Effect of Electroacupuncture on the Pathomorphology of the Sciatic Nerve and the Sensitization of P2X3 Receptors in the Dorsal Root Ganglion in Rats with Chronic Constrictive Injury

Objective： To explore the effect of electroacupuncture （EA） on the pathomorphology of the sciatic nerve and the role of P2X3 receptors in EA analgesia. Methods： The chronic constriction injury （CCI） model was adopted in this study. A total of 32 rats were randomly divided into four groups： sham CCI, CCI, CCI plus contralateral EA （CCI ＋ conEA） and CCI plus ipsilateral EA （CCI ＋ ipsEA）. Mechanical withdrawal threshold （MWT） and thermal withdrawal latency OWL） were measured. EA began at day 7 after the CCI operation and was applied to the Zusanli （ST 36） and Yanglingquan acupoints （GB 34）. At day 14, the pathomorphologic changes of the operated sciatic nerve were demonstrated by hematoxylin and eosin staining. In addition, dorsal root ganglion （DRG） neurons isolated from rats were examined by electrophysiological recording to determine if the P2X3 receptor agonists, adenosine 5＇-tdphosphate disodium （ATP） and α, 13 -methylen-ATP （or, 13 -meATP） evoked inward currents. Results： Pain thresholds in the CCI group were obviously decreased post CCI surgery （P〈0.01）. In the EA groups, thermal and mechanical threshold values were increased after the last EA treatment （P〈0.05, P〈0.01）. There was no significant difference in light microscopic examination among the four groups （P〉0.05）. Current amplitude after application of ATP and or, 13 -meATP in DRG neurons were much larger in the CCI group compared to those obtained in sham CCI （P〈0.05）. ATP and α, 13 -meATP invoked amplitudes in the CCI ＋ EA groups were reduced. There was no significant difference between the CCI ＋ conEA group and the CCI ＋ ipsEA group （P〉0.05）. Conclusion： EA analgesia may be mediated by decreasing the response of P2X8 receptors to the agonists ATP and or, 13 -meATP in the DRG of rats with CCI. No pathological changes of the sciatic nerve of rats were observed after EA treatment.