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Ständer S, Schmelz M. Skin Innervation. J Invest Dermatol 2024; 144:1716-1723. [PMID: 38402477 DOI: 10.1016/j.jid.2023.10.047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2023] [Revised: 10/18/2023] [Accepted: 10/31/2023] [Indexed: 02/26/2024]
Abstract
All layers and appendages of the skin are densely innervated by afferent and efferent neurons providing sensory information and controlling skin perfusion and sweating. In mice, neuronal functions have been comprehensively linked to unique single-cell expression patterns and to characteristic arborization of nerve endings in skin and dorsal horn, whereas for humans, specific molecular markers for functional classes of afferent neurons are still lacking. Moreover, bidirectional communication between sensory neurons and local skin cells has become of particular interest, resulting in a broader physiological understanding of sensory function but also of trophic functions and immunomodulation in disease states.
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Affiliation(s)
- Sonja Ständer
- Department of Dermatology and Center for Chronic Pruritus, University Hospital, Münster, Germany
| | - Martin Schmelz
- Department of Experimental Pain Research, Mannheim Center for Translational Neuroscience (MCTN), Faculty of Medicine Mannheim, University of Heidelberg, Mannheim, Germany.
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2
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Eliav T, Benoliel R, Korczeniewska OA. Post-Traumatic Trigeminal Neuropathy: Neurobiology and Pathophysiology. BIOLOGY 2024; 13:167. [PMID: 38534437 DOI: 10.3390/biology13030167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2023] [Revised: 02/23/2024] [Accepted: 02/26/2024] [Indexed: 03/28/2024]
Abstract
Painful traumatic trigeminal neuropathy (PTTN) is a chronic neuropathic pain that may develop following injury to the trigeminal nerve. Etiologies include cranio-orofacial trauma that may result from dental, surgical, or anesthetic procedures or physical trauma, such as a motor vehicle accident. Following nerve injury, there are various mechanisms, including peripheral and central, as well as phenotypic changes and genetic predispositions that may contribute to the development of neuropathic pain. In this article, we review current literature pertaining to the cellular processes that occur following traumatic damage to the trigeminal nerve, also called cranial nerve V, that results in chronic neuropathic pain. We examine the neurobiology and pathophysiology based mostly on pre-clinical animal models of neuropathic/trigeminal pain.
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Affiliation(s)
- Tal Eliav
- Medical School for International Health, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva 8410501, Israel
| | - Rafael Benoliel
- Center for Orofacial Pain and Temporomandibular Disorders, Department of Diagnostic Sciences, Rutgers School of Dental Medicine, Rutgers, The State University of New Jersey, Room D-837, 110 Bergen Street, Newark, NJ 07101, USA
| | - Olga A Korczeniewska
- Center for Orofacial Pain and Temporomandibular Disorders, Department of Diagnostic Sciences, Rutgers School of Dental Medicine, Rutgers, The State University of New Jersey, Room D-837, 110 Bergen Street, Newark, NJ 07101, USA
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3
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Sas D, Gaudel F, Verdier D, Kolta A. Hyperexcitability of muscle spindle afferents in jaw-closing muscles in experimental myalgia: Evidence for large primary afferents involvement in chronic pain. Exp Physiol 2024; 109:100-111. [PMID: 38103003 PMCID: PMC10988680 DOI: 10.1113/ep090769] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Accepted: 11/30/2023] [Indexed: 12/17/2023]
Abstract
The goals of this review are to improve understanding of the aetiology of chronic muscle pain and identify new targets for treatments. Muscle pain is usually associated with trigger points in syndromes such as fibromyalgia and myofascial syndrome, and with small spots associated with spontaneous electrical activity that seems to emanate from fibers inside muscle spindles in EMG studies. These observations, added to the reports that large-diameter primary afferents, such as those innervating muscle spindles, become hyperexcitable and develop spontaneous ectopic firing in conditions leading to neuropathic pain, suggest that changes in excitability of these afferents might make an important contribution to the development of pathological pain. Here, we review evidence that the muscle spindle afferents (MSAs) of the jaw-closing muscles become hyperexcitable in a model of chronic orofacial myalgia. In these afferents, as in other large-diameter primary afferents in dorsal root ganglia, firing emerges from fast membrane potential oscillations that are supported by a persistent sodium current (INaP ) mediated by Na+ channels containing the α-subunit NaV 1.6. The current flowing through NaV 1.6 channels increases when the extracellular Ca2+ concentration decreases, and studies have shown that INaP -driven firing is increased by S100β, an astrocytic protein that chelates Ca2+ when released in the extracellular space. We review evidence of how astrocytes, which are known to be activated in pain conditions, might, through their regulation of extracellular Ca2+ , contribute to the generation of ectopic firing in MSAs. To explain how ectopic firing in MSAs might cause pain, we review evidence supporting the hypothesis that cross-talk between proprioceptive and nociceptive pathways might occur in the periphery, within the spindle capsule.
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Affiliation(s)
- Dar'ya Sas
- Département de NeurosciencesUniversité de MontréalMontréalQuébecCanada
- Centre Interdisciplinaire de Recherche sur le Cerveau et l'Apprentissage (CIRCA)MontréalQuébecCanada
| | - Fanny Gaudel
- Département de NeurosciencesUniversité de MontréalMontréalQuébecCanada
- Centre Interdisciplinaire de Recherche sur le Cerveau et l'Apprentissage (CIRCA)MontréalQuébecCanada
| | - Dorly Verdier
- Département de NeurosciencesUniversité de MontréalMontréalQuébecCanada
- Centre Interdisciplinaire de Recherche sur le Cerveau et l'Apprentissage (CIRCA)MontréalQuébecCanada
| | - Arlette Kolta
- Département de NeurosciencesUniversité de MontréalMontréalQuébecCanada
- Centre Interdisciplinaire de Recherche sur le Cerveau et l'Apprentissage (CIRCA)MontréalQuébecCanada
- Faculté de Médecine DentaireUniversité de MontréalMontréalQuébecCanada
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Resurgent neuropathic discharge: an obstacle to the therapeutic use of neuroma resection? Pain 2023; 164:349-361. [PMID: 35639421 DOI: 10.1097/j.pain.0000000000002704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2022] [Accepted: 05/20/2022] [Indexed: 02/06/2023]
Abstract
ABSTRACT Ectopic discharge ("ectopia") in damaged afferent axons is a major contributor to chronic neuropathic pain. Clinical opinion discourages surgical resection of nerves proximal to the original injury site for fear of resurgence of ectopia and exacerbated pain. We tested this concept in a well-established animal neuroma model. Teased-fiber recordings were made of ectopic spontaneous discharge originating in the experimental nerve-end neuroma and associated dorsal root ganglia in rats that underwent either a single transection (with ligation) of the sciatic nerve or 2 consecutive transections separated by 7, 14, 21, or 30 days. Ectopia emerged in afferent A and C fibers after a single cut with kinetics anticipated from previous studies. When resection was performed during the early period of intense A-fiber activity, a brief period of resurgence was observed. However, resection of neuromas of more than 14 days was followed by low levels of activity with no indication of resurgence. This remained the case in trials out to 60 days after the first cut. Similarly, we saw no indication of resurgent ectopia originating in axotomized dorsal root ganglion neuronal somata and no behavioral reflection of resurgence. In summary, we failed to validate the concern that proximal resection of a problematic nerve would lead to intense resurgent ectopic discharge and pain. As the well-entrenched concept of resurgence is based more on case reports and anecdotes than on solid evidence, it may be justified to relax the stricture against resecting neuromas as a therapeutic strategy, at least within the framework of controlled clinical trials.
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Pathophysiology of Post-Traumatic Trigeminal Neuropathic Pain. Biomolecules 2022; 12:biom12121753. [PMID: 36551181 PMCID: PMC9775491 DOI: 10.3390/biom12121753] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 11/11/2022] [Accepted: 11/12/2022] [Indexed: 11/29/2022] Open
Abstract
Trigeminal nerve injury is one of the causes of chronic orofacial pain. Patients suffering from this condition have a significantly reduced quality of life. The currently available management modalities are associated with limited success. This article reviews some of the common causes and clinical features associated with post-traumatic trigeminal neuropathic pain (PTNP). A cascade of events in the peripheral and central nervous system function is involved in the pathophysiology of pain following nerve injuries. Central and peripheral processes occur in tandem and may often be co-dependent. Due to the complexity of central mechanisms, only peripheral events contributing to the pathophysiology have been reviewed in this article. Future investigations will hopefully help gain insight into trigeminal-specific events in the pathophysiology of the development and maintenance of neuropathic pain secondary to nerve injury and enable the development of new therapeutic modalities.
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Nemenov MI, Singleton JR, Premkumar LS. Role of Mechanoinsensitive Nociceptors in Painful Diabetic Peripheral Neuropathy. Curr Diabetes Rev 2022; 18:e081221198649. [PMID: 34879806 DOI: 10.2174/1573399818666211208101555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 03/08/2021] [Accepted: 07/09/2021] [Indexed: 11/22/2022]
Abstract
The cutaneous mechanisms that trigger spontaneous neuropathic pain in diabetic peripheral neuropathy (PDPN) are far from clear. Two types of nociceptors are found within the epidermal and dermal skin layers. Small-diameter lightly myelinated Aδ and unmyelinated C cutaneous mechano and heat-sensitive (AMH and CMH) and C mechanoinsensitive (CMi) nociceptors transmit pain from the periphery to central nervous system. AMH and CMH fibers are mainly located in the epidermis, and CMi fibers are distributed in the dermis. In DPN, dying back intra-epidermal AMH and CMH fibers leads to reduced pain sensitivity, and the patients exhibit significantly increased pain thresholds to acute pain when tested using traditional methods. The role of CMi fibers in painful neuropathies has not been fully explored. Microneurography has been the only tool to access CMi fibers and differentiate AMH, CMH, and CMi fiber types. Due to the complexity, its use is impractical in clinical settings. In contrast, a newly developed diode laser fiber selective stimulation (DLss) technique allows to safely and selectively stimulate Aδ and C fibers in the superficial and deep skin layers. DLss data demonstrate that patients with painful DPN have increased Aδ fiber pain thresholds, while C-fiber thresholds are intact because, in these patients, CMi fibers are abnormally spontaneously active. It is also possible to determine the involvement of CMi fibers by measuring the area of DLss-induced neurogenic axon reflex flare. The differences in AMH, CMH, and CMi fibers identify patients with painful and painless neuropathy. In this review, we will discuss the role of CMi fibers in PDPN.
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Affiliation(s)
- Mikhail I Nemenov
- Department of Anesthesia, Stanford University, Palo Alto, CA, USA
- Lasmed LLC, Mountain View, CA, USA
| | | | - Louis S Premkumar
- Department of Pharmacology, SIU School of Medicine, Springfield, Illinois, USA and Ion Channel Pharmacology LLC, Springfield, IL, USA
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Raja SN, Ringkamp M, Guan Y, Campbell JN. John J. Bonica Award Lecture: Peripheral neuronal hyperexcitability: the "low-hanging" target for safe therapeutic strategies in neuropathic pain. Pain 2021; 161 Suppl 1:S14-S26. [PMID: 33090736 DOI: 10.1097/j.pain.0000000000001838] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
| | - Matthias Ringkamp
- Neurological Surgery, Department of Neurosurgery, Johns Hopkins University, School of Medicine, Baltimore, MD, United States
| | - Yun Guan
- Departments of Anesthesiology and Critical Care Medicine and.,Neurological Surgery, Department of Neurosurgery, Johns Hopkins University, School of Medicine, Baltimore, MD, United States
| | - James N Campbell
- Neurological Surgery, Department of Neurosurgery, Johns Hopkins University, School of Medicine, Baltimore, MD, United States
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Mansiz Kaplan B, Akyuz G, Kokar S, Yagci I. Comparison of the effectiveness of orthotic intervention, kinesiotaping, and paraffin treatments in patients with carpal tunnel syndrome: A single-blind and randomized controlled study. J Hand Ther 2020; 32:297-304. [PMID: 29463420 DOI: 10.1016/j.jht.2017.12.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 12/23/2017] [Accepted: 12/30/2017] [Indexed: 02/03/2023]
Abstract
PURPOSE The aim of the study was to compare different conservative treatments in patients with carpal tunnel syndrome (CTS). STUDY DESIGN A single-blind randomized controlled study. METHODS Patients (n = 169) diagnosed with mild or moderate CTS were screened; 110 met study requirements. The patients were randomized into 3 groups. The control (CON) comparison provided to all patients was a fabricated night orthotic which held the wrist in a neutral position. The second group received adjunctive kinesiotaping (KIN) and the third group received paraffin (PARA). All patients were evaluated clinically, electrophysiologically, and ultrasonographically before treatment and at 3 weeks, 3 months, and 6 months. RESULTS There were 36 patients in CON, 37 in KIN, and 37 in PARA. Pain reduction in KIN was better than the other groups at 3 weeks (mean difference [MD] in CON 2.4 ± 2.5, KIN 3.7 ± 2.0, PARA 2.7 ± 2.3; P < .01) and 6 months (MD in CON 3.4 ± 3.0, KIN 4.9 ± 3.1, PARA 3.7 ± 2.9; P < .05). KIN pain reduction was better than CON at 3 months (MD in CON 3.8 ± 2.8, KIN 5.0 ± 2.5; P < .05). Reduction of the cross-sectional area of median nerve at the level of radioulnar joint was greater for KIN than CON at 3 weeks (MD in CON 0.0 ± 0.5, KIN 0.3 ± 0.7; P < .01) than PARA at 3 months (MD in KIN 0.3 ± 0.8, PARA 0.0 ± 0.8; P < .05) and both groups at 6 months (MD in CON 0.1 ± 0.8, KIN 0.5 ± 0.9, PARA 0.0 ± 1.0 P < .05). CONCLUSION Adding KIN to night use of an orthotic was more effective in achieving symptomatic and structural improvements than either the orthotic alone or adjunctive use of paraffin in patients with mild and moderate CTS.
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Affiliation(s)
- Basak Mansiz Kaplan
- Department of Physical Medicine and Rehabilitation, University of Health Sciences, Ankara Training and Research Hospital, Ankara, Turkey.
| | - Gulseren Akyuz
- Department of Physical Medicine and Rehabilitation, Marmara University School of Medicine, Istanbul, Turkey
| | - Serdar Kokar
- Department of Physical Medicine and Rehabilitation, Marmara University School of Medicine, Istanbul, Turkey
| | - Ilker Yagci
- Department of Physical Medicine and Rehabilitation, Marmara University School of Medicine, Istanbul, Turkey
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North RY, Lazaro TT, Dougherty PM. Ectopic Spontaneous Afferent Activity and Neuropathic Pain. Neurosurgery 2018; 65:49-54. [PMID: 31076785 DOI: 10.1093/neuros/nyy119] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Accepted: 04/04/2018] [Indexed: 12/17/2022] Open
Affiliation(s)
- Robert Y North
- Department of Neurosurgery, Baylor College of Medicine, Houston, Texas
| | - Tyler T Lazaro
- Department of Neurosurgery, Baylor College of Medicine, Houston, Texas
| | - Patrick M Dougherty
- The Departments of Pain Medicine Research, The Division of Anesthesia, Critical Care and Pain Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas
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Park SB, Kiernan MC. Oxaliplatin and neuropathy: A role for sodium channels. Clin Neurophysiol 2018; 129:670-671. [DOI: 10.1016/j.clinph.2017.12.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2017] [Accepted: 12/19/2017] [Indexed: 11/25/2022]
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Heide R, Bostock H, Ventzel L, Grafe P, Bergmans J, Fuglsang-Frederiksen A, Finnerup NB, Tankisi H. Axonal excitability changes and acute symptoms of oxaliplatin treatment: In vivo evidence for slowed sodium channel inactivation. Clin Neurophysiol 2017; 129:694-706. [PMID: 29233604 DOI: 10.1016/j.clinph.2017.11.015] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2016] [Revised: 10/16/2017] [Accepted: 11/05/2017] [Indexed: 01/28/2023]
Abstract
OBJECTIVE Neurotoxicity is the most frequent dose-limiting side effect of the anti-cancer agent oxaliplatin, but the mechanisms are not well understood. This study used nerve excitability testing to investigate the pathophysiology of the acute neurotoxicity. METHODS Questionnaires, quantitative sensory tests, nerve conduction studies and nerve excitability testing were undertaken in 12 patients with high-risk colorectal cancer treated with adjuvant oxaliplatin and in 16 sex- and age-matched healthy controls. Examinations were performed twice for patients: once within 3 days after oxaliplatin treatment (post-infusion examination) and once shortly before the following treatment (recovery examination). RESULTS The most frequent post-infusion symptoms were tingling paresthesias and cold allodynia. The most prominent nerve excitability change was decreased superexcitability of motor axons which correlated with the average intensity of abnormal sensations (Spearman Rho = 0.80, p < .01). The motor nerve excitability changes were well modeled by a slowing of sodium channel inactivation, and were proportional to dose/m2 with a half-life of about 10d. CONCLUSIONS Oxaliplatin induces reversible slowing of sodium channel inactivation in motor axons, and these changes are closely related to the reversible cold allodynia. However, further studies are required due to small sample size in this study. SIGNIFICANCE Nerve excitability data provide an index of sodium channel dysfunction: an objective biomarker of acute oxaliplatin neurotoxicity.
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Affiliation(s)
- Rikke Heide
- Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark; Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Hugh Bostock
- Institute of Neurology, Queen Square House, London, United Kingdom
| | - Lise Ventzel
- Department of Clinical Oncology, Aarhus University Hospital, Aarhus, Denmark
| | - Peter Grafe
- Institute of Physiology, Ludwig-Maximilians University Munich, Munich, Germany
| | - Joseph Bergmans
- Laboratory of Clinical Neurophysiology, Faculty of Medicine, University of Louvain, Brussels, Belgium
| | | | - Nanna B Finnerup
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | - Hatice Tankisi
- Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark.
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Buonocore M, Demartini L, Aloisi AM, Bonezzi C. Dynamic Mechanical Allodynia--One Clinical Sign, Several Mechanisms: Five Illustrative Cases. Pain Pract 2016; 16:E48-55. [PMID: 26879154 DOI: 10.1111/papr.12416] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Accepted: 10/09/2015] [Indexed: 12/21/2022]
Abstract
Pain evoked by tangential movement across the skin is usually defined as dynamic mechanical allodynia (DMA). Some patients complain of DMA as troublesome as spontaneous pain and refer a marked interfering with activities of daily living and sleep. Pathophysiology of DMA is complex and can be related to several mechanisms, both nociceptive and neuropathic. Five exemplificative clinical cases of DMA are presented, each associated to a possible specific mechanism: injured skin DMA, peri-injured skin DMA, far injury DMA, nerve-confined DMA and fear DMA (pseudo allodynia). The identification of these subcategories of DMA can stimulate further studies aimed at evaluating the usefulness of a mechanism-based therapy for the different clinical forms of DMA.
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Affiliation(s)
- Michelangelo Buonocore
- Unit of Clinical Neurophysiology & Neurodiagnostic Skin Biopsy, Fondazione Salvatore Maugeri, Pavia, Italy
| | - Laura Demartini
- Unit of Pain Medicine, Fondazione Salvatore Maugeri, Pavia, Italy
| | | | - Cesare Bonezzi
- Unit of Pain Medicine, Fondazione Salvatore Maugeri, Pavia, Italy
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Tomás-Juan J, Murueta-Goyena Larrañaga A, Hanneken L. Corneal Regeneration After Photorefractive Keratectomy: A Review. JOURNAL OF OPTOMETRY 2015; 8:149-69. [PMID: 25444646 PMCID: PMC4502084 DOI: 10.1016/j.optom.2014.09.001] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2014] [Revised: 08/01/2014] [Indexed: 05/20/2023]
Abstract
Photorefractive keratectomy (PRK) remodels corneal stroma to compensate refractive errors. The removal of epithelium and the ablation of stroma provoke the disruption of corneal nerves and a release of several peptides from tears, epithelium, stroma and nerves. A myriad of cytokines, growth factors, and matrix metalloproteases participate in the process of corneal wound healing. Their balance will determine if reepithelization and stromal remodeling are appropriate. The final aim is to achieve corneal transparency for restoring corneal function, and a proper visual quality. Therefore, wound-healing response is critical for a successful refractive surgery. Our goal is to provide an overview into how corneal wounding develops following PRK. We will also review the influence of intraoperative application of mitomycin C, bandage contact lenses, anti-inflammatory and other drugs in preventing corneal haze and post-PRK pain.
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Affiliation(s)
- Javier Tomás-Juan
- Department of Visual Science, VallmedicVision International Eye Clinic, Andorra.
| | | | - Ludger Hanneken
- Department of Visual Science, VallmedicVision International Eye Clinic, Andorra
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Mario Campero S. ¿Es posible objetivar el dolor? REVISTA MÉDICA CLÍNICA LAS CONDES 2014. [DOI: 10.1016/s0716-8640(14)70080-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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Quiroz-González S, Segura-Alegría B, Jiménez-Estrada I. Depressing effect of electroacupuncture on the spinal non-painful sensory input of the rat. Exp Brain Res 2014; 232:2721-9. [DOI: 10.1007/s00221-014-3965-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Accepted: 04/12/2014] [Indexed: 01/27/2023]
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16
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Thompson SJ, Millecamps M, Aliaga A, Seminowicz DA, Low LA, Bedell BJ, Stone LS, Schweinhardt P, Bushnell MC. Metabolic brain activity suggestive of persistent pain in a rat model of neuropathic pain. Neuroimage 2014; 91:344-52. [PMID: 24462776 DOI: 10.1016/j.neuroimage.2014.01.020] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 11/07/2013] [Accepted: 01/13/2014] [Indexed: 10/25/2022] Open
Abstract
Persistent pain is a central characteristic of neuropathic pain conditions in humans. Knowing whether rodent models of neuropathic pain produce persistent pain is therefore crucial to their translational applicability. We investigated the spared nerve injury (SNI) model of neuropathic pain and the formalin pain model in rats using positron emission tomography (PET) with the metabolic tracer [18F]fluorodeoxyglucose (FDG) to determine if there is ongoing brain activity suggestive of persistent pain. For the formalin model, under brief anesthesia we injected one hindpaw with 5% formalin and the FDG tracer into a tail vein. We then allowed the animals to awaken and observed pain behavior for 30min during the FDG uptake period. The rat was then anesthetized and placed in the scanner for static image acquisition, which took place between minutes 45 and 75 post-tracer injection. A single reference rat brain magnetic resonance image (MRI) was used to align the PET images with the Paxinos and Watson rat brain atlas. Increased glucose metabolism was observed in the somatosensory region associated with the injection site (S1 hindlimb contralateral), S1 jaw/upper lip and cingulate cortex. Decreases were observed in the prelimbic cortex and hippocampus. Second, SNI rats were scanned 3weeks post-surgery using the same scanning paradigm, and region-of-interest analyses revealed increased metabolic activity in the contralateral S1 hindlimb. Finally, a second cohort of SNI rats was scanned while anesthetized during the tracer uptake period, and the S1 hindlimb increase was not observed. Increased brain activity in the somatosensory cortex of SNI rats resembled the activity produced with the injection of formalin, suggesting that the SNI model may produce persistent pain. The lack of increased activity in S1 hindlimb with general anesthetic demonstrates that this effect can be blocked, as well as highlights the importance of investigating brain activity in awake and behaving rodents.
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Affiliation(s)
- Scott J Thompson
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC H3G 0G1, Canada; Integrated Program in Neuroscience, McGill University, Montreal, QC H3A 2T5, Canada.
| | - Magali Millecamps
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC H3G 0G1, Canada; Faculty of Dentistry, McGill University, Montreal, QC H3A 2T5, Canada
| | - Antonio Aliaga
- Small Animal Imaging Lab, McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, QC H3A 2B4, Canada
| | - David A Seminowicz
- Department of Neural and Pain Sciences, University of Maryland School of Dentistry, Baltimore, MD 21201, USA
| | - Lucie A Low
- Division of Intramural Research, National Center for Complementary and Alternative Medicine, National Institutes of Health, Bethesda, MD 20892, USA
| | - Barry J Bedell
- Small Animal Imaging Lab, McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, QC H3A 2B4, Canada; Department of Neurology & Neurosurgery, McGill University, Montreal, QC H3A 2B4, Canada
| | - Laura S Stone
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC H3G 0G1, Canada; Faculty of Dentistry, McGill University, Montreal, QC H3A 2T5, Canada; Department of Neurology & Neurosurgery, McGill University, Montreal, QC H3A 2B4, Canada
| | - Petra Schweinhardt
- Alan Edwards Centre for Research on Pain, McGill University, Montreal, QC H3G 0G1, Canada; Faculty of Dentistry, McGill University, Montreal, QC H3A 2T5, Canada; Department of Neurology & Neurosurgery, McGill University, Montreal, QC H3A 2B4, Canada
| | - M Catherine Bushnell
- Division of Intramural Research, National Center for Complementary and Alternative Medicine, National Institutes of Health, Bethesda, MD 20892, USA
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18
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Systemic morphine treatment induces changes in firing patterns and responses of nociceptive afferent fibers in mouse glabrous skin. Pain 2013; 154:2297-2309. [PMID: 23711478 DOI: 10.1016/j.pain.2013.05.033] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 04/26/2013] [Accepted: 05/17/2013] [Indexed: 01/22/2023]
Abstract
Patients receiving opioids for pain may experience decreased effectiveness of the drug and even abnormal pain sensitivity-hyperalgesia and/or allodynia. We hypothesized that peripheral nociceptor hyperexcitability contributes to opioid-induced hyperalgesia and tested this using an in vitro mouse glabrous skin-nerve preparation. Mice were injected intraperitoneally with escalating doses of morphine (5, 8, 10, 15 mg/kg) or saline every 12 hours for 48 hours and killed approximately 12 hours after the last injection. Receptive fields of nociceptors were tested for mechanical, heat, and cold sensitivity. Activity was also measured during an initial 2-minute period and during 5-minute periods between stimuli. Aberrant activity was common in fibers from morphine-treated mice but rare in saline-treated mice. Resting background activity was elevated in C-fibers from morphine-treated mice. Both C- and Aδ-fibers had afterdischarge in response to mechanical, heat, and/or cold stimulation of the skin as well as spontaneous, unevoked activity. Compared to saline, morphine treatment increased the proportion of fibers displaying polymodal rather than mechanical-only responses. A significant increase in Aδ-mechanoreceptive fibers responding to cold accounted for most of this change. In agreement with this, morphine-treated mice showed increased sensitivity in the cold tail flick test. In morphine-treated mice, aberrant activity and hyperexcitability of nociceptors could contribute to increased pain sensitivity. Importantly, this activity is likely driving central sensitization, a phenomenon contributing to abnormal sensory processing and chronic pain. If similar changes occur in human patients, aberrant nociceptor activity is likely to be interpreted as pain and could contribute to opioid-induced hyperalgesia.
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Pitcher GM, Ritchie J, Henry JL. Peripheral neuropathy induces cutaneous hypersensitivity in chronically spinalized rats. PAIN MEDICINE 2013; 14:1057-71. [PMID: 23855791 DOI: 10.1111/pme.12123] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND/OBJECTIVES The present study was aimed at the issue of whether peripheral nerve injury-induced chronic pain is maintained by supraspinal structures governing descending facilitation to the spinal dorsal horn, or whether altered peripheral nociceptive mechanisms sustain central hyperexcitability and, in turn, neuropathic pain. We examined this question by determining the contribution of peripheral/spinal mechanisms, isolated from supraspinal influence(s), in cutaneous hypersensitivity in an animal model of peripheral neuropathy. METHODS Adult rats were spinalized at T8-T9; 8 days later, peripheral neuropathy was induced by implanting a 2-mm polyethylene cuff around the left sciatic nerve. Hind paw withdrawal responses to mechanical or thermal plantar stimulation were evaluated using von Frey filaments or a heat lamp, respectively. RESULTS Spinalized rats without cuff implantation exhibited a moderate decrease in mechanical withdrawal threshold on ~day 10 (P < 0.05) and in thermal withdrawal threshold on ~day 18 (P < 0.05). However, cuff-implanted spinalized rats developed a more rapid and significant decrease in mechanical (~day 4; P < 0.001) and thermal (~day 10; P < 0.05) withdrawal thresholds that remained significantly decreased through the duration of the study. CONCLUSIONS Our findings demonstrate an aberrant peripheral/spinal mechanism that induces and maintains thermal and to a greater degree tactile cutaneous hypersensitivity in the cuff model of neuropathic pain, and raise the prospect that altered peripheral/spinal nociceptive mechanisms in humans with peripheral neuropathy may have a pathologically relevant role in both inducing and sustaining neuropathic pain.
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Affiliation(s)
- Graham M Pitcher
- Departments of Physiology and Psychiatry, McGill University, Montreal, Quebec, Canada.
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Sensory neuron downregulation of the Kv9.1 potassium channel subunit mediates neuropathic pain following nerve injury. J Neurosci 2013. [PMID: 23197740 DOI: 10.1523/jneurosci.3561-12.2012] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Chronic neuropathic pain affects millions of individuals worldwide, is typically long-lasting, and remains poorly treated with existing therapies. Neuropathic pain arising from peripheral nerve lesions is known to be dependent on the emergence of spontaneous and evoked hyperexcitability in damaged nerves. Here, we report that the potassium channel subunit Kv9.1 is expressed in myelinated sensory neurons, but is absent from small unmyelinated neurons. Kv9.1 expression was strongly and rapidly downregulated following axotomy, with a time course that matches the development of spontaneous activity and pain hypersensitivity in animal models. Interestingly, siRNA-mediated knock-down of Kv9.1 in naive rats led to neuropathic pain behaviors. Diminished Kv9.1 function also augmented myelinated sensory neuron excitability, manifested as spontaneous firing, hyper-responsiveness to stimulation, and persistent after-discharge. Intracellular recordings from ex vivo dorsal root ganglion preparations revealed that Kv9.1 knock-down was linked to lowered firing thresholds and increased firing rates under physiologically relevant conditions of extracellular potassium accumulation during prolonged activity. Similar neurophysiological changes were detected in animals subjected to traumatic nerve injury and provide an explanation for neuropathic pain symptoms, including poorly understood conditions such as hyperpathia and paresthesias. In summary, our results demonstrate that Kv9.1 dysfunction leads to spontaneous and evoked neuronal hyperexcitability in myelinated fibers, coupled with development of neuropathic pain behaviors.
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Bennett GJ. What Is Spontaneous Pain and Who Has It? THE JOURNAL OF PAIN 2012; 13:921-9. [DOI: 10.1016/j.jpain.2012.05.008] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 05/08/2012] [Accepted: 05/10/2012] [Indexed: 01/05/2023]
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Buonocore M, Gatti AM, Amato G, Aloisi AM, Bonezzi C. Allodynic skin in post-herpetic neuralgia: histological correlates. J Cell Physiol 2012; 227:934-8. [PMID: 21503891 DOI: 10.1002/jcp.22804] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Most post-herpetic neuralgia (PHN) patients suffer from tactile allodynia (pain evoked by lightly touching the skin) and it is frequently the dominant clinical manifestation. The pathophysiology of tactile allodynia in PHN patients is poorly understood and this is one of the major limits to the development of appropriate therapies. Epidermal nerve fibres (ENFs) are free nerve endings of small-diameter A-delta and C primary afferents, which can easily be assessed by neurodiagnostic skin biopsy (NSB). The aim of this study was to establish the correlation between the residual epidermal innervation of the allodynic skin and the intensity of tactile allodynia in that area. Twenty-five patients (13 males and 12 females) with PHN were enrolled. Eighteen patients had PHN in the thoracic dermatome, four in the cervical, two in the trigeminal and one in the lumbar. The severity of allodynia evoked by a paintbrush was graded according to an eleven-point numerical scale. A skin biopsy was obtained from the maximal allodynia area and from the contralateral skin. Nerve fibres were labelled with indirect immunofluorescence. Results showed that epidermal innervation was lower in the allodynic skin than in the contralateral skin, although there was great variability among patients. There was no correlation between severity of allodynia and epidermal innervation of the PHN skin. In conclusion, the present study further indicates peripheral nervous system involvement in PHN but does not support a direct correlation between epidermal innervation changes and tactile allodynia.
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Affiliation(s)
- Michelangelo Buonocore
- Unit of Clinical Neurophysiology and Neurodiagnostic Skin Biopsy, Fondazione Salvatore Maugeri, Pavia, Italy.
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Cao XH, Chen SR, Li L, Pan HL. Nerve injury increases brain-derived neurotrophic factor levels to suppress BK channel activity in primary sensory neurons. J Neurochem 2012; 121:944-53. [PMID: 22428625 DOI: 10.1111/j.1471-4159.2012.07736.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Abnormal hyperexcitability of primary sensory neurons contributes to neuropathic pain development after nerve injury. Nerve injury profoundly reduces the expression of big conductance Ca(2+) -activated K(+) (BK) channels in the dorsal root ganglion (DRG). However, little is known about how nerve injury affects BK channel activity in DRG neurons. In this study, we determined the changes in BK channel activity in DRG neurons in a rat model of neuropathic pain and the contribution of brain-derived neurotrophic factor (BDNF) to reduced BK channel activity. The BK channel activity was present predominantly in small and medium DRG neurons, and ligation of L5 and L6 spinal nerves profoundly decreased the BK current density in these neurons. Blocking BK channels significantly increased neuronal excitability in sham control, but not in nerve-injured, rats. The BDNF concentration in the DRG was significantly greater in nerve-injured rats than in control rats. BDNF treatment largely reduced BK currents in DRG neurons in control rats, which was blocked by either anti-BDNF antibody or K252a, a Trk receptor inhibitor. Furthermore, either anti-BDNF antibody or K252a reversed reduction in BK currents in injured DRG neurons. BDNF treatment reduced the mRNA levels of BKα1 subunit in DRG neurons, and anti-BDNF antibody attenuated the reduction in the BKα1 mRNA level in injured DRG neurons. These findings suggest that nerve injury primarily diminishes the BK channel activity in small and medium DRG neurons. Increased BDNF levels contribute to reduced BK channel activity in DRG neurons through epigenetic and transcriptional mechanisms in neuropathic pain.
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Affiliation(s)
- Xue-Hong Cao
- Center for Neuroscience and Pain Research, Department of Anesthesiology and Perioperative Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA
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Li L, Cao XH, Chen SR, Han HD, Lopez-Berestein G, Sood AK, Pan HL. Up-regulation of Cavβ3 subunit in primary sensory neurons increases voltage-activated Ca2+ channel activity and nociceptive input in neuropathic pain. J Biol Chem 2011; 287:6002-13. [PMID: 22187436 DOI: 10.1074/jbc.m111.310110] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
High voltage-activated calcium channels (HVACCs) are essential for synaptic and nociceptive transmission. Although blocking HVACCs can effectively reduce pain, this treatment strategy is associated with intolerable adverse effects. Neuronal HVACCs are typically composed of α(1), β (Cavβ), and α(2)δ subunits. The Cavβ subunit plays a crucial role in the membrane expression and gating properties of the pore-forming α(1) subunit. However, little is known about how nerve injury affects the expression and function of Cavβ subunits in primary sensory neurons. In this study, we found that Cavβ(3) and Cavβ(4) are the most prominent subtypes expressed in the rat dorsal root ganglion (DRG) and dorsal spinal cord. Spinal nerve ligation (SNL) in rats significantly increased mRNA and protein levels of the Cavβ(3), but not Cavβ(4), subunit in the DRG. SNL also significantly increased HVACC currents in small DRG neurons and monosynaptic excitatory postsynaptic currents of spinal dorsal horn neurons evoked from the dorsal root. Intrathecal injection of Cavβ(3)-specific siRNA significantly reduced HVACC currents in small DRG neurons and the amplitude of monosynaptic excitatory postsynaptic currents of dorsal horn neurons in SNL rats. Furthermore, intrathecal treatment with Cavβ(3)-specific siRNA normalized mechanical hyperalgesia and tactile allodynia caused by SNL but had no significant effect on the normal nociceptive threshold. Our findings provide novel evidence that increased expression of the Cavβ(3) subunit augments HVACC activity in primary sensory neurons and nociceptive input to dorsal horn neurons in neuropathic pain. Targeting the Cavβ(3) subunit at the spinal level represents an effective strategy for treating neuropathic pain.
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Affiliation(s)
- Li Li
- Department of Anesthesiology and Perioperative Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA
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Shenoy R, Roberts K, Papadaki A, McRobbie D, Timmers M, Meert T, Anand P. Functional MRI brain imaging studies using the Contact Heat Evoked Potential Stimulator (CHEPS) in a human volunteer topical capsaicin pain model. J Pain Res 2011; 4:365-71. [PMID: 22090805 PMCID: PMC3215516 DOI: 10.2147/jpr.s24810] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Acute application of topical capsaicin produces spontaneous burning and stinging pain similar to that seen in some neuropathic states, with local hyperalgesia. Use of capsaicin applied topically or injected intradermally has been described as a model for neuropathic pain, with patterns of activation in brain regions assessed using functional magnetic resonance imaging (fMRI) and positron emission tomography. The Contact Heat Evoked Potential Stimulator (CHEPS) is a noninvasive clinically practical method of stimulating cutaneous A-delta nociceptors. In this study, topical capsaicin (1%) was applied to the left volar forearm for 15 minutes of twelve adult healthy human volunteers. fMRI scans and a visual analog pain score were recorded during CHEPS stimulation precapsaicin and postcapsaicin application. Following capsaicin application there was a significant increase in visual analog scale (mean ± standard error of the mean; precapsaicin 26.4 ± 5.3; postcapsaicin 48.9 ± 6.0; P < 0.0001). fMRI demonstrated an overall increase in areas of activation, with a significant increase in the contralateral insular signal (mean ± standard error of the mean; precapsaicin 0.434 ± 0.03; postcapsaicin 0.561 ± 0.07; P = 0.047). The authors of this paper recently published a study in which CHEPS-evoked A-delta cerebral potential amplitudes were found to be decreased postcapsaicin application. In patients with neuropathic pain, evoked pain and fMRI brain responses are typically increased, while A-delta evoked potential amplitudes are decreased. The protocol of recording fMRI following CHEPS stimulation after topical application of capsaicin could be combined with recording of evoked potentials to provide a simple, rapid, and robust volunteer model to develop novel drugs for neuropathic pain.
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Affiliation(s)
- Ravikiran Shenoy
- Peripheral Neuropathy Unit, Hammersmith Hospital, Imperial College London
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Microneurographic identification of spontaneous activity in C-nociceptors in neuropathic pain states in humans and rats. Pain 2011; 153:42-55. [PMID: 21993185 DOI: 10.1016/j.pain.2011.08.015] [Citation(s) in RCA: 149] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Revised: 07/11/2011] [Accepted: 08/15/2011] [Indexed: 12/21/2022]
Abstract
C-nociceptors do not normally fire action potentials unless challenged by adequate noxious stimuli. However, in pathological states nociceptors may become hyperexcitable and may generate spontaneous ectopic discharges. The aim of this study was to compare rat neuropathic pain models and to assess their suitability to model the spontaneous C-nociceptor activity found in neuropathic pain patients. Studies were performed in normal rats (n=40), healthy human subjects (n=15), peripheral neuropathic pain patients (n=20), and in five rat neuropathic pain models: nerve crush (n=24), suture (n=14), chronic constriction injury (n=12), STZ-induced diabetic neuropathy (n=56), and ddC-induced neuropathy (n=15). Microneurographic recordings were combined with electrical stimulation to monitor activity in multiple C fibers. Stimulation at 0.25 Hz allowed spontaneous impulses to be identified by fluctuations in baseline latency. Abnormal latency fluctuations could be produced by several mechanisms, and spontaneous activity was most reliably identified by the presence of unexplained latency increases corresponding to two or more additional action potentials. Spontaneous activity was present in a proportion of mechano-insensitive C-nociceptors in the patients and all rat models. The three focal traumatic nerve injury models provided the highest proportion (59.5%), whereas the two polyneuropathy models had fewer (18.6%), and the patients had an intermediate proportion (33.3%). Spontaneously active mechano-sensitive C-nociceptors were not recorded. Microneurographic recordings of spontaneous activity in diseased C-nociceptors may be useful for both short- and long-term drug studies, both in animals and in humans.
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Leone C, Biasiotta A, La Cesa S, Di Stefano G, Cruccu G, Truini A. Pathophysiological mechanisms of neuropathic pain. FUTURE NEUROLOGY 2011. [DOI: 10.2217/fnl.11.23] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Neuropathic pain is a common problem in clinical practice and one that adversely affects patients’ quality of life. Converging evidence from animal and human studies demonstrates that neuropathic pain arises from a lesion in the somatosensory system. Injured peripheral nerve fibers give rise to an intense and prolonged ectopic input to the CNS and, in some cases, also to secondary changes in dorsal horn neuronal excitability. Convincing evidence now suggests that classifying neuropathic pain according to a mechanism-based rather than an etiology-based approach might help in targeting therapy to the individual patient and would be useful in testing new drugs. This article summarizes our current understanding of the peripheral and central pathophysiological mechanisms underlying neuropathic pain and focuses on how symptoms translate into mechanisms.
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Affiliation(s)
- Caterina Leone
- Department of Neurological Sciences, University La Sapienza, Viale Università 30 00185 – Rome, Italy
| | - Antonella Biasiotta
- Department of Neurological Sciences, University La Sapienza, Viale Università 30 00185 – Rome, Italy
| | - Silvia La Cesa
- Department of Neurological Sciences, University La Sapienza, Viale Università 30 00185 – Rome, Italy
| | - Giulia Di Stefano
- Department of Neurological Sciences, University La Sapienza, Viale Università 30 00185 – Rome, Italy
| | - Giorgio Cruccu
- Department of Neurological Sciences, University La Sapienza, Viale Università 30 00185 – Rome, Italy
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A novel human volunteer pain model using contact heat evoked potentials (CHEP) following topical skin application of transient receptor potential agonists capsaicin, menthol and cinnamaldehyde. J Clin Neurosci 2011; 18:926-32. [DOI: 10.1016/j.jocn.2010.11.015] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2010] [Revised: 11/11/2010] [Accepted: 11/15/2010] [Indexed: 01/06/2023]
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The conundrum of sensitization when recording from nociceptors. J Neurosci Methods 2010; 188:213-8. [PMID: 20171245 DOI: 10.1016/j.jneumeth.2010.02.010] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2009] [Revised: 01/26/2010] [Accepted: 02/09/2010] [Indexed: 11/24/2022]
Abstract
Nociceptors are sensory neurons that detect harmful, or potentially harmful, stimuli, and can become sensitized following injury or repetitive stimulation. When sensitized, nociceptors often exhibit activity in the absence of apparent or additional stimulation, called ongoing (or spontaneous) activity (OA). In this report, we provide evidence that OA in nociceptors can be caused by the stimuli typically used to identify and characterize the neuron, which must by definition be noxious and therefore potentially sensitizing. Such OA caused by the experimental methodology can confound interpretation. In our nerve inflammation model, OA can potentially arise from multiple sites, including the lesion site and the receptive field. We provide evidence that the OA rate recorded during these experiments may be related to the site and cause of OA generation. We suggest that there are two types of OA, characterized by their rates. Very slow rates of ongoing activity (<0.2 Hz) are likely to arise from the receptive field and may indicate sensitization during the experiment. Faster rates are likely to arise from the nerve trunk, i.e. the neuritis, or the neuronal cell body. Without appropriate methodological consideration, interpretations of results from such studies of nociceptor function may be methodologically confounded.
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Microneurography: an opportunity for translational drug development in neuropathic pain. Neurosci Lett 2009; 470:155-7. [PMID: 20045040 DOI: 10.1016/j.neulet.2009.12.065] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Murayama RA, Stuginski-Barbosa J, Moraes NP, Speciali JG. Toothache referred from auriculotemporal neuralgia: case report. Int Endod J 2009; 42:845-51. [DOI: 10.1111/j.1365-2591.2009.01599.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Namer B, Handwerker HO. Translational nociceptor research as guide to human pain perceptions and pathophysiology. Exp Brain Res 2009; 196:163-72. [PMID: 19350229 DOI: 10.1007/s00221-009-1777-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Accepted: 03/17/2009] [Indexed: 01/12/2023]
Abstract
Microneurography is a method for recording single unit action potentials with microelectrodes from the nerves of awake cooperating humans. Although this method is now in use since almost 40 years, its potency has been strengthened by the recent technical developments. A great progress was the discovery that different functional groups of nociceptors are characterized by a distinctly different post-excitatory slowing of their conduction velocities. Microneurography is now powerful enough to analyze the nerve activity pattern of enigmatic sensations such as pruritus. Furthermore, it is the only method providing direct insight in the changes which human nerves undergo with aging. Recently, reliable recordings from patients suffering from painful neuropathies came into reach. It has been shown that different types of neuropathies are characterized by different patterns of abnormal nociceptor functions. Although some of them are characterized by abnormal spontaneous activity in C-nociceptors, others show mainly signs of denervation. Microneurography is, therefore, a tool for translational studies on human nociceptor functions by linking direct animal studies on experimental neuropathies with human diseases.
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Affiliation(s)
- Barbara Namer
- Department of Physiology and Pathophysiology, Institut für Physiologie und Pathophysiologie, University of Erlangen/Nuernberg, Universitätsstr. 17, 91054 Erlangen, Germany
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Kuwabara S. Ionic mechanisms for paresthesias arising from human sensory axons. Clin Neurophysiol 2008; 119:1945-6. [PMID: 18571980 DOI: 10.1016/j.clinph.2008.04.296] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2008] [Revised: 04/26/2008] [Accepted: 04/29/2008] [Indexed: 11/29/2022]
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Neurophysiological evidence of antidromic activation of large myelinated fibres in lower limbs during spinal cord stimulation. Spine (Phila Pa 1976) 2008; 33:E90-3. [PMID: 18277861 DOI: 10.1097/brs.0b013e3181642a97] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
STUDY DESIGN This study was designed to verify the hypothesis of a constant, antidromic activation of fibers traveling along peripheral sensory nerves during spinal cord stimulation (SCS). OBJECTIVE To investigate the neurophysiological characteristics (latency, amplitude, waveform) of potentials recorded in peripheral sensory nerves during the SCS. SUMMARY OF BACKGROUND DATA SCS is widely used for the relief of chronic benign pain resistant to conservative therapies, but its antalgic mechanism is poorly understood. Antidromic activation of peripheral nerve fibers is one of the hypothesized antalgic mechanisms, but very few neurophysiological studies have been conducted on this subject. METHODS Sixteen patients undergoing a percutaneous test trial of SCS for chronic pain in the lower limb (4 males, 12 females, mean age of 54.2, and age range 41-77 years) were enrolled. Diagnoses included: failed back surgery syndrome, complex regional pain syndrome type I, painful lumbosacral radiculopathy, and painful peripheral neuropathy. All patients had a lead percutaneously implanted in the epidural space at a vertebral level ranging from T9-T12. Nerve action potentials were generally recorded in nonpainful leg but, when the pain was outside the investigated nerve territory, a bilateral recording was performed. Twenty-one different studies were carried out on 16 patients. RESULTS The results confirmed the hypothesis that cutaneous afferents were regularly activated by SCS. CONCLUSION The authors hypothesize that this antidromic activation could represent a possible antalgic mechanism of SCS in patients with peripheral neuropathic pain, but further neurophysiological studies will be needed to elucidate this hypothesis.
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Enhanced sensory re-learning after nerve repair using 3D audio-visual signals and kinaesthesia--preliminary results. ACTA NEUROCHIRURGICA. SUPPLEMENT 2007; 100:127-9. [PMID: 17985561 DOI: 10.1007/978-3-211-72958-8_27] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
Sensory re-learning methods and basics on cortical reorganization after peripheral nerve lesion are well documented. The aim of enhanced sensory re-learning using 3D audio-visual signals and kinaesthetic training is the augmentation of cognitive memory (visual and acoustic sensory memory) and cognitive function for the improvement of cerebral plasticity processes and starts as soon as possible after nerve repair. Preliminary results are shown.
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Abstract
Supraorbital neuralgia is a rare disorder clinically characterized by the following triad: 1) forehead pain in the territory supplied by the supraorbital nerve, without side shift; 2) tenderness on either the supraorbital notch or traject of the nerve; and 3) absolute, but transitory relief of symptoms upon supraorbital nerve blockade. The pain presents with a chronic or intermittent pattern. In addition, there may be signs and symptoms of sensory dysfunction (hypoesthesia, paresthesia and allodynia), and typical "neuralgic features" (lightning pain and exteroceptive precipitating mechanisms). However, sensitive and neuralgic features are not constantly present and seem to be more frequent in the secondary, usually post-traumatic, forms.
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Affiliation(s)
- Juan A Pareja
- Department of Neurology, Fundación Hospital Alcorcón, Madrid, Spain.
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Brookoff D. Neurophysiological Underpinnings of Electronic Analgesic Neuromodulation for Dummies. PAIN MEDICINE 2006. [DOI: 10.1111/j.1526-4637.2006.00126.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Attal N, Bouhassira D. Translating basic research on sodium channels in human neuropathic pain. THE JOURNAL OF PAIN 2006; 7:S31-7. [PMID: 16426999 DOI: 10.1016/j.jpain.2005.09.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
UNLABELLED A number of experimental studies in animals have suggested that voltage-gated sodium channels may play a crucial role in neuropathic pain. However, it is still difficult to translate the pathophysiological mechanisms identified in animal studies to the clinic and several questions regarding the role of sodium channels in neuropathic pain must therefore be addressed primarily in the clinical setting. Despite providing indirect information, pharmacologic challenge using sodium channel blockers, such as some antiepileptics, local anesthetics and derivatives, is the best way to investigate the role of sodium channels in the various clinical symptoms of neuropathies (eg, spontaneous pain, mechanical or thermal allodynia, and hyperalgesia). Randomized controlled trials have demonstrated the efficacy of these compounds for various neuropathic pain conditions. Recent psychophysical studies in which symptoms and signs are more accurately assessed indicate that these compounds act as antihyperalgesic agents rather than as simple analgesics. They also show that the sensitivity to these drugs is not affected by the aetiology of pain and the peripheral or central location of the nerve lesion. These data emphasize the role of peripheral and central sodium channels in neuropathic pain. Studies using more selective sodium channel blockers are required to gain further insight into the role of the various subtypes of sodium channel in these pain conditions. PERSPECTIVE Pharmacological challenge using sodium channel blockers is the best way to translate basic research on sodium channels in human neuropathic pain. To date, the role of sodium channels in neuropathic pain symptoms/signs is mostly documented for mechanical static and dynamic allodynia, and either peripheral or central sodium channels may be involved.
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Affiliation(s)
- Nadine Attal
- Centre d'Evaluation et de Traitement de la Douleur, Hôpital Ambroise Paré, AP-HP and Université Versailles-Saint-Quentin, France.
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Marchettini P. Chapter 37 Pain after surgical interventions. HANDBOOK OF CLINICAL NEUROLOGY 2006; 81:565-571. [PMID: 18808859 DOI: 10.1016/s0072-9752(06)80041-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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Jørum E, Schmelz M. Chapter 29 Microneurography in the assessment of neuropathic pain. HANDBOOK OF CLINICAL NEUROLOGY 2006; 81:427-38. [DOI: 10.1016/s0072-9752(06)80033-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Priestley T, Hunter JC. Voltage-gated sodium channels as molecular targets for neuropathic pain. Drug Dev Res 2006. [DOI: 10.1002/ddr.20100] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Bostock H, Campero M, Serra J, Ochoa JL. Temperature-dependent double spikes in C-nociceptors of neuropathic pain patients. Brain 2005; 128:2154-63. [PMID: 15947060 DOI: 10.1093/brain/awh552] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Five patients with small-fibre neuropathy characterized by temperature-dependent spontaneous pain, hyperalgesia/allodynia and signs of neurogenic inflammation were studied clinically and thermographically, and by microneurography. Thermography revealed hyperthermia confined to painful and hyperalgesic skin of distal extremities, in absence of sympathetic vasomotor denervation. Quantitative sensory testing documented either reduced thresholds or increased suprathreshold magnitude for heat pain. Microneurography identified 13 primary cutaneous C-nociceptors generating abnormal impulses in response to electrical stimuli and, in one patient, nociceptors firing spontaneously. All five patients showed examples of double spikes, in which a single brief electrical stimulus occasionally or regularly evoked two impulses. In one case, a second impulse occurred at one of three different delays. In all five patients, warming of the skin increased the probability of a second impulse occurring. Impulse doubling has previously been reported as occurring rarely in normal subjects and is attributable to unfiltering of multiple orthodromic impulses due to unidirectional conduction failure at branch points. A higher incidence of double firing in neuropathic pain patients is probably due to a reduced safety factor for conduction in the terminal arborizations of their C-nociceptors. These observations show that unidirectional conduction block provides a peripheral mechanism of temperature-dependent nociceptor hyperactivity in small-fibre neuropathy that may contribute to hyperalgesia.
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Chizh BA, Dusch M, Puthawala M, Schmelz M, Cookson LM, Martina R, Brown J, Koppert W. The Effect of Intravenous Infusion of Adenosine on Electrically Evoked Hyperalgesia in a Healthy Volunteer Model of Central Sensitization. Anesth Analg 2004; 99:816-822. [PMID: 15333416 DOI: 10.1213/01.ane.0000132995.35119.99] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Human pain models invoking central sensitization, one of the key mechanisms of chronic pain, may be useful for characterizing new analgesics. A new model of electrical hyperalgesia can detect the efficacy of several analgesic mechanisms. Because IV adenosine can alleviate neuropathic pain, we investigated its effect on experimental sensitization. This was a double-blinded, randomized, two-period crossover study in 20 healthy volunteers. Current pulses (0.5 ms; 1 Hz) were applied intracutaneously to achieve pain rating of approximately 5 on a 0-10 numeric rating scale. Pain, areas of pinprick hyperalgesia, and tactile allodynia were assessed during the 2.5-h stimulation period. Adenosine (50 microg. kg(-1). min(-1)) and placebo were infused IV over 60 min. Additional testing was performed 24 h after each treatment. Adenosine reduced the area of pinprick hyperalgesia during the infusion compared with placebo; there was no significant effect on tactile allodynia or pain rating. The effect on hyperalgesia developed over 15 min and was significant (P < or = 0.05) for the rest of the infusion period. There was no difference between treatments at 24 h. Thus, in accordance with reports on neuropathic pain, adenosine reduced central sensitization in the human model of electrical hyperalgesia. However, adenosine did not have the long-term effects seen in patients. The model can investigate mechanisms of drugs for the treatment of chronic pain.
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Affiliation(s)
- Boris A Chizh
- *Translational Medicine and ‡Statistics, GlaxoSmithKline, Cambridge, United Kingdom; and †Department of Physiology, University of Erlangen, Erlangen, Germany
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Pitcher GM, Henry JL. Nociceptive response to innocuous mechanical stimulation is mediated via myelinated afferents and NK-1 receptor activation in a rat model of neuropathic pain. Exp Neurol 2004; 186:173-97. [PMID: 15026255 DOI: 10.1016/j.expneurol.2003.10.019] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2002] [Revised: 10/08/2003] [Accepted: 10/16/2003] [Indexed: 12/29/2022]
Abstract
Peripheral nerve injury in humans can produce a persistent pain state characterized by spontaneous pain and painful responses to normally innocuous stimuli (allodynia). Here we attempt to identify some of the neurophysiological and neurochemical mechanisms underlying neuropathic pain using an animal model of peripheral neuropathy induced in male Sprague-Dawley rats by placing a 2-mm polyethylene cuff around the left sciatic nerve according to the method of Mosconi and Kruger. von Frey hair testing confirmed tactile allodynia in all cuff-implanted rats before electrophysiological testing. Rats were anesthetized and spinalized for extracellular recording from single spinal wide dynamic range neurons (L(3-4)). In neuropathic rats (days 11-14 and 42-52 after cuff implantation), ongoing discharge was greater and hind paw receptive field size was expanded compared to control rats. Activation of low-threshold sensory afferents by innocuous mechanical stimulation (0.2 N for 3 s) in the hind paw receptive field evoked the typical brief excitation in control rats. However, in neuropathic rats, innocuous stimulation also induced a nociceptive-like afterdischarge that persisted 2-3 min. This afterdischarge was never observed in control rats, and, in this model, is the distinguishing feature of the spinal neural correlate of tactile allodynia. Electrical stimulation of the sciatic nerve at 4 and at 20 Hz each produced an initial discharge that was identical in control and in neuropathic rats. This stimulation also produced an afterdischarge that was similar at the two frequencies in control rats. However, in neuropathic rats, the afterdischarge produced by 20-Hz stimulation was greater than that produced by 4-Hz stimulation. Given that acutely spinalized rats were studied, only peripheral and/or spinal mechanisms can account for the data obtained; as synaptic responses from C fibers begin to fail above approximately 5-Hz stimulation [Pain 46 (1991) 327], the afterdischarge in response to 20-Hz stimulation suggests a change mainly in myelinated afferents and a predominant role of these fibers in eliciting this afterdischarge. These data are consistent with the suggestion that peripheral neuropathy induces phenotypic changes predominantly in myelinated afferents, the sensory neurons that normally respond to mechanical stimulation. The NK-1 receptor antagonist, CP-99,994 (0.5 mg/kg, i.v.), depressed the innocuous pressure-evoked afterdischarge but not the brief initial discharge of wide dynamic range neurons, and decreased the elevated ongoing rate of discharge in neuropathic rats. These results support the concept that following peripheral neuropathy, myelinated afferents may now synthesize and release substance P. A result of this is that tonic release of substance P from the central terminals of these phenotypically altered neurons would lead to ongoing excitation of NK-1-expressing nociceptive spinal neurons. In addition, these spinal neurons would also exhibit exaggerated responses to innocuous pressure stimulation. The data in this study put forth a possible neurophysiological and neurochemical basis of neuropathic pain and identify substance P and the NK-1 receptor as potential neurochemical targets for its management.
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Affiliation(s)
- Graham M Pitcher
- Department of Physiology, McGill University, Montreal, Quebec, Canada H3G 1Y6
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Affiliation(s)
- José L Ochoa
- Oregon Nerve Center, Department of Neurology, 1040 N.W. 22nd Ave., Suite 600, Portland, OR 97210, USA.
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Khan GM, Chen SR, Pan HL. Role of primary afferent nerves in allodynia caused by diabetic neuropathy in rats. Neuroscience 2002; 114:291-9. [PMID: 12204199 DOI: 10.1016/s0306-4522(02)00372-x] [Citation(s) in RCA: 181] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Both myelinated and unmyelinated afferents are implicated in transmitting diabetic neuropathic pain. Although unmyelinated afferents are generally considered to play a significant role in diabetic neuropathic pain, pathological changes in diabetic neuropathy occur mostly in myelinated A-fibers. In the present study, we first examined the role of capsaicin-sensitive C-fibers in the development of allodynia induced by diabetic neuropathy. We then studied the functional changes of afferent nerves pertinent to diabetic neuropathic pain. Diabetes was induced in rats by i.p. streptozotocin. To deplete capsaicin-sensitive C-fibers, rats were treated with i.p. resiniferatoxin (300 microg/kg). Mechanical and thermal sensitivities were measured using von Frey filaments and a radiant heat stimulus. Single-unit activity of afferents was recorded from the tibial nerve. Tactile allodynia, but not thermal hyperalgesia, developed in diabetic rats. Resiniferatoxin treatment did not alter significantly the degree and time course of allodynia. Post-treatment with resiniferatoxin also failed to attenuate allodynia in diabetic rats. The electrophysiological recordings revealed ectopic discharges and a higher spontaneous activity mainly in Adelta- and Abeta-fiber afferents in diabetic rats regardless of resiniferatoxin treatment. Furthermore, these afferent fibers had a lower threshold for activation and augmented responses to mechanical stimuli. Thus, our study suggests that capsaicin-sensitive C-fiber afferents are not required in the development of allodynia in this rat model of diabetes. Our electrophysiological data provide substantial new evidence that the abnormal sensory input from Adelta- and Abeta-fiber afferents may play an important role in diabetic neuropathic pain.
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MESH Headings
- Afferent Pathways/drug effects
- Afferent Pathways/pathology
- Afferent Pathways/physiopathology
- Animals
- Diabetes Mellitus, Experimental/complications
- Diabetes Mellitus, Experimental/physiopathology
- Diabetic Neuropathies/pathology
- Diabetic Neuropathies/physiopathology
- Disease Models, Animal
- Diterpenes/pharmacology
- Ganglia, Spinal/drug effects
- Ganglia, Spinal/pathology
- Ganglia, Spinal/physiopathology
- Hyperalgesia/pathology
- Hyperalgesia/physiopathology
- Male
- Microscopy, Electron
- Nerve Fibers, Myelinated/drug effects
- Nerve Fibers, Myelinated/pathology
- Nerve Fibers, Myelinated/physiology
- Nerve Fibers, Unmyelinated/drug effects
- Nerve Fibers, Unmyelinated/pathology
- Nerve Fibers, Unmyelinated/physiology
- Neurons, Afferent/drug effects
- Neurons, Afferent/pathology
- Neurons, Afferent/physiology
- Nociceptors/drug effects
- Nociceptors/physiopathology
- Pain Threshold/drug effects
- Pain Threshold/physiology
- Physical Stimulation
- Rats
- Rats, Sprague-Dawley
- Reaction Time/drug effects
- Reaction Time/physiology
- Tibial Nerve/pathology
- Tibial Nerve/physiology
- Tibial Nerve/ultrastructure
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Affiliation(s)
- G M Khan
- Department of Anesthesiology H187, Penn State University College of Medicine, 500 University Drive, Hershey, PA 17033, USA
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Wall JT, Xu J, Wang X. Human brain plasticity: an emerging view of the multiple substrates and mechanisms that cause cortical changes and related sensory dysfunctions after injuries of sensory inputs from the body. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 2002; 39:181-215. [PMID: 12423766 DOI: 10.1016/s0165-0173(02)00192-3] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Injuries of peripheral inputs from the body cause sensory dysfunctions that are thought to be attributable to functional changes in cerebral cortical maps of the body. Prevalent theories propose that these cortical changes are explained by mechanisms that preeminently operate within cortex. This paper reviews findings from humans and other primates that point to a very different explanation, i.e. that injury triggers an immediately initiated, and subsequently continuing, progression of mechanisms that alter substrates at multiple subcortical as well as cortical locations. As part of this progression, peripheral injuries cause surprisingly rapid neurochemical/molecular, functional, and structural changes in peripheral, spinal, and brainstem substrates. Moreover, recent comparisons of extents of subcortical and cortical map changes indicate that initial subcortical changes can be more extensive than cortical changes, and that over time cortical and subcortical extents of change reach new balances. Mechanisms for these changes are ubiquitous in subcortical and cortical substrates and include neurochemical/molecular changes that cause functional alterations of normal excitation and inhibition, atrophy and degeneration of normal substrates, and sprouting of new connections. The result is that injuries that begin in the body become rapidly further embodied in reorganizational make-overs of the entire core of the somatosensory brain, from peripheral sensory neurons to cortex. We suggest that sensory dysfunctions after nerve, root, dorsal column (spinal), and amputation injuries can be viewed as diseases of reorganization in this core.
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Affiliation(s)
- J T Wall
- Cellular and Molecular Neurobiology Program, Medical College of Ohio, Toledo 43614-5804, USA.
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Chen SR, Wozniak KM, Slusher BS, Pan HL. Effect of 2-(phosphono-methyl)-pentanedioic acid on allodynia and afferent ectopic discharges in a rat model of neuropathic pain. J Pharmacol Exp Ther 2002; 300:662-7. [PMID: 11805230 DOI: 10.1124/jpet.300.2.662] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Increased glutamate availability in the spinal cord and primary afferent nerves plays an important role in acute and chronic pain. Afferent ectopic discharges from the site of nerve injury constitute a source of abnormal sensory input to the spinal dorsal horn. The ectopic afferent activity is largely responsible for the development of hypersensitivity of dorsal horn neurons and neuropathic pain. Inhibition of glutamate carboxypeptidase II (GCP II) reduces glutamate release generated from N-acetyl-aspartyl-glutamate in nerve tissues and may have an analgesic effect on neuropathic pain. In the present study, we determined the effect of a GCP II inhibitor, 2-(phosphono-methyl)-pentanedioic acid (2-PMPA), on allodynia and ectopic afferent discharges in an animal model of neuropathic pain. Neuropathic pain was induced by partial ligation of the left sciatic nerve in rats. Tactile allodynia was assessed using von Frey filaments applied to the plantar surface of the injured hindpaw. Single-unit activity of ectopic discharges was recorded from the sciatic nerve proximal to the site of ligation. Intravenous injection of 50 to 100 mg/kg 2-PMPA significantly reduced allodynia in a dose-dependent manner. Furthermore, 2-PMPA dose-dependently attenuated the ectopic discharge activity of injured sciatic afferent nerves. At a dose of 100 mg/kg, 2-PMPA significantly inhibited the ectopic activity from 14.7 +/- 2.1 to 4.4 +/- 0.5 impulses/s without altering the conduction velocity of afferent nerves. Therefore, these data suggest that the antiallodynic effect of 2-PMPA may be mediated, at least in part, by inhibition of ectopic afferent discharges at the site of nerve injury.
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Affiliation(s)
- Shao-Rui Chen
- Department of Anesthesiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033-0850, USA
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Marchettini P, Barbieri A. Commentary: the peripheral mechanisms of abnormal temporal summation. Eur J Pain 2000; 4:15-7. [PMID: 10833551 DOI: 10.1053/eujp.1999.0163] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- P Marchettini
- Pain Medicine Center, Scientific Institute & Hospital San Raffaele, via Stamira D'Ancona 20, Milano, 20127, Italy.
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