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King SN, Hurley J, Carter Z, Bonomo N, Wang B, Dunlap N, Petruska J. Swallowing dysfunction following radiation to the rat mylohyoid muscle is associated with sensory neuron injury. J Appl Physiol (1985) 2021; 130:1274-1285. [PMID: 33600281 DOI: 10.1152/japplphysiol.00664.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Radiation-based treatments for oropharyngeal and hypopharyngeal cancers result in impairments in swallowing mobility, but the mechanisms behind the dysfunction are not clear. The purpose of this study was to determine if we could establish an animal model of radiation-induced dysphagia in which mechanisms could be examined. We hypothesized that 1) radiation focused at the depth of the mylohyoid muscle would alter normal bolus transport and bolus size and 2) radiation to the mylohyoid muscle will induce an injury/stress-like response in trigeminal sensory neurons whose input might modulate swallow. Rats were exposed to 48 or 64 Gy of radiation to the mylohyoid given 8 Gy in 6 or 8 fractions. Swallowing function was evaluated by videofluoroscopy 2 and 4 wk following treatment. Neuronal injury/stress was analyzed in trigeminal ganglion by assessing activating transcription factor (ATF)3 and GAP-43 mRNAs at 2, 4, and 8 wk post treatment. Irradiated rats exhibited decreases in bolus movement through the pharynx and alterations in bolus clearance. In addition, ATF3 and GAP-43 mRNAs were upregulated in trigeminal ganglion in irradiated rats, suggesting that radiation to mylohyoid muscle induced an injury/stress response in neurons with cell bodies that are remote from the irradiated tissue. These results suggest that radiation-induced dysphagia can be assessed in the rat and radiation induces injury/stress-like responses in sensory neurons.NEW & NOTEWORTHY Radiation-based treatments for head and neck cancer can cause significant impairments in swallowing mobility. This study provides new evidence supporting the possibility of a neural contribution to the mechanisms of swallowing dysfunction in postradiation dysphagia. Our data demonstrated that radiation to the mylohyoid muscle, which induces functional deficits in swallowing, also provokes an injury/stress-like response in the ganglion, innervating the irradiated muscle.
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Affiliation(s)
- Suzanne N King
- Department of Otolaryngology-Head and Neck Surgery and Communicative Disorders, University of Louisville, Louisville, Kentucky
| | - Justin Hurley
- Department of Radiation Oncology, University of Louisville, Louisville, Kentucky
| | - Zachary Carter
- Department of Radiation Oncology, University of Louisville, Louisville, Kentucky
| | - Nicholas Bonomo
- School of Medicine, University of Louisville, Louisville, Kentucky
| | - Brian Wang
- Department of Radiation Oncology, University of Louisville, Louisville, Kentucky.,Department of Therapeutic Radiology, Yale School of Medicine, New Haven, Connecticut
| | - Neal Dunlap
- Department of Radiation Oncology, University of Louisville, Louisville, Kentucky
| | - Jeffrey Petruska
- Department of Anatomical Sciences & Neurobiology, University of Louisville, Louisville, Kentucky.,Kentucky Spinal Cord Injury Research Center, Department of Neurological Surgery, University of Louisville, Louisville, Kentucky
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Watase T, Shimizu K, Ohara K, Komiya H, Kanno K, Hatori K, Noma N, Honda K, Tsuboi Y, Katagiri A, Shinoda M, Ogiso B, Iwata K. Role of medullary astroglial glutamine synthesis in tooth pulp hypersensitivity associated with frequent masseter muscle contraction. Mol Pain 2018; 14:1744806918763270. [PMID: 29448913 PMCID: PMC5858619 DOI: 10.1177/1744806918763270] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Background The mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle hyperalgesia remain largely underinvestigated. In the present study, we aimed to determine whether masseter muscle contraction induced by daily electrical stimulation influences the mechanical head-withdrawal threshold and genioglossus electromyography activity caused by the application of capsaicin to the upper first molar tooth pulp. We further investigated whether astroglial glutamine synthesis is involved in first molar tooth pulp hypersensitivity associated with masseter muscle contraction. Methods The first molar tooth pulp was treated with capsaicin or vehicle in masseter muscle contraction or sham rats, following which the astroglial glutamine synthetase inhibitor methionine sulfoximine or Phosphate buffered saline (PBS) was applied. Astroglial activation was assessed via immunohistochemistry. Results The mechanical head-withdrawal threshold of the ipsilateral masseter muscle was significantly decreased in masseter muscle contraction rats than in sham rats. Genioglossus electromyography activity was significantly higher in masseter muscle contraction rats than sham rats. Glial fibrillary acidic protein-immunoreactive cell density was significantly higher in masseter muscle contraction rats than in sham rats. Administration of methionine sulfoximine induced no significant changes in the density of glial fibrillary acidic protein-immunoreactive cells relative to PBS treatment. However, mechanical head-withdrawal threshold was significantly higher in masseter muscle contraction rats than PBS-treated rats after methionine sulfoximine administration. Genioglossus electromyography activity following first molar tooth pulp capsaicin treatment was significantly lower in methionine sulfoximine-treated rats than in PBS-treated rats. In the ipsilateral region, the total number of phosphorylated extracellular signal-regulated protein kinase immunoreactive cells in the medullary dorsal horn was significantly smaller upon first molar tooth pulp capsaicin application in methionine sulfoximine-treated rats than in PBS-treated rats. Conclusions Our results suggest that masseter muscle contraction induces astroglial activation, and that this activation spreads from caudal to the obex in the medullary dorsal horn, resulting in enhanced neuronal excitability associated with astroglial glutamine synthesis in medullary dorsal horn neurons receiving inputs from the tooth pulp. These findings provide significant insight into the mechanisms underlying tooth pulp hypersensitivity associated with masseter muscle contraction.
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Affiliation(s)
- Tetsuro Watase
- Department of Anatomy, Nihon University School of Dentistry, Japan
- Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Japan
| | - Kohei Shimizu
- Department of Endodontics, Nihon University School of Dentistry, Japan
- Division of Advanced Dental Treatment, Dental Research Center, Nihon University School of Dentistry, Japan
- Kohei Shimizu, Department of Endodontics, Nihon University School of Dentistry, 1-8-13 Kandasurugadai, Chiyoda-ku, Tokyo 101-8310, Japan.
| | - Kinuyo Ohara
- Department of Endodontics, Nihon University School of Dentistry, Japan
| | - Hiroki Komiya
- Department of Endodontics, Nihon University School of Dentistry, Japan
| | - Kohei Kanno
- Department of Endodontics, Nihon University School of Dentistry, Japan
| | - Keisuke Hatori
- Department of Endodontics, Nihon University School of Dentistry, Japan
- Division of Advanced Dental Treatment, Dental Research Center, Nihon University School of Dentistry, Japan
| | - Noboru Noma
- Department of Oral Diagnostic Sciences, Nihon University School of Dentistry, Japan
- Division of Clinical Research, Dental Research Center, Nihon University School of Dentistry, Japan
| | - Kuniya Honda
- Department of Physiology, Nihon University School of Dentistry, Japan
| | - Yoshiyuki Tsuboi
- Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Japan
- Department of Physiology, Nihon University School of Dentistry, Japan
| | - Ayano Katagiri
- Department of Oral Physiology, Osaka University Graduate School of Dentistry
| | - Masamichi Shinoda
- Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Japan
- Department of Physiology, Nihon University School of Dentistry, Japan
| | - Bunnai Ogiso
- Department of Endodontics, Nihon University School of Dentistry, Japan
- Division of Advanced Dental Treatment, Dental Research Center, Nihon University School of Dentistry, Japan
| | - Koichi Iwata
- Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, Japan
- Department of Physiology, Nihon University School of Dentistry, Japan
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Takeishi R, Magara J, Watanabe M, Tsujimura T, Hayashi H, Hori K, Inoue M. Effects of pharyngeal electrical stimulation on swallowing performance. PLoS One 2018; 13:e0190608. [PMID: 29293640 PMCID: PMC5749827 DOI: 10.1371/journal.pone.0190608] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 12/18/2017] [Indexed: 11/19/2022] Open
Abstract
Pharyngeal electrical stimulation (PEStim) has been found to facilitate voluntary swallowing. This study investigated how PEStim contributed to modulation of swallowing function in 15 healthy humans. In the involuntary swallowing test, water was injected onto the pharynx at 0.05 ml/s and the onset latency of the first swallow was measured. In the voluntary swallowing test, subjects swallowed their own saliva as quickly as possible for 30 s and the number of swallows was counted. Voluntary and involuntary swallowing was evaluated before (baseline), immediately after, and every 10 min after 10-min PEStim for 60 min. A voluntary swallowing test with simultaneous 30-s PEStim was also conducted before and 60 min after 10-min PEStim. The number of voluntary swallows with simultaneous PEStim significantly increased over 60 min after 10-min PEStim compared with the baseline. The onset latency of the first swallow in the involuntary swallowing test was not affected by 10-min PEStim. The results suggest that PEStim may have a long-term facilitatory effect on the initiation of voluntary swallowing in healthy humans, but not on peripherally-evoked swallowing. The physiological implications of this modulation are discussed.
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Affiliation(s)
- Ryosuke Takeishi
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Jin Magara
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Masahiro Watanabe
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Takanori Tsujimura
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Hirokazu Hayashi
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Kazuhiro Hori
- Division of Comprehensive Prosthodontics, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
| | - Makoto Inoue
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, 2–5274 Gakkocho-dori, Chuo-ku, Niigata, Japan
- * E-mail:
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Toyama M, Kudo C, Mukai C, Inoue M, Oyamaguchi A, Hanamoto H, Sugimura M, Niwa H. Trigeminal nervous system sensitization by infraorbital nerve injury enhances responses in a migraine model. Cephalalgia 2016; 37:1317-1328. [DOI: 10.1177/0333102416678387] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background Although the peripheral and central sensitizations of trigeminal nervous system may be one of the important factors of migraine, the precise mechanism is not fully understood. In this study, we examined the influence of the sensitization of the second division of the trigeminal nerve (V2) by chronic constriction injury (CCI) of the infraorbital nerve (ION) on migraine headache, using the capsaicin-induced migraine model. Methods Male Sprague-Dawley rats were assigned to four groups: (a) sham surgery and topical-dural vehicle application (Sham + Vehicle) group, (b) CCI-ION and topical-dural vehicle application (CCI-ION + Vehicle) group, (c) sham surgery and topical-dural capsaicin application (Sham + Capsaicin) group, (d) CCI-ION and topical-dural capsaicin application (CCI-ION + Capsaicin) group. Behavioral testing and immunohistochemical staining were performed. Results In the behavioral test, the Sham + Capsaicin group showed significantly longer duration of immobilization and shorter duration of exploration compared with the Sham + Vehicle group, which is similar to clinical features of migraine patients. Moreover, CCI-ION enhanced these effects in the CCI-ION + Capsaicin group. Immunohistochemical staining for phospho-extracellular signal-related kinase (pERK) in the trigeminal ganglion (TG) containing first and second divisions of the trigeminal nerve and the trigeminocervical complex (TCC) revealed that pERK expression was significantly increased in the CCI-ION + Capsaicin group compared with the other groups. However, comparing between effects of the peripheral and central sensitizations (in the TG and TCC), from our results, peripheral sensitization would play a much less or not significant role. Conclusions These data demonstrate that the sensitization of V2 could influence the activation and the sensitization of the first division of the trigeminal nerve in the TCC, subsequently exacerbating pain sensation and pain-related behaviors. We have shown for the first time that the existence of the central sensitization of V2 can be an exacerbating factor for migraine related nociceptive thresholds/activation.
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Affiliation(s)
- Midori Toyama
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Chiho Kudo
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Chikako Mukai
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Mika Inoue
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Aiko Oyamaguchi
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hiroshi Hanamoto
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Mitsutaka Sugimura
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Hitoshi Niwa
- Department of Dental Anesthesiology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan
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Nakaya Y, Tsuboi Y, Okada-Ogawa A, Shinoda M, Kubo A, Chen JY, Noma N, Batbold D, Imamura Y, Sessle BJ, Iwata K. ERK-GluR1 phosphorylation in trigeminal spinal subnucleus caudalis neurons is involved in pain associated with dry tongue. Mol Pain 2016; 12:12/0/1744806916641680. [PMID: 27118769 PMCID: PMC4956393 DOI: 10.1177/1744806916641680] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2015] [Accepted: 02/03/2016] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Dry mouth is known to cause severe pain in the intraoral structures, and many dry mouth patients have been suffering from intraoral pain. In development of an appropriate treatment, it is crucial to study the mechanisms underlying intraoral pain associated with dry mouth, yet the detailed mechanisms are not fully understood. To evaluate the mechanisms underlying pain related to dry mouth, the dry-tongue rat model was developed. Hence, the mechanical or heat nocifensive reflex, the phosphorylated extracellular signal-regulated kinase and phosphorylated GluR1-IR immunohistochemistries, and the single neuronal activity were examined in the trigeminal spinal subnucleus caudalis of dry-tongue rats. RESULTS The head-withdrawal reflex threshold to mechanical, but not heat, stimulation of the tongue was significantly decreased on day 7 after tongue drying. The mechanical, but not heat, responses of trigeminal spinal subnucleus caudalis nociceptive neurons were significantly enhanced in dry-tongue rats compared to sham rats on day 7. The number of phosphorylated extracellular signal-regulated kinase-immunoreactive cells was also significantly increased in the trigeminal spinal subnucleus caudalis following noxious stimulation of the tongue in dry-tongue rats compared to sham rats on day 7. The decrement of the mechanical head-withdrawal reflex threshold (HWT) was reversed during intracisternal administration of the mitogen-activated protein kinase kinase 1 inhibitor, PD98059. The trigeminal spinal subnucleus caudalis neuronal activities and the number of phosphorylated extracellular signal-regulated kinase-immunoreactive cells following noxious mechanical stimulation of dried tongue were also significantly decreased following intracisternal administration of PD98059 compared to vehicle-administrated rats. Increased number of the phosphorylated GluR1-IR cells was observed in the trigeminal spinal subnucleus caudalis of dry-tongue rats, and the number of phosphorylated GluR1-IR cells was significantly reduced in PD98059-administrated rats compared to the vehicle-administrated tongue-dry rats. CONCLUSIONS These findings suggest that the pERK-pGluR1 cascade is involved in central sensitization of trigeminal spinal subnucleus caudalis nociceptive neurons, thus resulting in tongue mechanical hyperalgesia associated with tongue drying.
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Affiliation(s)
- Yuka Nakaya
- Department of Oral Diagnostic Sciences, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Yoshiyuki Tsuboi
- Department of Physiology, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Akiko Okada-Ogawa
- Department of Oral Diagnostic Sciences, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Masamichi Shinoda
- Department of Physiology, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Asako Kubo
- Department of Physiology, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Jui Yen Chen
- Department of Physiology, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Noboru Noma
- Department of Oral Diagnostic Sciences, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Dulguun Batbold
- Department of Maxillofacial Surgery, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
| | - Yoshiki Imamura
- Department of Oral Diagnostic Sciences, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
| | - Barry J Sessle
- Department of Oral Physiology, Faculty of Dentistry, University of Toronto, Toronto, Canada
| | - Koichi Iwata
- Department of Physiology, Nihon University School of Dentistry, Chiyoda-ku, Tokyo, Japan
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Tsujimura T, Tsuji K, Magara J, Sakai S, Suzuki T, Nakamura Y, Nozawa-Inoue K, Inoue M. Differential response properties of peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats. Brain Res Bull 2016; 122:12-8. [PMID: 26899586 DOI: 10.1016/j.brainresbull.2016.02.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2015] [Revised: 12/24/2015] [Accepted: 02/15/2016] [Indexed: 12/01/2022]
Abstract
We compared onset latency, motor-response patterns, and the effect of electrical stimulation of the cortical masticatory area between peripherally and cortically evoked swallows by electrical stimulation in anesthetized rats. The number of swallows and the motor patterns were determined using electromyographic recordings from the thyrohyoid, digastric, and masseter muscles. The onset latency of the first swallow evoked by electrical stimulation of the cortical swallowing area (Cx) was significantly longer than that evoked by stimulation of the superior laryngeal nerve (SLN). The duration of thyrohyoid burst activity associated with SLN-evoked swallows was significantly longer than that associated with either Cx-evoked or spontaneous swallows. Combining Cx with SLN stimulation increased the number of swallows at low levels of SLN stimulation. Finally, A-area (the orofacial motor cortex) stimulation inhibited Cx-evoked swallows significantly more than it inhibited SLN-evoked swallows. These findings suggest that peripherally and cortically evoked swallows have different response properties and are affected differently by the mastication network.
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Affiliation(s)
- Takanori Tsujimura
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan.
| | - Kojun Tsuji
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Jin Magara
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Shogo Sakai
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Taku Suzuki
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Yuki Nakamura
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Kayoko Nozawa-Inoue
- Division of Oral Anatomy, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
| | - Makoto Inoue
- Division of Dysphagia Rehabilitation, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata 951-8514, Japan
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Gondim FDAA, Thomas FP. Generalized somatic dysesthesias induced by stimulation of teeth with cold water: an unreported form of brainstem integrative synesthesia. J Neurol Sci 2014; 346:360-1. [PMID: 25224386 DOI: 10.1016/j.jns.2014.09.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Revised: 08/30/2014] [Accepted: 09/02/2014] [Indexed: 10/24/2022]
Affiliation(s)
| | - Florian P Thomas
- Department of Neurology & Psychiatry, St. Louis University, St. Louis, MO, USA
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Metabotropic glutamate receptor 5 contributes to inflammatory tongue pain via extracellular signal-regulated kinase signaling in the trigeminal spinal subnucleus caudalis and upper cervical spinal cord. J Neuroinflammation 2012. [PMID: 23181395 PMCID: PMC3543209 DOI: 10.1186/1742-2094-9-258] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Background In the orofacial region, limited information is available concerning pathological tongue pain, such as inflammatory pain or neuropathic pain occurring in the tongue. Here, we tried for the first time to establish a novel animal model of inflammatory tongue pain in rats and to investigate the roles of metabotropic glutamate receptor 5 (mGluR5)-extracellular signal-regulated kinase (ERK) signaling in this process. Methods Complete Freund’s adjuvant (CFA) was submucosally injected into the tongue to induce the inflammatory pain phenotype that was confirmed by behavioral testing. Expression of phosphorylated ERK (pERK) and mGluR5 in the trigeminal subnucleus caudalis (Vc) and upper cervical spinal cord (C1-C2) were detected with immunohistochemical staining and Western blotting. pERK inhibitor, a selective mGluR5 antagonist or agonist was continuously administered for 7 days via an intrathecal (i.t.) route. Local inflammatory responses were verified by tongue histology. Results Submucosal injection of CFA into the tongue produced a long-lasting mechanical allodynia and heat hyperalgesia at the inflamed site, concomitant with an increase in the pERK immunoreactivity in the Vc and C1-C2. The distribution of pERK-IR cells was laminar specific, ipsilaterally dominant, somatotopically relevant, and rostrocaudally restricted. Western blot analysis also showed an enhanced activation of ERK in the Vc and C1-C2 following CFA injection. Continuous i.t. administration of the pERK inhibitor and a selective mGluR5 antagonist significantly depressed the mechanical allodynia and heat hyperalgesia in the CFA-injected tongue. In addition, the number of pERK-IR cells in ipsilateral Vc and C1-C2 was also decreased by both drugs. Moreover, continuous i.t. administration of a selective mGluR5 agonist induced mechanical allodynia in naive rats. Conclusions The present study constructed a new animal model of inflammatory tongue pain in rodents, and demonstrated pivotal roles of the mGluR5-pERK signaling in the development of mechanical and heat hypersensitivity that evolved in the inflamed tongue. This tongue-inflamed model might be useful for future studies to further elucidate molecular and cellular mechanisms of pathological tongue pain such as burning mouth syndrome.
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Hitomi S, Shinoda M, Suzuki I, Iwata K. Involvement of transient receptor potential vanilloid 1 in ectopic pain following inferior alveolar nerve transection in rats. Neurosci Lett 2012; 513:95-9. [PMID: 22366261 DOI: 10.1016/j.neulet.2012.02.018] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 02/07/2012] [Accepted: 02/07/2012] [Indexed: 12/13/2022]
Abstract
Chronic pain often develops in the orofacial region after inferior alveolar nerve (IAN) injury. In animal models IAN injury often causes severe neuropathic pain-like behavior in the IAN-innervated region as well as the adjacent region that includes the whisker pad skin. However, the basis for the spreading of pain to adjacent facial areas after IAN injury is still unknown. In this study we determined if the transient receptor potential vanilloid 1 (TRPV1) was associated with altered nocifensive behavior evoked by stimulation of the whisker pad skin following IAN transection. Grooming behavior after capsaicin injection into the whisker pad region was significantly increased after IAN transection and the increase in the behavior was reversed by systemic administration of a TRPV1 antagonist. The number of phosphorylated extracellular signal-regulated kinase immunoreactive (IR) neurons in trigeminal spinal subnucleus caudalis and upper cervical spinal cord following capsaicin injection into the whisker pad region was significantly greater in IAN-transected rats than sham-operated rats. The number of TRPV1-IR trigeminal ganglion (TG) neurons innervating the whisker pad skin was also increased significantly after IAN transection. The present findings suggest that an increase in TRPV1 expression in TG neurons innervating the whisker pad skin after IAN transection may underlie the spreading of pain to the adjacent whisker pad skin.
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Affiliation(s)
- Suzuro Hitomi
- Department of Biosciences, Kyushu Dental College, 2-6-1 Manazuru, Kitakyushu, Fukuoka 803-8580, Japan
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