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      Electroacupuncture Regulates Pain Transition by Inhibiting the mGluR5-PKCε Signaling Pathway in the Dorsal Root Ganglia

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          Abstract

          Background

          Acute pain can transition to chronic pain, presenting a major clinical challenge. Electroacupuncture (EA) can partly prevent the transition from acute to chronic pain. However, little is known about the mechanisms underlying the effect of EA. This study investigated the effect of EA on pain transition and the activation of metabotropic glutamate receptor 5 (mGluR5)–protein kinase C epsilon (PKCε) signaling pathway in the dorsal root ganglia (DRG).

          Methods

          The hyperalgesic priming model was established by the sequential intraplantar injection of carrageenan (1%, 100 μL) and prostaglandin E2 (PGE2) into the left hind paw of rats. EA treatment (2/100 Hz, 30 min, once/day) was applied at bilateral Zusanli (ST36) and Kunlun (BL60) acupoints in rats. Von Frey filaments were used to investigate the mechanical withdrawal threshold (MWT) at different time points. The protein expression levels of mGluR5 and PKCε in the ipsilateral L4-L6 DRGs of rats were detected by Western blot. Some pharmacological experiments were performed to evaluate the relationship between mGluR5, PKCε and the MWT. It was also used to test the effects of EA on the expression levels of mGluR5 and PKCε and changes in the MWT.

          Results

          Sequential injection of carrageenan and PGE2 significantly decreased the MWT of rats and up-regulated the expression level of mGluR5 and PKCε in the ipsilateral L4-L6 DRGs. EA can reverse the hyperalgesic priming induced by sequential injection of carrageenan/PGE and down-regulate the protein expression of mGluR5 and PKCε. Glutamate injection instead of PGE2 can mimic the hyperalgesic priming model. Pharmacological blocking of mGluR5 with specific antagonist MTEP can prevent the hyperalgesic priming and inhibit the activation of PKCε in DRGs. Furthermore, EA also produced analgesic effect on the hyperalgesic priming rats induced by carrageenan/mGluR5 injection and inhibited the high expression of PKCε. Sham EA produced none analgesic and regulatory effect.

          Conclusion

          EA can regulate pain transition and it may relate with its inhibitory effect on the activation of mGluR5-PKCε signaling pathway in the DRGs.

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          Most cited references 41

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          Risk of upper and lower gastrointestinal bleeding in patients taking nonsteroidal anti-inflammatory drugs, antiplatelet agents, or anticoagulants.

          Treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) or low-dose aspirin is associated with increased risk of upper gastrointestinal bleeding. There is little evidence on the risk of lower gastrointestinal bleeding with NSAIDs, antiplatelet agents (APAs), or anticoagulants. We aimed to quantify the relative risk (RR) of upper and lower gastrointestinal bleeding associated with use of NSAIDs, APAs, or anticoagulants.
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            Socio-economic differences in the prevalence of acute, chronic and disabling chronic pain among ageing employees.

            Pain is a strong predictor of reduced work ability and well-being, but there is little information on the prevalence of and socio-economic differences in acute, chronic and disabling chronic pain among employees. A questionnaire survey conducted in 2000-2002 among employees aged 40, 45, 50, 55 and 60 of the City of Helsinki (N=8970, response rate 67%) included socio-demographic and socio-economic factors and measures of current pain, pain duration and pain-related disability. Pain was acute when lasting a maximum of 3 months and chronic when persisting for more than 3 months. Disabling chronic pain was determined using the disability subscale of Von Korff's Chronic Pain Grade questionnaire. Acute pain was reported by 15% of women, chronic pain by 29% and disabling chronic pain by 7%. The corresponding figures for men were 12, 24 and 5%. Chronic and disabling chronic pain were more common in older age groups among both genders. Among women, those with secondary or basic education were more likely to report chronic or disabling chronic pain than those with higher education, and semi-professionals, routine non-manual employees and manual workers were more likely to report disabling chronic pain than managers. Among men, separated/divorced or widowed men were more likely to report acute pain than married men, and manual workers were more likely to report chronic pain than managers. Chronic pain was relatively common in this population, and those with older age, lower education and occupational class appear to be at excess risk for chronic pain, especially for disabling chronic pain.
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              Chronic hypersensitivity for inflammatory nociceptor sensitization mediated by the epsilon isozyme of protein kinase C.

              We have identified a mechanism, mediated by the epsilon isozyme of protein kinase C (PKCepsilon) in peripheral neurons, which may have a role in chronic inflammatory pain. Acute inflammation, produced by carrageenan injection in the rat hindpaw, produced mechanical hyperalgesia that resolved by 72 hr. However, for up to 3 weeks after carrageenan, injection of the inflammatory mediators prostaglandin E(2) or 5-hydroxytryptamine or of an adenosine A(2) agonist into the same site induced a markedly prolonged hyperalgesia (>24 hr compared with 5 hr or less in control rats not pretreated with carrageenan). A nonselective inhibitor of several PKC isozymes and a selective PKCepsilon inhibitor antagonized this prolonged hyperalgesic response equally. Acute carrageenan hyperalgesia could be inhibited by PKA or PKG antagonists. However, these antagonists did not inhibit development of the hypersensitivity to inflammatory mediators. Our findings indicate that different second messenger pathways underlie acute and prolonged inflammatory pain.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                JPR
                jpainres
                Journal of Pain Research
                Dove
                1178-7090
                19 June 2020
                2020
                : 13
                : 1471-1483
                Affiliations
                [1 ]Department of Neurobiology and Acupuncture Research, The Third Clinical Medical College, Zhejiang Chinese Medical University, Key Laboratory of Acupuncture and Neurology of Zhejiang Province , Hangzhou 310053, People’s Republic of China
                Author notes
                Correspondence: Jianqiao Fang; Junfan Fang Email fangjianqiao7532@163.com; fangjunfan0223@163.com;
                [*]

                These authors contributed equally to this work

                Article
                251948
                10.2147/JPR.S251948
                7311359
                © 2020 Wang et al.

                This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms ( https://www.dovepress.com/terms.php).

                Page count
                Figures: 5, References: 47, Pages: 13
                Funding
                Funded by: National Natural Science Foundation of China 10.13039/501100001809
                Funded by: Natural Science Foundation China
                Funded by: Association for Science and Technology
                The study was supported by grants from the National Natural Science Foundation of China (81603692, 81603690), the Zhejiang Provincial Natural Science Foundation China (LY19H270003, LY20H270006) and the Talent Project of Zhejiang Association for Science and Technology (2017YCGC004).
                Categories
                Original Research

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