The autonomic nervous system in functional bowel disorders

Communications along the brain-gut axis involve neural pathways as well as immune and endocrine mechanisms. The two branches of the autonomic nervous system are integrated anatomically and functionally with visceral sensory p athways, and are responsible for the homeostatic regulation of gut function . The autonomic nervous system is also a major mediator of the visceral res ponse to central influences such as psychological stress and other central factors. As presently defined, functional disorders represent a constellation of sym ptoms, some of which suggest the presence of altered perception while other symptoms point to disordered gastrointestinal function as the cause of the symptoms. There have been a growing number of reports demonstrating disord ered autonomic function in subgroups of functional bowel patients.(1-3) Whi le a number of different methods were used to assess autonomic function, th ey generally point to decreased vagal (parasympathetic) outflow or increase d sympathetic activity in conditions usually associated with slow or decrea sed gastrointestinal motility. Other studies found either increased choline rgic activity or decreased sympathetic activity in patients with symptoms c ompatible with increased motor activity.(3-4) Under certain conditions, alt ered autonomic balance (including low vagal tone and increased sympathetic activity) may also alter visceral perception. Autonomic dysfunction could also represent the physiological pathway accoun ting for many of the extraintestinal symptoms seen in irritable bowel syndr ome (IBS) patients, and for some of the frequent gastrointestinal complaint s reported by patients with disorders such as chronic fatigue and fibromyal gia.