Objective To observe the effect of electroacupuncture(EA) of "Tianshu"(ST 25) on colonic smooth muscle structure and interstitial cells of Cajal(ICC) in slow transit constipation(STC) rats

so as to investigate its mechanism underlying improving STC.Methods Wistar rats(n=56) were randomly allocated to control(n=20)

model and EA groups(n=18/group).STC model was established by feeding the rats with forage containing compound Diphenoxylate.EA(0.8-1.3 mA

2 Hz/15 Hz) was applied to bilateral "Tianshu"(ST 25) for 15 min

once daily for 14 days.The treatment was given beginning from the next day on after the rat's first black stool excretion was found.The colonic smooth muscle structure was observed under microscope after sectioning and HE staining.The immunoactivity(average optical density

OD) of intestinal immuno-reaction(IR) po-sitive ICC product was detected by immunohistochemistry.Results ①Microscopic observation displayed that after mode-ling

the rat's intestinal mucosa gland showed atrophy with reduction in the acinar number

being sparse in distribution;and the smooth muscle thickness was obviously thinner compared with the normal control group(P<0.05).Whereas this situation of the colonic smooth muscle in the EA group was close to that of the normal control group.Compared with the model group

the thickness of the intestinal smooth muscle in the EA group was significantly bigger(P<0.05).②Immunohistochemical results showed that the average OD values and number of IR-positive colonic ICC in the model group were obviously decreased in comparison with the normal control group(P<0.05).Compared with the model group

the average OD values and the number of IR-positive colonic ICC in the EA group were upregulated considerably(P<0.05).Conclusion EA of bilateral "Tianshu"(ST 25) is able to improve STC-induced structural changes of the colonic smooth muscle

and upregulate expression of colonic ICC in STC rats

which may be responsible for its efficacy in improving STC.