Electroacupuncture at "Jiaji" (EX-B2) induced down-regulation of OX-42 and P2X4 in lumbar spinal cord contributes to its analgesic after-effect in rats with chronic constriction injury

Abstract

To investigate the effect of electroacupuncture (EA) at "Jiaji" (EX-B2) at different time points on the expression of OX-42 (a monoclonal antibody with specific expression of complement receptor-3 in spinal microglial cells) and purinergic receptor P2X4 (P2X4) in rats with chronic constriction injury (CCI) of the sciatic nerve, as well as the possible after-effect mechanism of EA analgesia in neuropathic pain. Sprague-Dawley rats were randomly divided into blank group, model group, immediately after EA group, 0.5-hour after EA group, 1-hour after EA group, 2-hour after EA group, 4-hour after EA group, 12-hour after EA group, and 24-hour after EA group, with 6 rats in each group. The rats in the model group and the EA groups were used to establish a model of CCI-induced neuropathic pain, and those in the immediately after EA group and the 0.5, 1, 2, 4, 12 and 24 hours after EA groups were treated with EA at bilateral L3 and L5 "Jiaji" points for 20 min after 7 d of modeling. Samples were collected immediately and at 0.5, 1, 2, 4, 12, and 24 hours after EA, and for the rats in the blank group and the model group, samples were collected after fixation the rats for 20 min. Heat pain threshold was observed before and after intervention, and immunohistochemistry was used to measure the protein expression of OX-42 and P2X4 in the spinal cord lumbar enlargement. After 7 days of modeling (before intervention), compared with the blank group, the heat pain threshold had a significant reduction in the model group and the EA groups (P<0.01). Compared with the model group after intervention, the immediately after EA group and the 0.5, 1 and 2 hours after EA groups had a significant increase in heat pain threshold (P<0.05). Compared with the model group, immediately after EA, the 0.5, 1 and 2 hours after EA groups had a significant reduction in the protein expression of OX-42 (P<0.01), and immediately after EA, the 0.5 and 1 hour after EA groups had a significant reduction in the protein expression of P2X4 (P<0.01). EA at "Jiaji" points can significantly increase heat pain threshold and down-regulate the protein expression of OX-42 and P2X4 in the spinal cord of CCI rats. The analgesic effect can last for 2 h.