Figure 3 .

Model of the effect of 5-HT released from enterochromaffin cells or absorbed tegaserod, a partial 5-HT₄ agonist, on activation of intrinsic primary afferent neurones (for example, calcitonin gene related peptide (CGRP)), which in turn stimulate the "peristaltic reflex". This involves orad contraction, mediated through excitatory transmitters such as acetylcholine (ACh) or substance P (SP), and a caudad relaxation, mediated through inhibitory neurotransmitters such as vasoactive intestinal peptide (VIP), pituitary adenylate cyclase associated peptide (PACAP), or nitric oxide synthetase (NOS). MEC, median effective concentration. Adapted from Grider and colleagues.³⁸