Effects of autonomic nerve stimulation on colorectal motility in rats

Abstract

Background: Several disease processes of the colon and rectum, including constipation and incontinence, have been associated with abnormalities of the autonomic nervous system. However, the autonomic innervation to the colon and rectum are not fully understood. The aims of this study were to investigate the effect of stimulation of vagus nerves, pelvic nerves (PN) and hypogastric nerves (HGN) on colorectal motility in rats.

Methods: Four strain gauge transducers were implanted on the proximal colon, mid colon, distal colon and rectum to record circular muscle contractions in rats. Electrical stimulation was administered to the efferent distal ends of the cervical vagus nerve, PN and HGN. Motility index (MI) was evaluated before and during stimulation.

Key results: Electrical stimulation (5-20 Hz) of the cervical vagus elicited significant contractions in the mid colon and distal colon, whereas less pronounced contractions were observed in the proximal colon. Pelvic nerves stimulation elicited significant contractions in the rectum as well as the mid colon and distal colon. Atropine treatment almost completely abolished the contractions induced by vagus nerve and PN stimulation. Hypogastric nerves stimulation caused relaxations in the rectum, mid colon and distal colon. The relaxations in response to HGN stimulation were abolished by propranolol.

Conclusions & inferences: Vagal innervation extends to the distal colon, while the PN has projections in the distribution of the rectum through the mid colon. This suggests a pattern of dual parasympathetic innervation in the left colon. Parasympathetic fibers regulate colorectal contractions via muscarinic receptors. The HGN mainly regulates colorectal relaxations via beta-adrenoceptors.

Figure 1

Colorectal responses to vagal stimulation (a). Vagus efferent stimulation elicited significant contractions in the entire colon, which could be antagonized by atropine administration. MI changes in response to the vagal stimulation (b). ANOVA for repeated measures (p<0.001, F=12.09, r²=0.3482) followed by posthoc Bonferroni test compared to pre-stimulation (n=6, *P<0.05, **P<0.01). PC: proximal colon, MC: mid colon, DC: distal colon, R: rectum.

Figure 2

Colorectal responses to PN stimulation (a). PN efferent stimulation caused prominent contractions from the rectum extending to the mid colon, which could be antagonized by atropine administration. MI changes in response to PN stimulation (b). ANOVA for repeated measures (p<0.001, F=7.917, r²=0.2267) followed by posthoc Bonferroni test compared to pre-stimulation (n=6, *P<0.05, **P<0.01). PC: proximal colon, MC: mid colon, DC: distal colon, R: rectum.

Figure 3

Effects of HGN stimulation on colorectal motility (a). HGN efferent stimulation evoked apparent relaxation in the rectum, distal colon as well as mid colon, which could be abolished by propranolol administration. MI changes in response to HGN stimulation (b). ANOVA for repeated measures (p<0.01, F=4.495, r²=0.2725) followed by posthoc Bonferroni test compared to pre-stimulation (n=6, *P<0.05). PC: proximal colon, MC: mid colon, DC: distal colon, R: rectum.