Comparison of effects of electroacupuncture at "Tianshu" (ST25) and "Dachangshu" (BL25) on intestinal sensitivity and expression of muscarinic M3R and 5-HT3AR in irritable bowel syndrome rats

Abstract

To observe and compare the effect of electroacupuncture (EA) of "Tianshu" (ST25) and "Dachangshu" (BL25) on intestinal sensitivity and the expression of M3 muscarinic acetylcholine receptor (M3R) and 5-hydroxytryptamine 3A receptor (5-HT3AR) in the colon tissue in irritable bowel syndrome (IBS) rats, so as to explore its mechanism underlying improvement of IBS. Forty newborn Wistar rats were randomly divided into blank control, model, ST25 and BL25 groups (n＝10 rats per group). The IBS model was established by joint application of maternal separation, acetic acid enema plus colorectal distension from day 8 to 21 after birth. At the age of 9 weeks, EA (2 Hz/100 Hz, 0.1－0.3 mA) was applied to ST25 and BL25 for 20 min, once every other day for 5 times. The modified method was used to record the abdominal withdrawal reflex (AWR), so as to evaluate the visceral sensitivity by referring to the modified Al-Chaer's and colleagues' methods. The threshold (initial wave), the number and peak-peak value of contraction waves (AWR) within 90 s were recorded. The immunoactivity of M3R and 5-HT3AR in the colon tissue was detected by immunohistochemistry. After modeling, the latency was obviously shortened, the number and peak-peak values of contraction waves of intestine were significantly increased, and the immunoactivity of M3R and 5-HT3AR was notably up-regulated in the model group compared with the blank control group (P<0.01). After the EA intervention, the latency was obviously prolonged, the peak-peak value in both ST25 and BL25 groups, and the number of contraction waves in the ST25 group were significantly decreased (P<0.01), and the expression levels of M3 and 5-HT3A R were considerably down-regulated in both ST25 and BL25 groups relevant to the model group (P<0.01). The therapeutic effects were significantly better in the ST25 group than in the BL25 group in prolonging the latency and reducing the contraction wave number, and in down-regulating the expression of colonic M3R and 5-HT3AR (P<0.05, P<0.01). EA at ST25 and BL25 can reduce the intestinal sensitivity in IBS rats, which is probably associated with its effects in down-regulating the expression of M3R and 5-HT3AR in the colon. The therapeutic effects of ST25 were obviously better than those of BL25 in suppressing intestinal sensitivity and expression of colonic M3R and 5-HT3AR.