Serotonin Mediation of Intestinal Peristalsis
The pharmacological manipulation of 5-hydroxytryptamine (5-HT) receptors has generated wide clinical interest because of 5-HT's apparent importance in intestinal motility. This interest is especially strong with the substituted benzomides like cisapride, which likely act upon 5-HT4 receptors to increase propulsion. Many in vitro studies have aimed at identifying the intrinsic 5-HT receptor subtypes involved in intestinal motility. Such studies mainly examine the pharmacology of 5-HT using agonist or antagonist-induced changes. The chapter examines the relative importance of 5-HT in peristalsis and presents how 5-HT receptor subtypes may be involved in motility. The enteric nervous system is arranged in two neural networks called the myenteric and submucous plexus. The myenteric plexus lies between the longitudinal and circular muscle layers, and the submucosal plexus lies in the submucosa adjacent to the inner surface of the longitudinal muscle. Immunohistochemical studies have identified a small population of type I neurons in the myenteric plexus that synthesize 5-HT.