Interactions between neurogenic and myogenic control mechanisms of intestinal and colonic motility

The pacemaker cells of the gut, the interstitial cells of Cajal (ICC) orchestrate, in close collaboration with the enteric nervous system, the major motor patterns of the intestine, that is, segmentation (1) and the minute rhythm propulsive activity. Omnipresent myogenic ripples (low amplitude propulsive activity) are present at all times giving low level mixing and propulsion. The rhythm and propagation characteristics of the ripples are determined by ICC associated with the myenteric plexus (ICC-MP). To elicit the typical segmentation motor pattern described by Cannon (2), a second rhythmic pacemaker activity is evoked by medium chain fatty acids or substance P innervation involving the ICC of the deep muscular plexus. This low frequency activity interacts with the ICC-MP pacemaker through phase-amplitude coupling. This results in a waxing and waning of the ICC-MP slow wave amplitude and segmentation results. However, for this to occur, the propagation velocity of the ICC-DMP activity has to be low, if this occurs at a velocity similar to that of the ICC-MP slow waves, then the typical minute rhythm propulsive activity occurs. The ICC networks are systems of coupled oscillators and enteric neural regulation of the coupling strength can change propagation velocity, which has major consequences for the orchestration of motor patterns by the pacemaker networks. Very similar mechanisms occur in the human and rabbit colon where ripple activity orchestrated by colonic slow waves interacts with a lower frequency rhythm that is associated with minute rhythm propulsive activity that has developed as haustral boundary contractions. Supported by the Canadian Institutes of Health Research.