Electro‐acupuncture at ST37 and ST25 induce different effects on colonic motility via the enteric nervous system by affecting excitatory and inhibitory neurons

Background On the basis of the importance of the enteric nervous system (ENS) in gastrointestinal motility, we hypothesized that the ENS may mediate the therapeutic efficacy of electro‐acupuncture (EA) in constipation by regulating the mechanisms underlying the effects of EA on gastrointestinal function. Methods Model mice with constipation were generated by gastric instillation of 0‐4°C normal saline. Defecation time and stool (form and wet and dry weight) were assessed. The effect of EA at ST37 or ST25 on colorectal motility and proximal colonic motility was assessed using a water‐filled balloon. The expression of protein gene product 9.5 (PGP9.5), the cholinergic neuron marker acetyltransferase (ChAT) and the anticholinergic neuron marker nitric oxide synthase (nNOS) was detected by immunohistochemistry, real‐time quantitative polymerase chain reaction (qPCR) and western blot analysis. Key Results ST37 and ST25 improved colorectal pressure; however, ST37 but not ST25 improved proximal colonic pressure. In the proximal colon, the expression of PGP9.5 returned to normal after EA at ST 37, while EA at ST25 did not have this effect. In addition, qPCR and western blot analysis showed that ST37 could downregulate the expression of nNOS and upregulate the expression of ChAT to normal levels, while ST25 could only downregulate the expression of nNOS to normal levels. Conclusions and Inferences Electro‐acupuncture at specific acupoints can improve intestinal motility in constipation by altering the ENS and differentially affecting excitatory and inhibitory neurons, restoring the coordination between contraction and relaxation muscles, and working in concert with the central nervous system and peripheral neural pathways. EA stimulation at either ST 37 or ST 25 relieves the symptoms of constipation, but has different effects in the proximal colon. ST 37 alters both excitatory and inhibitory enteric neurons, while ST 25 only influences inhibitory neurons.