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Chen Y, Chen L, Ji T, Yu Y, Zhang T, Wang L. The purinergic receptor P2X3 promotes facial pain by activating neurons and cytokines in the trigeminal ganglion. Int Immunopharmacol 2024; 130:111801. [PMID: 38442578 DOI: 10.1016/j.intimp.2024.111801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Revised: 02/18/2024] [Accepted: 03/02/2024] [Indexed: 03/07/2024]
Abstract
The mechanism underlying allodynia/hyperalgesia caused by dental pulpitis has remained enigmatic. This investigation endeavored to characterize the influence of the purinergic receptor P2X3 on pain caused by experimental pulpitis and the mechanism involved. An experimental model of irreversible pulpitis was produced by the drilling and exposure of the dental pulp of the left upper first and second molars in rats, followed by measuring nociceptive responses in the oral and maxillofacial regions. Subsequently, neuronal activity and the expression of P2X3 and pertinent cytokines in the trigeminal ganglion (TG) were meticulously examined and analyzed. Histological evidence corroborated that significant pulpitis was produced in this model, which led to a distinct escalation in nociceptive responses in rats. The activation of neurons, coupled with the upregulated expression of c-fos, P2X3, p-p38, TNF-α and IL-1β, was identified subsequent to the pulpitis surgery within the TG. The selective inhibition of P2X3 with A-317491 effectively restrained the abnormal allodynia/hyperalgesia following the pulpitis surgery and concurrently inhibited the upregulation of p-p38, TNF-α and IL-1β within the TG. These findings suggest that the P2X3 signaling pathway plays a pivotal role in instigating and perpetuating pain subsequent to the induction of pulpitis in rats, implicating its association with the p38 MAPK signaling pathway and inflammatory factors.
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Affiliation(s)
- Yangxi Chen
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Emergency and General Dentistry, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Liangyu Chen
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Tuo Ji
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Yuan Yu
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Tiejun Zhang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China
| | - Li Wang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China; Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, People's Republic of China.
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Ronan EA, Nagel M, Emrick JJ. The anatomy, neurophysiology, and cellular mechanisms of intradental sensation. FRONTIERS IN PAIN RESEARCH 2024; 5:1376564. [PMID: 38590718 PMCID: PMC11000636 DOI: 10.3389/fpain.2024.1376564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2024] [Accepted: 03/11/2024] [Indexed: 04/10/2024] Open
Abstract
Somatosensory innervation of the oral cavity enables the detection of a range of environmental stimuli including minute and noxious mechanical forces. The trigeminal sensory neurons underlie sensation originating from the tooth. Prior work has provided important physiological and molecular characterization of dental pulp sensory innervation. Clinical dental experiences have informed our conception of the consequence of activating these neurons. However, the biological role of sensory innervation within the tooth is yet to be defined. Recent transcriptomic data, combined with mouse genetic tools, have the capacity to provide important cell-type resolution for the physiological and behavioral function of pulp-innervating sensory neurons. Importantly, these tools can be applied to determine the neuronal origin of acute dental pain that coincides with tooth damage as well as pain stemming from tissue inflammation (i.e., pulpitis) toward developing treatment strategies aimed at relieving these distinct forms of pain.
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Affiliation(s)
- Elizabeth A. Ronan
- Department of Biologic and Materials Sciences & Prosthodontics, School of Dentistry, University of Michigan, Ann Arbor, MI, United States
| | - Maximilian Nagel
- Sensory Cells and Circuits Section, National Center for Complementary and Integrative Health, Bethesda, MD, United States
| | - Joshua J. Emrick
- Department of Biologic and Materials Sciences & Prosthodontics, School of Dentistry, University of Michigan, Ann Arbor, MI, United States
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Chen Y, Hu J, Qi F, Kang Y, Zhang T, Wang L. Acute pulpitis promotes purinergic signaling to induce pain in rats via P38MAPK/NF-κB signaling pathway. Mol Pain 2024; 20:17448069241234451. [PMID: 38325814 PMCID: PMC10868473 DOI: 10.1177/17448069241234451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2023] [Revised: 01/01/2024] [Accepted: 02/01/2024] [Indexed: 02/09/2024] Open
Abstract
Toothache is one of the most common types of pain, but the mechanisms underlying pulpitis-induced pain remain unknown. The ionotropic purinergic receptor family (P2X) is reported to mediate nociception in the nervous system. This study aims to investigate the involvement of P2X3 in the sensitisation of the trigeminal ganglion (TG) and the inflammation caused by acute pulpitis. An acute tooth inflammation model was established by applying LPS to the pulp of SD rats. We found that the increased expression of P2X3 was induced by acute pulpitis. A selective P2X3 inhibitor (A-317491) reduced pain-like behavior in the maxillofacial region of rats and depressed the activation of neurons in the trigeminal ganglion induced by pulpitis. The upregulated MAPK signaling (p-p38, p-ERK1/2) expression in the ipsilateral TG induced by pulpitis could also be depressed by the application of the P2X3 inhibitor. Furthermore, the expression of markers of inflammatory processes, such as NF-κB, TNF-α and IL-1β, could be induced by acute pulpitis and deduced by the intraperitoneal injection of P2X3 antagonists. Our findings demonstrate that purinergic P2X3 receptor signaling in TG neurons contributes to pulpitis-induced pain in rats and that P2X3 signaling may be a potential therapeutic target for tooth pain.
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Affiliation(s)
- Yangxi Chen
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Emergency and General Dentistry, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Jun Hu
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Emergency and General Dentistry, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Fang Qi
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Yiqun Kang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Tiejun Zhang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, China
| | - Li Wang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, Key Laboratory of Oral Biomedicine Ministry of Education, Hubei Key Laboratory of Stomatology, School & Hospital of Stomatology, Wuhan University, Wuhan, China
- Department of Anesthesiology, School and Hospital of Stomatology, Wuhan University, Wuhan, China
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Neural Regulations in Tooth Development and Tooth-Periodontium Complex Homeostasis: A Literature Review. Int J Mol Sci 2022; 23:ijms232214150. [PMID: 36430624 PMCID: PMC9698398 DOI: 10.3390/ijms232214150] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Revised: 11/10/2022] [Accepted: 11/14/2022] [Indexed: 11/19/2022] Open
Abstract
The tooth-periodontium complex and its nerves have active reciprocal regulation during development and homeostasis. These effects are predominantly mediated by a range of molecules secreted from either the nervous system or the tooth-periodontium complex. Different strategies mimicking tooth development or physiological reparation have been applied to tooth regeneration studies, where the application of these nerve- or tooth-derived molecules has been proven effective. However, to date, basic studies in this field leave many vacancies to be filled. This literature review summarizes the recent advances in the basic studies on neural responses and regulation during tooth-periodontium development and homeostasis and points out some research gaps to instruct future studies. Deepening our understanding of the underlying mechanisms of tooth development and diseases will provide more clues for tooth regeneration.
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Shang Y, Li Y, Yang Z, Zhou Z. Upregulation of TACAN in the trigeminal ganglion affects pain transduction in acute pulpitis. Arch Oral Biol 2022; 143:105530. [PMID: 36088852 DOI: 10.1016/j.archoralbio.2022.105530] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 07/28/2022] [Accepted: 08/23/2022] [Indexed: 11/02/2022]
Abstract
OBJECTIVE Acute pulpitis is one of the common causes of tooth pain. TACAN (Tmem120a) is a newly identified ion channel that senses mechanical pain. In this experiment, we studied the expression of the TACAN ion channel in the trigeminal ganglia in a rat model of pulpitis to explore the correlation between the expression of this ion channel and inflammatory pain. DESIGN Lipopolysaccharide was used to induce acute pulpitis in rats, and pulpitis was assessed histologically. The facial pain threshold of the rats was measured by the von Frey test. TACAN mRNA expression in rat dental pulp and the trigeminal nerve was measured by qPCR, and TACAN protein expression in the trigeminal ganglia was evaluated by western blot analysis and immunofluorescence. Antisense oligonucleotides were used to reduce TACAN protein expression in the trigeminal ganglia, and the change in the pain threshold in the rats with acute pulpitis was determined. RESULTS The results showed that the TACAN transcript level in rat pulp tissue increased under inflammatory conditions, and we proved that pulpitis increased TACAN protein expression in the rat ipsilateral trigeminal ganglia. The facial pain threshold was decreased in rats with pulpitis. A short-term decrease in TACAN protein expression could improve the pain threshold. CONCLUSIONS With the development of pulpitis after bacterial infection, the upregulation of TACAN expression in the trigeminal ganglia promoted pain sensitivity. A short-term reduction in TACAN expression relieved pain. Therefore, this study indicated that TACAN is a potential target channel for new analgesics.
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Affiliation(s)
- Yicong Shang
- College of Stomatology, Chongqing Medical University, Chongqing, China; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China; Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Yueheng Li
- College of Stomatology, Chongqing Medical University, Chongqing, China; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China; Chongqing Municipal Key Laboratory of Oral Biomedical Engineering of Higher Education, Chongqing, China
| | - Zhengyan Yang
- College of Stomatology, Chongqing Medical University, Chongqing, China; Chongqing Key Laboratory of Oral Diseases and Biomedical Sciences, Chongqing, China.
| | - Zhi Zhou
- College of Stomatology, Chongqing Medical University, Chongqing, China.
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Chalazias A, Plemmenos G, Evangeliou E, Piperi C. Pivotal role of Transient Receptor Potential Channels in oral physiology. Curr Med Chem 2021; 29:1408-1425. [PMID: 34365940 DOI: 10.2174/0929867328666210806113132] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 06/08/2021] [Accepted: 06/11/2021] [Indexed: 11/22/2022]
Abstract
BACKGROUND Transient Receptor Potential (TRP) Channels constitute a large family of non-selective permeable ion channels involved in the perception of environmental stimuli with a central and continuously expanding role in oral tissue homeostasis. Recent studies indicate the regulatory role of TRPs in pulp physiology, oral mucosa sensation, dental pain nociception and salivary gland secretion. This review provides an update on the diverse functions of TRP channels in the physiology of oral cavity, with emphasis on their cellular location, the underlying molecular mechanisms and clinical significance. METHODS A structured search of bibliographic databases (PubMed and MEDLINE) was performed for peer reviewed studies on TRP channels function on oral cavity physiology the last ten years. A qualitative content analysis was performed in screened papers and a critical discussion of main findings is provided. RESULTS TRPs expression has been detected in major cell types of the oral cavity, including odontoblasts, periodontal ligament, oral epithelial, salivary gland cells, and chondrocytes of temporomandibular joints, where they mediate signal perception and transduction of mechanical, thermal, and osmotic stimuli. They contribute to pulp physiology through dentin formation, mineralization, and periodontal ligament formation along with alveolar bone remodeling in dental pulp and periodontal ligament cells. TRPs are also involved in oral mucosa sensation, dental pain nociception, saliva secretion, swallowing reflex and temporomandibular joints' development. CONCLUSION Various TRP channels regulate oral cavity homeostasis, playing an important role in the transduction of external stimuli to intracellular signals in a cell type-specific manner and presenting promising drug targets for the development of pharmacological strategies to manage oral diseases.
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Affiliation(s)
- Andreas Chalazias
- School of Dentistry, National and Kapodistrian University of Athens, 2 Thivon Str, Goudi, 115 27 Athens. Greece
| | - Grigorios Plemmenos
- School of Dentistry, National and Kapodistrian University of Athens, 2 Thivon Str, Goudi, 115 27 Athens. Greece
| | - Evangelos Evangeliou
- School of Dentistry, National and Kapodistrian University of Athens, 2 Thivon Str, Goudi, 115 27 Athens. Greece
| | - Christina Piperi
- School of Dentistry, National and Kapodistrian University of Athens, 2 Thivon Str, Goudi, 115 27 Athens. Greece
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7
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Transient Receptor Potential (TRP) Ion Channels in Orofacial Pain. Mol Neurobiol 2021; 58:2836-2850. [PMID: 33515176 DOI: 10.1007/s12035-021-02284-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2020] [Accepted: 01/05/2021] [Indexed: 02/07/2023]
Abstract
Orofacial pain, including temporomandibular joint disorders pain, trigeminal neuralgia, dental pain, and debilitating headaches, affects millions of Americans each year with significant population health impact. Despite the existence of a large body of information on the subject, the molecular underpinnings of orofacial pain remain elusive. Two decades of research has identified that transient receptor potential (TRP) ion channels play a crucial role in pathological pain. A number of TRP ion channels are clearly expressed in the trigeminal sensory system and have critical functions in the transduction and pathogenesis of orofacial pain. Although there are many similarities, the orofacial sensory system shows some distinct peripheral and central pain processing and different sensitivities from the spinal sensory system. Relative to the extensive review on TRPs in spinally-mediated pain, the summary of TRPs in trigeminally-mediated pain has not been well-documented. This review focuses on the current experimental evidence involving TRP ion channels, particularly TRPV1, TRPA1, TRPV4, and TRPM8 in orofacial pain, and discusses their possible cellular and molecular mechanisms.
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8
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Allison JR, Stone SJ, Pigg M. The painful tooth: mechanisms, presentation and differential diagnosis of odontogenic pain. ACTA ACUST UNITED AC 2020. [DOI: 10.1111/ors.12481] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- J. R. Allison
- School of Dental Sciences Faculty of Medical Sciences Newcastle University Newcastle upon Tyne UK
| | - S. J. Stone
- School of Dental Sciences Faculty of Medical Sciences Newcastle University Newcastle upon Tyne UK
| | - M. Pigg
- Department of Endodontics Faculty of Odontology Scandinavian Centre for Orofacial Neurosciences (SCON) Malmö University Malmö Sweden
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Souza Monteiro de Araujo D, Nassini R, Geppetti P, De Logu F. TRPA1 as a therapeutic target for nociceptive pain. Expert Opin Ther Targets 2020; 24:997-1008. [PMID: 32838583 PMCID: PMC7610834 DOI: 10.1080/14728222.2020.1815191] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Introduction Chronic pain affects approximatively 30–50% of the population globally. Pathologies such as migraine, diabetic neuropathy, nerve injury and treatment with chemotherapeutic agents, can induce chronic pain. Members of the transient receptor potential (TRP) channels, including the TRP ankyrin 1 (TRPA1), have a major role in pain. Areas covered We focus on TRPA1 as a therapeutic target for pain relief. The structure, localization, and activation of the channel and its implication in different pathways to signal pain are described. This paper underlines the role of pharmacological interventions on TRPA1 to reduce pain in numerous pain conditions. We conducted a literature search in PubMed up to and including July 2020. Expert opinion Our understanding of the molecular mechanisms underlying the sensitization of central and peripheral nociceptive pathways is limited. Preclinical evidence indicates that, in murine models of pain diseases, numerous mechanisms converge on the pathway that encompasses oxidative stress and Schwann cell TRPA1 to sustain chronic pain. Programs to identify and develop treatments to attenuate TRPA1-mediated chronic pain have emerged from this knowledge. Antagonists explored as a novel class of analgesics have a new and promising target in the TRPA1 expressed by peripheral glial cells.
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Affiliation(s)
| | - Romina Nassini
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence , Florence, Italy
| | - Pierangelo Geppetti
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence , Florence, Italy
| | - Francesco De Logu
- Department of Health Sciences, Clinical Pharmacology Unit, University of Florence , Florence, Italy
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Emrick JJ, von Buchholtz LJ, Ryba NJP. Transcriptomic Classification of Neurons Innervating Teeth. J Dent Res 2020; 99:1478-1485. [PMID: 32702253 DOI: 10.1177/0022034520941837] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Toothache is a common painful consequence of damage to the teeth, particularly when coupled to infection. Clinical restoration of tooth integrity, sometimes involving physical and chemical sterilization of the tooth with nerve fiber ablation (i.e., endodontic therapy), generally alleviates pain and allows long-lasting dental function. These observations raise questions regarding the biological role of tooth-innervating fibers. Here, we determined the transcriptomic diversity of the sensory neurons that can be retrogradely labeled from mouse molar teeth. Our results demonstrate that individual molars are each targeted by a dedicated population of about 50 specialized trigeminal neurons. Transcriptomic profiling identifies the majority of these as expressing markers of fast-conducting neurons, with about two-thirds containing nociceptive markers. Our data provide a new view of dental innervation, extending previous reports that used candidate gene approaches. Importantly, almost all retrogradely labeled neurons, including nociceptors, express the recently characterized mechanosensor Piezo2, an ion channel that endows cells with sensitivity to gentle touch. Intriguingly, about a quarter of the labeled neurons do not appear to be nociceptors, perhaps insinuating a role for them in discriminative touch. We hypothesize that dental neurons are capable of providing mechanosensitive information to drive rapid behavioral responses and protect teeth from damage. Damage to the teeth and exposure of the large population of molar nociceptors may trigger prolonged or abnormal activation driving toothache. Future studies examining the responses of these transcriptomically defined classes of neurons will help define their significance in oral sensation.
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Affiliation(s)
- J J Emrick
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
| | - L J von Buchholtz
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
| | - N J P Ryba
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
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Lee BM, Lee C, Lahiji SF, Jung UW, Chung G, Jung H. Dissolving Microneedles for Rapid and Painless Local Anesthesia. Pharmaceutics 2020; 12:pharmaceutics12040366. [PMID: 32316406 PMCID: PMC7238259 DOI: 10.3390/pharmaceutics12040366] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2020] [Revised: 04/13/2020] [Accepted: 04/15/2020] [Indexed: 12/29/2022] Open
Abstract
Microneedles are emerging drug delivery methods for painless treatment. The current study tested dissolving microneedles containing lidocaine (Li-DMN) for use in local anesthesia. An Li-DMN patch was fabricated by centrifugal lithography with carboxymethyl cellulose as a structural polymer and assessed for physical properties by optical microscopy and a fracture force analyzer. The biocompatibility was evaluated by a histology section in vitro and by ear thickness in vivo. The efficacy of the Li-DMN patch was assessed by electrophysiological recordings in primary cultured sensory neurons in vitro and a von Frey test on rats’ hind paws in vivo. The physical properties of the microneedle showed enough rigidity for transdermal penetration. The maximal capacity of lidocaine-HCl in the Li-DMN patch was 331.20 ± 6.30 µg. The cytotoxicity of the dissolving microneedle to neuronal cells was negligible under an effective dose of lidocaine for 18 h. Electrophysiological recordings verified the inhibitory effect of the voltage-gated sodium channel current by the Li-DMN patch in vitro. A skin reaction to the edema test and histologic analysis of the rats’ ears after application of the Li-DMN patch were negligible. Also, the application of the Li-DMN patch reduced the nocifensive behavior of the rats almost immediately. In conclusion, the dissolving microneedle patch with carboxymethyl cellulose is a promising candidate method for the painless delivery of lidocaine-HCl.
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Affiliation(s)
- Byeong-Min Lee
- Department of Oral Physiology and Program in Neurobiology, School of Dentistry, Seoul National University, Seoul 08826, Korea
- Dental Research Institute, Seoul National University, Seoul 08826, Korea
| | - Chisong Lee
- Department of Biotechnology, Building 123, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
| | - Shayan Fakhraei Lahiji
- Department of Biotechnology, Building 123, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
| | - Ui-Won Jung
- Department of Periodontology, Research Institute for Periodontal Regeneration, Yonsei University College of Dentistry, Seoul 03722, Korea
| | - Gehoon Chung
- Department of Oral Physiology and Program in Neurobiology, School of Dentistry, Seoul National University, Seoul 08826, Korea
- Dental Research Institute, Seoul National University, Seoul 08826, Korea
- Correspondence: (G.C.); (H.J.); Tel.: +82-2-880-2332 (G.C.); +82-2-2123-2884 (H.J.); Fax: +82-2-762-5107 (G.C.); +82-2-362-7265 (H.J.)
| | - Hyungil Jung
- Department of Biotechnology, Building 123, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea
- Juvic Biotech, Inc., No. 208, Digital-ro 272, Guro-gu, Seoul 08389, Korea
- Correspondence: (G.C.); (H.J.); Tel.: +82-2-880-2332 (G.C.); +82-2-2123-2884 (H.J.); Fax: +82-2-762-5107 (G.C.); +82-2-362-7265 (H.J.)
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12
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Morii A, Miyamura Y, Sago MI, Mizuhara M, Shikayama T, Naniwa M, Hitomi S, Ujihara I, Kuroishi KN, Gunjigake KK, Shiga M, Morimoto Y, Kawamoto T, Ono K. Orthodontic force-induced oxidative stress in the periodontal tissue and dental pulp elicits nociception via activation/sensitization of TRPA1 on nociceptive fibers. Free Radic Biol Med 2020; 147:175-186. [PMID: 31866360 DOI: 10.1016/j.freeradbiomed.2019.12.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 12/11/2019] [Accepted: 12/16/2019] [Indexed: 11/18/2022]
Abstract
Orthodontic patients complain of pain for the first few days after insertion of appliances. Mechanical force has been reported to produce oxidants in periodontal ligament (PDL) cells. It has not been studied whether orthodontic force-induced oxidative stress elicits nociception. Herein, we focused on the role of the oxidant-sensitive channel TRPA1 on nociception in orthodontic pain. In a rat model of loaded orthodontic force between the maxillary first molar and incisor, the behavioral signs of orofacial nociception, facial rubbing and wiping, increased to a peak on day 1 and gradually diminished to the control level on day 5. Administration of free radical scavengers (Tempol and PBN) and TRPA1 antagonist (HC-030031) inhibited nociceptive behaviors on day 1. In the PDL, the oxidative stress marker 8-OHdG was highly detected on day 1 and recovered on day 5 to the sham-operated level. The dental pulp showed similar results as the PDL. TRPA1 mRNA was abundantly expressed in the trigeminal ganglion relative to PDL tissue, and there were TRPA1-immunopositive neuronal fibers in the PDL and pulp. In dissociated trigeminal ganglion neurons, H2O2 at 5 mM induced a Ca2+ response that was inhibited by HC-030031. Although H2O2 at 100 μM did not yield any response, it enhanced the mechanically activated TRPA1-dependent Ca2+ response. These results suggest that oxidative stress in the PDL and dental pulp following orthodontic force activates and/or mechanically sensitizes TRPA1 on nociceptive fibers, resulting in orthodontic nociception. Later, the disappearance of nociception seems to be related to a decrease in oxidative stress, probably due to tissue remodeling.
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Affiliation(s)
- Aoi Morii
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan; Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Yuichi Miyamura
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan; Division of Oral and Maxillofacial Radiology, Kyushu Dental University, Fukuoka, Japan
| | - Misa I Sago
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Masahiro Mizuhara
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Takemi Shikayama
- Division of Periodontology, Kyushu Dental University, Fukuoka, Japan
| | - Mako Naniwa
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan
| | - Suzuro Hitomi
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan
| | - Izumi Ujihara
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan
| | - Kayoko N Kuroishi
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Kaori K Gunjigake
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Momotoshi Shiga
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Yasuhiro Morimoto
- Division of Oral and Maxillofacial Radiology, Kyushu Dental University, Fukuoka, Japan
| | - Tatsuo Kawamoto
- Division of Orofacial Functions and Orthodontics, Kyushu Dental University, Fukuoka, Japan
| | - Kentaro Ono
- Division of Physiology, Kyushu Dental University, Fukuoka, Japan.
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13
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Lee PR, Lee JY, Kim HB, Lee JH, Oh SB. TRPM8 Mediates Hyperosmotic Stimuli-Induced Nociception in Dental Afferents. J Dent Res 2019; 99:107-114. [PMID: 31718465 DOI: 10.1177/0022034519886847] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Hyperosmolar sweet foods onto exposed tooth dentin evoke sudden and intense dental pain, called dentin hypersensitivity. However, it remains unclear how hyperosmolar stimuli excite dental primary afferent (DPA) neurons and thereby lead to dentin hypersensitivity. This study elucidated whether TRPM8, which is well known as a cold temperature- or menthol-activated receptor, additionally mediates nociception in response to hyperosmolar stimuli in adult mouse DPA neurons, which are identified by a fluorescent retrograde tracer: DiI. Single-cell reverse transcription polymerase chain reaction revealed that TRPM8 was expressed in subsets of DPA neurons and that TRPM8 was highly colocalized with TRPV1 and Piezo2. Immunohistochemical analysis also confirmed TRPM8 expression in DPA neurons. By using Fura-2-based calcium imaging, application of hyperosmolar sucrose solutions elicited calcium transients in subsets of the trigeminal ganglion neurons, which was significantly abolished by a selective TRPM8 antagonist: N-(3-Aminopropyl)-2-[(3-methylphenyl)methoxy]-N-(2-thienylmethyl)benzamide (AMTB) hydrochloride. When we further examined changes of c-fos expression (a neuronal activation marker) in the spinal trigeminal nucleus after hyperosmolar stimulation onto exposed tooth dentin, c-fos mRNA and protein expression were increased and were also significantly reduced by AMTB, especially in the spinal trigeminal interpolaris-caudalis transition zone (Vi/Vc). Taken together, our results provide strong evidence that TRPM8 expressed in DPA neurons might mediate dental pain as a hyperosmosensor in adult mice.
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Affiliation(s)
- P R Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - J Y Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - H B Kim
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - J H Lee
- Dental Research Institute and Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
| | - S B Oh
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea.,Dental Research Institute and Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
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14
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Circuit-Specific Early Impairment of Proprioceptive Sensory Neurons in the SOD1 G93A Mouse Model for ALS. J Neurosci 2019; 39:8798-8815. [PMID: 31530644 DOI: 10.1523/jneurosci.1214-19.2019] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 07/24/2019] [Accepted: 09/02/2019] [Indexed: 12/12/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease in which motor neurons degenerate, resulting in muscle atrophy, paralysis, and fatality. Studies using mouse models of ALS indicate a protracted period of disease development with progressive motor neuron pathology, evident as early as embryonic and postnatal stages. Key missing information includes concomitant alterations in the sensorimotor circuit essential for normal development and function of the neuromuscular system. Leveraging unique brainstem circuitry, we show in vitro evidence for reflex circuit-specific postnatal abnormalities in the jaw proprioceptive sensory neurons in the well-studied SOD1G93A mouse. These include impaired and arrhythmic action potential burst discharge associated with a deficit in Nav1.6 Na+ channels. However, the mechanoreceptive and nociceptive trigeminal ganglion neurons and the visual sensory retinal ganglion neurons were resistant to excitability changes in age-matched SOD1G93A mice. Computational modeling of the observed disruption in sensory patterns predicted asynchronous self-sustained motor neuron discharge suggestive of imminent reflexive defects, such as muscle fasciculations in ALS. These results demonstrate a novel reflex circuit-specific proprioceptive sensory abnormality in ALS.SIGNIFICANCE STATEMENT Neurodegenerative diseases have prolonged periods of disease development and progression. Identifying early markers of vulnerability can therefore help devise better diagnostic and treatment strategies. In this study, we examined postnatal abnormalities in the electrical excitability of muscle spindle afferent proprioceptive neurons in the well-studied SOD1G93A mouse model for neurodegenerative motor neuron disease, amyotrophic lateral sclerosis. Our findings suggest that these proprioceptive sensory neurons are exclusively afflicted early in the disease process relative to sensory neurons of other modalities. Moreover, they presented Nav1.6 Na+ channel deficiency, which contributed to arrhythmic burst discharge. Such sensory arrhythmia could initiate reflexive defects, such as muscle fasciculations in amyotrophic lateral sclerosis, as suggested by our computational model.
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15
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Lee K, Lee BM, Park CK, Kim YH, Chung G. Ion Channels Involved in Tooth Pain. Int J Mol Sci 2019; 20:ijms20092266. [PMID: 31071917 PMCID: PMC6539952 DOI: 10.3390/ijms20092266] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Revised: 05/03/2019] [Accepted: 05/03/2019] [Indexed: 01/05/2023] Open
Abstract
The tooth has an unusual sensory system that converts external stimuli predominantly into pain, yet its sensory afferents in teeth demonstrate cytochemical properties of non-nociceptive neurons. This review summarizes the recent knowledge underlying this paradoxical nociception, with a focus on the ion channels involved in tooth pain. The expression of temperature-sensitive ion channels has been extensively investigated because thermal stimulation often evokes tooth pain. However, temperature-sensitive ion channels cannot explain the sudden intense tooth pain evoked by innocuous temperatures or light air puffs, leading to the hydrodynamic theory emphasizing the microfluidic movement within the dentinal tubules for detection by mechanosensitive ion channels. Several mechanosensitive ion channels expressed in dental sensory systems have been suggested as key players in the hydrodynamic theory, and TRPM7, which is abundant in the odontoblasts, and recently discovered PIEZO receptors are promising candidates. Several ligand-gated ion channels and voltage-gated ion channels expressed in dental primary afferent neurons have been discussed in relation to their potential contribution to tooth pain. In addition, in recent years, there has been growing interest in the potential sensory role of odontoblasts; thus, the expression of ion channels in odontoblasts and their potential relation to tooth pain is also reviewed.
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Affiliation(s)
- Kihwan Lee
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 406-799, Korea.
| | - Byeong-Min Lee
- Department of Oral Physiology and Program in Neurobiology, School of Dentistry, Seoul National University, Seoul 08826, Korea.
| | - Chul-Kyu Park
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 406-799, Korea.
| | - Yong Ho Kim
- Gachon Pain Center and Department of Physiology, College of Medicine, Gachon University, Incheon 406-799, Korea.
| | - Gehoon Chung
- Department of Oral Physiology and Program in Neurobiology, School of Dentistry, Seoul National University, Seoul 08826, Korea.
- Dental Research Institute, Seoul National University, Seoul 03080, Korea.
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16
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Donnelly CR, Shah AA, Suh EB, Pierchala BA. Ret Signaling Is Required for Tooth Pulp Innervation during Organogenesis. J Dent Res 2019; 98:705-712. [PMID: 30958726 DOI: 10.1177/0022034519837971] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
During organogenesis, the timing and patterning of dental pulp innervation require both chemoattractive and chemorepellent cues for precise spatiotemporal regulation. Our understanding of the signaling mechanisms that regulate tooth innervation during development, as well as the basic biology of these sensory neurons, remains rudimentary. In this study, we analyzed the expression and function of glial cell line-derived neurotrophic factor (GDNF) and its receptor tyrosine kinase, Ret, in the regulation of innervation of the mouse tooth pulp by dental pulpal afferent (DPA) neurons of the trigeminal ganglion (TG). Using reporter mouse models, we demonstrate that Ret is highly expressed by a subpopulation of DPA neurons projecting to the tooth pulp at both postnatal day 7 (P7) and in the adult. In the adult tooth, GDNF is highly expressed by many cell types throughout the dental pulp. Using a ubiquitous tamoxifen (TMX)-inducible Cre ( UBC-Cre/ERT2) line crossed to Ret conditional knockout mice ( Retfx/fx), Ret was deleted immediately prior to tooth innervation, and the neural projections into P7 molars were analyzed. TMX treatment was efficient in ablating >95% of Ret protein. We observed that UBC-Cre/ERT2; Retfx/fx mice had a significant reduction in the total number of neurites present within the pulp at P7, with a significant accumulation of aberrant fibers in the dental follicle and periodontium. In agreement with these findings, inhibition of Ret signaling through in vivo administration of a highly specific pharmacologic inhibitor (1NM-PP1) of Ret also caused a substantial reduction in pulpal innervation. Taken together, these findings indicate that Ret signaling regulates the timing and patterning of tooth innervation by dental primary afferent neurons of the TG during organogenesis and provide a rationale to explore whether alterations in the GDNF-Ret pathway contribute to pathophysiological conditions in the adult dentition.
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Affiliation(s)
- C R Donnelly
- 1 Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, MI, USA
| | - A A Shah
- 1 Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, MI, USA
| | - E B Suh
- 1 Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, MI, USA
| | - B A Pierchala
- 1 Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, MI, USA
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17
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Hossain MZ, Bakri MM, Yahya F, Ando H, Unno S, Kitagawa J. The Role of Transient Receptor Potential (TRP) Channels in the Transduction of Dental Pain. Int J Mol Sci 2019; 20:ijms20030526. [PMID: 30691193 PMCID: PMC6387147 DOI: 10.3390/ijms20030526] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 01/18/2019] [Accepted: 01/24/2019] [Indexed: 12/18/2022] Open
Abstract
Dental pain is a common health problem that negatively impacts the activities of daily living. Dentine hypersensitivity and pulpitis-associated pain are among the most common types of dental pain. Patients with these conditions feel pain upon exposure of the affected tooth to various external stimuli. However, the molecular mechanisms underlying dental pain, especially the transduction of external stimuli to electrical signals in the nerve, remain unclear. Numerous ion channels and receptors localized in the dental primary afferent neurons (DPAs) and odontoblasts have been implicated in the transduction of dental pain, and functional expression of various polymodal transient receptor potential (TRP) channels has been detected in DPAs and odontoblasts. External stimuli-induced dentinal tubular fluid movement can activate TRP channels on DPAs and odontoblasts. The odontoblasts can in turn activate the DPAs by paracrine signaling through ATP and glutamate release. In pulpitis, inflammatory mediators may sensitize the DPAs. They could also induce post-translational modifications of TRP channels, increase trafficking of these channels to nerve terminals, and increase the sensitivity of these channels to stimuli. Additionally, in caries-induced pulpitis, bacterial products can directly activate TRP channels on DPAs. In this review, we provide an overview of the TRP channels expressed in the various tooth structures, and we discuss their involvement in the development of dental pain.
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Affiliation(s)
- Mohammad Zakir Hossain
- Department of Oral Physiology, School of Dentistry, Matsumoto Dental University, 1780 Gobara Hirooka, Shiojiri, Nagano 399-0781, Japan.
| | - Marina Mohd Bakri
- Department of Oral and Craniofacial Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur 50603, Malaysia.
| | - Farhana Yahya
- Department of Oral and Craniofacial Sciences, Faculty of Dentistry, University of Malaya, Kuala Lumpur 50603, Malaysia.
| | - Hiroshi Ando
- Department of Biology, School of Dentistry, Matsumoto Dental University, 1780 Gobara, Hirooka, Shiojiri, Nagano 399-0781, Japan.
| | - Shumpei Unno
- Department of Oral Physiology, School of Dentistry, Matsumoto Dental University, 1780 Gobara Hirooka, Shiojiri, Nagano 399-0781, Japan.
| | - Junichi Kitagawa
- Department of Oral Physiology, School of Dentistry, Matsumoto Dental University, 1780 Gobara Hirooka, Shiojiri, Nagano 399-0781, Japan.
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18
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Kern KU, Schwickert-Nieswandt M, Maihöfner C, Gaul C. Topical Ambroxol 20% for the Treatment of Classical Trigeminal Neuralgia - A New Option? Initial Clinical Case Observations. Headache 2019; 59:418-429. [PMID: 30653673 DOI: 10.1111/head.13475] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/30/2018] [Indexed: 12/17/2022]
Abstract
BACKGROUND Trigeminal neuralgia is difficult to treat and shows upregulation of sodium channels. The expectorant ambroxol acts as a strong local anesthetic, about 40 times stronger than lidocaine. It preferentially inhibits the channel subtype Nav 1.8, expressed especially in nociceptive C-fibers. It seemed reasonable to try ambroxol for the treatment with neuropathic facial pain unresponsive to other standard options. MATERIAL AND METHODS Medical records of patients suffering from classical trigeminal neuralgia (n = 5) and successful pain reduction following topical ambroxol 20% cream in addition to standard treatment are reported. RESULTS All patients reported pain attacks with pain intensity between 4 and 10 NRS (numeric pain scale). In all cases they could be triggered, 3 patients reported additional spontaneous pain. Attacks were reduced in all 5 patients. Pain reduction achieved following ambroxol 20% cream was 2-8 points (NRS) earliest within 15-30 minutes and lasted for 4-6 hours mostly. This was reproducible in all cases; in one case pain was eliminated after 1 week. No patient reported side effects or skin changes; oral medication was reduced in 2 patients. CONCLUSION For the first time, a clinically significant pain relief following topical ambroxol 20% cream in patients with trigeminal neuralgia is reported. In view of the positive side effect profile, topical ambroxol for patients with such a highly impaired quality of life should be investigated further as a matter of urgency.
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Affiliation(s)
- Kai-Uwe Kern
- Institute for Pain Medicine/Pain Practice Wiesbaden, Wiesbaden, Germany
| | | | | | - Charly Gaul
- Migraine and Headache Clinic, Königstein, Germany
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19
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Sato M, Ogura K, Kimura M, Nishi K, Ando M, Tazaki M, Shibukawa Y. Activation of Mechanosensitive Transient Receptor Potential/Piezo Channels in Odontoblasts Generates Action Potentials in Cocultured Isolectin B 4-negative Medium-sized Trigeminal Ganglion Neurons. J Endod 2018; 44:984-991.e2. [PMID: 29709295 DOI: 10.1016/j.joen.2018.02.020] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2017] [Revised: 02/15/2018] [Accepted: 02/20/2018] [Indexed: 01/22/2023]
Abstract
INTRODUCTION Various stimuli to the dentin surface elicit dentinal pain by inducing dentinal fluid movement causing cellular deformation in odontoblasts. Although odontoblasts detect deformation by the activation of mechanosensitive ionic channels, it is still unclear whether odontoblasts are capable of establishing neurotransmission with myelinated A delta (Aδ) neurons. Additionally, it is still unclear whether these neurons evoke action potentials by neurotransmitters from odontoblasts to mediate sensory transduction in dentin. Thus, we investigated evoked inward currents and evoked action potentials form trigeminal ganglion (TG) neurons after odontoblast mechanical stimulation. METHODS We used patch clamp recordings to identify electrophysiological properties and record evoked responses in TG neurons. RESULTS We classified TG cells into small-sized and medium-sized neurons. In both types of neurons, we observed voltage-dependent inward currents. The currents from medium-sized neurons showed fast inactivation kinetics. When mechanical stimuli were applied to odontoblasts, evoked inward currents were recorded from medium-sized neurons. Antagonists for the ionotropic adenosine triphosphate receptor (P2X3), transient receptor potential channel subfamilies, and Piezo1 channel significantly inhibited these inward currents. Mechanical stimulation to odontoblasts also generated action potentials in the isolectin B4-negative medium-sized neurons. Action potentials in these isolectin B4-negative medium-sized neurons showed a short duration. Overall, electrophysiological properties of neurons indicate that the TG neurons with recorded evoked responses after odontoblast mechanical stimulation were myelinated Aδ neurons. CONCLUSIONS Odontoblasts established neurotransmission with myelinated Aδ neurons via P2X3 receptor activation. The results also indicated that mechanosensitive TRP/Piezo1 channels were functionally expressed in odontoblasts. The activation of P2X3 receptors induced an action potential in the Aδ neurons, underlying a sensory generation mechanism of dentinal pain.
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Affiliation(s)
- Masaki Sato
- Department of Physiology, Tokyo Dental College, Tokyo, Japan
| | - Kazuhiro Ogura
- Department of Physiology, Tokyo Dental College, Tokyo, Japan
| | - Maki Kimura
- Department of Physiology, Tokyo Dental College, Tokyo, Japan
| | - Koichi Nishi
- Removable Prosthodontics and Gerodontology, Tokyo Dental College, Tokyo, Japan
| | - Masayuki Ando
- Department of Physiology, Tokyo Dental College, Tokyo, Japan
| | - Masakazu Tazaki
- Department of Physiology, Tokyo Dental College, Tokyo, Japan
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20
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Le Fur-Bonnabesse A, Bodéré C, Hélou C, Chevalier V, Goulet JP. Dental pain induced by an ambient thermal differential: pathophysiological hypothesis. J Pain Res 2017; 10:2845-2851. [PMID: 29290692 PMCID: PMC5736355 DOI: 10.2147/jpr.s142539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Dental pain triggered by temperature differential is a misrecognized condition and a form of dental allodynia. Dental allodynia is characterized by recurrent episodes of diffuse, dull and throbbing tooth pain that develops when returning to an indoor room temperature after being exposed for a long period to cold weather. The pain episode may last up to few hours before subsiding. Effective treatment is to properly shield the pulpal tissue of the offending tooth by increasing the protective layer of the dentin/enamel complex. This review underscores the difference in dentin hypersensitivity and offers a mechanistic hypothesis based on the following processes. Repeated exposure to significant positive temperature gradients (from cold to warm) generates phenotypic changes of dental primary afferents on selected teeth with subsequent development of a “low-grade” neurogenic inflammation. As a result, nociceptive C-fibers become sensitized and responsive to innocuous temperature gradients because the activation threshold of specific TRP ion channels is lowered and central sensitization takes place. Comprehensive overviews that cover dental innervation and sensory modalities, thermodynamics of tooth structure, mechanisms of dental nociception and the thermal pain are also provided.
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Affiliation(s)
- Anaïs Le Fur-Bonnabesse
- Laboratory of Neurosciences of Brest (EA4685), University of Western Brittany, Brest, France.,Dental School, University of Western Brittany, Brest, France
| | - Céline Bodéré
- Laboratory of Neurosciences of Brest (EA4685), University of Western Brittany, Brest, France.,Dental School, University of Western Brittany, Brest, France.,Assessment and Treatment Center of Pain, Regional and University Hospital Center, Brest, France
| | - Cyrielle Hélou
- Dental School, University of Western Brittany, Brest, France
| | - Valérie Chevalier
- Dental School, University of Western Brittany, Brest, France.,Laboratory IRDL, FRE CNRS 3744, University of Western Brittany, Brest, France
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21
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Kadala A, Sotelo-Hitschfeld P, Ahmad Z, Tripal P, Schmid B, Mueller A, Bernal L, Winter Z, Brauchi S, Lohbauer U, Messlinger K, Lennerz JK, Zimmermann K. Fluorescent Labeling and 2-Photon Imaging of Mouse Tooth Pulp Nociceptors. J Dent Res 2017; 97:460-466. [PMID: 29130364 DOI: 10.1177/0022034517740577] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Retrograde fluorescent labeling of dental primary afferent neurons (DPANs) has been described in rats through crystalline fluorescent DiI, while in the mouse, this technique was achieved with only Fluoro-Gold, a neurotoxic fluorescent dye with membrane penetration characteristics superior to the carbocyanine dyes. We reevaluated this technique in the rat with the aim to transfer it to the mouse because comprehensive physiologic studies require access to the mouse as a model organism. Using conventional immunohistochemistry, we assessed in rats and mice the speed of axonal dye transport from the application site to the trigeminal ganglion, the numbers of stained DPANs, and the fluorescence intensity via 1) conventional crystalline DiI and 2) a novel DiI formulation with improved penetration properties and staining efficiency. A 3-dimensional reconstruction of an entire trigeminal ganglion with 2-photon laser scanning fluorescence microscopy permitted visualization of DPANs in all 3 divisions of the trigeminal nerve. We quantified DPANs in mice expressing the farnesylated enhanced green fluorescent protein (EGFPf) from the transient receptor potential cation channel subfamily M member 8 (TRPM8EGFPf/+) locus in the 3 branches. We also evaluated the viability of the labeled DPANs in dissociated trigeminal ganglion cultures using calcium microfluorometry, and we assessed the sensitivity to capsaicin, an agonist of the TRPV1 receptor. Reproducible DiI labeling of DPANs in the mouse is an important tool 1) to investigate the molecular and functional specialization of DPANs within the trigeminal nociceptive system and 2) to recognize exclusive molecular characteristics that differentiate nociception in the trigeminal system from that in the somatic system. A versatile tool to enhance our understanding of the molecular composition and characteristics of DPANs will be essential for the development of mechanism-based therapeutic approaches for dentine hypersensitivity and inflammatory tooth pain.
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Affiliation(s)
- A Kadala
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - P Sotelo-Hitschfeld
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
- 2 Instituto de Fisiología, Facultad de Medicina, Escuela de Graduados, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
| | - Z Ahmad
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - P Tripal
- 3 Optical Imaging Centre Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - B Schmid
- 3 Optical Imaging Centre Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - A Mueller
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - L Bernal
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Z Winter
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - S Brauchi
- 2 Instituto de Fisiología, Facultad de Medicina, Escuela de Graduados, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile
| | - U Lohbauer
- 4 Klinik für Zahnerhaltung und Parodontologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - K Messlinger
- 5 Institut für Physiologie und Pathophysiologie, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
| | - J K Lennerz
- 6 Center for Integrated Diagnostics, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA
| | - K Zimmermann
- 1 Klinik für Anästhesiologie, Universitätsklinikum Erlangen, Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Germany
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22
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Won J, Vang H, Lee P, Kim Y, Kim H, Kang Y, Oh S. Piezo2 Expression in Mechanosensitive Dental Primary Afferent Neurons. J Dent Res 2017; 96:931-937. [DOI: 10.1177/0022034517702342] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Mechanosensitive ion channels have been suggested to be expressed in dental primary afferent (DPA) neurons to transduce the movement of dentinal fluid since the proposal of hydrodynamic theory. Piezo2, a mechanosensitive, rapidly inactivating (RI) ion channel, has been recently identified in dorsal root ganglion (DRG) neurons to mediate tactile transduction. Here, we examined the expression of Piezo2 in DPA neurons by in situ hybridization, single-cell reverse transcriptase polymerase chain reaction, and whole-cell patch-clamp recordings. DPA neurons with Piezo2 messenger RNA (mRNA) or Piezo2-like currents were further characterized based on their neurochemical and electrophysiological properties. Piezo2 mRNA was found mostly in medium- to large-sized DPA neurons, with the majority of these neurons also positive for Nav1.8, CGRP, and NF200, whereas only a minor population was positive for IB4 and peripherin. Whole-cell patch-clamp recordings revealed Piezo2-like, RI currents evoked by mechanical stimulation in a subpopulation of DPA neurons. RI currents were pharmacologically blocked by ruthenium red, a compound known to block Piezo2, and were also reduced by small interfering RNA-mediated Piezo2 knockdown. Piezo2-like currents were observed almost exclusively in IB4-negative DPA neurons, with the current amplitude larger in capsaicin-insensitive DPA neurons than the capsaicin-sensitive population. Our findings show that subpopulation of DPA neurons is indeed mechanically sensitive. Within this subpopulation of mechanosensitive DPA neurons, we have identified the Piezo2 ion channel as a potential transducer for mechanical stimuli, contributing to RI inward currents. Piezo2-positive DPA neurons were characterized as medium- to large-sized neurons with myelinated A-fibers, containing nociceptive peptidergic neurotransmitters.
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Affiliation(s)
- J. Won
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - H. Vang
- Dental Research Institute and Department of Neurobiology & Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
| | - P.R. Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - Y.H. Kim
- Dental Research Institute and Department of Neurobiology & Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
- Department of Physiology, College of Medicine, Gachon University, Incheon, Republic of Korea (present address)
| | - H.W. Kim
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
| | - Y. Kang
- Dental Research Institute and Department of Neurobiology & Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Osaka, Japan
| | - S.B. Oh
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea
- Dental Research Institute and Department of Neurobiology & Physiology, School of Dentistry, Seoul National University, Seoul, Republic of Korea
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23
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Aghazadeh Tabrizi M, Baraldi PG, Baraldi S, Gessi S, Merighi S, Borea PA. Medicinal Chemistry, Pharmacology, and Clinical Implications of TRPV1 Receptor Antagonists. Med Res Rev 2016; 37:936-983. [PMID: 27976413 DOI: 10.1002/med.21427] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Revised: 10/24/2016] [Accepted: 11/01/2016] [Indexed: 12/28/2022]
Abstract
Transient receptor potential vanilloid 1 (TRPV1) is an ion channel expressed on sensory neurons triggering an influx of cations. TRPV1 receptors function as homotetramers responsive to heat, proinflammatory substances, lipoxygenase products, resiniferatoxin, endocannabinoids, protons, and peptide toxins. Its phosphorylation increases sensitivity to both chemical and thermal stimuli, while desensitization involves a calcium-dependent mechanism resulting in receptor dephosphorylation. TRPV1 functions as a sensor of noxious stimuli and may represent a target to avoid pain and injury. TRPV1 activation has been associated to chronic inflammatory pain and peripheral neuropathy. Its expression is also detected in nonneuronal areas such as bladder, lungs, and cochlea where TRPV1 activation is responsible for pathology development of cystitis, asthma, and hearing loss. This review offers a comprehensive overview about TRPV1 receptor in the pathophysiology of chronic pain, epilepsy, cough, bladder disorders, diabetes, obesity, and hearing loss, highlighting how drug development targeting this channel could have a clinical therapeutic potential. Furthermore, it summarizes the advances of medicinal chemistry research leading to the identification of highly selective TRPV1 antagonists and their analysis of structure-activity relationships (SARs) focusing on new strategies to target this channel.
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Affiliation(s)
- Mojgan Aghazadeh Tabrizi
- Department of Chemical and Pharmaceutical Sciences, University of Ferrara, 44121, Ferrara, Italy
| | - Pier Giovanni Baraldi
- Department of Chemical and Pharmaceutical Sciences, University of Ferrara, 44121, Ferrara, Italy
| | - Stefania Baraldi
- Department of Chemical and Pharmaceutical Sciences, University of Ferrara, 44121, Ferrara, Italy
| | - Stefania Gessi
- Section of Pharmacology, Department of Medical Sciences, University of Ferrara, 44121, Ferrara, Italy
| | - Stefania Merighi
- Section of Pharmacology, Department of Medical Sciences, University of Ferrara, 44121, Ferrara, Italy
| | - Pier Andrea Borea
- Section of Pharmacology, Department of Medical Sciences, University of Ferrara, 44121, Ferrara, Italy
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Mickle AD, Shepherd AJ, Mohapatra DP. Nociceptive TRP Channels: Sensory Detectors and Transducers in Multiple Pain Pathologies. Pharmaceuticals (Basel) 2016; 9:ph9040072. [PMID: 27854251 PMCID: PMC5198047 DOI: 10.3390/ph9040072] [Citation(s) in RCA: 83] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 11/07/2016] [Accepted: 11/09/2016] [Indexed: 02/07/2023] Open
Abstract
Specialized receptors belonging to the transient receptor potential (TRP) family of ligand-gated ion channels constitute the critical detectors and transducers of pain-causing stimuli. Nociceptive TRP channels are predominantly expressed by distinct subsets of sensory neurons of the peripheral nervous system. Several of these TRP channels are also expressed in neurons of the central nervous system, and in non-neuronal cells that communicate with sensory nerves. Nociceptive TRPs are activated by specific physico-chemical stimuli to provide the excitatory trigger in neurons. In addition, decades of research has identified a large number of immune and neuromodulators as mediators of nociceptive TRP channel activation during injury, inflammatory and other pathological conditions. These findings have led to aggressive targeting of TRP channels for the development of new-generation analgesics. This review summarizes the complex activation and/or modulation of nociceptive TRP channels under pathophysiological conditions, and how these changes underlie acute and chronic pain conditions. Furthermore, development of small-molecule antagonists for several TRP channels as analgesics, and the positive and negative outcomes of these drugs in clinical trials are discussed. Understanding the diverse functional and modulatory properties of nociceptive TRP channels is critical to function-based drug targeting for the development of evidence-based and efficacious new generation analgesics.
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Affiliation(s)
- Aaron D Mickle
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
- Washington University Pain Center, Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
| | - Andrew J Shepherd
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
- Washington University Pain Center, Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
| | - Durga P Mohapatra
- Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
- Washington University Pain Center, Department of Anesthesiology, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
- Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
- Siteman Cancer Center, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, MO 63110, USA.
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Polymodal Transient Receptor Potential Vanilloid Type 1 Nocisensor. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2016; 104:81-125. [DOI: 10.1016/bs.apcsb.2015.11.005] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Jin Y. La(3+) Alters the Response Properties of Neurons in the Mouse Primary Somatosensory Cortex to Low-Temperature Noxious Stimulation of the Dental Pulp. BIOCHEMISTRY INSIGHTS 2015; 8:9-20. [PMID: 26604777 PMCID: PMC4640426 DOI: 10.4137/bci.s30752] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 10/12/2015] [Accepted: 10/14/2015] [Indexed: 12/31/2022]
Abstract
Although dental pain is a serious health issue with high incidence among the human population, its cellular and molecular mechanisms are still unclear. Transient receptor potential (TRP) channels are assumed to be involved in the generation of dental pain. However, most of the studies were conducted with molecular biological or histological methods. In vivo functional studies on the role of TRP channels in the mechanisms of dental pain are lacking. This study uses in vivo cellular electrophysiological and neuropharmacological method to directly disclose the effect of LaCl3, a broad spectrum TRP channel blocker, on the response properties of neurons in the mouse primary somatosensory cortex to low-temperature noxious stimulation of the dental pulp. It was found that LaCl3 suppresses the high-firing-rate responses of all nociceptive neurons to noxious low-temperature stimulation and also inhibits the spontaneous activities in some nonnociceptive neurons. The effect of LaCl3 is reversible. Furthermore, this effect is persistent and stable unless LaCl3 is washed out. Washout of LaCl3 quickly revitalized the responsiveness of neurons to low-temperature noxious stimulation. This study adds direct evidence for the hypothesis that TRP channels are involved in the generation of dental pain and sensation. Blockade of TRP channels may provide a novel therapeutic treatment for dental pain.
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Affiliation(s)
- Yanjiao Jin
- Department of Stomatology, Tianjin Medical University General Hospital, Heping District, Tianjin, People's Republic of China
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Maresin 1 Inhibits TRPV1 in Temporomandibular Joint-Related Trigeminal Nociceptive Neurons and TMJ Inflammation-Induced Synaptic Plasticity in the Trigeminal Nucleus. Mediators Inflamm 2015; 2015:275126. [PMID: 26617436 PMCID: PMC4651643 DOI: 10.1155/2015/275126] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 10/20/2015] [Indexed: 12/21/2022] Open
Abstract
In the trigeminal system, disruption of acute resolution processing may lead to uncontrolled inflammation and chronic pain associated with the temporomandibular joint (TMJ). Currently, there are no effective treatments for TMJ pain. Recently, it has been recognized that maresin 1, a newly identified macrophage-derived mediator of inflammation resolution, is a potent analgesic for somatic inflammatory pain without noticeable side effects in mice and a potent endogenous inhibitor of transient receptor potential vanilloid 1 (TRPV1) in the somatic system. However, the molecular mechanisms underlying the analgesic actions of maresin 1 on TMJ pain are unclear in the trigeminal system. Here, by performing TMJ injection of a retrograde labeling tracer DiI (a fluorescent dye), I showed that maresin 1 potently inhibits capsaicin-induced TRPV1 currents and neuronal activity via Gαi-coupled G-protein coupled receptors in DiI-labeled trigeminal nociceptive neurons. Further, maresin 1 blocked TRPV1 agonist-evoked increases in spontaneous excitatory postsynaptic current frequency and abolished TMJ inflammation-induced synaptic plasticity in the trigeminal nucleus. These results demonstrate the potent actions of maresin 1 in regulating TRPV1 in the trigeminal system. Thus, maresin 1 may serve as a novel endogenous inhibitor for treating TMJ-inflammatory pain in the orofacial region.
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The TRPA1 channel in inflammatory and neuropathic pain and migraine. Rev Physiol Biochem Pharmacol 2015; 167:1-43. [PMID: 24668446 DOI: 10.1007/112_2014_18] [Citation(s) in RCA: 140] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily of channels, is primarily localized to a subpopulation of primary sensory neurons of the trigeminal, vagal, and dorsal root ganglia. This subset of nociceptors produces and releases the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP), which mediate neurogenic inflammatory responses. TRPA1 is activated by a number of exogenous compounds, including molecules of botanical origin, environmental irritants, and medicines. However, the most prominent feature of TRPA1 resides in its unique sensitivity for large series of reactive byproducts of oxidative and nitrative stress. Here, the role of TRPA1 in models of different types of pain, including inflammatory and neuropathic pain and migraine, is summarized. Specific attention is paid to TRPA1 as the main contributing mechanism to the transition of mechanical and cold hypersensitivity from an acute to a chronic condition and as the primary transducing pathway by which oxidative/nitrative stress produces acute nociception, allodynia, and hyperalgesia. A series of migraine triggers or medicines have been reported to modulate TRPA1 activity and the ensuing CGRP release. Thus, TRPA1 antagonists may be beneficial in the treatment of inflammatory and neuropathic pain and migraine.
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Mickle AD, Shepherd AJ, Mohapatra DP. Sensory TRP channels: the key transducers of nociception and pain. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 131:73-118. [PMID: 25744671 DOI: 10.1016/bs.pmbts.2015.01.002] [Citation(s) in RCA: 97] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Peripheral detection of nociceptive and painful stimuli by sensory neurons involves a complex repertoire of molecular detectors and/or transducers on distinct subsets of nerve fibers. The majority of such molecular detectors/transducers belong to the transient receptor potential (TRP) family of cation channels, which comprise both specific receptors for distinct nociceptive stimuli, as well as for multiple stimuli. This chapter discusses the classification, distribution, and functional properties of individual TRP channel types that have been implicated in various nociceptive and/or painful conditions.
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Affiliation(s)
- Aaron D Mickle
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Andrew J Shepherd
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Durga P Mohapatra
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, USA; Department of Anesthesia, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, USA; Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, USA.
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Liu Y, Tian X, Wu Y, Chen L, Yi CL, Li ZW, Zhang Y, Li CY. Phenotypes of ATP-activated current associated with their genotypes of P2X1-6 subunits in neurons innervating tooth-pulp. Biochem Biophys Res Commun 2015; 458:596-600. [PMID: 25680470 DOI: 10.1016/j.bbrc.2015.01.156] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 01/29/2015] [Indexed: 11/20/2022]
Abstract
To explore the association of the phenotype of ATP-activated current with the genotype of P2X1-6 subunits in nociceptors, we developed a method that allows us to label nociceptive neurons innervating tooth-pulp in rat trigeminal ganglion (TG) neurons using a retrograde fluorescence-tracing method, to record ATP-activated current in freshly isolated fluorescence-labeled neurons, and then to conduct single cell immunohistochemical staining for P2X1-6 subunits in the same neuron. We found that fast application of 100 μM ATP to fluorescence-traced TG neurons produced robust inward current in 87% (96/110) of cells tested. The diameter of cells varied from 16 to 56 μm. Three types of ATP-activated current (F, I and S) were recorded with distinct rise times of the current (R10-90, P < 0.05). There was a positive correlation between the cell diameter and the value of R10-90 (P < 0.05): the value of R10-90 increased with increases in the cell diameter. Cells responsive to ATP with the type F current mainly showed positive staining for P2X3 and P2X5, but negative staining for P2X2; cells responsive to ATP with the type I current showed positive staining for P2X1-3 and P2X5, but negative staining for P2X4; and cells responsive to ATP with the type S current showed positive staining for P2X1-5, but negative staining for P2X6. The present findings suggest that in addition to P2X3 subunits, P2X5 subunits are also involved in the generation of the F type of ATP-activated current in small-sized nociceptive neurons. In addition to the P2X2/3 subunit-containing channels, more complex uncharacterized combinations of P2X1-5 subunits exist in native medium-sized nociceptive neurons exhibiting the I and S types of ATP-activated current. In addition, the P2X6 subunit is not a main subunit involved in the nociceptive signal in rat TG neurons innervating tooth-pulp.
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Affiliation(s)
- Yuwei Liu
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China; School of Medicine, Jianghan University, Wuhan, 430056, China
| | - Xiang Tian
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China
| | - Yuxiang Wu
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China
| | - Lin Chen
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China
| | - Chu-Li Yi
- School of Medicine, Jianghan University, Wuhan, 430056, China
| | - Zhi-Wang Li
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China
| | - Ying Zhang
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China
| | - Chao-Ying Li
- Wuhan Institutes of Biomedical Sciences, Jianghan University, Wuhan, 430056, Hubei Province, China.
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Abstract
TRP channels are expressed in taste buds, nerve fibers, and keratinocytes in the oronasal cavity. These channels play integral roles in transducing chemical stimuli, giving rise to sensations of taste, irritation, warmth, coolness, and pungency. Specifically, TRPM5 acts downstream of taste receptors in the taste transduction pathway. TRPM5 channels convert taste-evoked intracellular Ca(2+) release into membrane depolarization to trigger taste transmitter secretion. PKD2L1 is expressed in acid-sensitive (sour) taste bud cells but is unlikely to be the transducer for sour taste. TRPV1 is a receptor for pungent chemical stimuli such as capsaicin and for several irritants (chemesthesis). It is controversial whether TRPV1 is present in the taste buds and plays a direct role in taste. Instead, TRPV1 is expressed in non-gustatory sensory afferent fibers and in keratinocytes of the oronasal cavity. In many sensory fibers and epithelial cells lining the oronasal cavity, TRPA1 is also co-expressed with TRPV1. As with TRPV1, TRPA1 transduces a wide variety of irritants and, in combination with TRPV1, assures that there is a broad response to noxious chemical stimuli. Other TRP channels, including TRPM8, TRPV3, and TRPV4, play less prominent roles in chemesthesis and no known role in taste, per se. The pungency of foods and beverages is likely highly influenced by the temperature at which they are consumed, their acidity, and, for beverages, their carbonation. All these factors modulate the activity of TRP channels in taste buds and in the oronasal mucosa.
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Affiliation(s)
- Stephen D Roper
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, 1600 NW 10th Ave., Miami, FL, 33136, USA,
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Nilius B, Szallasi A. Transient Receptor Potential Channels as Drug Targets: From the Science of Basic Research to the Art of Medicine. Pharmacol Rev 2014; 66:676-814. [DOI: 10.1124/pr.113.008268] [Citation(s) in RCA: 348] [Impact Index Per Article: 34.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
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Seo H, Li HY, Perez-Reyes E, Lee JH. Effects of eugenol on T-type Ca2+ channel isoforms. J Pharmacol Exp Ther 2013; 347:310-7. [PMID: 24014106 PMCID: PMC11047949 DOI: 10.1124/jpet.113.207936] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2013] [Accepted: 09/06/2013] [Indexed: 02/06/2023] Open
Abstract
Eugenol has been used as an analgesic in dentistry. Previous studies have demonstrated that voltage-gated Na(+) channels and high-voltage-activated Ca(2+) channels expressed in trigeminal ganglion (TG) neurons sensing dental pain are molecular targets of eugenol for its analgesic effects. However, it has not been investigated whether eugenol can affect T-type Ca(2+) channels, which are known to be detected in the afferent neurons. In this report, we investigate how eugenol can influence cloned T-type channel isoforms expressed in HEK293 cells, using whole-cell patch clamp. Application of eugenol inhibited Cav3.1, Cav3.2, and Cav3.3 currents in a concentration-dependent manner with IC50 values of 463, 486, and 708 μM, respectively. Eugenol was found to negatively shift the steady-state inactivation curves of the T-type channel isoforms, but it did not shift their activation curves. In addition, eugenol had little effect on the current kinetics of Cav3.1 and Cav3.2, but it accelerated the inactivation kinetics of Cav3.3 currents. Reduction of channel availability enhanced eugenol inhibition sensitivity for Cav3.1 and Cav3.2, but not for Cav3.3. Moreover, eugenol inhibition of T-type channel isoforms was found to be use dependent. Finally, we show that the T-type currents recorded from rat TG neurons were inhibited by eugenol with a similar potency to Cav3.1 and Cav3.2 isoforms. Taken together, our findings suggest that T-type Ca(2+) channels are additional molecular targets for the pain-relieving effects of eugenol.
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Affiliation(s)
- Haengsoo Seo
- Department of Life Science and Basic Science Institute for Cell Damage Control, Sogang University, Seoul, Republic of Korea (H.S., H.Y.L., J.-H.L.); and Department of Pharmacology, University of Virginia, Charlottesville, Virginia (E.P.-R.)
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Abstract
Due, in part, to the unique structure of the tooth, dental pain is initiated via distinct mechanisms. Here we review recent advances in our understanding of inflammatory tooth pain and discuss 3 hypotheses proposed to explain dentinal hypersensitivity: The first hypothesis, supported by functional expression of temperature-sensitive transient receptor potential channels, emphasizes the direct transduction of noxious temperatures by dental primary afferent neurons. The second hypothesis, known as hydrodynamic theory, attributes dental pain to fluid movement within dentinal tubules, and we discuss several candidate cellular mechanical transducers for the detection of fluid movement. The third hypothesis focuses on the potential sensory function of odontoblasts in the detection of thermal or mechanical stimuli, and we discuss the accumulating evidence that supports their excitability. We also briefly update on a novel strategy for local nociceptive anesthesia via nociceptive transducer molecules in dental primary afferents with the potential to specifically silence pain fibers during dental treatment. Further understanding of the molecular mechanisms of dental pain would greatly enhance the development of therapeutics that target dental pain.
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Affiliation(s)
- G Chung
- Pain Cognitive Function Research Center, Dental Research Institute and Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul 110-749, Republic of Korea
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35
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Shokoohinia Y, Chianese G, Appendino G, Di Marzo V, De Petrocellis L, Ghannadi A, Taghvayi R, Fattahian K, Soltani R, Taglialatela-Scafati O. Some like it pungent and vile. TRPA1 as a molecular target for the malodorous vinyl disulfides from asafoetida. Fitoterapia 2013; 90:247-51. [PMID: 23954176 DOI: 10.1016/j.fitote.2013.08.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2013] [Revised: 07/29/2013] [Accepted: 08/04/2013] [Indexed: 10/26/2022]
Abstract
Ferula assa-foetida L. is a major source of asafoetida, a foul-smelling gum-resin of dietary and medicinal relevance. Investigation of the roots and latex of F. assa-foetida yielded various mixed vinyl disulfides, including two novel asadisulfide-type esters. The reactivity of asadisulfide was investigated in the cysteamine NMR assay, where it behaved as disulfide shuffling agents due to the high mobility of the vinyl sulfide moiety. In accordance with their transthiolation capacity, these compounds potently activated TRPA1, the target of mustard oil and the pungent sulfur compounds from onion and garlic, qualifying S-alkyl-S-alkenyldisulfides, a rare class of natural products, as a novel class of dietary TRPA1 activators. These observations provide a mechanistic basis for rationalizing some of the sensory properties and potential beneficial health claims associated to the use of asafoetida as a spice and as a medicine.
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Affiliation(s)
- Yalda Shokoohinia
- Novel Drug Delivery Research Center, School of Pharmacy, Kermanshah University of Medical Sciences, Kermanshah, Iran; Department of Pharmacognosy and Biotechnology, School of Pharmacy, Kermanshah University of Medical Sciences, Kermanshah, Iran
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Ruparel S, Hargreaves KM, Eskander M, Rowan S, de Almeida JFA, Roman L, Henry MA. Oxidized linoleic acid metabolite-cytochrome P450 system (OLAM-CYP) is active in biopsy samples from patients with inflammatory dental pain. Pain 2013; 154:2363-2371. [PMID: 23867730 DOI: 10.1016/j.pain.2013.07.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 06/26/2013] [Accepted: 07/10/2013] [Indexed: 11/26/2022]
Abstract
Endogenous TRPV1 agonists such as oxidized linoleic acid metabolites (OLAMs) and the enzymes releasing them [eg, cytochrome P450 (CYP)] are up-regulated after inflammation in the rat. However, it is not known whether such agonists are elevated in human inflammatory pain conditions. Because TRPV1 is expressed in human dental pulp nociceptors, we hypothesized that OLAM-CYP machinery is active in this tissue type and is increased under painful inflammatory conditions such as irreversible pulpitis (IP). The aim of this study was to compare CYP expression and linoleic acid (LA) metabolism in normal vs inflamed human dental pulp. Our data showed that exogenous LA metabolism was significantly increased in IP tissues compared to normal tissues and that pretreatment with a CYP inhibitor, ketoconazole, significantly inhibited LA metabolism. Additionally, extracts obtained from LA-treated inflamed tissues evoked significant inward currents in trigeminal ganglia neurons and were blocked by pretreatment with the TRPV1 antagonist IRTX. Moreover, extracts obtained from ketoconazole-pretreated inflamed tissues significantly reduced inward currents in trigeminal ganglia neurons. These data suggest that LA metabolites produced in human inflamed tissues act as TRPV1 agonists and that the metabolite production can be targeted by CYP inhibition. In addition, immunohistochemical analysis of 2 CYP isoforms, CYP2J and CYP3A1, were shown to be predominately expressed in immune cells infiltrating the inflamed dental pulp, emphasizing the paracrine role of CYP enzymes in OLAM regulation. Collectively, our data indicate that the machinery responsible for OLAM production is up-regulated during inflammation and can be targeted to develop potential analgesics for inflammatory-induced dental pain.
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Affiliation(s)
- Shivani Ruparel
- Department of Endodontics, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA Department of Biochemistry, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA Department of Pharmacology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
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Maurin JC, Couble ML, Thivichon-Prince B, Magloire H. [Odontoblast: a key cell involved in the perception of dentinal pain]. Med Sci (Paris) 2013; 29:293-9. [PMID: 23544384 DOI: 10.1051/medsci/2013293016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Dentinal sensitivity is a clinical condition daily encountered by practitioners and constitutes the symptoms of dentinal hypersensitivity, a common dental pain affecting on average 30% of the population. However, the management of this pathology is not always effective due to the lack of knowledge particularly concerning the means by which dental nociceptive signals are transduced. The mechanisms underlying dentin sensitivity still remain unclear probably due to the structural and functional complexity of the players including odontoblasts, nerve endings and dentinal fluid running in the dentinal tubules. The unique spatial situation of odontoblasts, ciliated cells in close relationship with nerve terminals, suggests that they could play a pivotal role in the transduction of sensory events occurring within the dentin tissue. Our studies have identified mechano-thermosensitive transient receptor potential ion channels (TRPV1-4, TRPA8, TRPM3, KCa, TREK-1, PC1, PC2) localised on the odontoblastic membrane and at the base of the cilium. They could sense temperature variations or movements of dentinal fluid within tubules. Moreover, several voltage-gated sodium channels confer excitable properties to odontoblasts in response to injection of depolarizing currents. In vivo, these channels co-localize with nerve endings at the apical pole of odontoblasts, and their expression pattern seems to be correlated with the spatial distribution of stretch-activated KCa channels. All these data strengthen the hypothesis that odontoblasts could act as sensor cells able to transmit nociceptive signals. However, how cells sense signals and how the latter are transmitted to axons represent the main issue to be solved.
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Affiliation(s)
- Jean-Christophe Maurin
- EA 4691 biomatériaux et inflammation en site osseux, SFR CAP-Santé, université Reims Champagne-Ardenne, UFR d'odontologie, 2, rue du Général Koenig, 51100 Reims, France.
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Abstract
Musculoskeletal pain conditions, particularly those associated with temporomandibular disorders (TMD) affect a large percentage of the population. Identifying mechanisms underlying hyperalgesia could contribute to the development of new treatment strategies for the management of TMD and other muscle pain conditions. In this study, we provide evidence of functional interactions between two ligand-gated channels, P2X₃ and transient receptor potential V1 (TRPV1), in trigeminal sensory neurons, and propose that the interactions serve as an underlying mechanism for the development of mechanical hyperalgesia. Mechanical sensitivity of the masseter muscle was assessed in lightly anesthetized rats via an electronic anesthesiometer (Ro et al., 2009). Direct intramuscular injection of a selective P2X₃ agonist, alpha,beta-methylene adenosine triphosphate (αβmeATP), induced a dose- and time-dependent hyperalgesia. Mechanical sensitivity in the contralateral muscle was unaffected suggesting local P2X₃ mediate hyperalgesia. Anesthetizing the overlying skin had no effect on αβmeATP-induced hyperalgesia confirming the contribution of P2X₃ from the muscle. Importantly, the αβmeATP-induced hyperalgesia was prevented by pretreatment of the muscle with a TRPV1 antagonist, AMG9810. P2X₃ was co-expressed with TRPV1 in the masseter muscle afferents confirming the possibility for intracellular interactions. Additionally, in a subpopulation of P2Xv/TRPV1 positive neurons, capsaicin-induced Ca(2+) transients were significantly amplified following P2X₃ activation. Finally, activation of P2X₃ induced phosphorylation of serine, but not threonine, residues in TRPV1 in trigeminal ganglia cultures. Significant phosphorylation was observed at 15 min, the time point at which behavioral hyperalgesia was prominent. Previously, activation of either P2X₃ or TRPV1 had been independently implicated in the development of mechanical hyperalgesia. Our data propose P2X₃ and TRPV1 interact in a facilitatory manner, which could contribute to the peripheral sensitization known to underlie masseter hyperalgesia.
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Kim YS, Jung HK, Kwon TK, Kim CS, Cho JH, Ahn DK, Bae YC. Expression of Transient Receptor Potential Ankyrin 1 in Human Dental Pulp. J Endod 2012; 38:1087-92. [DOI: 10.1016/j.joen.2012.04.024] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 04/18/2012] [Accepted: 04/27/2012] [Indexed: 01/11/2023]
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Chung MK, Jue SS, Dong X. Projection of non-peptidergic afferents to mouse tooth pulp. J Dent Res 2012; 91:777-82. [PMID: 22668597 DOI: 10.1177/0022034512450298] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
A large proportion of pulpal nociceptors are known to contain neuropeptides such as CGRP. However, the projection of non-peptidergic nociceptors to tooth pulp is controversial. Recently, the non- peptidergic subset of nociceptors has been implicated in mechanical pain in the skin. Since mechanical irritation of pulpal nociceptors is critical for evoking tooth pain under pathophysiological conditions, we investigated whether the non-peptidergic afferents project to tooth pulp as potential mechanotransducing afferents. For clear visualization of the non-peptidergic afferents, we took advantage of a recently generated knock-in mouse model in which an axonal tracer, farnesylated green fluorescence protein (GFP), is expressed from the locus of a sensory neuron-specific gene, Mrgprd. In the trigeminal ganglia (TG), we demonstrated that GFP is exclusively expressed in afferents binding to isolectin B4 (IB4), a neurochemical marker of non-peptidergic nociceptors, but is rarely co-localized with CGRP. Retrograde labeling of pulpal afferents demonstrated that a low proportion of pulpal afferents was co-localized with GFP. Immunohistochemical detection of the axonal tracer revealed that GFP-positive afferent terminals were densely projected into the tooth pulp. These results provide convincing evidence that non-peptidergic nociceptors are projected into the tooth pulp and suggest a potential role for these afferents in tooth pain.
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Affiliation(s)
- M-K Chung
- Department of Neural and Pain Sciences, School of Dentistry, University of Maryland, Baltimore, MD 21201, USA.
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Vang H, Chung G, Kim HY, Park SB, Jung SJ, Kim JS, Oh SB. Neurochemical properties of dental primary afferent neurons. Exp Neurobiol 2012; 21:68-74. [PMID: 22792027 PMCID: PMC3381214 DOI: 10.5607/en.2012.21.2.68] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Accepted: 04/04/2012] [Indexed: 11/19/2022] Open
Abstract
The long belief that dental primary afferent (DPA) neurons are entirely composed of nociceptive neurons has been challenged by several anatomical and functional investigations. In order to characterize non-nociceptivepopulation among DPA neurons, retrograde transport fluorescent dye was placed in upper molars of rats and immunohistochemical detection of peripherin and neurofilament 200 in the labeled trigeminal ganglia was performed. As the results, majority ofDPA neurons were peripherin-expressing small-sized neurons, showing characteristic ofnociceptive C-fibers. However, 25.7% of DPA were stained with antibody against neurofilament 200, indicating significant portion of DPA neurons are related to large myelinated Aβ fibers. There were a small number of neurons thatexpressed both peripherin and neurofilament 200, suggestive of Aδ fibers. The possible transition of neurochemical properties by neuronal injury induced by retrograde labeling technique was ruled out by detection of minimal expression of neuronal injury marker, ATF-3. These results suggest that in addition to the large population of C-fiber-related nociceptive neurons, a subset of DPA neurons is myelinated large neurons, which is related to low-threshold mechanosensitive Aβ fibers. We suggest that these Aβ fiber-related neurons might play a role as mechanotransducers of fluid movement within dentinal tubules.
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Affiliation(s)
- Hue Vang
- National Research Laboratory for Pain, Dental Research Institute and Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul 110-749, Korea
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Tooth injury increases expression of the cold sensitive TRP channel TRPA1 in trigeminal neurons. Arch Oral Biol 2011; 56:1604-9. [PMID: 21783172 DOI: 10.1016/j.archoralbio.2011.06.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 05/03/2011] [Accepted: 06/24/2011] [Indexed: 01/22/2023]
Abstract
OBJECTIVE Transient receptor potential (TRP) channels, a family of structurally related proteins have been implicated in the sensation of pain and hyperalgesia caused by exogenous and endogenous agonists, as well as touch, pH, and temperature. The objective of this study was to determine the effects of tooth injury on the expression of the cold sensitive channel TRPA1, in the trigeminal ganglion, the primary source of sensory and nociceptive innervation of teeth. DESIGN We analyzed TRPA1 expression in a rodent model of tooth injury, by Western blot analyses of proteins extracted from trigeminal ganglia. RESULTS We found that TRPA1 was selectively increased in trigeminal ganglia innervating injured teeth when compared to TRPA1 expression in trigeminal ganglia innervating healthy teeth. CONCLUSIONS Our results provide the first evidence of increased expression of a cold-sensitive TRP channel in trigeminal ganglia after pulp exposure, and are consistent with the possibility that increased expression and function of TRPA1 in trigeminal neurons contributes to hyperalgesia and allodynia following tooth injury.
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