# Possible Involvement of Descending Monoaminergic Pathways in Colorectal Dysmotility Using a Rat Model of Colitis

## TL;DR

This study shows that inflammation in the colon can disrupt gut movement through central nervous system pathways involving serotonin and dopamine.

## Contribution

The study reveals a novel central neural mechanism involving descending monoaminergic pathways in inflammation-induced gut motility changes.

## Key findings

- Colonic inflammation suppresses motility responses to noxious stimuli in inflamed regions.
- Enhanced basal motility in noninflamed regions during colitis is mediated by descending monoaminergic pathways.
- Monoaminergic receptor antagonists can suppress hyperactive motility in noninflamed regions.

## Abstract

Colonic inflammation is known to cause intestinal dysmotility. We examined the possible involvement of descending monoaminergic neurons projecting to the lumbosacral spinal cord in colorectal dysmotility using a rat model of colitis.

Colitis was induced in rats by intracolonic administration of 2,4,6‐trinitrobenzenesulfonic acid. Motility in inflamed and noninflamed colorectal regions was assessed in vivo under anesthesia.

Colonic inflammation suppressed colorectal motility responses to noxious stimulus applied on inflamed colonic regions. The suppressed responses recovered as inflammation improved. In a subset of rats with colitis, basal motility in noninflamed regions was significantly enhanced, and this was abolished by intrathecal administration of serotonergic and dopaminergic receptor antagonists to the lumbosacral spinal cord. In some rats, enhanced basal motility spontaneously subsided then returned to a hyperactive state. The re‐enhanced basal motility was also suppressed by monoaminergic receptor antagonists, suggesting intermittent activity of the descending monoaminergic neurons.

This study suggested that persistent noxious input from an inflamed colon activates descending monoaminergic neurons, leading to enhanced basal motility in noninflamed regions. Our findings provide important insights into the pathophysiology of inflammation‐associated dysmotility.

Colonic inflammation impaired motor function at the inflamed site and altered the motility of noninflamed colorectal regions through central neural mechanisms.Descending serotonergic and dopaminergic pathways, which are normally involved in pain modulation, contribute to enhanced motility in noninflamed colorectal regions during colitis.Our findings shed light on a previously underappreciated central mechanism of dysmotility in colitis and provided important insights into the pathophysiology of defecation abnormalities caused by colitis.

Colonic inflammation impaired motor function at the inflamed site and altered the motility of noninflamed colorectal regions through central neural mechanisms.

Descending serotonergic and dopaminergic pathways, which are normally involved in pain modulation, contribute to enhanced motility in noninflamed colorectal regions during colitis.

Our findings shed light on a previously underappreciated central mechanism of dysmotility in colitis and provided important insights into the pathophysiology of defecation abnormalities caused by colitis.

Colonic inflammation impaired motor function at the inflamed region and altered the motility of noninflamed colorectal regions through central neural mechanisms in rats. Descending serotonergic and dopaminergic pathways, which are normally involved in pain modulation, contribute to enhanced motility in noninflamed colorectal regions during colitis.