ABSTRACT
More than 90% of the serotonin (5-HT) in the body is stored within the enterochromaffin cells of the gastrointestinal mucosa. These cells, together with other enteroendocrine cells, have a morphology that is consistent with a paracrine “sensory” role. In extrinsic afferent innervation it has been long recognized that phenyldiguanide is potent agent for afferent stimulation, raising the possibility that 5-HT may also be involved in the transduction of extrinsic sensory impulses. Intuitively, one might consider extrinsic mucosal afferents to be primarily 5-HT-sensitive, since these are likely to be exposed to 5-HT released from enterochrommaffin cells. Vagal mucosal afferents throughout the gastrointestinal tract appear to have an exquisite sensitivity to 5-HT. The response is dose-dependent and typically consists of a high frequency burst of action potentials lasting just a few seconds. Nausea and vomiting are two components of a system that protects the body against toxins accidentally ingested with food and, therefore, emetic reflex is intimately associated with the gastrointestinal tract.
