Objective: To observe the effect of electroacupuncture (EA) of "Hegu"(LI4) and "Zusanli"(ST36)on changes of intestinal sensitivity and colonic motility and expression of colonic 5-hydroxytryptamine 3A receptor (5-HT_3AR) in irritable bowel syndrome (IBS) rats, so as to reveal its mechanism underlying improvement of IBS.

Methods: A total of 40 neonatal Wistar rats were randomly and equally divided into normal control, model, LI4 and ST36 groups (n＝10). The IBS model was induced by mother-infant separation, acetic acid enema and colorectal distension (CRD). EA (2 Hz/100 Hz, a tolerable strength) was applied to bilateral LI4 and ST36 for 20 min, once every other day for 5 times. The Bristol stool form scale was used to assess the gastrointestinal function, and the latency and number of abdominal muscular contraction waves of abdominal withdrawal reflex (AWR) were used to evaluate the intestinal sensitivity and motility respectively. The immunoactivity of 5-HT_3AR of the colon tissue was detected by immunohistochemistry.

Results: After modeling, the score of Bristol fecal form scale, number of muscular contraction waves and expression levels of colonic 5-HT_3AR in the myometrium and mucosal layers were significantly increased (P<0.01), and the latency of muscular initial contraction wave was obviously shortened in the model group relevant to the normal control group (P<0.01). After the intervention, the increased Bristol fecal form score, number of muscular contraction waves and expression levels of 5-HT_3AR in the myometrium and mucosal layers as well as the decreased latency of muscular contraction were reversed in both LI4 and ST36 groups (P<0.01, P<0.05). The effect of EA of ST36 was significantly superior to those of EA-LI4 in lowering Bristol fecal scale score and 5-HT_3AR expression in the muscular layer (P<0.01), but obviously inferior to those of EA-LI4 in increasing the latency of of muscular initial contraction wave and down-regulating muscular contraction waves and 5-HT_3AR expression in the mucosal layer (P<0.05, P<0.01).

Conclusion: Both EA-LI4 and EA-ST36 can significantly improve the symptoms of abdominal pain and diarrhea, but EA-LI4 is better in suppressing intestinal high sensitivity, and EA-ST36 is better in promoting intestinal motility, suggesting a specificity of effect of acupoints of different meridians.