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Page AJ. Plasticity of gastrointestinal vagal afferents in terms of feeding-related physiology and pathophysiology. J Physiol 2023. [PMID: 37737742 DOI: 10.1113/jp284075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Accepted: 09/07/2023] [Indexed: 09/23/2023] Open
Abstract
Gastrointestinal vagal afferents play an important role in communicating food related information from the gut to the brain. This information initiates vago-vagal reflexes essential for gut functions, including gut motility and secretions. These afferents also play a role in energy homeostasis, signalling the arrival, amount and nutrient composition of a meal to the central nervous system where it is processed ultimately leading to termination of a meal. Vagal afferent responses to food related stimuli demonstrate a high degree of plasticity, responding to short term changes in nutritional demand, such as the fluctuations that occur across a 24-hr or in response to a fast, as well as long term changes in energy demand, such as occurs during pregnancy. This plasticity is disrupted in disease states, such as obesity or chronic stress where there is hypo- and hypersensitivity of these afferents, respectively. Improved understanding of the plasticity of these afferents will enable identification of new treatment options for diseases associated with vagal afferent function.
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Affiliation(s)
- Amanda J Page
- Vagal Afferent Research Group, School of Biomedicine, University of Adelaide, Adelaide, South Australia, Australia
- Nutrition, Diabetes & Gut Health, Lifelong Health Theme, South Australian Health and Medical Research Institute, SAHMRI, Adelaide, South Australia, Australia
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2
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Perelló M, Cornejo MP, De Francesco PN, Fernandez G, Gautron L, Valdivia LS. The controversial role of the vagus nerve in mediating ghrelin´s actions: gut feelings and beyond. IBRO Neurosci Rep 2022; 12:228-239. [PMID: 35746965 PMCID: PMC9210457 DOI: 10.1016/j.ibneur.2022.03.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 03/08/2022] [Accepted: 03/08/2022] [Indexed: 12/26/2022] Open
Abstract
Ghrelin is a stomach-derived peptide hormone that acts via the growth hormone secretagogue receptor (GHSR) and displays a plethora of neuroendocrine, metabolic, autonomic and behavioral actions. It has been proposed that some actions of ghrelin are exerted via the vagus nerve, which provides a bidirectional communication between the central nervous system and peripheral systems. The vagus nerve comprises sensory fibers, which originate from neurons of the nodose and jugular ganglia, and motor fibers, which originate from neurons of the medulla. Many anatomical studies have mapped GHSR expression in vagal sensory or motor neurons. Also, numerous functional studies investigated the role of the vagus nerve mediating specific actions of ghrelin. Here, we critically review the topic and discuss the available evidence supporting, or not, a role for the vagus nerve mediating some specific actions of ghrelin. We conclude that studies using rats have provided the most congruent evidence indicating that the vagus nerve mediates some actions of ghrelin on the digestive and cardiovascular systems, whereas studies in mice resulted in conflicting observations. Even considering exclusively studies performed in rats, the putative role of the vagus nerve in mediating the orexigenic and growth hormone (GH) secretagogue properties of ghrelin remains debated. In humans, studies are still insufficient to draw definitive conclusions regarding the role of the vagus nerve mediating most of the actions of ghrelin. Thus, the extent to which the vagus nerve mediates ghrelin actions, particularly in humans, is still uncertain and likely one of the most intriguing unsolved aspects of the field.
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Davis EA, Wald HS, Suarez AN, Zubcevic J, Liu CM, Cortella AM, Kamitakahara AK, Polson JW, Arnold M, Grill HJ, de Lartigue G, Kanoski SE. Ghrelin Signaling Affects Feeding Behavior, Metabolism, and Memory through the Vagus Nerve. Curr Biol 2020; 30:4510-4518.e6. [PMID: 32946754 PMCID: PMC7674191 DOI: 10.1016/j.cub.2020.08.069] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 07/10/2020] [Accepted: 08/20/2020] [Indexed: 02/07/2023]
Abstract
Vagal afferent neuron (VAN) signaling sends information from the gut to the brain and is fundamental in the control of feeding behavior and metabolism [1]. Recent findings reveal that VAN signaling also plays a critical role in cognitive processes, including affective motivational behaviors and hippocampus (HPC)-dependent memory [2-5]. VANs, located in nodose ganglia, express receptors for various gut-derived peptide signals; however, the function of these receptors with regard to feeding behavior, metabolism, and memory control is poorly understood. We hypothesized that VAN-mediated processes are influenced by ghrelin, a stomach-derived orexigenic hormone, via communication to its receptor (GHSR) expressed on gut-innervating VANs. To examine this hypothesis, rats received nodose ganglia injections of an adeno-associated virus (AAV) expressing short hairpin RNAs targeting GHSR (or a control AAV) for RNAi-mediated VAN-specific GHSR knockdown. Results reveal that VAN GHSR knockdown induced various feeding and metabolic disturbances, including increased meal frequency, impaired glucose tolerance, delayed gastric emptying, and increased body weight compared to controls. Additionally, VAN-specific GHSR knockdown impaired HPC-dependent contextual episodic memory and reduced HPC brain-derived neurotrophic factor expression, but did not affect anxiety-like behavior or general activity levels. A functional role for endogenous VAN GHSR signaling was further confirmed by results revealing that VAN signaling is required for the hyperphagic effects of ghrelin administered at dark onset, and that gut-restricted ghrelin-induced increases in VAN firing rate require intact VAN GHSR expression. Collective results reveal that VAN GHSR signaling is required for both normal feeding and metabolic function as well as HPC-dependent memory.
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Affiliation(s)
- Elizabeth A Davis
- Department of Biological Sciences, Human and Evolutionary Biology Section, Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | - Hallie S Wald
- Institute of Diabetes, Obesity and Metabolism, Graduate Groups of Psychology and Neuroscience, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Andrea N Suarez
- Department of Biological Sciences, Human and Evolutionary Biology Section, Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | - Jasenka Zubcevic
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Clarissa M Liu
- Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA
| | - Alyssa M Cortella
- Department of Biological Sciences, Human and Evolutionary Biology Section, Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | | | - Jaimie W Polson
- School of Medical Sciences & Bosch Institute, The University of Sydney, Sydney 2006, Australia
| | - Myrtha Arnold
- Department of Health Sciences and Technology, ETH Zurich, Zurich 8092, Switzerland
| | - Harvey J Grill
- Institute of Diabetes, Obesity and Metabolism, Graduate Groups of Psychology and Neuroscience, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Guillaume de Lartigue
- Pharmacodynamics Department, College of Pharmacy, University of Florida, Gainesville, FL 32610, USA; Center for Integrative Cardiovascular and Metabolic Disease, University of Florida, Gainesville, FL 32610, USA.
| | - Scott E Kanoski
- Department of Biological Sciences, Human and Evolutionary Biology Section, Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA 90089, USA; Neuroscience Graduate Program, University of Southern California, Los Angeles, CA, USA.
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Landgraf D, Neumann AM, Oster H. Circadian clock-gastrointestinal peptide interaction in peripheral tissues and the brain. Best Pract Res Clin Endocrinol Metab 2017; 31:561-571. [PMID: 29224668 DOI: 10.1016/j.beem.2017.10.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Food intake and sleep are two mutually exclusive behaviors and both are normally confined to opposing phases of the diurnal cycle. The temporal coordination of behavior and physiology along the 24-h day-night cycle is organized by a network of circadian clocks that orchestrate transcriptional programs controlling cellular physiology. Many of the peptide hormones of the gastrointestinal tract are not only secreted in a circadian fashion, they can also affect circadian clock function in peripheral metabolic tissues and the brain, thus providing metabolic feedback to metabolic and neurobehavioral circuits. In this review, we summarize the current knowledge on this gastrointestinal peptide crosstalk and its potential role in the coordination of nutrition and the maintenance of metabolic homeostasis.
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Affiliation(s)
- Dominic Landgraf
- Department of Psychiatry, Ludwig Maximilian University of Munich, Germany
| | - Anne-Marie Neumann
- Institute of Neurobiology, Center of Brain, Behavior & Metabolism, University of Lübeck, Germany
| | - Henrik Oster
- Institute of Neurobiology, Center of Brain, Behavior & Metabolism, University of Lübeck, Germany.
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Browning KN, Verheijden S, Boeckxstaens GE. The Vagus Nerve in Appetite Regulation, Mood, and Intestinal Inflammation. Gastroenterology 2017; 152:730-744. [PMID: 27988382 PMCID: PMC5337130 DOI: 10.1053/j.gastro.2016.10.046] [Citation(s) in RCA: 197] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 09/27/2016] [Accepted: 10/27/2016] [Indexed: 02/07/2023]
Abstract
Although the gastrointestinal tract contains intrinsic neural plexuses that allow a significant degree of independent control over gastrointestinal functions, the central nervous system provides extrinsic neural inputs that modulate, regulate, and integrate these functions. In particular, the vagus nerve provides the parasympathetic innervation to the gastrointestinal tract, coordinating the complex interactions between central and peripheral neural control mechanisms. This review discusses the physiological roles of the afferent (sensory) and motor (efferent) vagus in regulation of appetite, mood, and the immune system, as well as the pathophysiological outcomes of vagus nerve dysfunction resulting in obesity, mood disorders, and inflammation. The therapeutic potential of vagus nerve modulation to attenuate or reverse these pathophysiological outcomes and restore autonomic homeostasis is also discussed.
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Affiliation(s)
- Kirsteen N. Browning
- Department of Neural and Behavioral Science Penn State College of Medicine 500 University Drive MC H109 Hershey, PA 17033
| | - Simon Verheijden
- Translational Research Center of Gastrointestinal Disorders (TARGID) KU Leuven Herestraat 49 3000 Leuven, Belgium
| | - Guy E. Boeckxstaens
- Translational Research Center of Gastrointestinal Disorders (TARGID) KU Leuven Herestraat 49 3000 Leuven, Belgium,Division of Gastroenterology & Hepatology University Hospital Leuven Herestraat 49 3000 Leuven, Belgium,Address of correspondence: Prof. dr. Guy Boeckxstaens,
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Kong J, Chuddy J, Stock IA, Loria PM, Straub SV, Vage C, Cameron KO, Bhattacharya SK, Lapham K, McClure KF, Zhang Y, Jackson VM. Pharmacological characterization of the first in class clinical candidate PF-05190457: a selective ghrelin receptor competitive antagonist with inverse agonism that increases vagal afferent firing and glucose-dependent insulin secretion ex vivo. Br J Pharmacol 2016; 173:1452-64. [PMID: 26784385 DOI: 10.1111/bph.13439] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 01/08/2016] [Accepted: 01/08/2016] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND AND PURPOSE Ghrelin increases growth hormone secretion, gastric acid secretion, gastric motility and hunger but decreases glucose-dependent insulin secretion and insulin sensitivity in humans. Antagonizing the ghrelin receptor has potential as a therapeutic approach in the treatment of obesity and type 2 diabetes. Therefore, the aim was to pharmacologically characterize the novel small-molecule antagonist PF-05190457 and assess translational pharmacology ex vivo. EXPERIMENTAL APPROACH Radioligand binding in filter and scintillation proximity assay formats were used to evaluate affinity, and europium-labelled GTP to assess functional activity. Rat vagal afferent firing and calcium imaging in dispersed islets were used as native tissues underlying food intake and insulin secretion respectively. KEY RESULTS PF-05190457 was a potent and selective inverse agonist on constitutively active ghrelin receptors and acted as a competitive antagonist of ghrelin action, with a human Kd of 3 nM requiring 4 h to achieve equilibrium. Potency of PF-05190457 was similar across different species. PF-05190457 increased intracellular calcium within dispersed islets and increased vagal afferent firing in a concentration-dependent manner with similar potency but was threefold less potent as compared with the in vitro Ki in recombinant overexpressing cells. The effect of PF-05190457 on rodent islets was comparable with glibenclamide, but glucose-dependent and additive with the insulin secretagogue glucagon-like peptide-1. CONCLUSIONS AND IMPLICATIONS Together, these data provide the pharmacological in vitro and ex vivo characterization of the first ghrelin receptor inverse agonist, which has advanced into clinical trials to evaluate the therapeutic potential of blocking ghrelin receptors in obesity and type 2 diabetes.
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Affiliation(s)
- J Kong
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - J Chuddy
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - I A Stock
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - P M Loria
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - S V Straub
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - C Vage
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - K O Cameron
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - S K Bhattacharya
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - K Lapham
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - K F McClure
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - Y Zhang
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
| | - V M Jackson
- Cardiovascular and Metabolic Diseases Research Unit, Pfizer Worldwide Research and Development, Cambridge, MA, 01239, USA
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Heldsinger A, Grabauskas G, Wu X, Zhou S, Lu Y, Song I, Owyang C. Ghrelin induces leptin resistance by activation of suppressor of cytokine signaling 3 expression in male rats: implications in satiety regulation. Endocrinology 2014; 155:3956-69. [PMID: 25060362 PMCID: PMC4164930 DOI: 10.1210/en.2013-2095] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The anorexigenic adipocyte-derived hormone leptin and the orexigenic hormone ghrelin act in opposition to regulate feeding behavior via the vagal afferent pathways. The mechanisms by which ghrelin exerts its inhibitory effects on leptin are unknown. We hypothesized that ghrelin activates the exchange protein activated by cAMP (Epac), inducing increased SOCS3 expression, which negatively affects leptin signal transduction and neuronal firing in nodose ganglia (NG) neurons. We showed that 91 ± 3% of leptin receptor (LRb) -bearing neurons contained ghrelin receptors (GHS-R1a) and that ghrelin significantly inhibited leptin-stimulated STAT3 phosphorylation in rat NG neurons. Studies of the signaling cascades used by ghrelin showed that ghrelin caused a significant increase in Epac and suppressor of cytokine signaling 3 (SOCS3) expression in cultured rat NG neurons. Transient transfection of cultured NG neurons to silence SOCS3 and Epac genes reversed the inhibitory effects of ghrelin on leptin-stimulated STAT3 phosphorylation. Patch-clamp studies and recordings of single neuronal discharges of vagal primary afferent neurons showed that ghrelin markedly inhibited leptin-stimulated neuronal firing, an action abolished by silencing SOCS3 expression in NG. Plasma ghrelin levels increased significantly during fasting. This was accompanied by enhanced SOCS3 expression in the NG and prevented by treatment with a ghrelin antagonist. Feeding studies showed that silencing SOCS3 expression in the NG reduced food intake evoked by endogenous leptin. We conclude that ghrelin exerts its inhibitory effects on leptin-stimulated neuronal firing by increasing SOCS3 expression. The SOCS3 signaling pathway plays a pivotal role in ghrelin's inhibitory effect on STAT3 phosphorylation, neuronal firing, and feeding behavior.
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Affiliation(s)
- Andrea Heldsinger
- Division of Gastroenterology, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48019
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8
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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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9
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Avau B, De Smet B, Thijs T, Geuzens A, Tack J, Vanden Berghe P, Depoortere I. Ghrelin is involved in the paracrine communication between neurons and glial cells. Neurogastroenterol Motil 2013; 25:e599-608. [PMID: 23781841 DOI: 10.1111/nmo.12171] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/12/2012] [Accepted: 05/20/2013] [Indexed: 02/08/2023]
Abstract
BACKGROUND Ghrelin is the only known peripherally active orexigenic hormone produced by the stomach that activates vagal afferents to stimulate food intake and to accelerate gastric emptying. Vagal sensory neurons within the nodose ganglia are surrounded by glial cells, which are able to receive and transmit chemical signals. We aimed to investigate whether ghrelin activates or influences the interaction between both types of cells. The effect of ghrelin was compared with that of leptin and cholecystokinin (CCK). METHODS Cultures of rat nodose ganglia were characterized by immunohistochemistry and the functional effects of peptides, neurotransmitters, and pharmacological blockers were measured by Ca(2+) imaging using Fluo-4-AM as an indicator. KEY RESULTS Neurons responded to KCl and were immunoreactive for PGP-9.5 whereas glial cells responded to lysophosphatidic acid and had the typical SOX-10-positive nuclear staining. Neurons were only responsive to CCK (31 ± 5%) whereas glial cells responded equally to the applied stimuli: ghrelin (27 ± 2%), leptin (21 ± 2%), and CCK (30 ± 2%). In contrast, neurons stained more intensively for the ghrelin receptor than glial cells. ATP induced [Ca(2+) ]i rises in 90% of the neurons whereas ACh and the NO donor, SIN-1, mainly induced [Ca(2+) ]i changes in glial cells (41 and 51%, respectively). The percentage of ghrelin-responsive glial cells was not affected by pretreatment with suramin, atropine, hexamethonium or 1400 W, but was reduced by l-NAME and by tetrodotoxin. Neurons were shown to be immunoreactive for neuronal NO-synthase (nNOS). CONCLUSIONS & INFERENCES Our data show that ghrelin induces Ca(2+) signaling in glial cells of the nodose ganglion via the release of NO originating from the neurons.
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Affiliation(s)
- B Avau
- Translational Research Center for Gastrointestinal Disorders, University of Leuven, Leuven, Belgium
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10
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Bron R, Yin L, Russo D, Furness JB. Expression of the ghrelin receptor gene in neurons of the medulla oblongata of the rat. J Comp Neurol 2013; 521:2680-702. [DOI: 10.1002/cne.23309] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Revised: 12/12/2012] [Accepted: 01/17/2013] [Indexed: 01/29/2023]
Affiliation(s)
- Romke Bron
- Department of Anatomy & Neuroscience; University of Melbourne; Parkville; Victoria 3010; Australia
| | - Lei Yin
- Department of Anatomy & Neuroscience; University of Melbourne; Parkville; Victoria 3010; Australia
| | - Domenico Russo
- Department of Veterinary Morphophysiology and Animal Production; University of Bologna; 40064 Ozzano Emilia; Bologna; Italy
| | - John B. Furness
- Department of Anatomy & Neuroscience; University of Melbourne; Parkville; Victoria 3010; Australia
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Hamada N, Nishi Y, Tajiri Y, Setoyama K, Kamimura R, Miyahara K, Nuruki N, Hosoda H, Kangawa K, Kojima M, Mifune H. Disrupted regulation of ghrelin production under antihypertensive treatment in spontaneously hypertensive rats. Circ J 2012; 76:1423-9. [PMID: 22447011 DOI: 10.1253/circj.cj-11-1345] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND Ghrelin is an acylated peptide hormone mainly secreted from the stomach. When administrated externally it modulates vascular tone mainly through the regulation of autonomic nerve activity. However, the effects of blood pressure (BP) on the production and secretion of ghrelin remain to be clarified. METHODS AND RESULTS We examined the stomach and plasma levels of ghrelin in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats after a 4-week-intervention with antihypertensive agents (candesartan-cilexetil [ARB], doxazosin [DZN], metoprolol [MP], reserpine [RES]) to clarify the influence of BP on the secretion of ghrelin. The effect of these agents on ghrelin production and secretion were examined by comparing vehicle-treated controls (WKY-Intact, SHR-Intact). Treatment with the 4 antihypertensive drugs all yielded a significant decline in systolic BP in both SHR and WKY. Under these conditions, significantly lower levels of stomach and plasma ghrelin were detected in WKY treated with ARB (P<0.05), DZN (P<0.05), MP (P<0.05) and RES (P<0.05) compared with WKY-Intact, whereas no significant change in the ghrelin levels in the stomach and plasma were detected in SHR under the same treatments. CONCLUSIONS The findings imply that the production and secretion of ghrelin are controlled by the ambient vascular tone and vice versa in normotensive WKY. This inter-relationship between ghrelin and BP seems to be disrupted in SHR.
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Affiliation(s)
- Naokazu Hamada
- Department of Digestive and Life-Style Related Disease, Health Research Course, Human and Environmental Sciences, Kagoshima University Graduate School of Medicine and Dental Sciences, Kagoshima, Japan
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12
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Kentish S, Li H, Philp LK, O'Donnell TA, Isaacs NJ, Young RL, Wittert GA, Blackshaw LA, Page AJ. Diet-induced adaptation of vagal afferent function. J Physiol 2011; 590:209-21. [PMID: 22063628 DOI: 10.1113/jphysiol.2011.222158] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Afferent signals from the stomach play an important role in inhibition of food intake during a meal. The gastric hormone ghrelin can influence gastric satiety signalling by altering the sensitivity of gastric vagal afferents. Changes in diet, including food restriction and high fat diet (HFD) alter satiety signalling. We hypothesised that the function of gastric vagal afferent endings are affected by both a period of food restriction and a high fat diet, and that the inhibitory effect of ghrelin on vagal afferents is influenced by the different feeding conditions. We found that both fasting and HFD reduced the responses of gastric vagal tension receptors to distension, but not responses of mucosal receptors to mucosal contact. We traced vagal afferents anterogradely to their terminals in the mucosa where we found they were in close apposition to ghrelin-containing cells. Ghrelin receptor mRNA was expressed in vagal afferent cell bodies of the nodose ganglia, and increased in response to caloric restriction, but decreased in HFD mice. In control mice, ghrelin decreased the sensitivity of tension but not mucosal receptors. After caloric restriction or high fat diet, ghrelin inhibited mucosal receptors, and the inhibition of mechanosensitive tension receptors was enhanced. Therefore, both caloric restriction and HFD decrease mechanosensory vagal afferent signals, and augment the inhibitory effect of ghrelin on vagal afferents, but different mechanisms mediate the short- and longer-term changes.
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Affiliation(s)
- Stephen Kentish
- Nerve-Gut Research Laboratory, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia
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Zhao H, Yannaing S, Thanthan S, Kuwayama H. Sulfated gastrin stimulates ghrelin and growth hormone release but inhibits insulin secretion in cattle. Peptides 2011; 32:2218-24. [PMID: 22001226 DOI: 10.1016/j.peptides.2011.09.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 09/27/2011] [Accepted: 09/29/2011] [Indexed: 11/25/2022]
Abstract
This study was designed to determine the effects of gastrin on the circulating levels of ghrelin, growth hormone (GH), insulin, glucagon and glucose in ruminants. Two experiments were done in eight Holstein steers. Animals were randomly assigned to receive intravenous bolus injections: (1) 0.1% bovine serum albumin in saline as vehicle, 0.8, 4.0 and 20.0 μg/kg body weight (BW) of bovine sulfated gastrin-34; (2) vehicle, 0.53 μg/kg BW of bovine sulfated gastrin-17 alone or combined with 20.0 μg/kg BW of [D-Lys(3)]-GHRP-6, the selective antagonist of GHS-R1a. Blood samples were collected from -10 to 150 min relative to injection time. Concentrations of acyl and total ghrelin in response to gastrin-34 injection were significantly increased in a dose-dependent manner. Concentrations of GH were also markedly elevated by gastrin-34 injection; however, the effect of 20.0 μg/kg was weaker than that of 4.0 μg/kg. The three doses of gastrin-34 equally decreased insulin levels within 15 min and maintained the level until the time of last sampling. Gastrin-34 had no effect (P > 0.05) on the levels of glucagon and glucose. Levels of acyl ghrelin increased after administration of gastrin-17 alone or combined with [D-Lys(3)]-GHRP-6; however, [D-Lys(3)]-GHRP-6 did not block the elevation of GH by gastrin-17. The present results indicate that sulfated gastrin stimulates both ghrelin and GH release, but the GHS-R1a may not contribute to the release of GH by gastrin. Moreover, sulfated gastrin seems to indirectly maintain the homeostasis of blood glucose through the down-regulation of insulin in ruminants.
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Affiliation(s)
- Hongqiong Zhao
- Department of Life Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Nishi 2-11, Inada, Obihiro 080-8555, 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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Paulino G, Barbier de la Serre C, Knotts TA, Oort PJ, Newman JW, Adams SH, Raybould HE. Increased expression of receptors for orexigenic factors in nodose ganglion of diet-induced obese rats. Am J Physiol Endocrinol Metab 2009; 296:E898-903. [PMID: 19190260 PMCID: PMC2670626 DOI: 10.1152/ajpendo.90796.2008] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The vagal afferent pathway is important in short-term regulation of food intake, and decreased activation of this neural pathway with long-term ingestion of a high-fat diet may contribute to hyperphagic weight gain. We tested the hypothesis that expression of genes encoding receptors for orexigenic factors in vagal afferent neurons are increased by long-term ingestion of a high-fat diet, thus supporting orexigenic signals from the gut. Obesity-prone (DIO-P) rats fed a high-fat diet showed increased body weight and hyperleptinemia compared with low-fat diet-fed controls and high-fat diet-induced obesity-resistant (DIO-R) rats. Expression of the type I cannabinoid receptor and growth hormone secretagogue receptor 1a in the nodose ganglia was increased in DIO-P compared with low-fat diet-fed controls or DIO-R rats. Shifts in the balance between orexigenic and anorexigenic signals within the vagal afferent pathway may influence food intake and body weight gain induced by high fat diets.
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MESH Headings
- Animals
- Appetite Regulation/genetics
- Diet, Atherogenic
- Dietary Fats/pharmacology
- Male
- Nodose Ganglion/metabolism
- Obesity/etiology
- Obesity/genetics
- Obesity/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptor, Cannabinoid, CB1/genetics
- Receptor, Cannabinoid, CB1/metabolism
- Receptor, Melanocortin, Type 1/genetics
- Receptor, Melanocortin, Type 1/metabolism
- Receptors, Cholecystokinin/genetics
- Receptors, Cholecystokinin/metabolism
- Up-Regulation/drug effects
- Up-Regulation/genetics
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Affiliation(s)
- Gabriel Paulino
- Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, 1321 Haring Hall, Vet Med: APC, University of California, Davis, 1 Shields Ave., Davis, CA 95616, USA
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Dockray GJ. The versatility of the vagus. Physiol Behav 2009; 97:531-6. [PMID: 19419683 DOI: 10.1016/j.physbeh.2009.01.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2008] [Revised: 01/13/2009] [Accepted: 01/14/2009] [Indexed: 12/24/2022]
Abstract
The gut is one of several organs contributing to the peripheral signalling network that controls food intake. Afferent neurons of the vagus nerve provide an important pathway for gut signals that act by triggering ascending pathways from the brain stem to hypothalamus. Recent work indicates the existence of mechanisms operating at the level of vagal afferent neurons to modulate the effect of gastrointestinal satiety signals. Thus, the well known satiety hormone cholecystokinin (CCK) not only stimulates the discharge of these neurons but also controls their expression of both G-protein coupled receptors and peptide neurotransmitters known to influence food intake. When plasma CCK concentrations are low e.g. in fasting, the expression by vagal afferent neurons of cannabinoid (CB)-1 and melanin concentrating hormone (MCH)-1 receptors is increased. Release of CCK by feeding leads to a rapid down-regulation of expression of both receptors and to increased expression of Y2 receptors. In fasting, there is also increased expression in these neurons of the appetite-stimulating neuropeptide transmitter MCH, and depressed expression of the satiety-peptide cocaine and amphetamine regulated transcript (CARTp); endogenous CCK decreases MCH expression and stimulates CART expression. The gastric orexigenic hormone ghrelin blocks these actions of CCK at least in part by excluding phosphoCREB from the nucleus. The data suggest that CCK acts as a gatekeeper to determine the capacity of other neuroendocrine signals to act via vagal afferent neurons to influence food intake.
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Affiliation(s)
- Graham J Dockray
- Physiological Laboratory, School of Biomedical Sciences, University of Liverpool, Liverpool, UK.
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Fukumoto K, Nakahara K, Katayama T, Miyazatao M, Kangawa K, Murakami N. Synergistic action of gastrin and ghrelin on gastric acid secretion in rats. Biochem Biophys Res Commun 2008; 374:60-3. [PMID: 18611393 DOI: 10.1016/j.bbrc.2008.06.114] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Accepted: 06/24/2008] [Indexed: 10/21/2022]
Abstract
Gastrin and ghrelin are secreted from G cells and X/A-like cells in the stomach, respectively, and respective hormones stimulate gastric acid secretion by acting through histamine and the vagus nerve. In this study, we examined the relationship between gastrin, ghrelin and gastric acid secretion in rats. Intravenous (iv) administration of 3 and 10 nmol of gastrin induced transient increases of ghrelin levels within 10 min in a dose-dependent manner. Double immunostaining for ghrelin and gastrin receptor revealed that a proportion of ghrelin cells possess gastrin receptors. Although (iv) administration of gastrin or ghrelin induced significant gastric acid secretion, simultaneous treatment with both hormones resulted in a synergistic, rather than additive, increase of gastric acid secretion. This synergistic increase was not observed in vagotomized rats. These results suggest that gastrin may directly stimulate ghrelin release from the stomach, and that both hormones may increase gastric acid secretion synergistically.
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Affiliation(s)
- Kaori Fukumoto
- Department of Veterinary Physiology, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
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