Electroacupuncture Relieves Pain by Down-regulating Expression of Hippocampal High Mobility Group Protein 1 and Contents of TNF-α and IL-1 β in Rats with Chronic Neuropathic Pain

Abstract

To observe the effect of electroacupuncture (EA) on expression of high mobility group protein 1 (HMGB 1) and related downstream effectors of proinflammatory cytokines in the hippocampus in chronic neuropathic pain rats, so as to investigate its mechanism underlying neuropathic pain relief. Male SD rats were randomized into sham, model, and EA groups, with 12 rats in each group. The neuropathic pain model was established by ligature of the left sciatic nerve to induce chronic constriction injury (CCI). EA was applied to bilateral "Zusanli"(ST 36) and "Yanglingquan"(GB 34) for 30 min, once daily for 7 days. The mechanical withdrawal threshold (WMT) was detected using an electronic von Frey anesthesiometer. The expression level of HMGB 1 in the hippocampus was determined using quantitative RT-PCR and Western blot, separately, and the contents of hippocampal TNF-α and IL-1 β were detected by ELISA. Compared with the sham group, the MWT values were markedly decreased on day 7, 10 and 14 after modeling in the model group (P<0.001). On day 10 and 14 after modeling, the MWT values were significantly up-regulated in the EA group relevant to those of the model group (P<0.05, P<0.01). The expression levels of HMGB1 mRNA and protein, and the contents of hippocampal TNF-α and IL-1 β were markedly increased in the model group relevant to the sham group (P<0.001), and significantly down-regulated in the EA group relevant to the model group (P<0.001, P<0.01, P<0.05). EA stimulation of ST 36-GB 34 can relieve pain in chronic neuropathic pain rats, which may be related to its actions in down-regulating the levels of HMGB 1 and its downstream proinflammatory cytokines TNF-α and IL-1 β in the hippocampus.