The aim of the present study was to assess the effect of electro-acupuncture (EA) stimulation on remifentanil-induced postoperative hyperalgesia (RIPH) and the possible involvement of spinal microglia suppression. A model of RIPH was established using adult male Sprague-Dawley rats by administration of remifentanil at 0.08 mg/kg intravenously for 60 min. The Huantiao and Yanglingquan acupoints were stimulated continuously by EA (2 Hz, ~1 mA) for 90 min from before paw incision to the end of remifentanil administration. Sham acupoints were stimulated by EA in the sham group. Paw withdrawal threshold (PWT) and paw thermal withdrawal latency (PWL) were determined. Cluster of differentiation (CD)11b, tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6 levels in spinal cord samples were measured using immunohistochemistry and ELISA. PWT and PWL values were decreased following the administration of remifentanill; however, following EA, PWT and PWL values increased compared with the sham group (P<0.05), indicating that EA alleviates remifentanil-induced RIPH. CD11b, TNF-α, IL-1β and IL-6 levels were increased following remifentanil administration and these effects were counteracted by EA (all P<0.05). In the sham group, no significant differences were observed in PWT and PWL values or CD11b, TNF-α, IL-1β and IL-6 levels compared with the control group, suggesting that EA was responsible for the reduction in CD11b and pro-inflammatory cytokine expression following remifentanil administration. The results of the present study demonstrated that EA at the Huantiao and Yanglingquan acupoints may reduce remifentanil-induced postoperative hyperalgesia, likely by inhibiting spinal microglia via reduction of CD11b and pro-inflammatory cytokine expression. However, these results are preliminary and require further validation.
Keywords: electro-acupuncture; microglia; postoperative hyperalgesia; pro-inflammatory cytokines; remifentanil.