The irritable bowel syndrome (IBS) is a complex disorder that is associated with altered gastrointestinal motility, secretion, and sensation. Serotonin (5‐HT) is an important neurotransmitter and paracrine signalling molecule in the gastrointestinal tract. 5‐HT release from enterochromaffin (EC) cells initiates peristaltic, secretory, vasodilatory, vagal and nociceptive reflexes. The enteric nervous system (ENS) comprises a semiautonomous effector system that is connected to the central autonomic network. Parasympathetic and sympathetic nerves modulate the ENS via afferent and efferent communications. Ongoing, bidirectional brain–gut interactions involving 5‐HT pathways occur that significantly influence the effector systems. Altered 5‐HT signalling may lead to both intestinal and extraintestinal symptoms in IBS. 5‐HT directly and indirectly affects intestinal motor and secretory function and abnormalities may lead to either constipation or diarrhea. 5‐HT modulates sensation and perception of visceral stimulation at peripheral and central sites. Therapeutic agents targeting altered 5‐HT signalling may provide new, effective treatments for patients with IBS.

British Journal of Pharmacology (2004) 141, 1285–1293. doi:10.1038/sj.bjp.0705762