New insights into neurogenic cyclic motor activity in the isolated guinea-pig colon

Background: The contents of the guinea pig distal colon consist of multiple pellets that move anally in a coordinated manner. This row of pellets results in continued distention of the colon. In this study, we have investigated quantitatively the features of the neurally dependent colonic motor patterns that are evoked by constant distension of the full length of guinea-pig colon.

Methods: Constant distension was applied to the excised guinea-pig by high-resolution manometry catheters or by a series of hooks.

Key results: Constant distension elicited regular Cyclic Motor Complexes (CMCs) that originated at multiple different sites along the colon and propagated in an oral or anal direction extending distances of 18.3±10.3 cm. CMCs were blocked by tetrodotoxin (TTX; 0.6 μ mol L^-1 ), hexamethonium (100 μ mol L^-1 ) or hyoscine (1 μ mol L^-1 ). Application of TTX in a localized compartment or cutting the gut circumferentially disrupted the spatial continuity of CMCs. Localized smooth muscle contraction was not required for CMC propagation. Shortening the length of the preparations or disruption of circumferential pathways reduced the integrity and continuity of CMCs.

Conclusions & inferences: CMCs are a distinctive neurally dependent cyclic motor pattern, that emerge with distension over long lengths of the distal colon. They do not require changes in muscle tension or contractility to entrain the neural activity underlying CMC propagation. CMCs are likely to play an important role interacting with the neuromechanical processes that time the propulsion of multiple natural pellets and may be particularly relevant in conditions of impaction or obstruction, where long segments of colon are simultaneously distended.