptide Research (IFRMP 23), University of Rouen, Mont-Saint-Aignan, France
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7
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Domínguez L, López JM, González A. Distribution of Thyrotropin-Releasing Hormone (TRH) Immunoreactivity in the Brain of Urodele Amphibians. BRAIN, BEHAVIOR AND EVOLUTION 2008; 71:231-46. [DOI: 10.1159/000122835] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2007] [Accepted: 12/13/2007] [Indexed: 01/28/2023]
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Galas L, Bidaud I, Bulant M, Jenks BG, Ouwens DTWM, Jégou S, Ladram A, Roubos EW, Nicolas P, Tonon MC, Vaudry H. In situ hybridization localization of TRH precursor and TRH receptor mRNAs in the brain and pituitary of Xenopus laevis. Ann N Y Acad Sci 2006; 1040:95-105. [PMID: 15891012 DOI: 10.1196/annals.1327.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We examined the distribution of the mRNAs encoding proTRH and the three TRH receptor subtypes (xTRHR1, xTRHR2, and xTRHR3) in the Xenopus laevis CNS and pituitary. A positive correlation was generally observed between the expression patterns of proTRH and xTRHR mRNAs. xTRHRs were widely expressed in the telencephalon and diencephalon, where two or even three xTRHR mRNAs were often simultaneously observed within the same brain structures. In the pituitary, xTRHR2 was selectively expressed in the distal lobe, and xTRHR3 was found exclusively in the intermediate lobe of white background-adapted animals, indicating that, in amphibians, the effect of TRH on alpha-melanotropin (alpha-MSH) secretion from melanotrope cells is mediated through the novel receptor subtype xTRHR3.
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Affiliation(s)
- L Galas
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, UA CNRS, University of Rouen, Mont-Saint-Aignan, France
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9
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Calle M, Wang L, Kuijpers FJ, Cruijsen PMJM, Arckens L, Roubos EW. Brain-derived neurotrophic factor in the brain of Xenopus laevis may act as a pituitary neurohormone together with mesotocin. J Neuroendocrinol 2006; 18:454-65. [PMID: 16684135 DOI: 10.1111/j.1365-2826.2006.01433.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, occurs abundantly in the brain, where it exerts a variety of neural functions. We previously demonstrated that BDNF also exists in the endocrine melanotroph cells in the intermediate lobe of the pituitary gland of the amphibian Xenopus laevis, suggesting that BDNF, in addition to its neural actions within the brain, can act as a hormone. In the present study, we tested whether BDNF, in addition to its neural and hormonal roles, can be released as a neurohormone from the neural pituitary lobe of X. laevis. By light immunocytochemistry, we show that BDNF is present in perikarya, in ventrolaterally projecting axons of the hypothalamic magnocellular nucleus and in the neural lobe of the pituitary gland, and that it coexists in these structures with the amphibian neurohormone, mesotocin. The neural lobe was studied in detail at the ultrastructural level. Two types of neurohaemal axon terminals were observed, occurring intermingled and in similar numbers. Type A is filled with round, moderately electron-dense secretory granules with a mean diameter of approximately 145 nm. Type B terminals contain electron-dense and smaller, ellipsoid granules (long and short diameter approximately 140 and 100 nm, respectively). BDNF is exclusively present in secretory granules of type A axon terminals. Double gold-immunolabelling revealed that BDNF coexists in these granules with mesotocin. Furthermore, we demonstrate in an superfusion study performed in vitro that mesotocin stimulates peptide release from the endocrine melanotroph cells. On the basis of these data, we propose that BDNF can act on these cells as a neurohormone.
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Affiliation(s)
- M Calle
- Department of Cellular Animal Physiology, Institute for Neuroscience, Radboud University Nijmegen, Nijmegen, The Netherlands
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Desrues L, Castel H, Malagon MM, Vaudry H, Tonon MC. The regulation of alpha-MSH release by GABA is mediated by a chloride-dependent [Ca2+]c increase in frog melanotrope cells. Peptides 2005; 26:1936-43. [PMID: 15990198 DOI: 10.1016/j.peptides.2004.11.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2004] [Accepted: 11/23/2004] [Indexed: 11/30/2022]
Abstract
In frog melanotrope cells, gamma-aminobutyric acid (GABA) induces a biphasic effect, i.e. a transient stimulation followed by a more sustained inhibition of alpha-MSH release, and both phases of the GABA effect are mediated by GABAA receptors. We have previously shown that the stimulatory phase evoked by GABAA receptor agonists can be accounted for by calcium entry. In the present study, we have investigated the involvement of the chloride flux on GABA-induced [Ca2+]c increase and alpha-MSH release. We show that GABA evokes a concentration-dependent [Ca2+]c rise through specific activation of the GABAA receptor. The GABA-induced [Ca2+]c increase results from opening of voltage-activated L- and N-type calcium channels, and sodium channels. Variations of the extracellular Cl- concentration revealed that GABA-induced [Ca2+]c rise and alpha-MSH release both depend on the Cl- flux direction and driving force. These observations suggest for the first time that GABA-gated Cl- efflux provokes an increase in [Ca2+]c increase that is responsible for hormone secretion.
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Affiliation(s)
- Laurence Desrues
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, University of Rouen, 76821 Mont-Saint-Aignan, France
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Louiset E, Belmeguenai A, Desrues L, Leprince J, Tonon MC, Vaudry H. Signal transduction in Rana melanotrope cells: mechanism of action of neurotensin on secretory and electrical activities. Ann N Y Acad Sci 2005; 1040:131-6. [PMID: 15891016 DOI: 10.1196/annals.1327.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The pars intermedia of the frog (Rana esculenta) pituitary, which is composed of a single population of endocrine cells, the melanotrophs, is a very suitable model to study the mode of action of hypophysiotropic neuropeptides. We have recently characterized neurotensin (NT) in Rana esculenta and found that synthetic frog NT (fNT) stimulates the electrical and secretory activities of melanotrophs. By combining biochemical, pharmacological, microfluorimetric, and electrophysiological approaches, we observed that NT stimulates inositol-trisphosphate production that provokes Ca(2+) release from intracellular stores. The resulting increase in cytosolic Ca(2+) concentration ([Ca(2+)](c)) activates the secretion of alpha-melanocyte-stimulating hormone (alpha-MSH), stimulates Ca(2+)-dependent protein kinase (PKC) activity, and provokes a depolarizing chloride efflux. PKC reduces the amplitude, whereas membrane depolarization increases the frequency of L- and N-type Ca(2+) currents underlain by the action potential discharge. The complex regulatory processes exerted by NT on Ca(2+) signaling likely generate discrete variations in the [Ca(2+)](c) at various distances from secretory vesicles, contributing to the fine-tuning of alpha-MSH secretion.
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Affiliation(s)
- Estelle Louiset
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U413, University of Rouen, Mont-Saint-Aignan, France
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12
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Calle M, Corstens GJH, Wang L, Kozicz T, Denver RJ, Barendregt HP, Roubos EW. Evidence that urocortin I acts as a neurohormone to stimulate αMSH release in the toad Xenopus laevis. Brain Res 2005; 1040:14-28. [PMID: 15804422 DOI: 10.1016/j.brainres.2004.12.056] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2004] [Revised: 12/15/2004] [Accepted: 12/17/2004] [Indexed: 11/17/2022]
Abstract
We have raised the hypothesis that in the South African clawed toad Xenopus laevis, urocortin 1 (UCN1), a member of the corticotropin-releasing factor (CRF) peptide family, functions not only within the brain as a neurotransmitter/neuromodulator but also as a neurohormone, promoting the release of alpha-melanophore-stimulating hormone (alphaMSH) from the neuroendocrine melanotrope cells in the intermediate lobe of the pituitary gland. This hypothesis has been investigated by (1) assessing the distribution of UCN1 and CRF by light immunocytochemistry, (2) determining the subcellular presence of UCN1 in the neural lobe of the pituitary gland by immuno-electron microscopy applying high-pressure freezing and cryosubstitution, and (3) testing the effect of UCN1 on MSH release from toad melanotrope cells using in vitro superfusion. In the X. laevis brain, the main site of UCN1-positive somata was found to be the Edinger-Westphal nucleus. UCN1 immunoreactivity (ir) also occurs in the nucleus posteroventralis tegmenti, central gray, nucleus reticularis medius, nucleus motorius nervi facialis, and nucleus motorius nervi vagi. UCN1 occurs together with CRF in the nucleus motorius nervi trigemini, and in the magnocellular nucleus, which send a UCN1- and CRF-containing fiber tract to the median eminence. Strong UCN1-ir and CRF-ir were found in the external zone of the median eminence. From the internal zone of the median eminence, UCN1-ir fibers, but few CRF-ir fibers, were found to project to the pituitary neural lobe, where they form numerous neurohemal axon terminals. Ultrastructurally, two types of terminal containing UCN1-ir secretory granules were distinguished: type A contains large, moderately electron-dense, round secretory granules and type B is filled with smaller, strongly electron-dense, ellipsoid secretory granules. In vitro superfusion studies showed that UCN1 stimulated the release of alphaMSH from melanotrope cells in a dose-dependent manner. Our results support the hypothesis that in X. laevis, UCN1 released from neurohemal axon terminals in the pituitary neural lobe functions as a stimulatory neurohormone for alphaMSH release from melanotrope cells of the pituitary intermediate lobe.
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Affiliation(s)
- Marinella Calle
- Department of Cellular Animal Physiology, Radboud University Nijmegen, Nijmegen, The Netherlands.
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13
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Bidaud I, Galas L, Bulant M, Jenks BG, Ouwens DTWM, Jégou S, Ladram A, Roubos EW, Tonon MC, Nicolas P, Vaudry H. Distribution of the mRNAs encoding the thyrotropin-releasing hormone (TRH) precursor and three TRH receptors in the brain and pituitary of Xenopus laevis: effect of background color adaptation on TRH and TRH receptor gene expression. J Comp Neurol 2004; 477:11-28. [PMID: 15281077 DOI: 10.1002/cne.20235] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
In amphibians, thyrotropin-releasing hormone (TRH) is a potent stimulator of alpha-melanotropin (alpha-MSH) secretion, so TRH plays a major role in the neuroendocrine regulation of skin-color adaptation. We have recently cloned a third type of TRH receptor in Xenopus laevis (xTRHR3) that has not yet been characterized in any other vertebrate species. In the present study, we have examined the distribution of the mRNAs encoding proTRH and the three receptor subtypes (xTRHR1, xTRHR2, and xTRHR3) in the frog CNS and pituitary, and we have investigated the effect of background color adaptation on the expression of these mRNAs. A good correlation was generally observed between the expression patterns of proTRH and xTRHR mRNAs. xTRHRs, including the novel receptor subtype xTRHR3, were widely expressed in the telencephalon and diencephalon, where two or even three xTRHR mRNAs were often simultaneously observed within the same brain structures. In the pituitary, xTRHR2 was expressed selectively in the distal lobe, and xTRHR3 was found exclusively in the intermediate lobe. Adaptation of frog skin to background illumination had no effect on the expression of proTRH and xTRHRs in the brain. In contrast, adaptation of the animals to a white background provoked an 18-fold increase in xTRHR3 mRNA concentration in the intermediate lobe of the pituitary. These data demonstrate that, in amphibians, the effect of TRH on alpha-MSH secretion is mediated through the novel receptor subtype xTRHR3.
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Affiliation(s)
- Isabelle Bidaud
- Institute Jacques Monod, Laboratory of Bioactivation of Peptides, Centre National de la Recherche Scientifique, University of Paris 6-7, UMR 7592, 75251 Paris, France
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14
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Belmeguenai A, Desrues L, Leprince J, Vaudry H, Tonon MC, Louiset E. Neurotensin stimulates both calcium mobilization from inositol trisphosphate-sensitive intracellular stores and calcium influx through membrane channels in frog pituitary melanotrophs. Endocrinology 2003; 144:5556-67. [PMID: 14500581 DOI: 10.1210/en.2003-0176] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Neurotensin (NT) is a potent stimulator of electrical and secretory activities in frog pituitary melanotrophs. The aim of the present study was to characterize the transduction pathways associated with activation of NT receptors in frog melanotrophs. Application of synthetic frog NT (fNT) increased the cytosolic calcium concentration ([Ca2+]c) and stimulated the formation of inositol trisphosphate (IP3). The phospholipase C inhibitor U-73122 blocked the electrophysiological and secretory effects of fNT. Intracellular application of the IP3 receptor antagonist heparin abolished fNT-induced electrical activity. Suppression of Ca2+ in the incubation medium markedly reduced the effect of NT on [Ca2+]c, firing rate, and alpha-melanocyte-stimulating hormone (alphaMSH) secretion. Similarly, the inhibitor of IP3-induced Ca2+ release and store-operated Ca2+ channels, 2-Aminoethoxydiphenylborane, and the nonselective Ca2+ channel blockers GdCl3 and NiCl2, attenuated the [Ca2+]c increase and the electrical and secretory responses evoked by fNT. Coapplication of the L- and N-type Ca2+ channel blockers nifedipine and omega-CgTx GVIA reduced the effects of fNT on action potential discharge, [Ca2+]c increase, and alphaMSH release. The protein kinase C (PKC) inhibitors, PKC-(19-31) and chelerythrine, reduced the electrophysiological and secretory responses induced by iterative applications of fNT. Collectively, these results demonstrate that, in frog melanotrophs, NT stimulates the phospholipase C/PKC pathway and increases [Ca2+]c. Both Ca2+ release from intracellular stores and Ca2+ influx through L- and N-type Ca2+ channels are involved in fNT-induced alphaMSH secretion. In addition, the present data indicate that PKC plays a crucial role in maintenance of the responsiveness of melanotrophs to NT.
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Affiliation(s)
- Amor Belmeguenai
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale, Unité-413, University of Rouen, 76821 Mont-Saint-Aignan, France
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15
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Belmeguenai A, Leprince J, Tonon MC, Vaudry H, Louiset E. Neurotensin modulates the amplitude and frequency of voltage-activated Ca2+ currents in frog pituitary melanotrophs: implication of the inositol triphosphate/protein kinase C pathway. Eur J Neurosci 2002; 16:1907-16. [PMID: 12453054 DOI: 10.1046/j.1460-9568.2002.02296.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many excitatory neurotransmitters and neuropeptides regulate the activity of neuronal and endocrine cells by modulating voltage-operated Ca2+ channels. Paradoxically, however, excitatory neuromediators that provoke mobilization of intracellular calcium from inositol trisphosphate (IP3)-sensitive stores usually inhibit voltage-gated Ca2+ currents. We have recently demonstrated that neurotensin (NT) stimulates the electrical and secretory activities of frog pituitary melanotrophs, and increases intracellular calcium concentration in these cells. In the present study, we have investigated the effects of NT on Ca2+ currents in cultured frog melanotrophs by using the perforated patch-clamp technique. Frog neurotensin (f NT) reduced the amplitude and facilitated the inactivation of both L- and N-type Ca2+ currents. Application of the membrane-permeant Ca2+ chelator BAPTA-AM, the sarcoendoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin, or the IP3 receptor antagonist 2-APB suppressed the reduction of Ca2+ currents induced by f NT. Incubation of melanotrophs with the diacylglycerol analogue PMA, which causes desensitization of protein kinase C (PKC), or with the PKC inhibitors chelerythrine and calphostin C, reduced the inhibitory effect of f NT. The NT-induced action potential waveforms, applied as voltage-clamp commands, decreased the amplitude of Ca2+ currents, and enhanced Ca2+ influx by increasing the Ca2+ spike frequency. Altogether, these data indicate that the inhibitory effect of f NT on Ca2+ currents results from activation of the IP3/PKC pathway. The observation that NT controls Ca2+ signalling through both amplitude and frequency modulations of Ca2+ currents suggests that NT might induce spacial and temporal changes of intracellular Ca2+ concentration leading to stimulation of exocytosis.
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Affiliation(s)
- Amor Belmeguenai
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U-413, UA CNRS, University of Rouen, 76821 Mont-Saint-Aignan, France
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16
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Bidaud I, Lory P, Nicolas P, Bulant M, Ladram A. Characterization and functional expression of cDNAs encoding thyrotropin-releasing hormone receptor from Xenopus laevis. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:4566-76. [PMID: 12230569 DOI: 10.1046/j.1432-1033.2002.03152.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Thyrotropin-releasing hormone receptor (TRHR) has already been cloned in mammals wherethyrotropin-releasing hormone (TRH) is known to act as a powerful stimulator of thyroid-stimulating hormone (TSH) secretion. The TRH receptor of amphibians has not yet been characterized, although TRH is specifically important in the adaptation of skin color to environmental changes via the secretion of alpha-melanocyte-stimulating hormone (alpha-MSH). Using a dege-nerate PCR strategy, we report on the isolation of three distinct cDNA species encoding TRHR from the brain of Xenopus laevis. We have designated these as xTRHR1, xTRHR2 and xTRHR3. Analysis of the predicted amino acid sequences revealed that the three Xenopus TRHRs are only 54-62% identical and contain all the highly conserved residues constituting the TRH binding pocket. Amino acid sequences and phylogenetic analysis revealed that xTRHR1 is a member of TRHR subfamily 1 and xTRHR2 belongs to subfamily 2, while xTRHR3 is a new TRHR subtype awaiting discovery in other animal species. The three Xeno-pus TRHRs have distinct patterns of expression. xTRHR3 was abundant in the brain and much scarcer in the peripheral tissues, whereas xTRHR1 was found mainly in the stomach and xTRHR2 in the heart. The Xenopus TRHR subtype 1 was found specifically in the intestine, lung and urinary bladder. These observations suggest that the three xTRHRs each have specific functions that remain to be elucidated. Expression in Xenopus oocytes and HEK-293 cells indicates that the three Xenopus TRHRs are fully functional and are coupled to the inositol phosphate/calcium pathway. Interestingly, activation of xTRHR3 required larger concentrations of TRH compared with the other two receptors, suggesting marked differences in receptor binding, coupling or regulation.
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Affiliation(s)
- Isabelle Bidaud
- Laboratoire de Bioactivation des Peptides, Institut Jacques Monod, CNRS-Université Paris, Paris; Institut de Génétique Humaine, CNRS-UPR 1142, Montpellier, France
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17
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Lieste JR, Schoenmakers TJM, Scheenen WJJM, Willems PHGM, Roubos EW, Jenks BG. TRH signal transduction in melanotrope cells of Xenopus laevis. Gen Comp Endocrinol 2002; 127:80-8. [PMID: 12161205 DOI: 10.1016/s0016-6480(02)00028-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
TRH is a neuropeptide that activates phospholipase C and, when acting on secretory cells, usually induces a biphasic response consisting of a transitory increase in secretion (due to IP(3) mobilization of Ca(2+) from intracellular stores), followed by a sustained plateau phase of stimulated secretion (by protein kinase C-dependent influx of extracellular Ca(2+) through voltage-operated Ca(2+) channels). The melanotrope cell of the amphibian Xenopus laevis displays a unique secretory response to TRH, namely a broad transient but no sustained second phase, consistent with the observation that TRH induces a single Ca(2+) transient rather than the classic biphasic increase in [Ca(2+)](i). The purpose of the present study was to determine the signal transduction mechanism utilized by TRH in generating this Ca(2+) signaling response. Our hypothesis was that the transient reflects the operation of only one of the two signaling arms of the lipase (i.e., either IP(3)-induced mobilization of internal Ca(2+) or PKC-dependent influx of external Ca(2+)). Using video-imaging microscopy it is shown that the TRH-induced Ca(2+) transient is dramatically attenuated under Ca(2+)-free conditions and that thapsigargin has no noticeable effect on the TRH-induced transient. These observations indicate that an IP(3)-dependent mechanism plays no important role in the action of TRH. PKC also does not seem to be involved because an activator of PKC did not induce a Ca(2+) transient and an inhibitor of PKC did not affect the TRH response. Experiments with a bis-oxonol membrane potential probe showed that the TRH response also does not underlie a PKC-independent mechanism that would induce membrane depolarization. We conclude that the action of TRH on the Xenopus melanotrope does not rely on the classical phospholipase C-dependent mechanism.
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Affiliation(s)
- J R Lieste
- Department of Cellular Animal Physiology, University of Nijmegen, Toernooiveld 1, The Netherlands
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Galas L, Tonon MC, Beaujean D, Fredriksson R, Larhammar D, Lihrmann I, Jegou S, Fournier A, Chartrel N, Vaudry H. Neuropeptide Y inhibits spontaneous alpha-melanocyte-stimulating hormone (alpha-MSH) release via a Y(5) receptor and suppresses thyrotropin-releasing hormone-induced alpha-MSH secretion via a Y(1) receptor in frog melanotrope cells. Endocrinology 2002; 143:1686-94. [PMID: 11956150 DOI: 10.1210/endo.143.5.8761] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In amphibians, the secretion of alpha-MSH by melanotrope cells is stimulated by TRH and inhibited by NPY. We have previously shown that NPY abrogates the stimulatory effect of TRH on alpha-MSH secretion. The aim of the present study was to characterize the receptor subtypes mediating the action of NPY and to investigate the intracellular mechanisms involved in the inhibitory effect of NPY on basal and TRH-induced alpha-MSH secretion. Y(1) and Y(5) receptor mRNAs were detected by RT-PCR and visualized by in situ hybridization histochemistry in the intermediate lobe of the pituitary. Various NPY analogs inhibited in a dose-dependent manner the spontaneous secretion of alpha-MSH from perifused frog neurointermediate lobes with the following order of potency porcine peptide YY (pPYY) > frog NPY (fNPY) > porcine NPY (pNPY)-2-36) > pNPY-(13-36) > [D-Trp(32)]pNPY > [Leu(31),Pro(34)]pNPY. The stimulatory effect of TRH (10(-8)6 M) on alpha-MSH release was inhibited by fNPY, pPYY, and [Leu(31),Pro(34)]pNPY, but not by pNPY-(13-36) and [D-Trp(32)]pNPY. These data indicate that the inhibitory effect of fNPY on spontaneous alpha-MSH release is preferentially mediated through Y(5) receptors, whereas the suppression of TRH-induced alpha-MSH secretion by fNPY probably involves Y(1) receptors. Pretreatment of neurointermediate lobes with pertussis toxin (PTX; 1 microg/ml; 12 h) did not abolish the inhibitory effect of fNPY on cAMP formation and spontaneous alpha-MSH release, but restored the stimulatory effect of TRH on alpha-MSH secretion, indicating that the adenylyl cyclase pathway is not involved in the action of fNPY on TRH-evoked alpha-MSH secretion. In the majority of melanotrope cells, TRH induces a sustained and biphasic increase in cytosolic Ca(2+) concentration. Preincubation of cultured cells with fNPY (10(-7) M) or omega-conotoxin GVIA (10(-7) M) suppressed the plateau phase of the Ca(2+) response induced by TRH. However, although fNPY abrogated TRH-evoked alpha-MSH secretion, omega-conotoxin did not, showing dissociation between the cytosolic Ca(2+) concentration increase and the secretory response. Collectively, these data indicate that in frog melanotrope cells NPY inhibits spontaneous alpha-MSH release and cAMP formation through activation of a Y(5) receptor coupled to PTX- insensitive G protein, whereas NPY suppresses the stimulatory effect of TRH on alpha-MSH secretion through a Y(1) receptor coupled to a PTX-sensitive G protein-coupled receptor.
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Affiliation(s)
- Ludovic Galas
- European Institute for Peptide Research (IFRMP 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM, U-413, UA Centre National de la Recherche Scientifique, University of Rouen, 76821 Mont-Saint-Aignan, France
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Wong CJ, Johnson JD, Yunker WK, Chang JP. Caffeine stores and dopamine differentially require Ca(2+) channels in goldfish somatotropes. Am J Physiol Regul Integr Comp Physiol 2001; 280:R494-503. [PMID: 11208580 DOI: 10.1152/ajpregu.2001.280.2.r494] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The regulation of growth hormone (GH) secretion by intracellular Ca(2+) stores was studied in dissociated goldfish somatotropes. We characterized a caffeine-activated intracellular store that had been shown to mediate GH release in response to gonadotropin-releasing hormone. The peak response of caffeine stimulation was reduced by approximately 28% by 100 microM ryanodine in a use-dependent manner suggesting that the first 10 min of GH release is partially mediated by a caffeine-activated ryanodine receptor. The temporal sensitivities of caffeine- and dopamine-evoked GH release to blockade of Cd(2+)-sensitive Ca(2+) channels were compared. We demonstrated that the initial phase of dopamine-evoked release was dependent on Ca(2+) channels, whereas the initial phase of caffeine-evoked release was sensitive only to pretreatment blockade. This would suggest that the maintenance of one class of caffeine-activated intracellular stores requires entry of Ca(2+) through Cd(2+)-sensitive Ca(2+) channels. This differential temporal requirement for Ca(2+) channels in Ca(2+) signaling may be a mechanism to segregate intracellular signaling pathways of multiple neuroendocrine regulators in the teleost pituitary.
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Affiliation(s)
- C J Wong
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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Vaudry H, Chartrel N, Desrues L, Galas L, Kikuyama S, Mor A, Nicolas P, Tonon MC. The pituitary-skin connection in amphibians. Reciprocal regulation of melanotrope cells and dermal melanocytes. Ann N Y Acad Sci 1999; 885:41-56. [PMID: 10816640 DOI: 10.1111/j.1749-6632.1999.tb08664.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In amphibians, alpha-MSH secreted by the pars intermedia of the pituitary plays a pivotal role in the process of skin color adaptation. Reciprocally, the skin of amphibians contains a number of regulatory peptides, some of which have been found to regulate the activity of pituitary melanotrope cells. In particular, the skin of certain species of amphibians harbours considerable amounts of thyrotropin-releasing hormone, a highly potent stimulator of alpha-MSH release. Recently, we have isolated and sequenced from the skin of the frog Phyllomedusa bicolor--a novel peptide named skin peptide tyrosine tyrosine (SPYY), which exhibits 94% similarity with PYY from the frog Rana ridibunda. For concentrations ranging from 5 x 10(-10) to 10(-7) M, SPYY induces a dose-related inhibition of alpha-MSH secretion. At a dose of 10(-7) M, SPYY totally abolished alpha-MSH release. These data strongly suggest the existence of a regulatory loop between the pars intermedia of the pituitary and the skin in amphibians.
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Affiliation(s)
- H Vaudry
- European Institute for Peptide Research (IFRMP n(o) 23), Laboratory of Cellular and Molecular Neuroendocrinology, INSERM U 413, UA CNRS, University of Rouen, Mont-Saint-Aignan, France
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Soriani O, Le Foll F, Galas L, Roman F, Vaudry H, Cazin L. The sigma-ligand (+)-pentazocine depresses M current and enhances calcium conductances in frog melanotrophs. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:E73-80. [PMID: 10409130 DOI: 10.1152/ajpendo.1999.277.1.e73] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gramicidin-perforated patch clamp experiments and microfluorimetric measurements were performed to study the ionic mechanisms involved in the sigma-receptor-mediated stimulation of frog (Rana ridibunda) pituitary melanotrophs. The sigma-ligand (+)-pentazocine (50 microM) depressed a sustained outward K(+) current. The kinetic properties of this K(+) component, investigated by analyzing tail currents, were reminiscent of those of the M current (I(M)), with an activation threshold close to -60 mV, a -21-mV half-maximal activation potential, and two-component exponential deactivation kinetics at -90 mV. (+)-Pentazocine (20 microM) produced a 12-mV rightward shift of the activation curve and accelerated the deactivation rate of the tail current. It is also demonstrated that (+)-pentazocine (20 microM) reversibly increased both voltage-dependent calcium conductances and internal calcium level. Altogether, these results suggest that the sigma-receptor-induced modulation of I(M) and calcium currents likely underlies the increase of intracellular [Ca(2+)].
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Affiliation(s)
- O Soriani
- European Institute for Peptide Research, Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale U413, Institut Fédératif de Recherche Multidisciplinaire sur les Peptides no. 23, France
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Galas L, Lamacz M, Garnier M, Roubos EW, Tonon MC, Vaudry H. Involvement of protein kinase C and protein tyrosine kinase in thyrotropin-releasing hormone-induced stimulation of alpha-melanocyte-stimulating hormone secretion in frog melanotrope cells. Endocrinology 1999; 140:3264-72. [PMID: 10385423 DOI: 10.1210/endo.140.7.6772] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have previously shown that the stimulatory effect of TRH on alpha-MSH secretion from the frog pars intermedia is associated with Ca2+ influx through voltage-dependent Ca2+ channels, activation of a phospholipase C and mobilization of intracellular Ca2+ stores. The aim of the present study was to investigate the contribution of protein kinase C (PKC), adenylyl cyclase (AC), Ca2+/calmodulin-dependent protein kinase II (CAM KII), phospholipase A2, and protein tyrosine kinase (PTK) in TRH-induced alpha-MSH release. Incubation of frog neurointermediate lobes (NILs) with phorbol 12-myristate-13-acetate (24 h), which causes desensitization of PKC, or with the PKC inhibitor NPC-15437, reduced by approximately 50% of the effect of TRH on alpha-MSH release. In most melanotrope cells, TRH induces a sustained and biphasic increase in cytosolic Ca2+ concentration ([Ca2+]i). Preincubation with phorbol 12-myristate-13-acetate or NPC-15437 suppressed the plateau phase of the Ca2+ response. Incubation of NILs with TRH (10(-6) M; 20 min) had no effect on cAMP production. In addition, the AC inhibitor SQ 22,536 did not affect the secretory response of NILs to TRH. These data indicate that the phospholipase C/PKC pathway, but not the AC/protein kinase A pathway, is involved in TRH-induced alpha-MSH release. The calmodulin inhibitor W-7 and the CAM KII inhibitor KN-93 did not significantly reduce the response to TRH. Similarly, the phospholipase A2 inhibitors quinacrine and 7-7'-DEA did not impair the effect of TRH on alpha-MSH secretion. The PTK inhibitors ST638 and Tyr-A23 had no effect on TRH-induced [Ca2+]i increase but inhibited in a dose-dependent manner TRH-evoked alpha-MSH release (ED50 = 1.22x10(-5) M and ED50 = 1.47x10(-5) M, respectively). Taken together, these data indicate that, in frog melanotrope cells, PKC and PTK are involved in TRH-induced alpha-MSH secretion. Activation of PKC is responsible for the sustained phase of the increase in [Ca2+]i, whereas activation of PTK does not affect Ca2+ mobilization.
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Affiliation(s)
- L Galas
- Laboratory of Cellular and Molecular Neuroendocrinology, Institut National de la Santé et de la Recherche Médicale (INSERM U 413), University of Rouen, Mont-Saint-Aignan, France
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