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Tian X, Wang WT, Zhang MM, Yang QQ, Xu YL, Wu JB, Xie XX, Wang JY, Wang JY. Red nucleus mGluR1 and mGluR5 facilitate the development of neuropathic pain through stimulating the expressions of TNF-α and IL-1β. Neurochem Int 2024; 178:105786. [PMID: 38843952 DOI: 10.1016/j.neuint.2024.105786] [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: 03/09/2024] [Revised: 05/17/2024] [Accepted: 06/01/2024] [Indexed: 06/10/2024]
Abstract
Our previous study has identified that glutamate in the red nucleus (RN) facilitates the development of neuropathic pain through metabotropic glutamate receptors (mGluR). Here, we further explored the actions and possible molecular mechanisms of red nucleus mGluR Ⅰ (mGluR1 and mGluR5) in the development of neuropathic pain induced by spared nerve injury (SNI). Our data indicated that both mGluR1 and mGluR5 were constitutively expressed in the RN of normal rats. Two weeks after SNI, the expressions of mGluR1 and mGluR5 were significantly boosted in the RN contralateral to the nerve injury. Administration of mGluR1 antagonist LY367385 or mGluR5 antagonist MTEP to the RN contralateral to the nerve injury at 2 weeks post-SNI significantly ameliorated SNI-induced neuropathic pain. However, unilateral administration of mGluRⅠ agonist DHPG to the RN of normal rats provoked a significant mechanical allodynia, this effect could be blocked by LY367385 or MTEP. Further studies indicated that the expressions of TNF-α and IL-1β in the RN were also elevated at 2 weeks post-SNI. Administration of mGluR1 antagonist LY367385 or mGluR5 antagonist MTEP to the RN at 2 weeks post-SNI significantly inhibited the elevations of TNF-α and IL-1β. However, administration of mGluR Ⅰ agonist DHPG to the RN of normal rats significantly enhanced the expressions of TNF-α and IL-1β, these effects were blocked by LY367385 or MTEP. These results suggest that activation of red nucleus mGluR1 and mGluR5 facilitate the development of neuropathic pain by stimulating the expressions of TNF-α and IL-1β. mGluR Ⅰ maybe potential targets for drug development and clinical treatment of neuropathic pain.
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Affiliation(s)
- Xue Tian
- Department of Laboratory Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, 710061, Shaanxi, China; Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China; Shaanxi Blood Center, Xi'an, 710061, Shaanxi, China
| | - Wen-Tao Wang
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Miao-Miao Zhang
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Qing-Qing Yang
- Department of Laboratory Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, 710061, Shaanxi, China; Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Ya-Li Xu
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Ji-Bo Wu
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Xin-Xin Xie
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China
| | - Jun-Yang Wang
- Department of Pathogenic Biology and Immunology, Xi'an Jiaotong University Health Science Center, Xi'an, 710061, Shaanxi, China.
| | - Jing-Yuan Wang
- Department of Laboratory Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, 710061, Shaanxi, China.
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Liu J, Jia S, Huang F, He H, Fan W. Peripheral role of glutamate in orofacial pain. Front Neurosci 2022; 16:929136. [PMID: 36440288 PMCID: PMC9682037 DOI: 10.3389/fnins.2022.929136] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Accepted: 10/10/2022] [Indexed: 09/10/2023] Open
Abstract
Glutamate is the principal excitatory neurotransmitter in the central nervous system. In the periphery, glutamate acts as a transmitter and involves in the signaling and processing of sensory input. Glutamate acts at several types of receptors and also interacts with other transmitters/mediators under various physiological and pathophysiological conditions including chronic pain. The increasing amount of evidence suggests that glutamate may play a role through multiple mechanisms in orofacial pain processing. In this study, we reviewed the current understanding of how peripheral glutamate mediates orofacial pain, how glutamate is regulated in the periphery, and how these findings are translated into therapies for pain conditions.
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Affiliation(s)
- Jinyue Liu
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Shilin Jia
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Fang Huang
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Hongwen He
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
| | - Wenguo Fan
- Hospital of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, China
- Guangdong Provincial Key Laboratory of Stomatology, Sun Yat-sen University, Guangzhou, China
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Abstract
INTRODUCTION Migraine is a common and disabling neurological disorder. A greater understanding of the pathophysiological mechanisms underlying migraine has led to the availability of specific new drugs targeting calcitonin gene-related peptide (CGRP). The success of the CGRP inhibitors validates research efforts into migraine-specific therapies. AREAS COVERED There are additional promising therapeutic targets that will be covered in this paper, focusing on the pain phase. They include pituitary adenylate cyclase-activating polypeptide (PACAP), the orexinergic system, the nitric oxide signaling pathway specifically neuronal nitric oxide synthase inhibitors (nNOSi), and metabotropic glutamate receptor 5 (mGluR5). EXPERT OPINION Based on currently available research; the targets discussed in this paper are all on equal footing with each other in terms of their potential as effective novel migraine therapies. There is a need for more clinical trials to pinpoint which of these potential drug targets will be effective for migraine preventio.
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Affiliation(s)
- Oyindamola Ogunlaja
- NIHR-Wellcome Trust King's Clinical Research Facility, King's College, London, UK
| | - Nazia Karsan
- NIHR-Wellcome Trust King's Clinical Research Facility, King's College, London, UK
| | - Peter Goadsby
- NIHR-Wellcome Trust King's Clinical Research Facility, King's College, London, UK.,Department of Neurology, University of California, Los Angeles, CA, USA
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Nicot R, Barry F, Chijcheapaza-Flores H, Garcia-Fernandez MJ, Raoul G, Blanchemain N, Chai F. A Systematic Review of Rat Models With Temporomandibular Osteoarthritis Suitable for the Study of Emerging Prolonged Intra-Articular Drug Delivery Systems. J Oral Maxillofac Surg 2021; 79:1650-1671. [PMID: 33775650 DOI: 10.1016/j.joms.2021.02.034] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 02/20/2021] [Accepted: 02/22/2021] [Indexed: 11/29/2022]
Abstract
PURPOSE Development of minimally invasive therapies for temporomandibular joint osteoarthritis (TMJOA) has focused on drug intra-articular injections to avoid the systemic adverse effects experienced when these substances are administered orally. Therefore, we performed a systematic review to answer the question "Which method of induction of a TMJOA-related pain model in rats leads to prolonged painful symptoms, allowing the best assessment of a sustained drug delivery system?" MATERIALS AND METHODS Following the PRISMA guidelines, we searched MEDLINE for papers published from 1994 to July 2020 on a TMJ arthritis model using rats. We identified the means of pain induction and of nociception assessment. We assessed protocol bias using an adaptation of the QUADAS-2 tool. Animal selection, the reference standard method of pain assessment, applicability of a statistical assessment, and flow and timing were assessed. RESULTS Of the 59 full papers we reviewed, 41 performed no pain assessment after the first 7 days following induction of the TMJ-related pain model. We eventually identified 18 long-term TMJOA-related pain models. Pain was induced by injection of toxic substances, most commonly Freund's complete adjuvant (50 μg per 50 μl), formalin at various concentrations, or monosodium iodoacetate (0,5 mg per 50 μl), into the TMJ, or by physical methods. Few studies reported data on pain after 21 days of follow-up. Heterogeneity of induction methods, pain assessment methods, and flow and timing biases precluded a meta-analysis. CONCLUSIONS Given that pain is 1 of the main symptoms of TMJOA, experimental study protocols should include long-term pain assessment.
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Affiliation(s)
- Romain Nicot
- Associate Professor, Univ. Lille, CHU Lille, INSERM, Service de Chirurgie Maxillo-Faciale et Stomatologie, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France.
| | - Florent Barry
- Resident, Univ. Lille, CHU Lille, INSERM, Service de Chirurgie Maxillo-Faciale et Stomatologie, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
| | - Henry Chijcheapaza-Flores
- Research Assistant, Univ. Lille, INSERM, CHU Lille, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
| | - Maria José Garcia-Fernandez
- Associate Professor, Univ. Lille, INSERM, CHU Lille, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
| | - Gwénaël Raoul
- Professor, Univ. Lille, CHU Lille, INSERM, Service de Chirurgie Maxillo-Faciale et Stomatologie, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
| | - Nicolas Blanchemain
- Professor, Department Head, Univ. Lille, INSERM, CHU Lille, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
| | - Feng Chai
- Research engineer, Univ. Lille, INSERM, CHU Lille, U1008 - Controlled Drug Delivery Systems and Biomaterials, Lille, France
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Abstract
There is substantial evidence indicating a role for glutamate in migraine. Levels of glutamate are higher in the brain and possibly also in the peripheral circulation in migraine patients, particularly during attacks. Altered blood levels of kynurenines, endogenous modulators of glutamate receptors, have been reported in migraine patients. Population genetic studies implicate genes that are involved with glutamate signaling in migraine, and gene mutations responsible for familial hemiplegic migraine and other familial migraine syndromes may influence glutamate signaling. Animal studies indicate that glutamate plays a key role in pain transmission, central sensitization, and cortical spreading depression. Multiple therapies that target glutamate receptors including magnesium, topiramate, memantine, and ketamine have been reported to have efficacy in the treatment of migraine, although with the exception of topiramate, the evidence for the efficacy of these therapies is not strong. Also, because all of these therapies have other mechanisms of action, it is not possible to conclude that the efficacy of these drugs is entirely due to their effects on glutamate receptors. Further studies are needed to more clearly delineate the possible roles of glutamate and its specific receptor subtypes in migraine and to identify new ways of targeting glutamate for migraine therapy.
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Affiliation(s)
- Jan Hoffmann
- Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf (UKE), Martinistrasse 52, 20246 Hamburg, Germany
| | - Andrew Charles
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles (UCLA), 635 Charles Young Drive, Los Angeles, CA 90095 USA
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Ferrigno A, Berardo C, Di Pasqua LG, Siciliano V, Richelmi P, Vairetti M. Localization and role of metabotropic glutamate receptors subtype 5 in the gastrointestinal tract. World J Gastroenterol 2017; 23:4500-4507. [PMID: 28740338 PMCID: PMC5504365 DOI: 10.3748/wjg.v23.i25.4500] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2017] [Revised: 05/03/2017] [Accepted: 06/19/2017] [Indexed: 02/06/2023] Open
Abstract
Metabotropic glutamate receptor subtype 5 (mGluR5) is a Group I mGlu subfamily of receptors coupled to the inositol trisphosphate/diacylglycerol pathway. Like other mGluR subtypes, mGluR5s contain a phylogenetically conserved, extracellular orthosteric binding site and a more variable allosteric binding site, located on the heptahelical transmembrane domain. The mGluR5 receptor has proved to be a key pharmacological target in conditions affecting the central nervous system (CNS) but its presence outside the CNS underscores its potential role in pathologies affecting peripheral organs such as the gastrointestinal (GI) tract and accessory digestive organs such as the tongue, liver and pancreas. Following identification of mGluR5s in the mouth, various studies have subsequently demonstrated its involvement in mechanical allodynia, inflammation, pain and oral cancer. mGluR5 expression has also been identified in gastroesophageal vagal pathways. Indeed, experimental and human studies have demonstrated that mGluR5 blockade reduces transient lower sphincter relaxation and reflux episodes. In the intestine, mGluR5s have been shown to be involved in the control of intestinal inflammation, visceral pain and the epithelial barrier function. In the liver, mGluR5s have a permissive role in the onset of ischemic injury in rat and mice hepatocytes. Conversely, livers from mice treated with selective negative allosteric modulators and mGluR5 knockout mice are protected against ischemic injury. Similar results have been observed in experimental models of free-radical injury and in vivo mouse models of acetaminophen intoxication. Finally, mGluR5s in the pancreas are associated with insulin secretion control. The picture is, however, far from complete as the review attempts to establish in particular as regards identifying specific targets and innovative therapeutic approaches for the treatment of GI disorders.
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Weisshaar CL, Kras JV, Pall PS, Kartha S, Winkelstein BA. Ablation of IB4 non-peptidergic afferents in the rat facet joint prevents injury-induced pain and thalamic hyperexcitability via supraspinal glutamate transporters. Neurosci Lett 2017; 655:82-89. [PMID: 28689926 DOI: 10.1016/j.neulet.2017.07.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2017] [Revised: 07/04/2017] [Accepted: 07/05/2017] [Indexed: 12/12/2022]
Abstract
The facet joint is a common source of neck pain, particularly after excessive stretch of its capsular ligament. Peptidergic afferents have been shown to have an important role in the development and maintenance of mechanical hyperalgesia, dysregulated nociceptive signaling, and spinal hyperexcitability that develop after mechanical injury to the facet joint. However, the role of non-peptidergic isolectin-B4 (IB4) cells in mediating joint pain is unknown. Isolectin-B4 saporin (IB4-SAP) was injected into the facet joint to ablate non-peptidergic cells, and the facet joint later underwent a ligament stretch known to induce pain. Behavioral sensitivity, thalamic glutamate transporter expression, and thalamic hyperexcitability were evaluated up to and at day 7. Administering IB4-SAP prior to a painful injury prevented the development of mechanical hyperalgesia that is typically present. Intra-articular IB4-SAP also prevented the upregulation of the glutamate transporters GLT-1 and EAAC1 in the ventral posterolateral nucleus of the thalamus and reduced thalamic neuronal hyperexcitability at day 7. These findings suggest that a painful facet injury induces changes extending to supraspinal structures and that IB4-positive afferents in the facet joint may be critical for the development and maintenance of sensitization in the thalamus after a painful facet joint injury.
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Affiliation(s)
- Christine L Weisshaar
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd St Philadelphia, PA 19104, USA
| | - Jeffrey V Kras
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd St Philadelphia, PA 19104, USA
| | - Parul S Pall
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd St Philadelphia, PA 19104, USA
| | - Sonia Kartha
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd St Philadelphia, PA 19104, USA
| | - Beth A Winkelstein
- Department of Bioengineering, University of Pennsylvania, 240 Skirkanich Hall, 210 S. 33rd St Philadelphia, PA 19104, USA; Department of Neurosurgery, University of Pennsylvania, 105 Hayden Hall, 3320 Smith Walk, Philadelphia, PA 19104, USA.
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8
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Michot B, Deumens R, Hermans E. Immunohistochemical comparison of astrocytic mGluR5 upregulation in infraorbital nerve- versus sciatic nerve-ligated rat. Neurosci Lett 2017; 653:113-119. [PMID: 28533177 DOI: 10.1016/j.neulet.2017.05.035] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2017] [Revised: 05/13/2017] [Accepted: 05/17/2017] [Indexed: 01/16/2023]
Abstract
The differential pharmacological responsiveness of cephalic and extra-cephalic neuropathic pain has been proposed to relate to distinct mechanisms that may involve neuroinflammatory reactions mediated by glial cells. Astrocytes are particularly important for neuronal sensitization in neuropathic pain, in part through modulation of glutamatergic transmission. Because the metabotropic glutamate receptor 5 (mGluR5) is involved in the astrocytic regulation of the glutamatergic system, we investigated modifications of its expression in models of cephalic versus extra-cephalic neuropathic pain. Adult male rats underwent unilateral chronic constriction injury (CCI) of either the infraorbital nerve (ION) or the sciatic nerve (SN). Seven days later, mGluR5 and the astrocyte marker GFAP (glial fibrillary acidic protein) were overexpressed and appeared localized mainly in the superficial lamina of the trigeminal nucleus in CCI-ION and the spinal cord dorsal horn in CCI-SN rats. In addition, colocalization of GFAP and mGluR5 strongly suggested an increase of astrocytic mGluR5 expression in nerve-injured rats compared to sham animals. The present data show an upregulation of astrocytic mGluR5 in central structures in both CCI-ION and CCI-SN. This suggests that the pharmacological modulation of mGluR5 could be a new approach to reduce both cephalic and extra-cephalic neuropathic pain.
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Affiliation(s)
- Benoit Michot
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200 Brussels, Belgium.
| | - Ronald Deumens
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200 Brussels, Belgium
| | - Emmanuel Hermans
- Institute of Neuroscience, Université catholique de Louvain, Avenue Hippocrate B1.54.10, 1200 Brussels, Belgium
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Waung MW, Akerman S, Wakefield M, Keywood C, Goadsby PJ. Metabotropic glutamate receptor 5: a target for migraine therapy. Ann Clin Transl Neurol 2016; 3:560-71. [PMID: 27606340 PMCID: PMC4999590 DOI: 10.1002/acn3.302] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 02/22/2016] [Accepted: 02/25/2016] [Indexed: 01/01/2023] Open
Abstract
Introduction Many patients suffering from migraine gain little relief from existing treatments partly because many existing acute and preventive therapies used in migraine have been adopted from other neurologic conditions such as depression or epilepsy. Here, we present data supporting a new migraine‐specific target, the mGlu5 receptor. Methods We studied the effect of mGlu5 blockade using ADX10059, on neuronal firing in the trigeminocervical complex (TCC) and durovascular effects of nociceptive trigeminovascular activation in the anesthetized rat. The clinical potential of the mGlu5 mechanism was tested with ADX10059 orally in a double‐blind placebo‐controlled, parallel group, clinical trial. Results The negative allosteric mGlu5 modulator ADX10059 attenuated dural vasodilator responses to meningeal stimulation in a dose‐dependent manner, comparable to naratriptan, while the N‐methyl‐d‐aspartate receptor blocker MK‐801 had no effect. ADX10059 reduced responses of trigeminocervical neurons to dural stimulation, most strikingly affecting their spontaneous firing rate. Immunostaining identified mGlu5 and not mGlu1a receptors in the TCC. The primary efficacy endpoint for the clinical trial, 2 h pain free, demonstrated a significant effect of ADX10059 375 mg, 17%, versus placebo, 5%. No serious adverse events were reported at the primary dose, with transient dizziness being the most common treatment‐emergent event at 48%. Interpretation Our findings provide preclinical and clinical proof of concept establishing mGlu5 as a novel therapeutic target in the treatment of migraine. Although ADX10059 is unsuitable as a therapeutic candidate, because of hepatoxicity detected in a subsequent study, the data open a new direction for migraine research and therapy.
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Affiliation(s)
- Maggie W Waung
- Department of Neurology University of California, San Francisco San Francisco California
| | - Simon Akerman
- Department of Neurology University of California, San Francisco San Francisco California; Present address: Department of Oral and Maxillofacial Pathology, Radiology and Medicine New York University College of Dentistry New York City New York
| | - Mark Wakefield
- Addex Pharma Geneva Switzerland; Present address: Outsourcing Management (Ext)Oncology Business Unit Novartis Pharma AGPostfach CH-4002 Basel Switzerland
| | - Charlotte Keywood
- Addex Pharma Geneva Switzerland; Present address: Minerva Pharmaceutical Consulting Ltd London United Kingdom
| | - Peter J Goadsby
- Department of Neurology University of California, San Francisco San Francisco California; Basic and Clinical Neurosciences Institute of Psychiatry, Psychology and Neuroscience Kings College London London United Kingdom
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Tashiro A, Nishida Y, Bereiter DA. Local group I mGluR antagonists reduce TMJ-evoked activity of trigeminal subnucleus caudalis neurons in female rats. Neuroscience 2015; 299:125-33. [PMID: 25934040 DOI: 10.1016/j.neuroscience.2015.04.051] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Revised: 04/17/2015] [Accepted: 04/21/2015] [Indexed: 10/23/2022]
Abstract
Group I metabotropic glutamate receptors (mGluR1 and mGluR5) are functionally linked to estrogen receptors and play a key role in the plasticity of central neurons. Estrogen status strongly influences sensory input from the temporomandibular joint (TMJ) to neurons at the spinomedullary (Vc/C1-2) region. This study tested the hypothesis that TMJ input to trigeminal subnucleus caudalis/upper cervical cord (Vc/C1-2) neurons involved group I mGluR activation and depended on estrogen status. TMJ-responsive neurons were recorded in superficial laminae at the Vc/C1-2 region in ovariectomized (OvX) female rats treated with low-dose estradiol (2 μg/day, LE) or high-dose estradiol (20 μg/day, HE) for 2 days. TMJ-responsive units were activated by adenosine triphosphate (ATP, 1mM) injected into the joint space. Receptor antagonists selective for mGluR1 (CPCCOEt) or mGluR5 (MPEP) were applied topically to the Vc/C1-2 surface at the site of recording 10 min prior to the intra-TMJ ATP stimulus. In HE rats, CPCCOEt (50 and 500 μM) markedly reduced ATP-evoked unit activity. By contrast, in LE rats, a small but significant increase in neural activity was seen after 50 μM CPCCOEt, while 500 μM caused a large reduction in activity that was similar in magnitude as that seen in HE rats. Local application of MPEP produced a significant inhibition of TMJ-evoked unit activity independent of estrogen status. Neither mGluR1 nor mGluR5 antagonism altered the spontaneous activity of TMJ units in HE or LE rats. High-dose MPEP caused a small reduction in the size of the convergent cutaneous receptive field in HE rats, while CPCCOEt had no effect. These data suggest that group I mGluRs play a key role in sensory integration of TMJ nociceptive input to the Vc/C1-2 region and are largely independent of estrogen status.
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Affiliation(s)
- A Tashiro
- Department of Physiology, National Defense Medical College, Namiki 3-2, Tokorozawa City, Saitama 359-8513, Japan.
| | - Y Nishida
- Department of Physiology, National Defense Medical College, Namiki 3-2, Tokorozawa City, Saitama 359-8513, Japan
| | - D A Bereiter
- Department of Diagnostic and Biological Sciences, University of Minnesota School of Dentistry, Moos Tower 18-214, 515 Delaware Street SE, Minneapolis, MN 55455, USA
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Glutamate dysregulation in the trigeminal ganglion: a novel mechanism for peripheral sensitization of the craniofacial region. Neuroscience 2013; 256:23-35. [PMID: 24144624 DOI: 10.1016/j.neuroscience.2013.10.009] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/24/2013] [Accepted: 10/07/2013] [Indexed: 10/26/2022]
Abstract
In the trigeminal ganglion (TG), satellite glial cells (SGCs) form a functional unit with neurons. It has been proposed that SGCs participate in regulating extracellular glutamate levels and that dysfunction of this SGC capacity can impact nociceptive transmission in craniofacial pain conditions. This study investigated whether SGCs release glutamate and whether elevation of TG glutamate concentration alters response properties of trigeminal afferent fibers. Immunohistochemistry was used to assess glutamate content and the expression of excitatory amino acid transporter (EAAT)1 and EAAT2 in TG sections. SGCs contained glutamate and expressed EAAT1 and EAAT2. Potassium chloride (10 mM) was used to evoke glutamate release from cultured rat SGCs treated with the EAAT1/2 inhibitor (3S)-3-[[3-[[4-(trifluoromethyl)ben zoyl]amino]phenyl]methoxy]-L-aspartic acid (TFB-TBOA) or control. Treatment with TFB-TBOA (1 and 10 μM) significantly reduced the glutamate concentration from 10.6 ± 1.1 to 5.8 ± 1.4 μM and 3.0 ± 0.8 μM, respectively (p<0.05). Electrophysiology experiments were conducted in anaesthetized rats to determine the effect of intraganglionic injections of glutamate on the response properties of ganglion neurons that innervated either the temporalis or masseter muscle. Intraganglionic injection of glutamate (500 mM, 3 μl) evoked afferent discharge and significantly reduced muscle afferent mechanical threshold. Glutamate-evoked discharge was attenuated bythe N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovalerate (APV) and increased by TFB-TBOA, whereas mechanical sensitization was only sensitive to APV. Antidromic invasion of muscle afferent fibers by electrical stimulation of the caudal brainstem (10 Hz) or local anesthesia of the brainstem with lidocaine did not alter glutamate-induced mechanical sensitization. These findings provide a novel mechanism whereby dysfunctional trigeminal SGCs could contribute to cranial muscle tenderness in craniofacial pain conditions such as migraine headache.
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