Coordinated activities of the central, autonomic, and enteric nervous syste
ms modulate intestinal motor, sensory, and secretory activities that may co
ntribute to the triad of dysfunction (altered motility, altered sensation,
and psychosocial distress) observed in patients with irritable bowel syndro
me (IBS). Autonomic modulation of gastrointestinal (GI) function occurs via
the actions of neurotransmitters and neuromodulators such as serotonin (5-
hydroxytryptamine, or 5-MT), norepinephrine, and dopamine.
Of those modulators, serotonin has received the most attention with respect
to disorders of GI function. Serotonin exerts its effects via neurocrine,
paracrine, and endocrine pathways. Recent studies have demonstrated that se
rotonin, acting primarily through 5-MT, and 5-MT, receptors, is intricately
involved in initiating the peristaltic reflex and facilitating intralumina
l secretions. Serotonin receptors mediate reflex control of CI motility and
secretion and may influence the perception of bowel function and pain unde
r some circumstances. GI motor activity and sensory dysfunction in patients
with IBS may be a result of alterations in serotonin levels or associated
5-HT receptors. Serotonin agonists and antagonists such as tegaserod, a 5-H
T4 agonist, may offer new treatments that normalize GI motor and sensory fu
nctions in patients with disorders of CI function.