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Barrile F, Cassano D, Fernandez G, De Francesco PN, Reynaldo M, Cantel S, Fehrentz JA, Donato J, Schiöth HB, Zigman JM, Perello M. Ghrelin's orexigenic action in the lateral hypothalamic area involves indirect recruitment of orexin neurons and arcuate nucleus activation. Psychoneuroendocrinology 2023; 156:106333. [PMID: 37454647 PMCID: PMC10530520 DOI: 10.1016/j.psyneuen.2023.106333] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Revised: 05/30/2023] [Accepted: 07/10/2023] [Indexed: 07/18/2023]
Abstract
OBJECTIVE Ghrelin is a potent orexigenic hormone, and the lateral hypothalamic area (LHA) has been suggested as a putative target mediating ghrelin's effects on food intake. Here, we aimed to investigate the presence of neurons expressing ghrelin receptor (a.k.a. growth hormone secretagogue receptor, GHSR) in the mouse LHA (LHAGHSR neurons), its physiological implications and the neuronal circuit recruited by local ghrelin action. METHODS We investigated the distribution of LHAGHSR neurons using different histologic strategies, including the use of a reporter mice expressing enhanced green fluorescent protein under the control of the GHSR promoter. Also, we investigated the physiological implications of local injections of ghrelin within the LHA, and the extent to which the orexigenic effect of intra-LHA-injected ghrelin involves the arcuate nucleus (ARH) and orexin neurons of the LHA (LHAorexin neurons) RESULTS: We found that: 1) LHAGHSR neurons are homogeneously distributed throughout the entire LHA; 2) intra-LHA injections of ghrelin transiently increase food intake and locomotor activity; 3) ghrelin's orexigenic effect in the LHA involves the indirect recruitment of LHAorexin neurons and the activation of ARH neurons; and 4) LHAGHSR neurons are not targeted by plasma ghrelin. CONCLUSIONS We provide a compelling neuroanatomical and functional characterization of LHAGHSR neurons in male mice that indicates that LHAGHSR cells are part of a hypothalamic neuronal circuit that potently induces food intake.
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Affiliation(s)
- Franco Barrile
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina
| | - Daniela Cassano
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina
| | - Gimena Fernandez
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina
| | - Pablo N De Francesco
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina
| | - Mirta Reynaldo
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina
| | - Sonia Cantel
- Institut des Biomolécules Max Mousseron, Univ Montpellier, CNRS, ENSCM, Montpellier, France
| | - Jean-Alain Fehrentz
- Institut des Biomolécules Max Mousseron, Univ Montpellier, CNRS, ENSCM, Montpellier, France
| | - José Donato
- Department of Physiology and Biophysics, Instituto de Ciencias Biomedicas, Universidade de São Paulo, São Paulo, Brazil
| | - Helgi B Schiöth
- Department of Surgical Sciences, Functional Pharmacology and Neuroscience, University of Uppsala, Uppsala, Sweden
| | - Jeffrey M Zigman
- Center for Hypothalamic Research, Department of Internal Medicine, UT Southwestern Medical Center, Dallas, TX, USA
| | - Mario Perello
- Laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology [IMBICE, Argentine Research Council (CONICET) and Scientific Research Commission, Province of Buenos Aires (CIC-PBA), National University of La Plata], La Plata, Buenos Aires, Argentina; Department of Surgical Sciences, Functional Pharmacology and Neuroscience, University of Uppsala, Uppsala, Sweden.
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Akalu Y, Molla MD, Dessie G, Ayelign B. Physiological Effect of Ghrelin on Body Systems. Int J Endocrinol 2020; 2020:1385138. [PMID: 32565790 PMCID: PMC7267865 DOI: 10.1155/2020/1385138] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 02/08/2020] [Accepted: 05/13/2020] [Indexed: 02/06/2023] Open
Abstract
Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.
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Affiliation(s)
- Yonas Akalu
- Department of Physiology, School of Medicine, College of Medicine and Health Sciences, University of Gondar, Gondar, Ethiopia
| | - Meseret Derbew Molla
- Department of Biochemistry, School of Medicine, College of Medicine and Health Sciences, University of Gondar, Gondar, Ethiopia
| | - Gashaw Dessie
- Department of Biochemistry, School of Medicine, College of Medicine and Health Sciences, University of Gondar, Gondar, Ethiopia
| | - Birhanu Ayelign
- Department of Immunology and Molecular Biology, School of Biomedical and Laboratory Science, College of Medicine and Health Sciences, University of Gondar, Gondar, Ethiopia
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3
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Lockie SH, Stark R, Spanswick DC, Andrews ZB. Glucose availability regulates ghrelin-induced food intake in the ventral tegmental area. J Neuroendocrinol 2019; 31:e12696. [PMID: 30742723 DOI: 10.1111/jne.12696] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Revised: 12/13/2018] [Accepted: 02/08/2019] [Indexed: 12/23/2022]
Abstract
Information about metabolic status arrives in the brain in the form of a complex milieu of circulating signalling factors, including glucose and fatty acids, ghrelin, leptin and insulin. The specific interactions between humoural factors, brain sites of action and how they influence behaviour are largely unknown. We have previously observed interactions between glucose availability and the actions of ghrelin mediated via the agouti-related peptide neurones of the hypothalamus. In the present study, we examine whether these effects generalise to another ghrelin-sensitive brain nucleus, the ventral tegmental area (VTA). We altered glucose availability by injecting mice with glucose or 2-deoxyglucose i.p. to induce hyperglycaemia and glucopenia, respectively. Thirty minutes later, we injected ghrelin in the VTA. Glucose administration suppressed intra-VTA ghrelin-induced feeding. Leptin, a longer-term signal of positive energy balance, did not affect intra-VTA ghrelin-induced feeding. 2-Deoxyglucose and ghrelin both increased food intake in their own right and, together, they additively increased feeding. These results add support to the idea that calculation of metabolic need depends on multiple signals across multiple brain regions and identifies that VTA circuits are sensitive to the integration of signals reflecting internal homeostatic state and influencing food intake.
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Affiliation(s)
- Sarah H Lockie
- Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Romana Stark
- Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - David C Spanswick
- Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Zane B Andrews
- Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Department of Physiology, Monash University, Clayton, Victoria, Australia
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4
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Dos-Santos RC, Reis LC, Perello M, Ferguson AV, Mecawi AS. The actions of ghrelin in the paraventricular nucleus: energy balance and neuroendocrine implications. Ann N Y Acad Sci 2019; 1455:81-97. [PMID: 31008525 DOI: 10.1111/nyas.14087] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 02/28/2019] [Accepted: 03/10/2019] [Indexed: 12/15/2022]
Abstract
Ghrelin is a peptide mainly produced and secreted by the stomach. Since its discovery, the impact of ghrelin on the regulation of food intake has been the most studied function of this hormone; however, ghrelin affects a wide range of physiological systems, many of which are controlled by the hypothalamic paraventricular nucleus (PVN). Several pathways may mediate the effects of ghrelin on PVN neurons, such as direct or indirect effects mediated by circumventricular organs and/or the arcuate nucleus. The ghrelin receptor is expressed in PVN neurons, and the peripheral or intracerebroventricular administration of ghrelin affects PVN neuronal activity. Intra-PVN application of ghrelin increases food intake and decreases fat oxidation, which chronically contribute to the increased adiposity. Additionally, ghrelin modulates the neuroendocrine axes controlled by the PVN, increasing the release of vasopressin and oxytocin by magnocellular neurons and corticotropin-releasing hormone by neuroendocrine parvocellular neurons, while possibly inhibiting the release of thyrotropin-releasing hormone. Thus, the PVN is an important target for the actions of ghrelin. Our review discusses the mechanisms of ghrelin actions in the PVN, and its potential implications for energy balance, neuroendocrine, and integrative physiological control.
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Affiliation(s)
- Raoni C Dos-Santos
- Department of Physiological Sciences, Federal Rural University of Rio de Janeiro, Seropédica, Brazil
| | - Luís C Reis
- Department of Physiological Sciences, Federal Rural University of Rio de Janeiro, Seropédica, Brazil
| | - Mario Perello
- Laboratory of Neurophysiology, Multidisciplinary Institute of Cell Biology, La Plata, Argentina
| | - Alastair V Ferguson
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario, Canada
| | - André S Mecawi
- Laboratory of Neuroendocrinology, Department of Biophysics, Paulista Medical School, Federal University of São Paulo, São Paulo, Brazil
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Abstract
Ghrelin and motilin are released from gastrointestinal endocrine cells during hunger, to act through G protein-coupled receptors that have closely related amino acid sequences. The actions of ghrelin are more complex than motilin because ghrelin also exists outside the GI tract, it is processed to des-acyl ghrelin which has activity, ghrelin can exist in truncated forms and retain activity, the ghrelin receptor can have constitutive activity and is subject to biased agonism and finally additional ghrelin-like and des-acyl ghrelin receptors are proposed. Both ghrelin and motilin can stimulate gastric emptying, acting via different pathways, perhaps influenced by biased agonism at the receptors, but research is revealing additional pathways of activity. For example, it is becoming apparent that reduction of nausea may be a key therapeutic target for ghrelin receptor agonists and perhaps for compounds that modulate the constitutive activity of the ghrelin receptor. Reduction of nausea may be the mechanism through which gastroparesis symptoms are reduced. Intriguingly, a potential ability of motilin to influence nausea is also becoming apparent. Ghrelin interacts with digestive function through its effects on appetite, and ghrelin antagonists may have a place in treating Prader-Willi syndrome. Unlike motilin, ghrelin receptor agonists also have the potential to treat constipation by acting at the lumbosacral defecation centres. In conclusion, agonists of both ghrelin and motilin receptors hold potential as treatments for specific subsets of digestive system disorders.
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Plyler KS, Daniels D. Fourth ventricle injection of ghrelin decreases angiotensin II-induced fluid intake and neuronal activation in the paraventricular nucleus of the hypothalamus. Physiol Behav 2017; 178:35-42. [PMID: 27876637 PMCID: PMC5438304 DOI: 10.1016/j.physbeh.2016.11.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 10/18/2016] [Accepted: 11/18/2016] [Indexed: 02/04/2023]
Abstract
Ghrelin acts in the CNS to decrease fluid intake under a variety of dipsogenic and natriorexigenic conditions. Previous studies on this topic, however, focused on the forebrain as a site of action for this effect of ghrelin. Because the hindbrain contains neural substrates that are capable of mediating the well-established orexigenic effects of ghrelin, the current study tested the hypothesis that ghrelin applied to the hindbrain also would affect fluid intake. To this end, water and saline intakes were stimulated by central injection of angiotensin II (AngII) in rats that also received injections of ghrelin (0.5μg/μl) into either the lateral or fourth ventricle. Ghrelin injected into either ventricle reduced both water and 1.8% NaCl intake that was stimulated by AngII. The nature of the intake effect revealed some differences between the injection sites. For example, forebrain application of ghrelin reduced saline intake by a reduction in both the number of licking bursts and the size of each licking burst, but hindbrain application of ghrelin had a more selective effect on burst number. In an attempt to elucidate a brain structure in which hindbrain-administered ghrelin and forebrain-administered AngII interact to cause the ingestive response, we used Fos-immunohistochemistry in rats given the treatments used in the behavioral experiments. Although several brain areas were found to respond to either ghrelin or AngII, of the sites examined, only the paraventricular nucleus of the hypothalamus (PVN) emerged as a potential site of interaction. Specifically, AngII treatment caused expression of Fos in the PVN that was attenuated by concomitant treatment with ghrelin. These experiments provide the novel finding that the hindbrain contains elements that can respond to ghrelin and cause decreases in AngII-induced fluid intake, and that direct actions by ghrelin on forebrain structures is not necessary. Moreover, these studies suggest that the PVN is an important site of interaction between these two peptides.
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Affiliation(s)
- Kimberly S Plyler
- Behavioral Neuroscience Program, Department of Psychology, The State University of New York at Buffalo, Buffalo, NY 14260, USA
| | - Derek Daniels
- Behavioral Neuroscience Program, Department of Psychology, The State University of New York at Buffalo, Buffalo, NY 14260, USA.
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Abstract
Obesity, a major risk factor for the development of diabetes mellitus, cardiovascular diseases and certain types of cancer, arises from a chronic positive energy balance that is often due to unlimited access to food and an increasingly sedentary lifestyle on the background of a genetic and epigenetic vulnerability. Our understanding of the humoral and neuronal systems that mediate the control of energy homeostasis has improved dramatically in the past few decades. However, our ability to develop effective strategies to slow the current epidemic of obesity has been hampered, largely owing to the limited knowledge of the mechanisms underlying resistance to the action of metabolic hormones such as leptin and ghrelin. The development of resistance to leptin and ghrelin, hormones that are crucial for the neuroendocrine control of energy homeostasis, is a hallmark of obesity. Intensive research over the past several years has yielded tremendous progress in our understanding of the cellular pathways that disrupt the action of leptin and ghrelin. In this Review, we discuss the molecular mechanisms underpinning resistance to leptin and ghrelin and how they can be exploited as targets for pharmacological management of obesity.
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Affiliation(s)
- Huxing Cui
- Department of Pharmacology, University of Iowa, Iowa City, Iowa 52246, USA
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa 52242, USA
| | - Miguel López
- Department of Physiology, Center for Research in Molecular Medicine and Chronic Diseases (CiMUS), University of Santiago de Compostela-Instituto de Investigación Sanitaria, Santiago de Compostela 15782, Spain
- Centro de Investigación Biomédica en Red-Fisiopatología de la Obesidad y Nutrición (CIBERobn), Santiago de Compostela 15706, Spain
| | - Kamal Rahmouni
- Department of Pharmacology, University of Iowa, Iowa City, Iowa 52246, USA
- Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, Iowa 52242, USA
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8
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Clarifying the Ghrelin System's Ability to Regulate Feeding Behaviours Despite Enigmatic Spatial Separation of the GHSR and Its Endogenous Ligand. Int J Mol Sci 2017; 18:ijms18040859. [PMID: 28422060 PMCID: PMC5412441 DOI: 10.3390/ijms18040859] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 04/04/2017] [Accepted: 04/11/2017] [Indexed: 12/23/2022] Open
Abstract
Ghrelin is a hormone predominantly produced in and secreted from the stomach. Ghrelin is involved in many physiological processes including feeding, the stress response, and in modulating learning, memory and motivational processes. Ghrelin does this by binding to its receptor, the growth hormone secretagogue receptor (GHSR), a receptor found in relatively high concentrations in hypothalamic and mesolimbic brain regions. While the feeding and metabolic effects of ghrelin can be explained by the effects of this hormone on regions of the brain that have a more permeable blood brain barrier (BBB), ghrelin produced within the periphery demonstrates a limited ability to reach extrahypothalamic regions where GHSRs are expressed. Therefore, one of the most pressing unanswered questions plaguing ghrelin research is how GHSRs, distributed in brain regions protected by the BBB, are activated despite ghrelin’s predominant peripheral production and poor ability to transverse the BBB. This manuscript will describe how peripheral ghrelin activates central GHSRs to encourage feeding, and how central ghrelin synthesis and ghrelin independent activation of GHSRs may also contribute to the modulation of feeding behaviours.
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9
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Ghrelin's control of food reward and body weight in the lateral hypothalamic area is sexually dimorphic. Physiol Behav 2017; 176:40-49. [PMID: 28213203 DOI: 10.1016/j.physbeh.2017.02.011] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Revised: 01/18/2017] [Accepted: 02/10/2017] [Indexed: 12/18/2022]
Abstract
Ghrelin is a stomach-produced hormone that stimulates ingestive behavior and increases motivated behavior to obtain palatable foods. Ghrelin receptors (growth hormone secretagogue receptors; Ghsr) are expressed in the lateral hypothalamic area (LHA), and LHA-targeted ghrelin application increases ingestive behavior in male rodents. However, the effects of LHA ghrelin signaling in females are unexplored. Here we investigated whether LHA ghrelin signaling is necessary and sufficient for control of ingestive and motivated behavior for food in male and female rats. Ghrelin delivered to the LHA increased food intake and motivated behavior for sucrose in both male and female rats, whereas increased food-seeking behavior and body weight were only observed in females. Females had slightly higher Ghsr levels in the LHA compared to males, and importantly, acute blockade of the Ghsr in the LHA significantly reduced food intake, body weight, and motivated behavior for sucrose in female but not male rats. Chronic LHA Ghsr reduction in female rats achieved by RNA inference-mediated Ghsr knockdown, resulting in a 25% reduction in LHA Ghsr mRNA, abolished the reward-driven behavioral effects of LHA-targeted ghrelin, but was not sufficient to affect baseline food intake or food reward responding. Collectively we show that ghrelin acts in the LHA to alter ingestive and motivated behaviors in a sex-specific manner.
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Sominsky L, Ziko I, Nguyen TX, Andrews ZB, Spencer SJ. Early life disruption to the ghrelin system with over-eating is resolved in adulthood in male rats. Neuropharmacology 2017; 113:21-30. [DOI: 10.1016/j.neuropharm.2016.09.023] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 09/21/2016] [Accepted: 09/22/2016] [Indexed: 12/11/2022]
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Yalcin O, Iseri E, Bukan N, Ercin U. Effects of Long Acting Methylphenidate on Ghrelin Levels in Male Children with Attention Deficit Hyperactivity Disorder: An Open Label Trial. ACTA ACUST UNITED AC 2016. [DOI: 10.5455/bcp.20130708042604] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Ozhan Yalcin
- Bakirkoy Training and Research Hospital for Mental Disorders and Neurological Diseases, Istanbul - Turkey
| | - Elvan Iseri
- Gazi University School of Medicine, Department of Child and Adolescent Psychiatry, Ankara - Turkey
| | - Neslihan Bukan
- Gazi University School of Medicine, Department of Medical Biochemistry, Ankara - Turkey
| | - Ugur Ercin
- Gazi University School of Medicine, Department of Medical Biochemistry, Ankara - Turkey
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Brockway ET, Krater KR, Selva JA, Wauson SER, Currie PJ. Impact of [d-Lys(3)]-GHRP-6 and feeding status on hypothalamic ghrelin-induced stress activation. Peptides 2016; 79:95-102. [PMID: 27020248 DOI: 10.1016/j.peptides.2016.03.013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Revised: 03/20/2016] [Accepted: 03/23/2016] [Indexed: 12/18/2022]
Abstract
Ghrelin administration directly into hypothalamic nuclei, including the arcuate nucleus (ArcN) and the paraventricular nucleus (PVN), alters the expression of stress-related behaviors. In the present study we investigated the effect of feeding status on the ability of ghrelin to induce stress and anxiogenesis. Adult male Sprague Dawley rats were implanted with guide cannula targeting either the ArcN or PVN. In the first experiment we confirmed that ArcN and PVN ghrelin treatment produced anxiety-like behavior as measured using the elevated plus maze (EPM) paradigm. Ghrelin was administered during the early dark cycle. Immediately after microinjections rats were placed in the EPM for 5min. Both ArcN and PVN treatment reduced open arm exploration. The effect was attenuated by pretreatment with the ghrelin 1a receptor antagonist [d-Lys(3)]-GHRP-6. In a separate group of animals ghrelin was injected into either nucleus and rats were returned to their home cages for 60min with free access to food. An additional group of rats was returned to home cages with no food access. After 60min with or without food access all rats were tested in the EPM. Results indicated that food consumption just prior to EPM testing reversed the avoidance of the open arms of the EPM. In contrast, rats injected with ghrelin, placed in their home cage for 60min without food, and subsequently tested in the EPM, exhibited an increased avoidance of the open arms, consistent with stress activation. Overall, our findings demonstrate that ghrelin 1a receptor blockade and feeding status appear to impact the ability of ArcN and PVN ghrelin to elicit stress and anxiety-like behaviors.
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Affiliation(s)
- Emma T Brockway
- Department of Psychology, Reed College, Portland, OR 97202, United States
| | - Katherine R Krater
- Department of Psychology, Reed College, Portland, OR 97202, United States
| | - Joaquín A Selva
- Department of Psychology, Reed College, Portland, OR 97202, United States
| | - Shelby E R Wauson
- Department of Psychology, Reed College, Portland, OR 97202, United States
| | - Paul J Currie
- Department of Psychology, Reed College, Portland, OR 97202, United States.
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Abstract
The gastrointestinal tract is the major source of the related hormones ghrelin and motilin, which act on structurally similar G protein-coupled receptors. Nevertheless, selective receptor agonists are available. The primary roles of endogenous ghrelin and motilin in the digestive system are to increase appetite or hedonic eating (ghrelin) and initiate phase III of gastric migrating myoelectric complexes (motilin). Ghrelin and motilin also both inhibit nausea. In clinical trials, the motilin receptor agonist camicinal increased gastric emptying, but at lower doses reduced gastroparesis symptoms and improved appetite. Ghrelin receptor agonists have been trialled for the treatment of diabetic gastroparesis because of their ability to increase gastric emptying, but with mixed results; however, relamorelin, a ghrelin agonist, reduced nausea and vomiting in patients with this disorder. Treatment of postoperative ileus with a ghrelin receptor agonist proved unsuccessful. Centrally penetrant ghrelin receptor agonists stimulate defecation in animals and humans, although ghrelin itself does not seem to control colorectal function. Thus, the most promising uses of motilin receptor agonists are the treatment of gastroparesis or conditions with slow gastric emptying, and ghrelin receptor agonists hold potential for the reduction of nausea and vomiting, and the treatment of constipation. Therapeutic, gastrointestinal roles for receptor antagonists or inverse agonists have not been identified.
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Zigman JM, Bouret SG, Andrews ZB. Obesity Impairs the Action of the Neuroendocrine Ghrelin System. Trends Endocrinol Metab 2016; 27:54-63. [PMID: 26542050 PMCID: PMC4814209 DOI: 10.1016/j.tem.2015.09.010] [Citation(s) in RCA: 93] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 09/22/2015] [Accepted: 09/28/2015] [Indexed: 01/08/2023]
Abstract
Ghrelin is a metabolic hormone that promotes energy conservation by regulating appetite and energy expenditure. Although some studies suggest that antagonizing ghrelin function attenuates body weight gain and glucose intolerance on a high calorie diet, there is little information about the metabolic actions of ghrelin in the obese state. In this review, we discuss the novel concept of obesity-induced central ghrelin resistance in neural circuits regulating behavior, and impaired ghrelin secretion from the stomach. Interestingly, weight loss restores ghrelin secretion and function, and we hypothesize that ghrelin resistance is a mechanism designed to protect a higher body weight set-point established during times of food availability, to maximize energy reserves during a time of food scarcity.
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Affiliation(s)
- Jeffrey M Zigman
- Departments of Internal Medicine (Divisions of Hypothalamic Research and Endocrinology and Metabolism) and Psychiatry, The University of Texas Southwestern Medical Center, Dallas, TX, 75390-9077, USA.
| | - Sebastien G Bouret
- The Saban Research Institute, Developmental Neuroscience Program, Children's Hospital Los Angeles, University of Southern California, Los Angeles, CA 90027, USA; Inserm, Jean-Pierre Aubert Research Center, U1172, University Lille 2, Lille, 59045, France
| | - Zane B Andrews
- Metabolic Disease and Obesity Theme, Biomedicine Discovery Institute, Department of Physiology, Monash University, Clayton, Victoria 3183, Australia
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Stark R, Reichenbach A, Lockie SH, Pracht C, Wu Q, Tups A, Andrews ZB. Acyl ghrelin acts in the brain to control liver function and peripheral glucose homeostasis in male mice. Endocrinology 2015; 156:858-68. [PMID: 25535832 DOI: 10.1210/en.2014-1733] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Recent evidence suggests that peripheral ghrelin regulates glucose metabolism. Here, we designed experiments to examine how central acyl ghrelin infusion affects peripheral glucose metabolism under pair-fed or ad libitum feeding conditions. Mice received intracerebroventricular (icv) infusion of artificial cerebrospinal fluid (aCSF), ghrelin, and allowed to eat ad libitum (icv ghrelin ad lib) or ghrelin and pair-fed to the aCSF group (icv ghrelin pf). Minipumps delivered acyl ghrelin at a dose of 0.25 μg/h at 0.5 μL/h for 7 days. There was no difference in daily blood glucose, insulin, glucagon, triglycerides, or nonesterified fatty acids. Body weight gain and food intake was significantly higher in icv ghrelin ad lib mice. However, both icv ghrelin ad lib and icv ghrelin pf groups exhibited heavier white adipose mass. Icv ghrelin pf mice exhibited better glucose tolerance than aCSF or icv ghrelin ad lib mice during a glucose tolerance test, although both icv ghrelin ad lib and icv ghrelin pf increased insulin release during the glucose tolerance test. Central acyl ghrelin infusion and pair feeding also increased breakdown of liver glycogen and triglyceride, and regulated genes involved in hepatic lipid and glucose metabolism. Icv ghrelin pf mice had an increase in plasma blood glucose during a pyruvate tolerance test relative to icv ghrelin ad lib or aCSF mice. Our results suggest that under conditions of negative energy (icv ghrelin pf), central acyl ghrelin engages a neural circuit that influences hepatic glucose function. Metabolic status affects the ability of central acyl ghrelin to regulate peripheral glucose homeostasis.
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Affiliation(s)
- Romana Stark
- Department of Physiology (R.S., A.R., S.H.L., Q.W., Z.B.A.), Monash University, Clayton, Victoria 3800, Australia; Traditional Chinese Medicine Department (Q.W.), Peking Union Medical College Hospital, Dongcheng District, Beijing 100730, China; Department of Animal Physiology (C.P., A.T.), Faculty of Biology, Phillips University, D-35043 Marburg, Germany; and Department of Physiology (A.T.), Otago School of Medical Sciences, University of Otago, Dunedin 9054, New Zealand
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Nutritional state-dependent ghrelin activation of vasopressin neurons via retrograde trans-neuronal-glial stimulation of excitatory GABA circuits. J Neurosci 2014; 34:6201-13. [PMID: 24790191 DOI: 10.1523/jneurosci.3178-13.2014] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Behavioral and physiological coupling between energy balance and fluid homeostasis is critical for survival. The orexigenic hormone ghrelin has been shown to stimulate the secretion of the osmoregulatory hormone vasopressin (VP), linking nutritional status to the control of blood osmolality, although the mechanism of this systemic crosstalk is unknown. Here, we show using electrophysiological recordings and calcium imaging in rat brain slices that ghrelin stimulates VP neurons in the hypothalamic paraventricular nucleus (PVN) in a nutritional state-dependent manner by activating an excitatory GABAergic synaptic input via a retrograde neuronal-glial circuit. In slices from fasted rats, ghrelin activation of a postsynaptic ghrelin receptor, the growth hormone secretagogue receptor type 1a (GHS-R1a), in VP neurons caused the dendritic release of VP, which stimulated astrocytes to release the gliotransmitter adenosine triphosphate (ATP). ATP activation of P2X receptors excited presynaptic GABA neurons to increase GABA release, which was excitatory to the VP neurons. This trans-neuronal-glial retrograde circuit activated by ghrelin provides an alternative means of stimulation of VP release and represents a novel mechanism of neuronal control by local neuronal-glial circuits. It also provides a potential cellular mechanism for the physiological integration of energy and fluid homeostasis.
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Mason BL, Wang Q, Zigman JM. The central nervous system sites mediating the orexigenic actions of ghrelin. Annu Rev Physiol 2013; 76:519-33. [PMID: 24111557 DOI: 10.1146/annurev-physiol-021113-170310] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The peptide hormone ghrelin is important for both homeostatic and hedonic eating behaviors, and its orexigenic actions occur mainly via binding to the only known ghrelin receptor, the growth hormone secretagogue receptor (GHSR). GHSRs are located in several distinct regions of the central nervous system. This review discusses those central nervous system sites that have been found to play critical roles in the orexigenic actions of ghrelin, including hypothalamic nuclei, the hippocampus, the amygdala, the caudal brain stem, and midbrain dopaminergic neurons. Hopefully, this review can be used as a stepping stone for the reader wanting to gain a clearer understanding of the central nervous system sites of direct ghrelin action on feeding behavior, and as inspiration for future studies to provide an even-more-detailed map of the neurocircuitry controlling eating and body weight.
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Affiliation(s)
- B L Mason
- Departments of Internal Medicine (Divisions of Hypothalamic Research and of Endocrinology & Metabolism) and Psychiatry, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9077; , ,
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Xu L, Qu Z, Guo F, Pang M, Gao S, Zhu H, Gu F, Sun X. Effects of ghrelin on gastric distention sensitive neurons in the arcuate nucleus of hypothalamus and gastric motility in diabetic rats. Peptides 2013; 48:137-46. [PMID: 23965296 DOI: 10.1016/j.peptides.2013.08.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2013] [Revised: 08/08/2013] [Accepted: 08/08/2013] [Indexed: 02/08/2023]
Abstract
This study was performed to observe the effects of ghrelin on the activity of gastric distention (GD) sensitive neurons in the arcuate nucleus of hypothalamus (Arc) and on gastric motility in vivo in streptozocin (STZ) induced diabetes mellitus (DM) rats. Electrophysiological results showed that ghrelin could excite GD-excitatory (GD-E) neurons and inhibit GD-inhibitory (GD-I) neurons in the Arc. However, fewer GD-E neurons were excited by ghrelin and the excitatory effect of ghrelin on GD-E neurons was much weaker in DM rats. Gastric motility research in vivo showed that microinjection of ghrelin into the Arc could significantly promote gastric motility and it showed a dose-dependent manner. The effect of ghrelin promoting gastric motility in DM rats was weaker than that in normal rats. The effects induced by ghrelin could be blocked by growth hormone secretagogue receptor (GHSR) antagonist [d-Lys-3]-GHRP-6 or BIM28163. RIA and real-time PCR data showed that the levels of ghrelin in the plasma, stomach and ghrelin mRNA in the Arc increased at first but decreased later and the expression of GHSR-1a mRNA in the Arc maintained a low level in DM rats. The present findings indicate that ghrelin could regulate the activity of GD sensitive neurons and gastric motility via ghrelin receptors in the Arc. The reduced effects of promoting gastric motility induced by ghrelin could be connected with the decreased expression of ghrelin receptors in the Arc in diabetes. Our data provide new experimental evidence for the role of ghrelin in gastric motility disorder in diabetes.
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Affiliation(s)
- Luo Xu
- Department of Pathophysiology, Medical College of Qingdao University, Qingdao 266021, China.
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Scott MM, Perello M, Chuang JC, Sakata I, Gautron L, Lee CE, Lauzon D, Elmquist JK, Zigman JM. Hindbrain ghrelin receptor signaling is sufficient to maintain fasting glucose. PLoS One 2012; 7:e44089. [PMID: 22952883 PMCID: PMC3432098 DOI: 10.1371/journal.pone.0044089] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Accepted: 08/01/2012] [Indexed: 11/19/2022] Open
Abstract
The neuronal coordination of metabolic homeostasis requires the integration of hormonal signals with multiple interrelated central neuronal circuits to produce appropriate levels of food intake, energy expenditure and fuel availability. Ghrelin, a peripherally produced peptide hormone, circulates at high concentrations during nutrient scarcity. Ghrelin promotes food intake, an action lost in ghrelin receptor null mice and also helps maintain fasting blood glucose levels, ensuring an adequate supply of nutrients to the central nervous system. To better understand mechanisms of ghrelin action, we have examined the roles of ghrelin receptor (GHSR) expression in the mouse hindbrain. Notably, selective hindbrain ghrelin receptor expression was not sufficient to restore ghrelin-stimulated food intake. In contrast, the lowered fasting blood glucose levels observed in ghrelin receptor-deficient mice were returned to wild-type levels by selective re-expression of the ghrelin receptor in the hindbrain. Our results demonstrate the distributed nature of the neurons mediating ghrelin action.
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Affiliation(s)
- Michael M. Scott
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia, United States of America
| | - Mario Perello
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Jen-Chieh Chuang
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Ichiro Sakata
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Laurent Gautron
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Charlotte E. Lee
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Danielle Lauzon
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
| | - Joel K. Elmquist
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Division of Endocrinology & Metabolism, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Department of Psychiatry, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Department of Pharmacology, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- * E-mail: (JKE); (JMZ)
| | - Jeffrey M. Zigman
- Division of Hypothalamic Research, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Division of Endocrinology & Metabolism, Department of Internal Medicine, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- Department of Psychiatry, The University of Texas Southwestern Medical Center at Dallas, Dallas, Texas, United States of America
- * E-mail: (JKE); (JMZ)
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Nemoto T, Sugihara H, Mano A, Kano T, Shibasaki T. The effects of ghrelin/GHSs on AVP mRNA expression and release in cultured hypothalamic cells in rats. Peptides 2011; 32:1281-8. [PMID: 21514337 DOI: 10.1016/j.peptides.2011.04.007] [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: 11/24/2010] [Revised: 04/07/2011] [Accepted: 04/07/2011] [Indexed: 11/26/2022]
Abstract
Ghrelin, the endogenous ligand for growth hormone secretagogues (GHSs) receptor (GHS-R), increases adrenocorticotropin (ACTH) and cortisol (corticosterone) as well as GH secretion in humans and animals. However, the site of GHSs action to induce ACTH secretion is not fully understood. To clarify the mechanisms of the action of ghrelin/GHSs on ACTH secretion, we analyzed the effects of KP-102 and ghrelin on the mRNA expression and release of corticotropin releasing factor (CRF) and arginine vasopressin (AVP), ACTH secretagogues, in monolayer-cultured hypothalamic cells of rats. Incubation of cells with KP-102 for 4h and 8h and with ghrelin for 4h significantly increased AVP mRNA expression and release without changing CRF mRNA expression. CRF levels in culture media were undetectable. Suppression of GHS-R expression by siRNA blocked ghrelin- and KP-102-induced AVP mRNA expression and release. NPY significantly increased AVP mRNA expression and release. Furthermore, treatment of cells with anti-NPY IgG blocked KP-102-induced AVP mRNA expression and release. We previously reported that KP-102 significantly increases NPY mRNA expression in cultured hypothalamic cells. Taken together, these results suggest that ACTH secretion by ghrelin/GHSs is induced mainly through hypothalamic AVP, and that NPY mediates the action of ghrelin/GHSs.
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Affiliation(s)
- Takahiro Nemoto
- Department of Physiology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8602, Japan.
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Ghrelin inhibits visceral afferent activation of catecholamine neurons in the solitary tract nucleus. J Neurosci 2011; 31:3484-92. [PMID: 21368060 DOI: 10.1523/jneurosci.3187-10.2011] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Brainstem A2/C2 catecholamine (CA) neurons in the solitary tract nucleus (NTS) are thought to play an important role in the control of food intake and other homeostatic functions. We have previously demonstrated that these neurons, which send extensive projections to brain regions involved in the regulation of appetite, are strongly and directly activated by solitary tract (ST) visceral afferents. Ghrelin, a potent orexigenic peptide released from the stomach, is proposed to act in part through modulating NTS CA neurons but the underlying cellular mechanisms are unknown. Here, we identified CA neurons using transgenic mice that express enhanced green fluorescent protein driven by the tyrosine hydroxylase promoter (TH-EGFP). We then determined how ghrelin modulates TH-EGFP neurons using patch-clamp techniques in a horizontal brain slice preparation. Ghrelin inhibited the frequency of spontaneous glutamate inputs (spontaneous EPSCs) onto TH-EGFP neurons, including cholecystokinin-sensitive neurons, an effect blocked by the GHSR1 antagonist, d-Lys-3-GHRP-6. This resulted in a decrease in the basal firing rate of NTS TH-EGFP neurons, an effect blocked by the glutamate antagonist NBQX. Ghrelin also dose-dependently inhibited the amplitude of ST afferent evoked EPSCs (ST-EPSCs) in TH-EGFP NTS neurons, decreasing the success rate for ST-evoked action potentials. In addition, ghrelin decreased the frequency of mini-EPSCs suggesting its actions are presynaptic to reduce glutamate release. Last, inhibition by ghrelin of the ST-EPSCs was significantly increased by an 18 h fast. These results demonstrate a potential mechanism by which ghrelin inhibits NTS TH neurons through a pathway whose responsiveness is increased during fasting.
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Sanger GJ, Hellström PM, Näslund E. The hungry stomach: physiology, disease, and drug development opportunities. Front Pharmacol 2011; 1:145. [PMID: 21927604 PMCID: PMC3174087 DOI: 10.3389/fphar.2010.00145] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Accepted: 12/22/2010] [Indexed: 01/28/2023] Open
Abstract
During hunger, a series of high-amplitude contractions of the stomach and small intestine (phase III), which form part of a cycle of quiescence and contractions (known as the migrating motor complex, MMC), play a "housekeeping" role prior to the next meal, and may contribute toward the development of hunger. Several gastrointestinal (GI) hormones are associated with phase III MMC activity, but currently the most prominent is motilin, thought to at least partly mediate phase III contractions of the gastric MMC. Additional GI endocrine and neuronal systems play even more powerful roles in the development of hunger. In particular, the ghrelin-precursor gene is proving to have a complex physiology, giving rise to three different products: ghrelin itself, which is formed from a post-translational modification of des-acyl-ghrelin, and obestatin. The receptors acted on by des-acyl-ghrelin and by obestatin are currently unknown but both these peptides seem able to exert actions which oppose that of ghrelin, either indirectly or directly. An increased understanding of the actions of these peptides is helping to unravel a number of different eating disorders and providing opportunities for the discovery of new drugs to regulate dysfunctional gastric behaviors and appetite. To date, ghrelin and motilin receptor agonists and antagonists have been described. The most advanced are compounds which activate the ghrelin and motilin receptors which are being progressed for disorders associated with gastric hypomotility.
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Affiliation(s)
- Gareth J. Sanger
- Wingate Institute of Neurogastroenterology, Barts and The London School of Medicine and Dentistry, Queen Mary University of LondonLondon, UK
| | - Per M. Hellström
- Department of Medical Sciences, Uppsala UniversityUppsala, Sweden
| | - Erik Näslund
- Division of Surgery, Department of Clinical Sciences, Danderyd Hospital, Karolinska InstitutetStockholm, Sweden
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De Vriese C, Perret J, Delporte C. Focus on the short- and long-term effects of ghrelin on energy homeostasis. Nutrition 2010; 26:579-84. [DOI: 10.1016/j.nut.2009.09.013] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Accepted: 09/17/2009] [Indexed: 02/06/2023]
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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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Veldhuis JD, Bowers CY. Integrating GHS into the Ghrelin System. INTERNATIONAL JOURNAL OF PEPTIDES 2010; 2010:879503. [PMID: 20798846 PMCID: PMC2925380 DOI: 10.1155/2010/879503] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 12/30/2009] [Indexed: 12/21/2022]
Abstract
Oligopeptide derivatives of metenkephalin were found to stimulate growth-hormone (GH) release directly by pituitary somatotrope cells in vitro in 1977. Members of this class of peptides and nonpeptidyl mimetics are referred to as GH secretagogues (GHSs). A specific guanosine triphosphatate-binding protein-associated heptahelical transmembrane receptor for GHS was cloned in 1996. An endogenous ligand for the GHS receptor, acylghrelin, was identified in 1999. Expression of ghrelin and homonymous receptor occurs in the brain, pituitary gland, stomach, endothelium/vascular smooth muscle, pancreas, placenta, intestine, heart, bone, and other tissues. Principal actions of this peptidergic system include stimulation of GH release via combined hypothalamopituitary mechanisms, orexigenesis (appetitive enhancement), insulinostasis (inhibition of insulin secretion), cardiovascular effects (decreased mean arterial pressure and vasodilation), stimulation of gastric motility and acid secretion, adipogenesis with repression of fat oxidation, and antiapoptosis (antagonism of endothelial, neuronal, and cardiomyocyte death). The array of known and proposed interactions of ghrelin with key metabolic signals makes ghrelin and its receptor prime targets for drug development.
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Affiliation(s)
- Johannes D. Veldhuis
- Department of Medicine, Endocrine Research Unit, Mayo School of Graduate Medical Education, Clinical Translational Science Center, Mayo Clinic, Rochester, MN 55905, USA
| | - Cyril Y. Bowers
- Division of Endocrinology, Department of Internal Medicine, Tulane University Health Sciences Center, New Orleans, LA 70112, USA
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Faulconbridge LF, Grill HJ, Kaplan JM, Daniels D. Caudal brainstem delivery of ghrelin induces fos expression in the nucleus of the solitary tract, but not in the arcuate or paraventricular nuclei of the hypothalamus. Brain Res 2008; 1218:151-7. [PMID: 18514175 DOI: 10.1016/j.brainres.2008.04.068] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2007] [Revised: 04/02/2008] [Accepted: 04/20/2008] [Indexed: 10/22/2022]
Abstract
Ghrelin increases food intake when injected into either the forebrain or hindbrain ventricles. Brain areas activated by ghrelin after forebrain delivery have been examined using Fos immunohistochemistry and include the hypothalamic arcuate (Arc) and paraventricular (PVN) nuclei, and the nucleus of the solitary tract (NTS) in the medulla. It is not clear, however, if ghrelin applied directly to the hindbrain activates forebrain structures. Therefore, we examined Fos expression in the Arc, PVN, and NTS after injecting ghrelin into the fourth ventricle. Animals treated with a hyperphagic dose of ghrelin had greater levels of Fos expression in the NTS at the level of the area postrema than animals injected with vehicle. Ghrelin did not, however, increase Fos expression in the Arc or PVN in rats with open or occluded cerebral aqueducts. Given the importance of caudal brainstem (CBS) catecholamine pathways in the control of food intake, we performed double-labeling experiments to evaluate the potential overlap between tyrosine hydroxylase TH and ghrelin-induced Fos expression. Ghrelin did not increase Fos in TH-positive neurons in the NTS, suggesting that ghrelin delivered to the fourth ventricle does not act through catecholaminergic pathways. Nevertheless, the local (NTS), but not distal (Arc and PVN), induction of Fos suggests the presence of partially independent forebrain and hindbrain circuits that respond to ghrelin. These data support the NTS as a target of ghrelin action by building upon prior findings of increases in food intake in response to third- and fourth-ventricle ghrelin delivery.
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Affiliation(s)
- Lucy F Faulconbridge
- Department of Psychology, University of Pennsylvania, 3720 Walnut Street, Philadelphia, PA 19104, USA
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Sanger GJ, Lee K. Hormones of the gut-brain axis as targets for the treatment of upper gastrointestinal disorders. Nat Rev Drug Discov 2008; 7:241-54. [PMID: 18309313 DOI: 10.1038/nrd2444] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The concept of the gut forming the centre of an integrated gut-brain-energy axis - modulating appetite, metabolism and digestion - opens up new paradigms for drugs that can tackle multiple symptoms in complex upper gastrointestinal disorders. These include eating disorders, nausea and vomiting, gastroesophageal reflux disease, gastroparesis, dyspepsia and irritable bowel syndrome. The hormones that modulate gastric motility represent targets for gastric prokinetic drugs, and peptides that modify eating behaviours may be targeted to develop drugs that reduce nausea, a currently poorly treated condition. The gut-brain axis may therefore provide a range of therapeutic opportunities that deliver a more holistic treatment of upper gastrointestinal disorders.
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Affiliation(s)
- Gareth J Sanger
- Immuno Inflammation Centre of Excellence for Drug Discovery, GlaxoSmithKline, Stevenage, Hertfordshire SG1 2NY, UK.
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Escobar C, Martínez-Merlos MT, Angeles-Castellanos M, del Carmen Miñana M, Buijs RM. Unpredictable feeding schedules unmask a system for daily resetting of behavioural and metabolic food entrainment. Eur J Neurosci 2008; 26:2804-14. [PMID: 18001277 DOI: 10.1111/j.1460-9568.2007.05893.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Restricted feeding schedules (RFS) are a potent Zeitgeber that uncouples daily metabolic and clock gene oscillations in peripheral tissues from the suprachiasmatic nucleus (SCN), which remains entrained to the light-dark cycle. Under RFS, animals develop food anticipatory activity (FAA), characterized by arousal and increased locomotion. Food availability in nature is not precise, which suggests that animals need to adjust their food-associated activity on a daily basis. This study explored the capacity of rats to adjust to variable and unpredictable feeding schedules. Rats were exposed either to RFS with fixed daily meal (RF) or to a variable meal time (VAR) during the light phase. RF and VAR rats exhibited daily metabolic oscillations driven by the last meal event; however, VAR rats were not able to show a robust adjustment in the anticipating corticosterone peak. VAR rats were unable to exhibit FAA but exhibited a daily activation pattern in phase with the previous meal. In both groups the dorsomedial nucleus of the hypothalamus and arcuate nucleus, involved in energy balance, exhibited increased c-Fos expression 24 h after the last meal, while only RF rats exhibited low c-Fos expression in the SCN. Data show that metabolic and behavioural food-entrained rhythms can be reset on a daily basis; the two conditions elicit a similar hypothalamic response, while only the SCN is inhibited in rats exhibiting anticipatory activity. The variable feeding strategy uncovered a rapid (24-h basis) resetting mechanism for metabolism and general behaviour.
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Affiliation(s)
- Carolina Escobar
- Departamento de Anatomía, Edificio B 4 piso, Facultad de Medicina, Circuito Escolar S/N, Universidad Nacional Autónoma de México, México DF 04510, México
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Abstract
PURPOSE OF REVIEW The purpose of this review is to provide updated information on the role of ghrelin in food intake and energy homeostasis, and on its mechanism of action. Moreover, the potential of ghrelin as a target for drugs to treat cachexia and obesity will be discussed. RECENT FINDINGS Whereas the effects of ghrelin in the regulation of appetite, food intake and energy homeostasis have been fairly well documented, the pathways responsible for the effects of ghrelin are now increasingly being understood. As a consequence, clinical applications of ghrelin are now being developed. SUMMARY Ghrelin is an endogenous orexigenic peptide recently discovered in the stomach. Ghrelin is involved in short-term regulation of food intake since its plasma levels increase before meals and decrease strongly postprandially. Ghrelin is also involved in long-term body-weight regulation by inducing adiposity. Ghrelin might be useful for cachexia and obesity treatment.
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Affiliation(s)
- Carine De Vriese
- Laboratory of Biological Chemistry and Nutrition, Université Libre de Bruxelles, Brussels, Belgium
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