Electrical neuromodulation at acupoint ST36 normalizes impaired colonic motility induced by rectal distension in dogs

Electroacupuncture (EA) has been shown to improve impaired gastric motility and slow waves in both humans and animals. However, its effects on colonic motility have rarely been investigated. The aim of this study was to investigate the effects and underlying mechanisms of EA on impaired colonic motility induced by rectal distension (RD) in dogs. Colon contractions and transit were measured in various sessions with and without EA in hound dogs chronically placed with a colonic cannula. Colonic contractile activity was assessed by motility index (MI). Autonomic functions were determined by the spectral analysis of the heart rate variability derived from the electrocardiogram. It was found 1) RD suppressed colonic motility by 40.5% (10.8 +/- 0.9 with RD vs. 6.4 +/- 0.8 at baseline, P < 0.002). EA at ST36 normalized colonic contractions suppressed by RD (12.9 +/- 2.8, P < 0.002 vs. RD and P = 0.1 vs. control). 2) Administration of atropine blocked the ameliorating effect of EA on colon motility. 3) RD also delayed colonic transit (65.0 +/- 2.0% with RD vs. 86.0 +/- 1.9% without RD, P < 0.001) that was restored with EA (84.0 +/- 1.9%, P = 0.178 vs. control). 4) EA increased vagal activity suppressed by RD (0.37 +/- 0.07 with RD + EA vs. 0.09 +/- 0.03 with RD without EA, P < 0.001). In conclusion, RD inhibits colonic contractions and delays colonic transit in dogs; EA at ST36 restores the RD-induced impairment in both colonic contraction and transit by enhancing vagal activity and mediated via the cholinergic pathway.