NEW DEVELOPMENTS IN THE ENTERIC NERVOUS-SYSTEM

Research on the enteric nervous system is important because the mechanism by which the motility of the bowel is locally controlled is still not understood and because this research is critical in developing effective therapies for functional bowel disease. Although the behaviors regulated by the enteric nervous system cannot yet be explained in terms of the activity of single cells, it should soon be possible to do so. Considerable progress has been made in determining the function of particular types of enteric neurons, including sensory neurons of the submucosal plexus, motor neurons, and interneurons of the myenteric plexus. Uncertainty persists as to the nature of the myenteric neuron classified electrophysiologically as type 2/AH and morphologically as Dogiel type II. These cells may act as sensory neurons, as interneurons, or both. Nitric oxide has clearly been established to play a critical role as an intrinsic inhibitory neurotransmitter, as has ATP and vasoactive intestinal peptide, although neurons, smooth muscle, and interstitial cells of Cajal may each be both sources nitric oxide and the targets of its action. Interstitial cells appear to play roles as both as pacemaker cells for the circular muscle and in transmitting neural signals to smooth muscle cells. Although one cannot yet map the components of an enteric microcircuit, it should soon be possible to do so.