The following article is the third in our series on the developmental biology of the nervous system and its relation to diseases and disorders that are found in newborn infants and children. In this article, Cheryl Gariepy describes the development of the enteric nervous system and the relation between genetic abnormalities of that system and enteric disease.
Alvin Zipursky Editor-in-ChiefIntestinal Motility Disorders and Development of the Enteric Nervous System The enteric nervous system (ENS) is an independent nervous system. It contains as many neurons as the spinal cord, every class of neurotransmitter found in the CNS, and reflex arcs capable of functioning independently of CNS input. Whereas the majority of enteric neurons are not directly innervated by the brain or spinal cord, the ENS is in two-way communication with the CNS via parasympathetic and sympathetic neurons. The ENS processes information regarding the state of the intestinal lumen and gut wall and modulates intestinal contractility, secretion, vascular supply, and inflammatory responses (1, 2).Complaints related to the ENS represent a large percentage of pediatric office visits. Common clinical complaints of gastrointestinal motility and sensation include gastroesophageal reflux, dyspeptic syndromes, constipation, chronic recurrent abdominal pain, and irritable bowel syndrome (3). Less common but life-threatening disorders of the ENS include Hirschsprung disease and neuropathic chronic intestinal pseudoobstruction. Our understanding of the pathophysiologic processes underlying these complaints is being aided by the study of ENS formation and structure. Ultimately, these studies will improve our diagnosis and treatment of these disorders.As our understanding of the ENS improves, it becomes very clear that it is no longer sufficient to simply determine whether enteric ganglion cells are present. We are learning the importance of determining whether the correct number and types of ganglion cells are present. This task is complicated by the fact that the morphology of the myenteric plexus varies with location as well as age (4, 5). Only through improved understanding of the normal development of the ENS can we hope to accurately diagnose relatively subtle abnormalities in ENS development (6, 7). Further, with continued basic research, we may be able to isolate an ENS stem cell population from postnatal individuals. The identification and study of multipotential stem cells may allow for their eventual use in transplantation to correct intestinal neuronal deficiencies (8).Recent studies have identified six genes causing Hirschsprung disease, as well as genes that may be related to other disorders of the ENS. This review focuses on studies of ENS development in rodents that have substantially improved our understanding of the genetic basis of human disorders of the ENS.
DISCUSSION
Origin of the ENSThe ENS is composed of autonomic ganglia in the myenteric and submucosal plexuses and associated connecting neural structures in the bowel wall. The ENS, ...