Neurogenic and myogenic motor activity in the colon of the guinea pig, mouse, rabbit, and rat

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Abstract
Gastrointestinal motility involves interactions between myogenic and neurogenic processes intrinsic to the gut wall. We have compared the presence of propagating myogenic contractions of the isolated colon in four experimental animals (guinea pig, mouse, rabbit, and rat), following blockade of enteric neural activity. Isolated colonic preparations were distended with fluid, with the anal end either closed or open. Spatiotemporal maps of changes in diameter were constructed from video recordings. Distension-induced peristaltic contractions were abolished by tetrodotoxin (TTX; 0.6 μM) in all animal species. Subsequent addition of carbachol (0.1–1 μM) did not evoke myogenic motor patterns in the mouse or guinea pig, although some activity was observed in rabbit and rat colon. These myogenic contractions propagated both orally and anally and differed from neurogenic propagating contractions in their frequency, extent of propagation, and polarity. Niflumic acid (300 μM), used to block myogenic activity, also blocked neural peristalsis and thus cannot be used to discriminate between these mechanisms. In all species, except the mouse colon, small myogenic “ripple” contractions were revealed in TTX, but in both rat and rabbit an additional, higher-frequency ripple-type contraction was superimposed. Following blockade of enteric nerve function, a muscarinic agonist can evoke propulsive myogenic peristaltic contractions in isolated rabbit and rat colon, but not in guinea pig or mouse colon. Marked differences between species exist in the ability of myogenic mechanisms to propel luminal content, but in all species there is normally a complex interplay between neurogenic and myogenic processes.

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