Review article: roles played by 5-hydroxytryptamine in the physiology of the bowel

The application of 5-HT to the gut elicits a wide variety of effects becaus e of the expression and wide distribution in the bowel of many subtypes of 5-HT. There is, however, no reason to believe that all of these receptors a re stimulated by endogenous 5-HT. 5-HT has been found to be the neurotransm itter of a subset of myenteric interneurons, which evoke a slow excitatory postsynaptic response mediated by 5-HT1P receptors. The major enteric depot of 5-HT is found in mucosal enterochromaffin cells, which are sensory tran sducers that utilize 5-HT to activate both intrinsic (via 5-HT1P and 5-HT4 receptors) and extrinsic (via 5-HT3 receptors) primary afferent nerves. Muc osal 5-HT is inactivated by uptake into epithelial cells mediated by the sa me 5-HT transporter utilized by serotonergic neurons. Antagonism of 5-HT3 r eceptors by compounds such as alosetron should be useful in treating functi onal bower disease because they can inhibit excitation of extrinsic sensory nerves by 5-HT without interfering with intrinsic enteric reflexes.