Effects of Electroacupuncture on Delta Opioid Receptor mRNA Expression in the Local Focus Tissues of Arthritis Rats

Objective: To observe the effect of electroacupuncture(EA) on delta(δ)-opioid receptor gene expression in the inflammatory tissue in adjuvant arthritis rats so as to study the underlying peripheral mechanism of EA analgesia.Methods: Thirty-two SD rats were randomized into control,model,EA(model+EA) and normal+EA(normal animals) groups with 8 cases in each group.EA(2-(4 V),20-(100 Hz)) was applied to Xuanzhong(GB 39) and Kunlun(BL 60) for(20 min),once daily,and 6 sessions all together.Arthritis model was established by injection of Freund's complete adjuvant((0.1 mL)) in the rat's right hind-paw.The latency of radiation-heat irradiation induced leg withdrawal was considered as the pain threshold.At the end of experiments,the animals anesthetized with 3% phenobarbital((30 mg/kg)) were transcardiacally perfused with 4% paraformaldehyde and 0.1% diethylpyrocarbonate,followed by taking the local focus tissue.After routine treatment,the tissue samples were embedded with paraffin,cut into sections((6 μm)) and processed with in situ hybridization histochemistry for observing the expression of delta opioid receptor mRNA.Results: ① Compared with control group,the pain threshold of model group declined significantly((P0.01)),while comparison between EA and model groups,and between normal+EA and model groups showed that the pain thresholds of two EA groups were significantly higher((P0.01)),and the threshold of normal+EA group was also significantly higher than that of EA group((P0.01)).No significant difference was found between control and EA groups in the pain threshold((P0.05)),indicating that EA could raise the pain threshold in both arthritis and normal rats.② Compared with model group,the number of δ opioid receptor mRNA expression-positive cells of EA group was remarkably more((P0.01)),showing marked upregulation of δ opioid receptor mRNA expression in the focal tissue after EA.Conclusion: EA has a definite analgesic effect in arthritis rats,which may be related to its effect in upregulating the expression of δ opioid receptor mRNA expression.