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Li ZY, Mao YQ, Hua Q, Sun YH, Wang HY, Ye XG, Hu JX, Wang YJ, Jiang M. Serotonin receptor 2B induces visceral hyperalgesia in rat model and patients with diarrhea-predominant irritable bowel syndrome. World J Gastroenterol 2024; 30:1431-1449. [PMID: 38596485 PMCID: PMC11000090 DOI: 10.3748/wjg.v30.i10.1431] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 12/29/2023] [Accepted: 02/06/2024] [Indexed: 03/14/2024] Open
Abstract
BACKGROUND Serotonin receptor 2B (5-HT2B receptor) plays a critical role in many chronic pain conditions. The possible involvement of the 5-HT2B receptor in the altered gut sensation of irritable bowel syndrome with diarrhea (IBS-D) was investigated in the present study. AIM To investigate the possible involvement of 5-HT2B receptor in the altered gut sensation in rat model and patients with IBS-D. METHODS Rectosigmoid biopsies were collected from 18 patients with IBS-D and 10 patients with irritable bowel syndrome with constipation who fulfilled the Rome IV criteria and 15 healthy controls. The expression level of the 5-HT2B receptor in colon tissue was measured using an enzyme-linked immunosorbent assay and correlated with abdominal pain scores. The IBS-D rat model was induced by intracolonic instillation of acetic acid and wrap restraint. Alterations in visceral sensitivity and 5-HT2B receptor and transient receptor potential vanilloid type 1 (TRPV1) expression were examined following 5-HT2B receptor antagonist administration. Changes in visceral sensitivity after administration of the TRPV1 antagonist were recorded. RESULTS Here, we observed greater expression of the 5-HT2B receptor in the colonic mucosa of patients with IBS-D than in that of controls, which was correlated with abdominal pain scores. Intracolonic instillation of acetic acid and wrap restraint induced obvious chronic visceral hypersensitivity and increased fecal weight and fecal water content. Exogenous 5-HT2B receptor agonist administration increased visceral hypersensitivity, which was alleviated by successive administration of a TRPV1 antagonist. IBS-D rats receiving the 5-HT2B receptor antagonist exhibited inhibited visceral hyperalgesia.Moreover, the percentage of 5-HT2B receptor-immunoreactive (IR) cells surrounded by TRPV1-positive cells (5-HT2B receptor I+) and total 5-HT2B receptor IR cells (5-HT2B receptor IT) in IBS-D rats was significantly reduced by the administration of a 5-HT2B receptor antagonist. CONCLUSION Our finding that increased expression of the 5-HT2B receptor contributes to visceral hyperalgesia by inducing TRPV1 expression in IBS-D patients provides important insights into the potential mechanisms underlying IBS-D-associated visceral hyperalgesia.
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Affiliation(s)
- Zheng-Yang Li
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Yu-Qing Mao
- Department of Gastroenterology, Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China
| | - Qian Hua
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Yong-Hong Sun
- Department of Gastroenterology, Dalian Friendship Hospital, Dalian 116001, Liaoning Province, China
| | - Hai-Yan Wang
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Xuan-Guang Ye
- Department of Pathology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Jing-Xian Hu
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Ya-Jie Wang
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
| | - Miao Jiang
- Department of Gastroenterology, Jinshan Hospital of Fudan University, Shanghai 201508, China
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Manjarres Z, Calvo M, Pacheco R. Regulation of Pain Perception by Microbiota in Parkinson Disease. Pharmacol Rev 2023; 76:7-36. [PMID: 37863655 DOI: 10.1124/pharmrev.122.000674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 10/03/2023] [Accepted: 10/10/2023] [Indexed: 10/22/2023] Open
Abstract
Pain perception involves current stimulation in peripheral nociceptive nerves and the subsequent stimulation of postsynaptic excitatory neurons in the spinal cord. Importantly, in chronic pain, the neural activity of both peripheral nociceptors and postsynaptic neurons in the central nervous system is influenced by several inflammatory mediators produced by the immune system. Growing evidence has indicated that the commensal microbiota plays an active role in regulating pain perception by either acting directly on nociceptors or indirectly through the modulation of the inflammatory activity on immune cells. This symbiotic relationship is mediated by soluble bacterial mediators or intrinsic structural components of bacteria that act on eukaryotic cells, including neurons, microglia, astrocytes, macrophages, T cells, enterochromaffin cells, and enteric glial cells. The molecular mechanisms involve bacterial molecules that act directly on neurons, affecting their excitability, or indirectly on non-neuronal cells, inducing changes in the production of proinflammatory or anti-inflammatory mediators. Importantly, Parkinson disease, a neurodegenerative and inflammatory disorder that affects mainly the dopaminergic neurons implicated in the control of voluntary movements, involves not only a motor decline but also nonmotor symptomatology, including chronic pain. Of note, several recent studies have shown that Parkinson disease involves a dysbiosis in the composition of the gut microbiota. In this review, we first summarize, integrate, and classify the molecular mechanisms implicated in the microbiota-mediated regulation of chronic pain. Second, we analyze the changes on the commensal microbiota associated to Parkinson disease and propose how these changes affect the development of chronic pain in this pathology. SIGNIFICANCE STATEMENT: The microbiota regulates chronic pain through the action of bacterial signals into two main locations: the peripheral nociceptors and the postsynaptic excitatory neurons in the spinal cord. The dysbiosis associated to Parkinson disease reveals increased representation of commensals that potentially exacerbate chronic pain and reduced levels of bacteria with beneficial effects on pain. This review encourages further research to better understand the signals involved in bacteria-bacteria and bacteria-host communication to get the clues for the development of probiotics with therapeutic potential.
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Affiliation(s)
- Zulmary Manjarres
- Laboratorio de Neuroinmunología, Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile (Z.M., R.P.); Facultad de Ciencias Biológicas (Z.M., M.C.) and División de Anestesiología, Escuela de Medicina (M.C.), Pontificia Universidad Católica de Chile, Santiago, Chile; Millennium Nucleus for the Study of Pain, Santiago, Chile (Z.M., M.C.); and Facultad de Medicina y Ciencia, Universidad San Sebastián, Santiago, Chile (R.P.)
| | - Margarita Calvo
- Laboratorio de Neuroinmunología, Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile (Z.M., R.P.); Facultad de Ciencias Biológicas (Z.M., M.C.) and División de Anestesiología, Escuela de Medicina (M.C.), Pontificia Universidad Católica de Chile, Santiago, Chile; Millennium Nucleus for the Study of Pain, Santiago, Chile (Z.M., M.C.); and Facultad de Medicina y Ciencia, Universidad San Sebastián, Santiago, Chile (R.P.)
| | - Rodrigo Pacheco
- Laboratorio de Neuroinmunología, Centro Científico y Tecnológico de Excelencia Ciencia & Vida, Fundación Ciencia & Vida, Santiago, Chile (Z.M., R.P.); Facultad de Ciencias Biológicas (Z.M., M.C.) and División de Anestesiología, Escuela de Medicina (M.C.), Pontificia Universidad Católica de Chile, Santiago, Chile; Millennium Nucleus for the Study of Pain, Santiago, Chile (Z.M., M.C.); and Facultad de Medicina y Ciencia, Universidad San Sebastián, Santiago, Chile (R.P.)
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Lin K, Deng T, Qu H, Ou H, Huang Q, Gao B, Li X, Wei N. Gastric protective effect of Alpinia officinarum flavonoids: mediating TLR4/NF-κB and TRPV1 signalling pathways and gastric mucosal healing. PHARMACEUTICAL BIOLOGY 2023; 61:50-60. [PMID: 36541204 PMCID: PMC9788718 DOI: 10.1080/13880209.2022.2152058] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/20/2022] [Revised: 10/03/2022] [Accepted: 11/19/2022] [Indexed: 06/17/2023]
Abstract
CONTEXT Our previous studies have found that total flavonoid of Alpinia officinarum Hance (Zingiberaceae) (F.AOH) had protective effects on gastric ulcer (GU). OBJECTIVE To investigate the protective mechanism of F.AOH on acetic acid-induced chronic GUs in rats and ethanol-induced GES-1 cells damage. MATERIALS AND METHODS In vivo: Gastric damage was induced in SD rats by administering acetic acid after oral treatment with F-AOH at 54, 27 and 13.5 mg/kg (2 weeks of continuous gavage). After a comprehensive evaluation of rats' serum and gastric tissue-related indicators, gene transcriptome sequencing, qPCR and Western blotting were used to investigate the mechanism further. In vivo: GES-1 cells were incubated with F-AOH (8, 4 and 2 μg/mL) for 16 h and treated with 7% ethanol for 4 h. Transwell and flow cytometry were employed to detect migration and apoptosis of cells. RESULTS F.AOH effectively reduced the area of GUs in rats (from 11.2 ± 1.89 to 2.19 ± 0.95), reversing ethanol-induced cells apoptosis (from 23 ± 1.3 to 8.11 ± 0.93%). It also inhibited the expression of endothelin-1 (ET-1) and iNOS proteins, decreasing the levels of TNF-α IL-6 in serum, improving oxidative stress levels and increasing the expression of Bcl-2/Bax dimer genes. In addition, 4005 differentially expressed genes between the acetic acid model and the drug groups. Through experimental verification, F.AOH can inhibit the activation of TLR4/NF-κB signalling pathway and TRPV1 receptor. CONCLUSIONS F.AOH, as an effective gastric protective plant component, had potential therapeutic value in anti-inflammatory pain and antioxidative stress gastrointestinal diseases.
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Affiliation(s)
- Kaiwen Lin
- School of Pharmacy, Hainan Medical University, Haikou, China
- Hainan Women and Children’s Medical Center, Haikou, China
| | - Tang Deng
- School of Pharmacy, Hainan Medical University, Haikou, China
- First Affiliated Hospital of Hainan Medical University, Haikou, China
| | - Huijuan Qu
- School of Pharmacy, Hainan Medical University, Haikou, China
| | - Hongya Ou
- School of Pharmacy, Hainan Medical University, Haikou, China
| | - Qifeng Huang
- School of Pharmacy, Hainan Medical University, Haikou, China
- First Affiliated Hospital of Hainan Medical University, Haikou, China
| | - Bingmiao Gao
- School of Pharmacy, Hainan Medical University, Haikou, China
| | - Xiaoliang Li
- School of Pharmacy, Hainan Medical University, Haikou, China
| | - Na Wei
- School of Pharmacy, Hainan Medical University, Haikou, China
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Li M, Li J, Chen H, Zhu M. VEGF-Expressing Mesenchymal Stem Cell Therapy for Safe and Effective Treatment of Pain in Parkinson's Disease. Cell Transplant 2023; 32:9636897221149130. [PMID: 36635947 PMCID: PMC9841873 DOI: 10.1177/09636897221149130] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Vascular endothelial growth factor (VEGF) is a pro-angiogenic factor that mediates the differentiation and function of vascular endothelial cells. VEGF has been implicated in modulating various pains. However, the effects of VEGF in Parkinson's disease (PD)-related pain have not been studied. The goal of this study was to understand the effects of VEGF-expressing mesenchymal stem cells (MSCs) on PD-related pain and the involved mechanisms. We used two types of MSCs: hAMSC-Vector-GFP and hAMSC-VEGF189-GFP in PD mice. Then, the expression of VEGF and the viability have been compared between two types of MSCs. To demonstrate the therapeutic effect of hAMSC-VEGF189-GFP, we transplanted each cell line in a PD mouse model. Head mechanical withdrawal thresholds were examined. hAMSC-VEGF189-GFP was associated with significantly increased VEGF expression and slightly increased viability, compared with hAMSC-Vector-GFP. The transplanted hAMSC-VEGF189-GFP significantly improved mechanical allodynia and inhibited transient receptor potential vanilloid 1 (TRPV1) expression in site. And such pain relief effects could be partially blocked by TRPV1 agonist. However, we did not observe tumor generation or neuron degeneration in hAMSC-VEGF189-GFP-transplanted animals. Taken together, our data suggest that hAMSC-VEGF189-GFP is safely therapeutically appropriate for treating PD-related pain. VEGF inhibits TRPV1 expression, which may contribute to its analgesic properties.
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Affiliation(s)
- Man Li
- Department of Anesthesiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China
| | - Ji Li
- Department of Anesthesiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China
| | - Hong Chen
- Department of Anesthesiology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China
| | - Mingxin Zhu
- Department of Neurosurgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, People’s Republic of China,Mingxin Zhu, Department of Neurosurgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, People’s Republic of China.
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Li M, Zhu M, Xu Q, Ding F, Tian Y, Zhang M. Sensation of TRPV1 via 5-hydroxytryptamine signaling modulates pain hypersensitivity in a 6-hydroxydopamine induced mice model of Parkinson’s disease. Biochem Biophys Res Commun 2020; 521:868-873. [DOI: 10.1016/j.bbrc.2019.10.204] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 10/31/2019] [Indexed: 12/24/2022]
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The Role of Descending Pain Modulation in Chronic Primary Pain: Potential Application of Drugs Targeting Serotonergic System. Neural Plast 2019; 2019:1389296. [PMID: 31933624 PMCID: PMC6942873 DOI: 10.1155/2019/1389296] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 11/02/2019] [Accepted: 11/27/2019] [Indexed: 11/24/2022] Open
Abstract
Chronic primary pain (CPP) is a group of diseases with long-term pain and functional disorders but without structural or specific tissue pathologies. CPP is becoming a serious health problem in clinical practice due to the unknown cause of intractable pain and high cost of health care yet has not been satisfactorily addressed. During the past decades, a significant role for the descending pain modulation and alterations due to specific diseases of CPP has been emphasized. It has been widely established that central sensitization and alterations in neuroplasticity induced by the enhancement of descending pain facilitation and/or the impairment of descending pain inhibition can explain many chronic pain states including CPP. The descending serotonergic neurons in the raphe nuclei target receptors along the descending pain circuits and exert either pro- or antinociceptive effects in different pain conditions. In this review, we summarize the possible underlying descending pain regulation mechanisms in CPP and the role of serotonin, thus providing evidence for potential application of analgesic medications based on the serotonergic system in CPP patients.
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Su YS, Mei HR, Wang CH, Sun WH. Peripheral 5-HT 3 mediates mirror-image pain by a cross-talk with acid-sensing ion channel 3. Neuropharmacology 2017; 130:92-104. [PMID: 29196182 DOI: 10.1016/j.neuropharm.2017.11.044] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 11/10/2017] [Accepted: 11/27/2017] [Indexed: 12/21/2022]
Abstract
Mirror-image pain (MIP), which occurs along with complex regional pain syndrome, rheumatoid arthritis and chronic migraine, is characterized by increased pain sensitivity of healthy body regions other than the actual injured or inflamed sites. A high level of peripheral inflammation may activate central or peripheral glia, triggering mirror-image pain. However, which receptors mediate inflammatory signals to contribute glial activation remains unclear. Intraplantarly injecting mice with 5-hydroxytryptamine (5-HT) or acidic buffer (proton) caused only unilateral hyperalgesia, but co-injection of 5-HT/acid induced bilateral hyperalgesia (MIP). Blocking 5-HT3 or acid-sensing ion channel 3 (ASIC3) abolished satellite glial activation, inhibiting MIP. Interestingly, intraplantar administration of a 5-HT3 agonist induced MIP, and 5-HT3-mediated MIP can be reversed by a 5-HT3 antagonist or an ASIC3 blocker. Similar results were found using a ASIC3 agonist. Furthermore, 5-HT3 was observed to co-localize with ASIC3 in DRG neurons; 5-HT3 activation-induced an increase in intracellular calcium that was inhibited by an ASIC3 blocker and vice versa. A cross-talk between 5-HT3 and ASIC3 mediates satellite glial activation, thereby triggering mirror-image pain.
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Affiliation(s)
- Yeu-Shiuan Su
- Department of Life Sciences, National Central University, Zhongli District, Taoyuan city, Taiwan.
| | - Hao-Ruei Mei
- Department of Life Sciences, National Central University, Zhongli District, Taoyuan city, Taiwan.
| | - Chun-Hung Wang
- Department of Life Sciences, National Central University, Zhongli District, Taoyuan city, Taiwan.
| | - Wei-Hsin Sun
- Department of Life Sciences, National Central University, Zhongli District, Taoyuan city, Taiwan; Department of Biomedical Sciences and Engineering, National Central University, Zhongli District, Taoyuan city, Taiwan.
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8
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Lin Z, Smith MD, Concepcion GP, Haygood MG, Olivera BM, Light A, Schmidt EW. Modulating the Serotonin Receptor Spectrum of Pulicatin Natural Products. JOURNAL OF NATURAL PRODUCTS 2017; 80:2360-2370. [PMID: 28745513 PMCID: PMC6025773 DOI: 10.1021/acs.jnatprod.7b00317] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Serotonin (5-HT) receptors are important in health and disease, but the existence of 14 subtypes necessitates selective ligands. Previously, the pulicatins were identified as ligands that specifically bound to the subtype 5-HT2B in the 500 nM to 10 μM range and that exhibited in vitro effects on cultured mouse neurons. Here, we examined the structure-activity relationship of 30 synthetic and natural pulicatin derivatives using binding, receptor functionality, and in vivo assays. The results reveal the 2-arylthiazoline scaffold as a tunable serotonin receptor-targeting pharmacophore. Tests in mice show potential antiseizure and antinociceptive activities at high doses without motor impairment.
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Affiliation(s)
- Zhenjian Lin
- Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112 USA
| | - Misty D. Smith
- Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah 84112 USA
- School of Dentistry, University of Utah, Salt Lake City, UT 84112 USA
| | - Gisela P. Concepcion
- Marine Science Institute, University of the Philippines, Diliman, Quezon City 1101 Philippines
| | - Margo G. Haygood
- Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112 USA
| | | | - Alan Light
- Department of Anesthesiology, University of Utah, Salt Lake City, Utah 84112 USA
| | - Eric W. Schmidt
- Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112 USA
- Department of Biology, University of Utah, Salt Lake City, Utah 84112 USA
- To whom correspondence should be addressed. Phone: (801) 585-5234. Fax: (801) 585-9119.
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Hsieh WS, Kung CC, Huang SL, Lin SC, Sun WH. TDAG8, TRPV1, and ASIC3 involved in establishing hyperalgesic priming in experimental rheumatoid arthritis. Sci Rep 2017; 7:8870. [PMID: 28827659 PMCID: PMC5566336 DOI: 10.1038/s41598-017-09200-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Accepted: 07/20/2017] [Indexed: 01/13/2023] Open
Abstract
Rheumatoid arthritis (RA), characterized by chronic inflammation of synovial joints, is often associated with ongoing pain and increased pain sensitivity. High hydrogen ion concentration (acidosis) found in synovial fluid in RA patients is associated with disease severity. Acidosis signaling acting on proton-sensing receptors may contribute to inflammation and pain. Previous studies focused on the early phase of arthritis (<5 weeks) and used different arthritis models, so elucidating the roles of different proton-sensing receptors in the chronic phase of arthritis is difficult. We intra-articularly injected complete Freund’s adjuvant into mice once a week for 4 weeks to establish chronic RA pain. Mice with knockout of acid-sensing ion channel 3 (ASIC3) or transient receptor potential/vanilloid receptor subtype 1 (TRPV1) showed attenuated chronic phase (>6 weeks) of RA pain. Mice with T-cell death-associated gene 8 (TDAG8) knockout showed attenuated acute and chronic phases of RA pain. TDAG8 likely participates in the initiation of RA pain, but all three genes, TDAG8, TRPV1, and ASIC3, are essential to establish hyperalgesic priming to regulate the chronic phase of RA pain.
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Affiliation(s)
- Wei-Shan Hsieh
- Department of Life Sciences, National Central University, Zhongli, Taoyuan city, Taiwan
| | - Chia-Chi Kung
- Department of Life Sciences, National Central University, Zhongli, Taoyuan city, Taiwan.,Department of Anesthesiology, National Taiwan University Hospital Hsin-Chu Branch, Hsin-Chu, Taiwan
| | - Shir-Ly Huang
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan
| | - Shih-Chang Lin
- Department of Immunology, Cathy General Hospital, Taipei, Taiwan
| | - Wei-Hsin Sun
- Department of Life Sciences, National Central University, Zhongli, Taoyuan city, Taiwan.
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Effects of fluoxetine on changes of pain sensitivity in chronic stress model rats. Neurosci Lett 2017; 651:16-20. [PMID: 28461139 DOI: 10.1016/j.neulet.2017.04.062] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 04/05/2017] [Accepted: 04/07/2017] [Indexed: 12/28/2022]
Abstract
Exposure to stress could facilitate or inhibit pain responses (stress-induced hyperalgesia or hypoalgesia, respectively). Fluoxetine is a selective serotonin (5-HT) reuptake inhibitor antidepressant. There have been contradictory reports on whether fluoxetine produces antinociceptive effects. The purpose of this study was to elucidate changes in pain sensitivity after chronic stress exposure, and the effects of fluoxetine on these changes. We measured thermal, mechanical, and formalin-induced acute and inflammatory pain by using the tail-flick, von Frey, and formalin tests respectively. The results showed that rats exposed to chronic stress exhibited thermal and formalin-induced acute and inflammatory hypoalgesia and transient mechanical hyperalgesia. Furthermore, fluoxetine promoted hypoalgesia in thermal and inflammatory pain and induced mechanical hyperalgesia. Our results indicate that the 5-HT system could be involved in hypoalgesia of thermal and inflammatory pain and induce transient mechanical hyperalgesia after stress exposure.
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