GASTROINTESTINAL-TRACT SENSIBILITY

This review analyzes current concepts of visceral afferent pathways an d their role in the perception, modulation and integration of stimuli arising from the gastrointestinal (GI) tract. It also analyzes the cli nical evidence supporting that altered visceral afferent mechanisms ha ve a role in the pathogenesis of functional bowel disorders. The GI tr act has a dual afferent innervation : the enteric nervous system, whic h is a complex network of ganglia and nervous fibers and allows partia l functional autonomy, especially in the regulation of peristaltic ref lexes, and the extrinsic nervous system which transmits sensitive info rmation from the mucosa and muscular wall to the medullar and supramed ullar centers of control, via the vagal and spinal afferent fibers. In formation from the gut is collected by specific or polymodal receptors . Visceral afferent fibers contain a wide variety of neuropeptides whi ch might have a specific function in the regulation of receptors or th e transmission of sensory information. Exploration of visceral afferen t fibers is difficult in humans, and involves the study of reflex loop s, especially sensory-motor reflexes. Both vagal and spinal afferents can transmit physiological and noxious information to the upper center s of control, but only a few of them are conscious. In human pathology , the hypersensitivity of the GI tract to various stimuli has been cle arly demonstrated in different functional bowel disorders, such as the irritable bowel syndrome, non cardiac chest pain and functional dyspe psia, and in ulcerative colitis. This hypersensitivity is not due to a lterations in the mechanical properties of the smooth muscle. Neither does it seem to be related to psychologic abnormalities. Up-regulation of gut receptors and perturbation of the neural transmission or retro -control of sensitive information by afferent fibers, might be involve d in this GI tract hypersensitivity. Drugs able to reduce visceral sen sitivity are required and, in this connection, somatostatin and 5-HT3 antagonists are currently being evaluated in man.