Sistema nervioso enterico

CLINICAL IMPLICATIONS OF NEUROSCIENCE RESEARCH Section Editor
Eduardo E. Benarroch, MD

Enteric nervous system
Functional organization and neurologic implications

Eduardo E. Benarroch, MD
Address correspondence and reprint requests to Dr. Eduardo Benarroch, Department of Neurology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905 Benarroch.eduardo@mayo.edu

The enteric nervoussystem (ENS) derives from the neural crest and consists of neurons distributed in two ganglionated plexuses, myenteric and submucosal, located within the walls of the gut. The ENS contains as many neurons as the spinal cord (approximately 80-100 million neurons) and controls intestinal motility and secretion largely independently of influences from the CNS.1-5 The ENS is affected by Lewy bodypathology at early stages of PD,6,7 and by many genetic8,9 or immune9,10 neurologic disorders associated with gastrointestinal dysmotility. The aim of this paper is to briefly review the functional and neurochemical organization of the ENS and its involvement in neurologic disorders. There are recent comprehensive reviews on these subjects.3,8,9,11,12
FUNCTIONAL ORGANIZATION AND NEUROCHEMISTRY OF THEENTERIC NERVOUS SYSTEM The control of motility and secretion in

the gastrointestinal tract depends on both extrinsic parasympathetic and sympathetic innervation and intrinsic innervation, provided by the ENS. Extrinsic parasympathetic inputs originate in the dorsal motor nucleus of the vagus, which controls primarily the motility of the esophagus and stomach, and the sacral parasympatheticnucleus, which contributes to control of motility of the distal colon and rectum. The prevertebral sympathetic ganglia mediate peripheral reflexes that inhibit motility of the gut. The intrinsic innervation of the gut consists of the ganglia of the ENS, which are grouped into two plexuses: the myenteric plexus (of Auerbach), located between the outer longitudinal and the inner circular muscle layers, andsubmucosal plexus (of Meissner), located between the circular muscle and the muscularis mucosae (figure).1-4 The ENS controls intestinal motility and secretion largely independently of extrinsic parasympathetic and sympathetic innervation, although these extrinsic influences have a modulatory role on ENS activ-

ity. Neurons of the myenteric plexus control the activity of the smooth muscle ofthe gut whereas those in the submucosal plexus also regulate mucosal secretion and blood flow.1-4 Enteric neurons are classified into different categories based on their histochemical, electrophysiologic, and functional properties1,3,5 (table 1). They include intrinsic primary afferent neurons (IPANs), interneurons, motor neurons, secretomotor neurons, and vasomotor neurons. These ENS neurons aresynaptically interconnected forming parallel reflex circuits (figure). The neurochemical signaling within the ENS is extremely complex. Most ENS neurons utilize acetylcholine (ACh), but many also utilize nitric oxide (NO), vasoactive intestinal polypeptide (VIP), substance P, neuropeptide Y (NPY), and adenosine-triphosphate (ATP), in various combinations. There is also a small proportion of neuronsthat synthesize dopamine,5 serotonin,11,12 or -aminobutyric acid (GABA) (table 1). The ENS controls gut motility and secretion via local reflexes that are triggered by several stimuli, including local distension of the intestinal wall, distortion of the mucosa, and chemical contents in the lumen.1-4,12 The IPANs, located in both the myenteric and submucosal plexuses, are the first neurons inthese reflexes. They have long dendritic processes that ramify extensively and project both in oral and anal directions to make synapses with interneurons, motor neurons, and other sensory neurons within the ENS. The IPANs also provide inputs to intestinofugal neurons that project to the sympathetic prevertebral and pelvic ganglia and mediate a peripheral reflex that inhibits gut activity. Stimuli...