Electro-acupuncture attenuates behavioral hyperalgesia and selectively reduces spinal Fos protein expression in rats with persistent inflammation

Abstract

This study examined the effect of electro-acupuncture (EA) on persistent inflammatory hyperalgesia in a rat model. Inflammation and hyperalgesia were induced by injecting complete Freund's adjuvant (CFA) into one hindpaw of the rat. Hyperalgesia was determined by a decrease in paw withdrawal latencies (PWL) to a noxious thermal stimulus. EA was applied bilaterally at the acupuncture point Huantiao (G30) at the rat's hindlimbs. EA-treated rats (n = 11) had significantly longer PWLs as compared with placebo control rats (n = 7) in the inflamed paw at 2.5 hours and 5 days after injection of CFA (P < .05) and longer PWLs as compared to sham control rats (n = 9) at 2.5 hours (P > .05). Paw edema was significantly reduced in EA-treated rats versus placebo controls at 24 hours after inflammation (P < .01). Inflammation-induced spinal Fos expression in the medial half of laminae I-II in EA-treated rats versus placebo rats (n = 5 per group) was significantly reduced (P < .01). These data showed that EA delayed the onset and facilitated the recovery of inflammatory hyperalgesia and suppressed the inflammation-induced spinal Fos expression in neurons (laminae I-II) involved in receiving noxious stimulation. This rat model of persistent pain and inflammation seems to be an ideal animal model for studying the effect of acupuncture.