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      Pulsed radiofrequency inhibits expression of P2X 3 receptors and alleviates neuropathic pain induced by chronic constriction injury in rats

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          Abstract

          Background:

          Pulsed radiofrequency (PRF) is a minimally invasive interventional technique that provides a novel and effective treatment strategy for neuropathic pain (NP). PRF is advantageous because it does not damage nerves and avoids sensory loss after treatment. At present, animal studies have demonstrated that PRF is safe and effective for relieving the NP associated with sciatic nerve damage in rats with chronic constriction injury (CCI). However, the mechanism through which this effect occurs is unknown. An increasing body of evidence shows that the expression of the P2X ligand-gated ion channel 3 (P2X 3) receptor is closely related to NP; this study was to investigate whether the expression of this receptor is involved in NP relief due to PRF.

          Methods:

          A total of 36 healthy adult male Sprague-Dawley (SD) rats were randomly divided into three groups: Sham group, CCI group, and PRF group. The right sciatic nerve was ligated in CCI group and PRF group to establish a CCI model; the right sciatic nerve was separated but not ligated in Sham group. On day 14 after the operation, PRF was administered to the ligated sciatic nerve in PRF group (42°C, 45 V, 2 min). A non-live electrode was placed at the exposed sciatic nerve for the rats in Sham and CCI groups. The hindpaw withdrawal threshold (HWT) and thermal withdrawal latency (TWL) were measured at the right hindpaw at different time points before and after PRF or sham therapy. On day 28 after treatment, the dorsal root ganglion (DRG) and spinal dorsal horn of the right L4–6 were harvested from each group to determine the mRNA and protein levels of the P2X 3 receptor.

          Results:

          On day 28 after PRF treatment, the HWT (8.33 ± 0.67 g vs. 3.62 ± 0.48 g) and TWL (25.42 ± 1.90 s vs. 15.10 ± 1.71 s) were significantly higher in PRF group as compared to CCI group ( P < 0.05). The mRNA expression of the P2X 3 receptor in the DRG in PRF group was 23.7% lower than that in CCI group ( P < 0.05), in the spinal dorsal horns in PRF group was 22.7% lower than that in CCI group ( P < 0.05). The protein expression of the P2X 3 receptor in the DRG in PRF group was 27.8% lower than that in CCI group ( P < 0.05), in the spinal dorsal horns in PRF group was 35.6% lower than that in CCI group ( P < 0.05).

          Conclusion:

          PRF possibly reduces NP in CCI rats by inhibiting the expression of the P2X 3 receptor in the L4–6 DRG and spinal dorsal horns.

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          Most cited references 31

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          Neuropathic pain: redefinition and a grading system for clinical and research purposes.

          Pain usually results from activation of nociceptive afferents by actually or potentially tissue-damaging stimuli. Pain may also arise by activity generated within the nervous system without adequate stimulation of its peripheral sensory endings. For this type of pain, the International Association for the Study of Pain introduced the term neuropathic pain, defined as "pain initiated or caused by a primary lesion or dysfunction in the nervous system." While this definition has been useful in distinguishing some characteristics of neuropathic and nociceptive types of pain, it lacks defined boundaries. Since the sensitivity of the nociceptive system is modulated by its adequate activation (e.g., by central sensitization), it has been difficult to distinguish neuropathic dysfunction from physiologic neuroplasticity. We present a more precise definition developed by a group of experts from the neurologic and pain community: pain arising as a direct consequence of a lesion or disease affecting the somatosensory system. This revised definition fits into the nosology of neurologic disorders. The reference to the somatosensory system was derived from a wide range of neuropathic pain conditions ranging from painful neuropathy to central poststroke pain. Because of the lack of a specific diagnostic tool for neuropathic pain, a grading system of definite, probable, and possible neuropathic pain is proposed. The grade possible can only be regarded as a working hypothesis, which does not exclude but does not diagnose neuropathic pain. The grades probable and definite require confirmatory evidence from a neurologic examination. This grading system is proposed for clinical and research purposes.
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            A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man.

             Gary Bennett,  Y. Xie (1988)
            A peripheral mononeuropathy was produced in adult rats by placing loosely constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and, possibly, spontaneous pain (or dysesthesia) were produced. Hyperalgesic responses to noxious radiant heat were evident on the second postoperative day and lasted for over 2 months. Hyperalgesic responses to chemogenic pain were also present. The presence of allodynia was inferred from the nocifensive responses evoked by standing on an innocuous, chilled metal floor or by innocuous mechanical stimulation, and by the rats' persistence in holding the hind paw in a guarded position. The presence of spontaneous pain was suggested by a suppression of appetite and by the frequent occurrence of apparently spontaneous nocifensive responses. The affected hind paw was abnormally warm or cool in about one-third of the rats. About one-half of the rats developed grossly overgrown claws on the affected side. Experiments with this animal model may advance our understanding of the neural mechanisms of neuropathic pain disorders in humans.
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              siRNA relieves chronic neuropathic pain.

              Double stranded, short interfering RNAs (siRNA) of 21-22 nt length initiate a sequence-specific, post-trancriptional gene silencing in animals and plants known as RNA interference (RNAi). Here we show that RNAi can block a pathophysiological pain response and provide relief from neuropathic pain in a rat disease model by down regulating an endogenous, neuronally expressed gene. Rats, intrathecally infused with a 21 nt siRNA perfectly complementary to the pain-related cation-channel P2X3, showed diminished pain responses compared to missense (MS) siRNA-treated and untreated controls in models of both agonist-evoked pain and chronic neuropathic pain. This form of delivery caused no adverse effects in any of the animals receiving P2X3 siRNA, MS siRNA or vehicle. Molecular analysis of tissues revealed that P2X3 mRNA expressed in dorsal root ganglia, and P2X3 protein translocated into the dorsal horn of the spinal cord, were significantly diminished. These observations open a path toward use of siRNA as a genetic tool for drug target validation in the mammalian central nervous system, as well as for proof of concept studies and as therapeutic agents in man.
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                Author and article information

                Journal
                Chin Med J (Engl)
                Chin. Med. J
                CM9
                Chinese Medical Journal
                Wolters Kluwer Health
                0366-6999
                2542-5641
                20 July 2019
                20 July 2019
                : 132
                : 14
                : 1706-1712
                Affiliations
                [1 ]Department of Anesthesiology, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital and Institute, Beijing 100142, China
                [2 ]Department of Pain Management, Beijing Tiantan Hospital, Capital Medical University, Beijing 100050, China
                [3 ]Department of Anesthesiology and Pain Management, Beijing Tiantan Hospital, Capital Medical University, Beijing 100050, China.
                Author notes
                Correspondence to: Prof. Fang Luo, Department of Pain Management, Beijing Tiantan Hospital, Capital Medical University, Beijing 100050, China E-Mail: luofangwt@ 123456yahoo.com
                Article
                CMJ-2018-362
                10.1097/CM9.0000000000000302
                6759093
                31261200
                Copyright © 2019 The Chinese Medical Association, produced by Wolters Kluwer, Inc. under the CC-BY-NC-ND license.

                This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. http://creativecommons.org/licenses/by-nc-nd/4.0

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