Role of 5-hydroxytryptamine in gastrointestinal chemosensitivity.

The present electrophysiological investigation examines the effect of 5-hydroxytryptamine (5-HT) on gastrointestinal afferent fiber discharge. 5-HT markedly and specifically stimulated vagal mucosal chemosensitive afferents. The response was mediated by 5-HT3 receptors as demonstrated by the action of 2-methyl-5-HT and antagonism by granisetron. At doses of granisetron that completely block the response to 5-HT, the afferent fibers still responded to both mechanical and chemical stimulation of the mucosa. This sensitivity of extrinsic afferents is in marked contrast to that reported for intrinsic afferents, suggesting fundamental differences in the organization of enteric and vagal reflexes.