ROLE OF 5-HYDROXYTRYPTAMINE IN GASTROINTESTINAL CHEMOSENSITIVITY

The present electrophysiological investigation examines the effect of 5-hydroxytryptamine (5-HT) on gastrointestinal afferent fiber discharg e. 5-HT markedly and specifically stimulated vagal mucosal chemosensit ive afferents. The response was mediated by 5-HT3 receptors as demonst rated 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 stimul ation of the mucosa. This sensitivity of extrinsic afferents is in mar ked contrast to that reported for intrinsic afferents, suggesting fund amental differences in the organization of enteric and vagal reflexes.