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Karm MH, Kwon HJ, Shin E, Bae H, Kim YK, Choi SS. Involvement of the spinal γ-aminobutyric acid receptor in the analgesic effects of intrathecally injected hypertonic saline in spinal nerve-ligated rats. Korean J Pain 2023; 36:441-449. [PMID: 37722756 PMCID: PMC10551396 DOI: 10.3344/kjp.23162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2023] [Revised: 07/26/2023] [Accepted: 08/05/2023] [Indexed: 09/20/2023] Open
Abstract
Background : Hypertonic saline is used for treating chronic pain; however, clinical studies that aid in optimizing therapeutic protocols are lacking. We aimed to determine the concentration of intrathecally injected hypertonic saline at which the effect reaches its peak as well as the underlying γ-aminobutyric acid (GABA) receptor-related antinociceptive mechanism. Methods : Spinal nerve ligation (SNL; left L5 and L6) was performed to induce neuropathic pain in rats weighing 250-300 g. Experiment 1: one week after implanting the intrathecal catheter, 60 rats were assigned randomly to intrathecal injection with 0.45%, 0.9%, 2.5%, 5%, 10%, and 20% NaCl, followed by behavioral testing at baseline and after 30 minutes, 2 hours, 1 day, and 1 week to determine the minimal concentration which produced maximal analgesia. Experiment 2: after determining the optimal intrathecal hypertonic saline concentration, 60 rats were randomly divided into four groups: Sham, hypertonic saline without pretreatment, and hypertonic saline after pretreatment with one of two GABA receptor antagonists (GABAA [bicuculline], or GABAB [phaclofen]). Behavioral tests were performed at weeks 1 and 3 following each treatment. Results : Hypertonic saline at concentrations greater than 5% alleviated SNL-induced mechanical allodynia and had a significant therapeutic effect, while showing a partial time- and dose-dependent antinociceptive effect on thermal and cold hyperalgesia. However, pretreatment with GABA receptor antagonists inhibited the antinociceptive effect of 5% NaCl. Conclusions : This study indicates that the optimal concentration of hypertonic saline for controlling mechanical allodynia in neuropathic pain is 5%, and that its analgesic effect is related to GABAA and GABAB receptors.
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Affiliation(s)
- Myong-Hwan Karm
- Department of Dental Anesthesiology, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea
| | - Hyun-Jung Kwon
- Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Euiyong Shin
- Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
| | - Honggyoon Bae
- Department of Anesthesiology and Pain Medicine, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea
| | - Young Ki Kim
- Department of Anesthesiology and Pain Medicine, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Korea
| | - Seong-Soo Choi
- Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea
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Loeza-Alcocer E, Gold MS. Peripheral GABAA receptor signaling contributes to visceral hypersensitivity in a mouse model of colitis. Pain 2022; 163:1402-1413. [PMID: 34726659 PMCID: PMC9056586 DOI: 10.1097/j.pain.0000000000002526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 09/16/2021] [Indexed: 11/26/2022]
Abstract
ABSTRACT Pain is a common and debilitating symptom of inflammatory bowel disease (IBD). Based on evidence that peripheral GABAA receptor (GAR) inhibition plays an important role in establishing colonic afferent excitability and nociceptive threshold, we hypothesized that the increase in pain associated with IBD is due to, at least in part, a decrease in peripheral GAR-mediated inhibition. Acute colitis was induced with 5 days of dextran sodium sulfate (DSS, 3%) in the drinking water. Visceral sensitivity was assessed with the visceromotor response (VMR) evoked with balloon distention of the colon in control and DSS-treated mice before and after intracolonic administration of GAR agonist muscimol, the high-affinity GAR preferring agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol (THIP), the GAR positive allosteric modulator diazepam, or the GAR antagonists gabazine and bicuculline. Low concentrations of muscimol or THIP increased the VMR in DSS-treated mice but not in control mice. However, high concentrations of muscimol decreased the VMR in both control and DSS-treated mice. Diazepam decreased the VMR in both DSS-treated and control mice. By contrast, at a concentration of gabazine that blocks only low-affinity GAR, there was no effect on the VMR in either DSS-treated or control mice, but at concentrations of the antagonist that block low-affinity and high-affinity GAR, the VMR was increased in control mice and decreased in DSS-treated mice. Furthermore, bicuculline increased the VMR in control mice but decreased it in DSS-treated mice. These data suggest that activating of low-affinity GAR or blocking high-affinity GAR may be effective therapeutic strategies for the management of pain in IBD.
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Affiliation(s)
- Emanuel Loeza-Alcocer
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Michael S Gold
- Department of Neurobiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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MicroRNA-96 is required to prevent allodynia by repressing voltage-gated sodium channels in spinal cord. Prog Neurobiol 2021; 202:102024. [PMID: 33636225 DOI: 10.1016/j.pneurobio.2021.102024] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 12/18/2020] [Accepted: 02/11/2021] [Indexed: 12/20/2022]
Abstract
Voltage-gated sodium channels (Navs) 1.7, 1.8, and 1.9 are predominately expressed in peripheral sensory neurons and are critical for action potential propagation in nociceptors. Unexpectedly, we found that expression of SCN9A, SCN10A, SCN11A, and SCN2A, the alpha subunit of Nav1.7, Nav1.8, Nav1.9 and Nav1.2, respectively, are up-regulated in spinal dorsal horn (SDH) neurons of miR-96 knockout mice. These mice also have de-repression of CACNA2D1/2 in DRG and display thermal and mechanical allodynia that could be attenuated by intrathecal or intraperitoneal injection of Nav1.7 or Nav1.8 blockers or Gabapentin. Moreover, Gad2::CreERT2 conditional miR-96 knockout mice phenocopied global knockout mice, implicating inhibitory neurons; nerve injury induced significant loss of miR-96 in SDH GABAergic and Glutamatergic neurons in mice which negatively correlated to up-regulation of Nav1.7, Nav1.8, Nav1.9 and Scn2a, this dis-regulation of miR-96 and Navs in SDH neurons contributed to neuropathic pain which can be alleviated by intrathecal injection of Nav1.7 or Nav1.8 blockers. In conclusion, miR-96 is required to avoid allodynia through limiting the expression of VGCCs and Navs in DRG and Navs in SDH in naïve and nerve injury-induced neuropathic pain mice. Our findings suggest that central nervous system penetrating Nav1.7 and Nav1.8 blockers may be efficacious for pain relief.
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Garrido-Suárez BB, Garrido G, Castro-Labrada M, Merino N, Valdés O, Pardo Z, Ochoa-Rodríguez E, Verdecia-Reyes Y, Delgado-Hernández R, Godoy-Figueiredo J, Ferreira SH. Anti-hypernociceptive and anti-inflammatory effects of JM-20: A novel hybrid neuroprotective compound. Brain Res Bull 2020; 165:185-197. [PMID: 33096198 DOI: 10.1016/j.brainresbull.2020.10.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Revised: 10/05/2020] [Accepted: 10/06/2020] [Indexed: 12/18/2022]
Abstract
The present study examines the possible effect of the novel hybrid molecule JM-20 (3-ethoxycarbonyl-2-methyl-4-(2-nitrophenyl)-411-dihydro-1H-pyrido[2,3-b] [1,5] benzodiazepine) on pain-related behaviours in a persistent pain model (5% formalin test) and in the neutrophil migration events during the inflammatory process. It further introduces JM-20 in a chronic constriction injury (CCI) model to clarify the possible subjacent mechanisms with its consequent clinical relevance. A single administration of JM-20 (20 or 40 mg/kg, per os [p.o.]) decreased licking/biting exclusively in the tonic phase of the formalin test in a GABA/benzodiazepine (BZD) receptor antagonist flumazenil-sensitive manner. JM-20 reduced in vivo neutrophil migration, rolling and adhesion to the endothelium induced by intraperitoneal administration of carrageenan in mice. In addition, plasma extravasation and tumour necrosis factor alpha production in the peritoneal fluid were decreased. Treatment with JM-20 (20 mg/kg, p.o.) for 7 days after CCI reduced mechanical hypersensitivity in a NG-monomethyl-l-arginine (L-NMMA)/methylene blue/glibenclamide-sensitive manner. Histopathological signs of Wallerian degeneration (WD) of the sciatic nerve were also attenuated, as well as interleukin-1 beta release in the spinal cord. The nitrate/nitrite concentration was increased centrally and did not show differences at the peripheral nerve level. The findings of this study suggest JM-20 can decrease persistent pain. A transient activity of its BDZ portion on nociceptive pathways mediated by GABA/BDZ receptors in association with its anti-inflammatory properties could be at least partially involved in this effect. JM-20 decreased CCI-induced mechanical hypersensitivity via the l-arginine/nitric oxide (NO)/cyclic GMP-sensitive ATP-sensitive potassium channel pathway. Its neuroprotective ability by preventing WD could be implicated in its anti-neuropathic mechanisms.
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Affiliation(s)
- Bárbara B Garrido-Suárez
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba.
| | - Gabino Garrido
- Departamento de Ciencias Farmacéuticas, Facultad de Ciencias, Edificio Ñ3, Universidad Católica del Norte, Angamos, 0610, Antofagasta, Chile.
| | - Marian Castro-Labrada
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba
| | - Nelson Merino
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba
| | - Odalys Valdés
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba
| | - Zenia Pardo
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba
| | - Estael Ochoa-Rodríguez
- Laboratorio de Síntesis Orgánica de La Facultad de Química de La Universidad de La Habana, Zapata s/n entre G y Carlitos Aguirre, Vedado Plaza de la Revolución, CP, 10400, La Habana, Cuba
| | - Yamila Verdecia-Reyes
- Laboratorio de Síntesis Orgánica de La Facultad de Química de La Universidad de La Habana, Zapata s/n entre G y Carlitos Aguirre, Vedado Plaza de la Revolución, CP, 10400, La Habana, Cuba
| | - René Delgado-Hernández
- Centro de Investigación y Desarrollo de Medicamentos, Ave 26, No. 1605 Boyeros y Puentes Grandes, CP, 10600, La Habana, Cuba
| | - Jozi Godoy-Figueiredo
- Department of Pharmacology, Faculty of Medicine of Ribeirão Preto University of São Paulo, Avenida Bandeirantes, 3900, 14049-900, Ribeirão Preto, SP, Brazil
| | - Sergio H Ferreira
- Department of Pharmacology, Faculty of Medicine of Ribeirão Preto University of São Paulo, Avenida Bandeirantes, 3900, 14049-900, Ribeirão Preto, SP, Brazil
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Dehkordi FM, Kaboutari J, Zendehdel M, Javdani M. The antinociceptive effect of artemisinin on the inflammatory pain and role of GABAergic and opioidergic systems. Korean J Pain 2019; 32:160-167. [PMID: 31257824 PMCID: PMC6615442 DOI: 10.3344/kjp.2019.32.3.160] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2018] [Revised: 03/11/2019] [Accepted: 03/19/2019] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Pain is a complex mechanism which involves different systems, including the opioidergic and GABAergic systems. Due to the side effects of chemical analgesic agents, attention toward natural agents have been increased. Artemisinin is an herbal compound with widespread modern and traditional therapeutic indications, which its interaction with the GABAergic system and antinoniceptive effects on neuropathic pain have shown. Therefore, this study was designed to evaluate the antinociceptive effects of artemisinin during inflammatory pain and interaction with the GABAergic and opioidergic systems by using a writhing response test. METHODS On the whole, 198 adult male albino mice were used in 4 experiments, including 9 groups (n = 6) each with three replicates, by intraperitoneal (i.p.) administration of artemisinin (2.5, 5, and 10 mg/kg), naloxone (2 mg/kg), bicuculline (2 mg/kg), saclofen (2 mg/kg), indomethacin (5 mg/kg), and ethanol (10 mL/kg). Writhing test responses were induced by i.p. injection of 10 mL/kg of 0.6% acetic acid, and the percentage of writhing inhibition was recorded. RESULTS Results showed significant dose dependent anti-nociceptive effects from artemisinin which, at a 10 mg/kg dose, was statistically similar to indomethacin. Neither saclofen nor naloxone had antinociceptive effects and did not antagonize antinociceptive effects of artemisinin, whereas bicuculline significantly inhibited the antinocicptive effect of artemisinin. CONCLUSIONS It seems that antinocicptive effects of artemisinin are mediated by GABAA receptors.
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Affiliation(s)
- Faraz Mahdian Dehkordi
- Department of Basic Sciences, Faculty of Veterinary Medicine, Shahrekord University, Shahrekord,
Iran
| | - Jahangir Kaboutari
- Department of Basic Sciences, Faculty of Veterinary Medicine, Shahrekord University, Shahrekord,
Iran
| | - Morteza Zendehdel
- Department of Physiology, Faculty of Veterinary Medicine, University of Tehran, Tehran,
Iran
| | - Moosa Javdani
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Shahrekord University, Shahrekord,
Iran
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Sánchez-Brualla I, Boulenguez P, Brocard C, Liabeuf S, Viallat-Lieutaud A, Navarro X, Udina E, Brocard F. Activation of 5-HT 2A Receptors Restores KCC2 Function and Reduces Neuropathic Pain after Spinal Cord Injury. Neuroscience 2018; 387:48-57. [PMID: 28844001 DOI: 10.1016/j.neuroscience.2017.08.033] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Revised: 07/26/2017] [Accepted: 08/14/2017] [Indexed: 11/30/2022]
Abstract
Downregulation of the potassium chloride cotransporter type 2 (KCC2) after a spinal cord injury (SCI) disinhibits motoneurons and dorsal horn interneurons causing spasticity and neuropathic pain, respectively. We showed recently (Bos et al., 2013) that specific activation of 5-HT2A receptors by TCB-2 [(4-bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine hydrobromide] upregulates KCC2 function, restores motoneuronal inhibition and reduces SCI-induced spasticity. Here, we tested the potential analgesic effect of TCB-2 on central (thoracic hemisection) and peripheral [spared nerve injury (SNI)] neuropathic pain. We found mechanical and thermal hyperalgesia reduced by an acute administration of TCB-2 in rats with SCI. This analgesic effect was associated with an increase in dorsal horn membrane KCC2 expression and was prevented by pharmacological blockade of KCC2 with an intrathecal injection of DIOA [(dihydroindenyl)oxy]alkanoic acid]. In contrast, the SNI-induced neuropathic pain was not attenuated by TCB-2 although there was a slight increase of membrane KCC2 expression in the dorsal horn ipsilateral to the lesion. Up-regulation of KCC2 function by targeting 5-HT2A receptors, therefore, has therapeutic potential in the treatment of neuropathic pain induced by SCI but not by SNI.
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Affiliation(s)
- Irene Sánchez-Brualla
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France; Department of Cell Biology, Physiology, and Immunology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, Institute of Neurosciences, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Pascale Boulenguez
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Cécile Brocard
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Sylvie Liabeuf
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Annelise Viallat-Lieutaud
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France
| | - Xavier Navarro
- Department of Cell Biology, Physiology, and Immunology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, Institute of Neurosciences, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Esther Udina
- Department of Cell Biology, Physiology, and Immunology, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, Institute of Neurosciences, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Frédéric Brocard
- Team P3M, Institut de Neurosciences de la Timone, UMR7289, Aix Marseille Université and Centre National de la Recherche Scientifique (CNRS), Marseille, France.
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Divergent Modulation of Nociception by Glutamatergic and GABAergic Neuronal Subpopulations in the Periaqueductal Gray. eNeuro 2017; 4:eN-NWR-0129-16. [PMID: 28374016 PMCID: PMC5370278 DOI: 10.1523/eneuro.0129-16.2017] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 03/01/2017] [Accepted: 03/03/2017] [Indexed: 12/27/2022] Open
Abstract
The ventrolateral periaqueductal gray (vlPAG) constitutes a major descending pain modulatory system and is a crucial site for opioid-induced analgesia. A number of previous studies have demonstrated that glutamate and GABA play critical opposing roles in nociceptive processing in the vlPAG. It has been suggested that glutamatergic neurotransmission exerts antinociceptive effects, whereas GABAergic neurotransmission exert pronociceptive effects on pain transmission, through descending pathways. The inability to exclusively manipulate subpopulations of neurons in the PAG has prevented direct testing of this hypothesis. Here, we demonstrate the different contributions of genetically defined glutamatergic and GABAergic vlPAG neurons in nociceptive processing by employing cell type-specific chemogenetic approaches in mice. Global chemogenetic manipulation of vlPAG neuronal activity suggests that vlPAG neural circuits exert tonic suppression of nociception, consistent with previous pharmacological and electrophysiological studies. However, selective modulation of GABAergic or glutamatergic neurons demonstrates an inverse regulation of nociceptive behaviors by these cell populations. Selective chemogenetic activation of glutamatergic neurons, or inhibition of GABAergic neurons, in vlPAG suppresses nociception. In contrast, inhibition of glutamatergic neurons, or activation of GABAergic neurons, in vlPAG facilitates nociception. Our findings provide direct experimental support for a model in which excitatory and inhibitory neurons in the PAG bidirectionally modulate nociception.
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8
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Neuroligin 2 regulates spinal GABAergic plasticity in hyperalgesic priming, a model of the transition from acute to chronic pain. Pain 2017; 157:1314-1324. [PMID: 26859820 DOI: 10.1097/j.pain.0000000000000513] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Plasticity in inhibitory receptors, neurotransmission, and networks is an important mechanism for nociceptive signal amplification in the spinal dorsal horn. We studied potential changes in GABAergic pharmacology and its underlying mechanisms in hyperalgesic priming, a model of the transition from acute to chronic pain. We find that while GABAA agonists and positive allosteric modulators reduce mechanical hypersensitivity to an acute insult, they fail to do so during the maintenance phase of hyperalgesic priming. In contrast, GABAA antagonism promotes antinociception and a reduction in facial grimacing after the transition to a chronic pain state. During the maintenance phase of hyperalgesic priming, we observed increased neuroligin (nlgn) 2 expression in the spinal dorsal horn. This protein increase was associated with an increase in nlgn2A splice variant mRNA, which promotes inhibitory synaptogenesis. Disruption of nlgn2 function with the peptide inhibitor, neurolide 2, produced mechanical hypersensitivity in naive mice but reversed hyperalgesic priming in mice previously exposed to brain-derived neurotrophic factor. Neurolide 2 treatment also reverses the change in polarity in GABAergic pharmacology observed in the maintenance of hyperalgesic priming. We propose that increased nlgn2 expression is associated with hyperalgesic priming where it promotes dysregulation of inhibitory networks. Our observations reveal new mechanisms involved in the spinal maintenance of a pain plasticity and further suggest that disinhibitory mechanisms are central features of neuroplasticity in the spinal dorsal horn.
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9
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Xue M, Liu J, Yang Y, Suo Z, Yang X, Hu X. Inhibition of α5 subunit-containing GABAAreceptors facilitated spinal nociceptive transmission and plasticity. Eur J Pain 2017; 21:1061-1071. [DOI: 10.1002/ejp.1009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/12/2016] [Indexed: 01/09/2023]
Affiliation(s)
- M. Xue
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
| | - J.P. Liu
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
| | - Y.H. Yang
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
| | - Z.W. Suo
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
| | - X. Yang
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
| | - X.D. Hu
- Department of Molecular Pharmacology, School of Pharmacy; Lanzhou University; China
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10
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Hachisuka J, Baumbauer KM, Omori Y, Snyder LM, Koerber HR, Ross SE. Semi-intact ex vivo approach to investigate spinal somatosensory circuits. eLife 2016; 5:e22866. [PMID: 27991851 PMCID: PMC5214752 DOI: 10.7554/elife.22866] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 12/16/2016] [Indexed: 11/19/2022] Open
Abstract
The somatosensory input that gives rise to the perceptions of pain, itch, cold and heat are initially integrated in the superficial dorsal horn of the spinal cord. Here, we describe a new approach to investigate these neural circuits in mouse. This semi-intact somatosensory preparation enables recording from spinal output neurons, while precisely controlling somatosensory input, and simultaneously manipulating specific populations of spinal interneurons. Our findings suggest that spinal interneurons show distinct temporal and spatial tuning properties. We also show that modality selectivity - mechanical, heat and cold - can be assessed in both retrogradely labeled spinoparabrachial projection neurons and genetically labeled spinal interneurons. Finally, we demonstrate that interneuron connectivity can be determined via optogenetic activation of specific interneuron subtypes. This new approach may facilitate key conceptual advances in our understanding of the spinal somatosensory circuits in health and disease.
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Affiliation(s)
- Junichi Hachisuka
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
| | - Kyle M Baumbauer
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
| | - Yu Omori
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
| | - Lindsey M Snyder
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
| | - H Richard Koerber
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
| | - Sarah E Ross
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, United States
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, United States
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11
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Abstract
It has been recently proposed that α5-subunit containing GABAA receptors (α5-GABAA receptors) that mediate tonic inhibition might be involved in pain. The purpose of this study was to investigate the contribution of α5-GABAA receptors in the loss of GABAergic inhibition and in formalin-induced, complete Freund's adjuvant (CFA)-induced and L5 and L6 spinal nerve ligation-induced long-lasting hypersensitivity. Formalin or CFA injection and L5 and L6 spinal nerve ligation produced long-lasting allodynia and hyperalgesia. Moreover, formalin injection impaired the rate-dependent depression of the Hofmann reflex. Peripheral and intrathecal pretreatment or post-treatment with the α5-GABAA receptor antagonist, L-655,708 (0.15-15 nmol), prevented and reversed, respectively, these long-lasting behaviors. Formalin injection increased α5-GABAA receptor mRNA expression in the spinal cord and dorsal root ganglia (DRG) mainly at 3 days. The α5-GABAA receptors were localized in the dorsal spinal cord and DRG colabeling with NeuN, CGRP, and IB4 which suggests their presence in peptidergic and nonpeptidergic neurons. These receptors were found mainly in small and medium sized neurons. Formalin injection enhanced α5-GABAA receptor fluorescence intensity in spinal cord and DRG at 3 and 6 days. Intrathecal administration of L-655,708 (15 nmol) prevented and reversed formalin-induced impairment of rate-dependent depression. These results suggest that α5-GABAA receptors play a role in the loss of GABAergic inhibition and contribute to long-lasting secondary allodynia and hyperalgesia.
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12
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Lee KY, Prescott SA. Chloride dysregulation and inhibitory receptor blockade yield equivalent disinhibition of spinal neurons yet are differentially reversed by carbonic anhydrase blockade. Pain 2015; 156:2431-2437. [PMID: 26186265 DOI: 10.1097/j.pain.0000000000000301] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Synaptic inhibition plays a key role in processing somatosensory information. Blocking inhibition at the spinal level is sufficient to produce mechanical allodynia, and many neuropathic pain conditions are associated with reduced inhibition. Disinhibition of spinal neurons can arise through decreased GABAA/glycine receptor activation or through dysregulation of intracellular chloride. We hypothesized that these distinct disinhibitory mechanisms, despite all causing allodynia, are differentially susceptible to therapeutic intervention. Specifically, we predicted that reducing bicarbonate efflux by blocking carbonic anhydrase with acetazolamide (ACTZ) would counteract disinhibition caused by chloride dysregulation without affecting normal inhibition or disinhibition caused by GABAA/glycine receptor blockade. To test this, responses to innocuous tactile stimulation were recorded in vivo from rat superficial dorsal horn neurons before and after different forms of pharmacological disinhibition and again after application of ACTZ. Blocking GABAA or glycine receptors caused hyperresponsiveness equivalent to that caused by blocking the potassium chloride cotransporter KCC2, but, consistent with our predictions, only disinhibition caused by KCC2 blockade was counteracted by ACTZ. ACTZ did not alter responses of neurons with intact inhibition. As pathological downregulation of KCC2 is triggered by brain-derived neurotrophic factor, we also confirmed that ACTZ was effective against brain-derived neurotrophic factor-induced hyperresponsiveness. Our results argue that intrathecal ACTZ has antiallodynic effects only if allodynia arises through chloride dysregulation; therefore, behavioral evidence that ACTZ is antiallodynic in nerve-injured animals affirms the contribution of chloride dysregulation as a key pathological mechanism. Although different disinhibitory mechanisms are not mutually exclusive, these results demonstrate that their relative contribution dictates which specific therapies will be effective.
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Affiliation(s)
- Kwan Yeop Lee
- Neurosciences and Mental Health, The Hospital for Sick Children, Toronto, ON, Canada; Department of Physiology, University of Toronto, Toronto, ON, Canada
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13
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Nakamura Y, Morioka N, Zhang FF, Hisaoka-Nakashima K, Nakata Y. Downregulation of connexin36 in mouse spinal dorsal horn neurons leads to mechanical allodynia. J Neurosci Res 2015; 93:584-91. [PMID: 25400139 DOI: 10.1002/jnr.23515] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 09/24/2014] [Accepted: 10/13/2014] [Indexed: 11/08/2022]
Abstract
Connexin36 (Cx36), a component of neuronal gap junctions, is crucial for interneuronal communication and regulation. Gap junction dysfunction underlies neurological disorders, including chronic pain. Following a peripheral nerve injury, Cx36 expression in the ipsilateral spinal dorsal horn was markedly decreased over time, which paralleled the time course of hind paw tactile allodynia. Intrathecal (i.t.) injection of Cx36 siRNA (1 and 5 pg) significantly reduced the expression of Cx36 protein in the lumbar spinal cord, peaking 3 days after the injection, which corresponded with the onset of hind paw tactile allodynia. It is possible that some of the tactile allodynia resulting from Cx36 downregulation could be mediated through excitatory neuromodulators, such as glutamate and substance P. The Cx36 knockdown-evoked tactile allodynia was significantly attenuated by i.t. treatment with the N-methyl-D-aspartate glutamate receptor antagonist MK-801 but not the substance P receptor antagonist CP96345. Immunohistochemistry showed that Cx36 was colocalized with glycine transporter-2, a marker for inhibitory glycinergic spinal interneurons, but not with glutamate decarboxylase 67, a marker for inhibitory GABAergic spinal interneurons. The results indicate that spinal inhibition through glycinergic interneurons is reduced, leading to increased glutamatergic neurotransmission, as a result of Cx36 downregulation. The current data suggest that gap junction dysfunction underlies neuropathic pain and further suggest a novel target for the development of analgesics.
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Affiliation(s)
- Yoki Nakamura
- Department of Pharmacology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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14
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Synaptic Inhibition and Disinhibition in the Spinal Dorsal Horn. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 131:359-83. [DOI: 10.1016/bs.pmbts.2014.11.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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15
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Emerging role of WNK1 in pathologic central nervous system signaling. Ann Neurosci 2014; 18:70-5. [PMID: 25205925 PMCID: PMC4117038 DOI: 10.5214/ans.0972.7531.1118212] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 03/30/2011] [Accepted: 04/21/2011] [Indexed: 01/28/2023] Open
Abstract
WNK1 (with no lysine (K)) is a widely expressed serine/threonine protein kinase. The role of this kinase was first described in the kidney where it dynamically controls ion channels that regulate changes in cell volume. WNK1, through intermediates oxidative stress-responsive kinase-1 (OSR1) and STE20/SPS1-related proline/alanine-rich kinase (SPAK), phosphorylates the inwardly directed Na+-K+-Cl---cotransporter 1 (NKCC1) and the outwardly directed K+-Cl--cotransporter 2 (KCC2), activating and deactivating these channels, respectively. WNK1, NKCC1 and KCC2 are also expressed in the central nervous system (CNS). Growing evidence implicates WNK1 playing a critical role in pathologic nervous system signaling where changes in intracellular ion concentration in response to γ-aminobutyric-acid (GABA) can activate otherwise silent pathways. This review will focus on current research about WNK1, its downstream effectors and role in GABA signaling. Future perspectives include investigating WNK1 expression in the CNS after spinal cord injury (SCI), where altered neuronal signaling could underlie pathological states such as neuropathic pain (NP).
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16
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Guo D, Hu J. Spinal presynaptic inhibition in pain control. Neuroscience 2014; 283:95-106. [PMID: 25255936 DOI: 10.1016/j.neuroscience.2014.09.032] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 09/10/2014] [Accepted: 09/14/2014] [Indexed: 12/22/2022]
Abstract
The gate control theory proposed that the nociceptive sensory information transmitted to the brain relies on an interplay between the inputs from nociceptive and non-nociceptive primary afferent fibers. Both inputs are normally under strong inhibitory control in the spinal cord. Under healthy conditions, presynaptic inhibition activated by non-nociceptive fibers modulates the afferent input from nociceptive fibers onto spinal cord neurons, while postsynaptic inhibition controls the excitability of dorsal horn neurons, and silences the non-nociceptive information flow to nociceptive-specific (NS) projection neurons. However, under pathological conditions, this spinal inhibition may be altered and lead to chronic pain. This review summarizes our knowledge of presynaptic inhibition in pain control, with particular focus on how its alteration after nerve or tissue injury contributes to neuropathic or inflammatory pain syndromes, respectively.
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Affiliation(s)
- D Guo
- Centre for Integrative Neuroscience (CIN), Otfried-Mueller-Straße 25, 72076 Tuebingen, Germany
| | - J Hu
- Centre for Integrative Neuroscience (CIN), Otfried-Mueller-Straße 25, 72076 Tuebingen, Germany.
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17
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Ma X, Bao W, Wang X, Wang Z, Liu Q, Yao Z, Zhang D, Jiang H, Cui S. Role of spinal GABAA receptor reduction induced by stress in rat thermal hyperalgesia. Exp Brain Res 2014; 232:3413-20. [PMID: 24992900 DOI: 10.1007/s00221-014-4027-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Accepted: 06/19/2014] [Indexed: 12/30/2022]
Abstract
The mechanisms underlying stress-induced hyperalgesia (SIH) remain poorly understood. Recent findings have provided strong evidence indicating that SIH could be related, at least in part, to alterations in spinal cord GABA activity. In the present study, we first investigated how acute restraint stress impacted pain responses as assessed using the tail flick immersion test. These results showed that rats developed hyperalgesia at 6 h after being subjected to 1-h acute restraint stress. Second, we measured the activation of spinal neurons and alterations in expression of GABAA receptor β2 and β3 subunits as related to stress-induced hyperalgesia. Results from Western blot and immunofluorescence assays showed that c-fos protein increased in the dorsal horn of the lumbar spinal cord and GABAA receptor β2 and β3 subunit proteins decreased significantly at 6 h after exposure to 1 h of acute restraint stress. Finally, the effects of spinal GABAA receptor alteration on SIH were evaluated. These results showed that intrathecal administration of muscimol inhibited hyperalgesia induced by stress while bicuculline enhanced hyperalgesia in the control groups. Taken together, the present data reveal that GABAA receptor β2 and β3 decrease following 1 h of acute restraint stress and may play a critical role in SIH.
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Affiliation(s)
- Xuelian Ma
- Department of Physiology, School of Medicine, Shandong University, Jinan, 250012, People's Republic of China,
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18
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Evidence for the participation of peripheral α5 subunit-containing GABAA receptors in GABAA agonists-induced nociception in rats. Eur J Pharmacol 2014; 734:91-7. [DOI: 10.1016/j.ejphar.2014.03.051] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 03/11/2014] [Accepted: 03/22/2014] [Indexed: 11/17/2022]
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19
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Tan SN, Song E, Dong XD, Somvanshi RK, Cairns BE. Peripheral GABAA receptor activation modulates rat tongue afferent mechanical sensitivity. Arch Oral Biol 2014; 59:251-7. [DOI: 10.1016/j.archoralbio.2013.11.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Revised: 11/07/2013] [Accepted: 11/27/2013] [Indexed: 10/25/2022]
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20
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McCarson KE, Enna SJ. GABA pharmacology: the search for analgesics. Neurochem Res 2014; 39:1948-63. [PMID: 24532294 DOI: 10.1007/s11064-014-1254-x] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 01/28/2014] [Accepted: 01/31/2014] [Indexed: 12/28/2022]
Abstract
Decades of research have been devoted to defining the role of GABAergic transmission in nociceptive processing. Much of this work was performed using rigid, orthosteric GABA analogs created by Povl Krogsgaard-Larsen and his associates. A relationship between GABA and pain is suggested by the anatomical distribution of GABA receptors and the ability of some GABA agonists to alter nociceptive responsiveness. Outlined in this report are data supporting this proposition, with particular emphasis on the anatomical localization and function of GABA-containing neurons and the molecular and pharmacological properties of GABAA and GABAB receptor subtypes. Reference is made to changes in overall GABAergic tone, GABA receptor expression and activity as a function of the duration and intensity of a painful stimulus or exposure to GABAergic agents. Evidence is presented that the plasticity of this receptor system may be responsible for the variability in the antinociceptive effectiveness of compounds that influence GABA transmission. These findings demonstrate that at least some types of persistent pain are associated with a regionally selective decline in GABAergic tone, highlighting the need for agents that enhance GABA activity in the affected regions without compromising GABA function over the long-term. As subtype selective positive allosteric modulators may accomplish these goals, such compounds might represent a new class of analgesic drugs.
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Affiliation(s)
- Kenneth E McCarson
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Boulevard, Mail Stop 1018, Kansas City, KS, 66160, USA
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Zhu Y, Zhang XL, Gold MS. Activity-dependent hyperpolarization of EGABA is absent in cutaneous DRG neurons from inflamed rats. Neuroscience 2013; 256:1-9. [PMID: 24135545 DOI: 10.1016/j.neuroscience.2013.10.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 09/30/2013] [Accepted: 10/03/2013] [Indexed: 12/22/2022]
Abstract
A shift in GABA(A) signaling from inhibition to excitation in primary afferent neurons appears to contribute to the inflammation-induced increase in afferent input to the CNS. An activity-dependent depolarization of the GABA(A) current equilibrium potential (E(GABA)) has been described in CNS neurons which drives a shift in GABA(A) signaling from inhibition to excitation. The purpose of the present study was to determine if such an activity-dependent depolarization of E(GABA) occurs in primary afferents and whether the depolarization is amplified with persistent inflammation. Acutely dissociated retrogradely labeled cutaneous dorsal root ganglion (DRG) neurons from naïve and inflamed rats were studied with gramicidin perforated patch recording. Rather than a depolarization, 200 action potentials delivered at 2 Hz resulted in a ∼10 mV hyperpolarization of E(GABA) in cutaneous neurons from naïve rats. No such hyperpolarization was observed in neurons from inflamed rats. The shift in E(GABA) was not blocked by 10 μM bumetanide. Furthermore, because activity-dependent hyperpolarization of E(GABA) was fully manifest in the absence of HCO₃⁻ in the bath solution, this shift was not dependent on a change in HCO₃⁻-Cl⁻ exchanger activity, despite evidence of HCO₃⁻-Cl⁻ exchangers in DRG neurons that may contribute to the establishment of E(GABA) in the presence of HCO₃⁻. While the mechanism underlying the activity-dependent hyperpolarization of E(GABA) has yet to be identified, because this mechanism appears to function as a form of feedback inhibition, facilitating GABA-mediated inhibition of afferent activity, it may serve as a novel target for the treatment of inflammatory pain.
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Affiliation(s)
- Y Zhu
- Department of Neural and Pain Sciences, University of Maryland, Baltimore School of Dentistry, Baltimore, MD, USA; Department of Anesthesiology, Division of Gastroenterology Hepatology and Nutrition, University of Pittsburgh, Pittsburgh, PA, USA
| | - X-L Zhang
- Department of Anesthesiology, Division of Gastroenterology Hepatology and Nutrition, University of Pittsburgh, Pittsburgh, PA, USA; Department of Pharmacology and Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA
| | - M S Gold
- Department of Anesthesiology, Division of Gastroenterology Hepatology and Nutrition, University of Pittsburgh, Pittsburgh, PA, USA; Department of Neurobiology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, USA; Department of Medicine, Division of Gastroenterology Hepatology and Nutrition, University of Pittsburgh, Pittsburgh, PA, USA; Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA; Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, PA, USA.
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Tavares I. Human neural stem cell transplantation in spinal cord injury models: how far from clinical application? Stem Cell Res Ther 2013; 4:61. [PMID: 23768980 PMCID: PMC3706911 DOI: 10.1186/scrt210] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Injuries of the spinal cord trigger local healing but hardly restore normal function. Spinal cord injury (SCI) has been deeply studied to develop strategies for functional recovery. The study by van Gorp and colleagues uses a rat model of acute SCI to characterize the effects of intraspinal grafting of human fetal spinal cord-derived neural stem cells (HSSCs). Among the range of results obtained, several positive outcomes related to a GABA-mediated inhibition were achieved. Their interesting article is a clear step forward in elucidating the neurobiology of SCI. Some issues to consider are related to the efficacy of the cell therapy in chronic spinal lesions and to pain responses, since the latter is a common complaint of people with SCI. Furthermore, the GABA-mediated hypothesis of recovery of function upon HSSC transplant needs to be fully tested by interfering with GABA receptors and analyzing neurobiological mechanisms that may invert the inhibitory role of GABA. The future challenge for SCI work will be the translation of knowledge acquired in basic research into clinically applicable strategies. The study by van Gorp and colleagues is an important contribution to that future.
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van Gorp S, Leerink M, Kakinohana O, Platoshyn O, Santucci C, Galik J, Joosten EA, Hruska-Plochan M, Goldberg D, Marsala S, Johe K, Ciacci JD, Marsala M. Amelioration of motor/sensory dysfunction and spasticity in a rat model of acute lumbar spinal cord injury by human neural stem cell transplantation. Stem Cell Res Ther 2013; 4:57. [PMID: 23710605 PMCID: PMC3706882 DOI: 10.1186/scrt209] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 04/25/2013] [Indexed: 12/15/2022] Open
Abstract
Introduction Intraspinal grafting of human neural stem cells represents a promising approach to promote recovery of function after spinal trauma. Such a treatment may serve to: I) provide trophic support to improve survival of host neurons; II) improve the structural integrity of the spinal parenchyma by reducing syringomyelia and scarring in trauma-injured regions; and III) provide neuronal populations to potentially form relays with host axons, segmental interneurons, and/or α-motoneurons. Here we characterized the effect of intraspinal grafting of clinical grade human fetal spinal cord-derived neural stem cells (HSSC) on the recovery of neurological function in a rat model of acute lumbar (L3) compression injury. Methods Three-month-old female Sprague–Dawley rats received L3 spinal compression injury. Three days post-injury, animals were randomized and received intraspinal injections of either HSSC, media-only, or no injections. All animals were immunosuppressed with tacrolimus, mycophenolate mofetil, and methylprednisolone acetate from the day of cell grafting and survived for eight weeks. Motor and sensory dysfunction were periodically assessed using open field locomotion scoring, thermal/tactile pain/escape thresholds and myogenic motor evoked potentials. The presence of spasticity was measured by gastrocnemius muscle resistance and electromyography response during computer-controlled ankle rotation. At the end-point, gait (CatWalk), ladder climbing, and single frame analyses were also assessed. Syrinx size, spinal cord dimensions, and extent of scarring were measured by magnetic resonance imaging. Differentiation and integration of grafted cells in the host tissue were validated with immunofluorescence staining using human-specific antibodies. Results Intraspinal grafting of HSSC led to a progressive and significant improvement in lower extremity paw placement, amelioration of spasticity, and normalization in thermal and tactile pain/escape thresholds at eight weeks post-grafting. No significant differences were detected in other CatWalk parameters, motor evoked potentials, open field locomotor (Basso, Beattie, and Bresnahan locomotion score (BBB)) score or ladder climbing test. Magnetic resonance imaging volume reconstruction and immunofluorescence analysis of grafted cell survival showed near complete injury-cavity-filling by grafted cells and development of putative GABA-ergic synapses between grafted and host neurons. Conclusions Peri-acute intraspinal grafting of HSSC can represent an effective therapy which ameliorates motor and sensory deficits after traumatic spinal cord injury.
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Zhu Y, Lu S, Gold MS. Persistent inflammation increases GABA-induced depolarization of rat cutaneous dorsal root ganglion neurons in vitro. Neuroscience 2012; 220:330-40. [PMID: 22728089 PMCID: PMC3412885 DOI: 10.1016/j.neuroscience.2012.06.025] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2012] [Revised: 06/07/2012] [Accepted: 06/09/2012] [Indexed: 11/18/2022]
Abstract
Persistent inflammation is associated with a shift in spinal GABA(A) signaling from inhibition to excitation such that GABA(A)-receptor activation contributes to inflammatory hyperalgesia. We tested the hypothesis that the primary afferent is the site of the persistent inflammation-induced shift in GABA(A) signaling which is due to a Na(+)-K(+)-Cl(-)-co-transporter (NKCC1)-dependent depolarization of the GABA(A) current equilibrium potential (E(GABA)). Acutely dissociated retrogradely labeled cutaneous dorsal root ganglion (DRG) neurons from naïve and inflamed (3 days after a subcutaneous injection of complete Freund's adjuvant) adult male rats were studied with Ca(2+) imaging, western blot and gramicidin-perforated patch recording. GABA evoked a Ca(2+) transient in a subpopulation of small- to medium-diameter capsaicin-sensitive cutaneous neurons. Inflammation was associated with a significant increase in the magnitude of GABA-induced depolarization as well as the percentage of neurons in which GABA evoked a Ca(2+) transient. There was no detectable change in NKCC1 protein or phosphoprotein at the whole ganglia level. Furthermore, the increase in excitatory response was comparable in both HEPES- and HCO(3)(-)-buffered solutions, but was only associated with a depolarization of E(GABA) in HCO(3)(-)-based solution. In contrast, under both recording conditions, the excitatory response was associated with an increase in GABA(A) current density, a decrease in low threshold K(+) current density, and resting membrane potential depolarization. Our results suggest that increasing K(+) conductance in afferents innervating a site of persistent inflammation may have greater efficacy in the inhibition of inflammatory hyperalgesia than attempting to drive a hyperpolarizing shift in E(GABA).
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Affiliation(s)
- Yi Zhu
- Dept of Neural and Pain Sciences, University of Maryland, Baltimore School of Dentistry, Baltimore, Maryland
- Dept of Anesthesiology, University of Pittsburgh, Pittsburgh, USA
| | - Shaogang Lu
- Dept of Medicine (Division of Gastroenterology Hepatology and Nutrition), University of Pittsburgh, Pittsburgh, USA
| | - Michael S. Gold
- Dept of Anesthesiology, University of Pittsburgh, Pittsburgh, USA
- Dept of Neurobiology, University of Pittsburgh, Pittsburgh, USA
- Dept of Medicine (Division of Gastroenterology Hepatology and Nutrition), University of Pittsburgh, Pittsburgh, USA
- Center for Neuroscience at the University of Pittsburgh, Pittsburgh, USA
- Pittsburgh Center for Pain Research, University of Pittsburgh, Pittsburgh, USA
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25
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Zhu Y, Dua S, Gold MS. Inflammation-induced shift in spinal GABA(A) signaling is associated with a tyrosine kinase-dependent increase in GABA(A) current density in nociceptive afferents. J Neurophysiol 2012; 108:2581-93. [PMID: 22914654 DOI: 10.1152/jn.00590.2012] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
To account for benzodiazepine-induced spinal analgesia observed in association with an inflammation-induced shift in the influence of the GABA(A) receptor antagonist gabazine on nociceptive threshold, the present study was designed to determine whether persistent inflammation is associated with the upregulation of high-affinity GABA(A) receptors in primary afferents. The cell bodies of afferents innervating the glabrous skin of the rat hind paw were retrogradely labeled, acutely dissociated, and studied before and after the induction of persistent inflammation. A time-dependent increase in GABA(A) current density was observed that was more than twofold by 72 h after the initiation of inflammation. This increase in current density included both high- and low-affinity currents and was restricted to neurons in which GABA increased intracellular Ca(2+). No increases in GABA(A) receptor subunit mRNA or protein were detected in whole ganglia. In contrast, the increased current density was completely reversed by 20-min preincubation with the tyrosine kinase inhibitor genistein and partially reversed with the Src kinase inhibitor PP2. Genistein reversal was partially blocked by the dynamin inhibitor peptide P4. Changes in nociceptive threshold following spinal administration of genistein and muscimol to inflamed rats indicated that the pronociceptive actions of muscimol observed in the presence of inflammation were reversed by genistein. These results suggest that persistent changes in relative levels of tyrosine kinase activity following inflammation provide not only a sensitive way to dynamically regulate spinal nociceptive signaling but a viable target for the development of novel therapeutic interventions for the treatment of inflammatory pain.
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Affiliation(s)
- Yi Zhu
- Department of Neural and Pain Sciences, University of Maryland, Baltimore School of Dentistry, Baltimore, Maryland, USA
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Asiedu MN, Mejia G, Ossipov MK, Malan TP, Kaila K, Price TJ. Modulation of spinal GABAergic analgesia by inhibition of chloride extrusion capacity in mice. THE JOURNAL OF PAIN 2012; 13:546-54. [PMID: 22537560 PMCID: PMC3367103 DOI: 10.1016/j.jpain.2012.03.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Revised: 02/27/2012] [Accepted: 03/02/2012] [Indexed: 10/28/2022]
Abstract
UNLABELLED Spinal gamma-aminobutyric acid receptor type A (GABA(A)) receptor modulation with agonists and allosteric modulators evokes analgesia and antinociception. Changes in K(+)-Cl(-) cotransporter isoform 2 (KCC2) expression or function that occur after peripheral nerve injury can result in an impairment in the Cl(-) extrusion capacity of spinal dorsal horn neurons. This, in turn, alters Cl(-)-mediated hyperpolarization via GABA(A) receptor activation, contributing to allodynia or hypersensitivity associated with nerve injury or inflammation. A gap in knowledge exists concerning how this loss of spinal KCC2 activity differentially impacts the analgesic efficacy or potency of GABA(A) agonists and allosteric modulators. We utilized intrathecal drug administration in the tail flick assay to measure the analgesic effects of general GABA(A) agonists muscimol and Z-3-[(aminoiminomethyl)thio]prop-2-enoic acid (ZAPA), the ∂-subunit-preferring agonist 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP), and allosteric modulators of the benzodiazepine (midazolam) and neurosteroid (ganaxolone) class, alone or in the presence of K(+)-Cl(-) cotransporter isoform (KCC) blockade. Intrathecal muscimol, ZAPA, THIP midazolam, and ganaxolone all evoked significant analgesia in the tail flick test. Coadministration of either agonists or allosteric modulators with [(dihydroindenyl)oxy] alkanoic acid (DIOA) (a drug that blocks KCC2) had no effect on agonist or allosteric modulator potency. On the other hand, the analgesic efficacy of muscimol and ZAPA and the allosteric modulator ganaxolone were markedly reduced whereas THIP and midazolam were unaffected. Finally, in the spared nerve injury model, midazolam significantly reversed tactile hypersensitivity while ganaxolone had no effect. These results indicate that the KCC2-dependent Cl(-) extrusion capacity differentially regulates the analgesic efficacy of agonists and allosteric modulators at the GABA(A) receptor complex. PERSPECTIVE Our work suggests that drug discovery efforts for the treatment of chronic pain disorders should target benzodiazepine or ∂-subunit-containing sites at the GABA(A) complex.
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Affiliation(s)
- M. N. Asiedu
- Department of Pharmacology, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
| | - G. Mejia
- Department of Pharmacology, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
| | - M. K. Ossipov
- Department of Pharmacology, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
| | - T. P. Malan
- Department of Pharmacology, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
| | - K. Kaila
- Department of Biosciences, University of Helsinki, POB 65, Helsinki, FIN-00014, Finland
- Neuroscience Center, University of Helsinki, POB 65, Helsinki, FIN-00014, Finland
| | - T. J. Price
- Department of Pharmacology, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
- Bio5 Institute, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
- Graduate Interdisciplinary Program in Neuroscience, The University of Arizona School of Medicine, 1501 N Campbell Ave, Tucson, AZ, 85724, USA
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Zeilhofer HU, Benke D, Yevenes GE. Chronic pain states: pharmacological strategies to restore diminished inhibitory spinal pain control. Annu Rev Pharmacol Toxicol 2012; 52:111-33. [PMID: 21854227 DOI: 10.1146/annurev-pharmtox-010611-134636] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Potentially noxious stimuli are sensed by specialized nerve cells named nociceptors, which convey nociceptive signals from peripheral tissues to the central nervous system. The spinal dorsal horn and the trigeminal nucleus serve as first relay stations for incoming nociceptive signals. At these sites, nociceptor terminals contact a local neuronal network consisting of excitatory and inhibitory interneurons as well as of projection neurons. Blockade of neuronal inhibition in this network causes an increased sensitivity to noxious stimuli (hyperalgesia), painful sensations occurring after activation of non-nociceptive fibers (allodynia), and spontaneous pain felt in the absence of any sensory stimulation. It thus mimics the major characteristics of chronic pain states. Diminished inhibitory pain control in the spinal dorsal horn occurs naturally, e.g., through changes in the function of inhibitory neurotransmitter receptors or through altered chloride homeo-stasis in the course of inflammation or nerve damage. This review summarizes our current knowledge about endogenous mechanisms leading to diminished spinal pain control and discusses possible ways that could restore proper inhibition through facilitation of fast inhibitory neurotransmission.
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Affiliation(s)
- Hanns Ulrich Zeilhofer
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zurich, Switzerland.
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Lee KY, Gold MS. Inflammatory mediators potentiate high affinity GABA(A) currents in rat dorsal root ganglion neurons. Neurosci Lett 2012; 518:128-32. [PMID: 22580064 DOI: 10.1016/j.neulet.2012.04.068] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Accepted: 04/25/2012] [Indexed: 11/30/2022]
Abstract
Following acute tissue injury action potentials may be initiated in afferent processes terminating in the dorsal horn of the spinal cord that are propagated back out to the periphery, a process referred to as a dorsal root reflex (DRR). The DRR is dependent on the activation of GABA(A) receptors. The prevailing hypothesis is that DRR is due to a depolarizing shift in the chloride equilibrium potential (E(Cl)) following an injury-induced activation of the Na(+)-K(+)-Cl(-)-cotransporter. Because inflammatory mediators (IM), such as prostaglandin E(2) are also released in the spinal cord following tissue injury, as well as evidence that E(Cl) is already depolarized in primary afferents, an alternative hypothesis is that an IM-induced increase in GABA(A) receptor mediated current (I(GABA)) could underlie the injury-induced increase in DRR. To test this hypothesis, we explored the impact of IM (prostaglandin E(2) (1 μM), bradykinin (10 μM), and histamine (1 μM)) on I(GABA) in dissociated rat dorsal root ganglion (DRG) neurons with standard whole cell patch clamp techniques. IM potentiated I(GABA) in a subpopulation of medium to large diameter capsaicin insensitive DRG neurons. This effect was dependent on the concentration of GABA, manifest only at low concentrations (<10 μM). THIP evoked current were also potentiated by IM and GABA (1 μM) induced tonic currents enhanced by IM were resistant to gabazine (20 μM). The present data are consistent with the hypothesis that an acute increase in I(GABA) contributes to the emergence of injury-induced DRR.
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Affiliation(s)
- Kwan Yeop Lee
- Dept of Anesthesiology, University of Pittsburgh, Pittsburgh, PA 15213, USA
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Abstract
The hypothalamus is one of the master regulators of various physiological processes, including energy balance and nutrient metabolism. These regulatory functions are mediated by discrete hypothalamic regions that integrate metabolic sensing with neuroendocrine and neural controls of systemic physiology. Neurons and nonneuronal cells in these hypothalamic regions act supportively to execute metabolic regulations. Under conditions of brain and hypothalamic inflammation, which may result from overnutrition-induced intracellular stresses or disease-associated systemic inflammatory factors, extracellular and intracellular environments of hypothalamic cells are disrupted, leading to central metabolic dysregulations and various diseases. Recent research has begun to elucidate the effects of hypothalamic inflammation in causing diverse components of metabolic syndrome leading to diabetes and cardiovascular disease. These new understandings have provocatively expanded previous knowledge on the cachectic roles of brain inflammatory response in diseases, such as infections and cancers. This review describes the molecular and cellular characteristics of hypothalamic inflammation in metabolic syndrome and related diseases as opposed to cachectic diseases, and also discusses concepts and potential applications of inhibiting central/hypothalamic inflammation to treat nutritional diseases.
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Affiliation(s)
- Dongsheng Cai
- Department of Molecular Pharmacology, Diabetes Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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Zeilhofer HU, Wildner H, Yévenes GE. Fast synaptic inhibition in spinal sensory processing and pain control. Physiol Rev 2012; 92:193-235. [PMID: 22298656 DOI: 10.1152/physrev.00043.2010] [Citation(s) in RCA: 260] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The two amino acids GABA and glycine mediate fast inhibitory neurotransmission in different CNS areas and serve pivotal roles in the spinal sensory processing. Under healthy conditions, they limit the excitability of spinal terminals of primary sensory nerve fibers and of intrinsic dorsal horn neurons through pre- and postsynaptic mechanisms, and thereby facilitate the spatial and temporal discrimination of sensory stimuli. Removal of fast inhibition not only reduces the fidelity of normal sensory processing but also provokes symptoms very much reminiscent of pathological and chronic pain syndromes. This review summarizes our knowledge of the molecular bases of spinal inhibitory neurotransmission and its organization in dorsal horn sensory circuits. Particular emphasis is placed on the role and mechanisms of spinal inhibitory malfunction in inflammatory and neuropathic chronic pain syndromes.
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Lee KY, Charbonnet M, Gold MS. Upregulation of high-affinity GABA(A) receptors in cultured rat dorsal root ganglion neurons. Neuroscience 2012; 208:133-42. [PMID: 22366297 DOI: 10.1016/j.neuroscience.2012.01.050] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 01/27/2012] [Accepted: 01/31/2012] [Indexed: 10/14/2022]
Abstract
Despite evidence that high-affinity GABA(A) receptor subunit mRNA and protein are present in dorsal root ganglia (DRG), low-affinity currents dominate those detected in acutely dissociated DRG neurons in vitro. This observation raises the possibility that high-affinity receptors are normally trafficked out of the DRG toward central and peripheral terminals. We therefore hypothesized that with time in culture, there would be an increase in high-affinity GABA(A) currents in DRG neurons. To test this hypothesis, we studied dissociated DRG neurons 2 h (acute) and 24 h (cultured) after plating with whole-cell patch-clamp techniques, Western blot, and semiquantitative reverse transcriptase polymerase chain reaction (sqRT-PCR) analysis. GABA(A) current density increases dramatically with time in culture in association with the emergence of two persistent currents with EC50's of 0.25±0.01 μM and 3.2±0.02 μM for GABA activation. In a subpopulation of neurons, there was also an increase in the potency of GABA activation of the transient current from an EC50 of 78.16±10.1 μM to 9.56±1.3 μM with time in culture. A fraction of the high-affinity current was potentiated by δ-subunit agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol (THIP). δ-subunit immunoreactivity was largely restricted to the cytosolic fraction in acute, but the membrane fraction in cultured, DRG neurons, with no detectable change in δ-subunit mRNA. However, the emergence of a high-affinity current blocked by THIP and insensitive to bicuculline was detected in a subpopulation of cultured neurons as well in association with an increase in ρ2- and ρ3-subunit mRNA in cultured DRG neurons. Our results suggest that high-affinity δ-subunit-containing GABA(A) receptors are normally trafficked out of the DRG where they are targeted to peripheral and central processes. They also highlight that the interpretation of data obtained from cultured DRG neurons should be made with caution.
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Affiliation(s)
- K Y Lee
- Department of Anesthesiology, University of Pittsburgh, Pittsburgh, PA, USA
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Deleterious impact of a γ-aminobutyric acid type A receptor preferring general anesthetic when used in the presence of persistent inflammation. Anesthesiology 2011; 115:782-90. [PMID: 21841466 DOI: 10.1097/aln.0b013e318215e1cb] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND Experimental data suggest general anesthetics preferring γ-aminobutyric acid receptor type A may increase postoperative pain in patients with persistent inflammation. The current study was designed to begin to test this hypothesis. METHODS Groups of rats were defined by the presence of inflammation, surgical intervention, and/or the type of general anesthetic used for a 3-h period of anesthesia. Persistent inflammation was induced with complete Freund adjuvant. The surgical intervention was a plantar incision. Three mechanistically distinct general anesthetics were used: pentobarbital, ketamine/xylazine, and isoflurane. Ongoing pain and hypersensitivity were assessed with guarding behavior analysis and the von Frey test, respectively. RESULTS There was no influence of general anesthetic type on the magnitude or time course of recovery from postoperative hypersensitivity in the absence of persistent inflammation. However, in the presence of persistent inflammation, recovery from hypersensitivity was significantly slower in the pentobarbital group than in the ketamine/xylazine or isoflurane groups. The pentobarbital effect was significant within 3 days of surgery and persisted through the remainder of the testing period. A comparable delay in recovery was observed in pentobarbital-anesthetized inflamed rats not subjected to hind paw incision. The time to 50% recovery in the pentobarbital-treated inflamed groups was almost double that in the other groups. No differences were observed between ketamine/xylazine and isoflurane. Pentobarbital exposure did not increase guarding scores. CONCLUSIONS These results suggest that general anesthetics preferring γ-aminobutyric acid receptor type A may have deleterious consequences when used in the presence of persistent inflammation.
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HSV delivery of a ligand-regulated endogenous ion channel gene to sensory neurons results in pain control following channel activation. Mol Ther 2010; 19:500-6. [PMID: 21081904 DOI: 10.1038/mt.2010.246] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Persistent pain remains a tremendous health problem due to both its prevalence and dearth of effective therapeutic interventions. To maximize pain relief while minimizing side effects, current gene therapy-based approaches have mostly exploited the expression of pain inhibitory products or interfered with pronociceptive ion channels. These methods do not enable control over the timing or duration of analgesia, nor titration to analgesic efficacy. Here, we describe a gene therapy strategy that potentially overcomes these limitations by providing exquisite control over therapy with efficacy in clinically relevant models of inflammatory pain. We utilize a herpes simplex viral (HSV) vector (vHGlyRα1) to express a ligand-regulated chloride ion channel, the glycine receptor (GlyR) in targeted sensory afferents; the subsequent exogenous addition of glycine provides the means for temporal and spatial control of afferent activity, and therefore pain. Use of an endogenous inhibitory receptor not normally present on sensory neurons both minimizes immunogenicity and maximizes therapeutic selectivity.
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Spinal cord mechanisms mediating behavioral hyperalgesia induced by neurokinin-1 tachykinin receptor activation in the rostral ventromedial medulla. Neuroscience 2010; 171:1341-56. [PMID: 20888891 DOI: 10.1016/j.neuroscience.2010.09.040] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 08/24/2010] [Accepted: 09/22/2010] [Indexed: 11/23/2022]
Abstract
Hyperalgesia in animal injury models is linked to activation of descending raphespinal modulatory circuits originating in the rostral ventromedial medulla (RVM). A neurokinin-1 (NK-1) receptor antagonist microinjected into the RVM before or after inflammation produced by complete Freund's adjuvant (CFA) resulted in an attenuation of thermal hyperalgesia. A transient (acute) or a continuous infusion of Substance P (SP) microinjected into the RVM of non-inflamed animals led to similar pain hypersensitivity. Intrathecal pretreatment or post-treatment of a 5-HT3 receptor antagonist (Y-25130 or ondansetron) blocked the SP-induced hyperalgesia. The SP-induced hyperalgesia was both GABA(A) and NMDA receptor-dependent after pre- and post-treatment with selective antagonists at the spinal level. A microinjection of SP into the RVM also led to increased NMDA NR1 receptor subunit phosphorylation in spinal cord tissue. The GABA(A) receptor-mediated hyperalgesia involved a shift in the anionic gradient in dorsal horn nociceptive neurons and an increase in phosphorylated NKCC1 protein (isoform of the Na-K-Cl cotransporter). Following a low dose of SP infused into the RVM, intrathecal muscimol (GABA(A) agonist) increased SP-induced thermal hyperalgesia, phosphorylated NKCC1 protein expression, and NMDA NR1 subunit phosphorylation in the spinal cord. The thermal hyperalgesia was blocked by intrathecal gabazine, the GABA(A) receptor antagonist, and MK-801, the NMDA receptor channel blocker. These findings indicate that NK-1 receptors in the RVM are involved in SP-induced thermal hyperalgesia, this hyperalgesia is 5-HT3-receptor dependent at the spinal level, and involves the functional interaction of spinal GABA(A) and NMDA receptors.
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Asiedu M, Ossipov MH, Kaila K, Price TJ. Acetazolamide and midazolam act synergistically to inhibit neuropathic pain. Pain 2009; 148:302-308. [PMID: 20007010 DOI: 10.1016/j.pain.2009.11.015] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Revised: 11/03/2009] [Accepted: 11/13/2009] [Indexed: 01/27/2023]
Abstract
Treatment of neuropathic pain is a major clinical challenge that has been met with minimal success. After peripheral nerve injury, a decrease in the expression of the K-Cl cotransporter KCC2, a major neuronal Cl(-) extruder, leads to pathologic alterations in GABA(A) and glycine receptor function in the spinal cord. The down-regulation of KCC2 is expected to cause a reduction in Cl(-) extrusion capacity in dorsal horn neurons, which, together with the depolarizing efflux of HCO(3)(-) anions via GABA(A) channels, would result in a decrease in the efficacy of GABA(A)-mediated inhibition. Carbonic anhydrases (CA) facilitate intracellular HCO(3)(-) generation and hence, we hypothesized that inhibition of CAs would enhance the efficacy of GABAergic inhibition in the context of neuropathic pain. Despite the decrease in KCC2 expression, spinal administration of benzodiazepines has been shown to be anti-allodynic in neuropathic conditions. Thus, we also hypothesized that spinal inhibition of CAs might enhance the anti-allodynic effects of spinally administered benzodiazepines. Here, we show that inhibition of spinal CA activity with acetazolamide (ACT) reduces neuropathic allodynia. Moreover, we demonstrate that spinal co-administration of ACT and midazolam (MZL) act synergistically to reduce neuropathic allodynia after peripheral nerve injury. These findings indicate that the combined use of CA inhibitors and benzodiazepines may be effective in the clinical management of neuropathic pain in humans.
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Affiliation(s)
- Marina Asiedu
- The University of Arizona School of Medicine, Department of Pharmacology, 1501 N Campbell Ave., Tucson, AZ 85724, USA University of Helsinki, Department of Biosciences and Neuroscience Center, PO Box 65, Helsinki FIN-00014, Finland
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Hernstadt H, Wang S, Lim G, Mao J. Spinal translocator protein (TSPO) modulates pain behavior in rats with CFA-induced monoarthritis. Brain Res 2009; 1286:42-52. [PMID: 19555675 DOI: 10.1016/j.brainres.2009.06.043] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2009] [Revised: 06/12/2009] [Accepted: 06/15/2009] [Indexed: 12/20/2022]
Abstract
Translocator protein 18 kDa (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), is predominantly located in the mitochondrial outer membrane and plays an important role in steroidogenesis, immunomodulation, cell survival and proliferation. Previous studies have shown an increased expression of TSPO centrally in neuropathology, as well as in injured nerves. TSPO has also been implicated in modulation of nociception. In the present study, we examined the hypothesis that TSPO is involved in the initiation and maintenance of inflammatory pain using a rat model of Complete Freund's Adjuvant (CFA)-induced monoarthritis of the tibio-tarsal joint. Immunohistochemistry was performed using Iba-1 (microglia), NeuN (neurons), anti-Glial Fibrillary Acidic Protein, GFAP (astrocytes) and anti-PBR (TSPO) on Days 1, 7 and 14 after CFA-induced arthritis. Rats with CFA-induced monoarthritis showed mechanical allodynia and thermal hyperalgesia on the ipsilateral hindpaw, which correlated with the increased TSPO expression in ipsilateral laminae I-II on all experimental days. Iba-1 expression in the ipsilateral dorsal horn was also increased on Days 7 and 14. Moreover, TSPO was colocalized with Iba-1, GFAP and NeuN within the spinal cord dorsal horn. The TSPO agonist Ro5-4864, given intrathecally, dose-dependently retarded or prevented the development of mechanical allodynia and thermal hyperalgesia in rats with CFA-induced monoarthritis. These findings provide evidence that spinal TSPO is involved in the development and maintenance of inflammatory pain behaviors in rats. Thus, spinal TSPO may present a central target as a complementary therapy to reduce inflammatory pain.
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Affiliation(s)
- Hayley Hernstadt
- Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Victoria 3010, Australia
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Abstract
Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.
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Affiliation(s)
- Jürgen Sandkühler
- Department of Neurophysiology, Center for Brain Research, Medical University of Vienna, Vienna, Austria
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Price TJ, Cervero F, Gold MS, Hammond DL, Prescott SA. Chloride regulation in the pain pathway. BRAIN RESEARCH REVIEWS 2009; 60:149-70. [PMID: 19167425 PMCID: PMC2903433 DOI: 10.1016/j.brainresrev.2008.12.015] [Citation(s) in RCA: 191] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 12/29/2008] [Indexed: 12/18/2022]
Abstract
Melzack and Wall's Gate Control Theory of Pain laid the theoretical groundwork for a role of spinal inhibition in endogenous pain control. While the Gate Control Theory was based on the notion that spinal inhibition is dynamically regulated, mechanisms underlying the regulation of inhibition have turned out to be far more complex than Melzack and Wall could have ever imagined. Recent evidence indicates that an exquisitely sensitive form of regulation involves changes in anion equilibrium potential (E(anion)), which subsequently impacts fast synaptic inhibition mediated by GABA(A), and to a lesser extent, glycine receptor activation, the prototypic ligand gated anion channels. The cation-chloride co-transporters (in particular NKCC1 and KCC2) have emerged as proteins that play a critical role in the dynamic regulation of E(anion) which in turn appears to play a critical role in hyperalgesia and allodynia following peripheral inflammation or nerve injury. This review summarizes the current state of knowledge in this area with particular attention to how such findings relate to endogenous mechanisms of hyperalgesia and allodynia and potential applications for therapeutics based on modulation of intracellular Cl(-) gradients or pharmacological interventions targeting GABA(A) receptors.
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Affiliation(s)
| | - Fernando Cervero
- McGill University, Department of Anesthesia, McGill Centre for Research on Pain,
| | | | - Donna L Hammond
- University of Iowa, Department of Anesthesia, Department of Pharmacology,
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Knabl J, Zeilhofer UB, Crestani F, Rudolph U, Zeilhofer HU. Genuine antihyperalgesia by systemic diazepam revealed by experiments in GABAA receptor point-mutated mice. Pain 2009; 141:233-238. [DOI: 10.1016/j.pain.2008.10.015] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2008] [Revised: 09/08/2008] [Accepted: 10/20/2008] [Indexed: 11/28/2022]
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