BACKGROUNDAcupuncture is an effective way to relieve pain, but the mechanism by which electroacupuncture (EA) decreases the visceral pain state still remains unclear. This study aimed to evaluate the effects of pre-electroacupuncture on pain behaviors, p38 phosphorylation, and c-Fos protein and mRNA expression in both the colonic wall and spinal dorsal horn of rats suffering from visceral pain. This study also investigated the probable signaling regulatory mechanism of the analgesic effect induced by electroacupuncture.

METHODSAll rats were randomized into the control (Con) group, the Con + EA group, the visceral pain (VP) group, and VP + EA group (n = 8 for all groups). The visceral pain model was established using 40 microl of 5% formalin solution injected into the colon of rats. EA was applied to the bilateral Jiaji acupoints for 20 minutes before application of visceral pain. Parameters for EA were set at a continuous wave (20 Hz) and intensity where the rats shook their whiskers but did not scrabble (< or = 1 mA). The visceral pain score was recorded and the expressions of p38 and c-Fos protein were detected using Western blotting. Real-time quantitative PCR was also used to determine the expression of c-Fos mRNA.

RESULTSRats in the VP group immediately presented with obvious visceral pain behaviors after being injected with formalin. p38 activity and c-Fos protein and mRNA expression in both the colonic wall and spinal dorsal horn were higher in the VP group than in the Con group (P < 0.05). By contrast, visceral pain behaviors were delayed in rats from the VP + EA group. p38 activity and c-Fos protein and mRNA expression were lower in the VP + EA group than that in the VP group (P < 0.01).

CONCLUSIONSPre-electroacupuncture of the Jiaji acupoint has prophylactic analgesic effects on rats suffering from visceral pain. The p38 signal transduction pathway may be partly involved in the regulatory mechanism of this analgesic effect.