Objective To observe the effect of electroacupuncture(EA)at"Tianshu"(ST 25)on visceral pain and colonic mast cell(MCs)number and tryptase and SP expression in post-infectious irritable bowel syndrome(PI-IBS)rats

so as to reveal its mechanisms underlying improvement of PI-IBS.Methods Forty-five female Wistar rats were randomly divided into control

model and EA groups(15 rats/group

3 rats/group used for H.E.staining

and 12 rats/group for immunohistochemistry).The PI-IBS model was established by intra-anal injection of mixed liquor of 50% ethyl alcohol and trinitro-benzene-sulfonic acid(TNBS).EA(2 Hz/15 Hz

0.5-1.0 mA)was applied to bilateral"Tianshu"(ST 25)for 30 min

once every day for 14 days.The visceral pain was measured by abdominal withdrawal reflex(AWR)

for which the rectal implanted air balloon was dilated by infusion of normal saline.The histopathological changes of the colon tissue were observed after H.E.staining

and the colonic MCs were displayed by Toluidine blue staining.The expression of tryptase and SP proteins in the colon specimens were detected by immunohistochemistry.Results The AWR threshold was significantly lowered in the model group relevant to the control group(P<0.05)and considerably increased after EA intervention in comparison with the model group(P<0.05).The number of MCs and the expression levels of colonic tryptase and SP proteins in the colon tissues were significantly higher in the model group than in the control group(P<0.05)

and obviously lower after EA intervention in the EA group than in the model group(P<0.05).Conclusion EA of"Tianshu"(ST 25)can inhibit visceral pain in PI-IBS rats

which may be associated with its effects in activating MCs and down-regulating the expression of tryptase and SP proteins in the colonic tissues.