title: 5-Hydroxytryptamine (serotonin) in the gastrointestinal tract.
abstract: OBJECTIVE
  Although the gut contains most of the body's 5-hydroxytryptamine (5-HT), many of its most important functions have recently been discovered. This review summarizes and directs attention to this new burst of knowledge.
  
  
  RESULTS
  Enteroendocrine cells have classically been regarded as pressure sensors, which secrete 5-HT to initiate peristaltic reflexes; nevertheless, recent data obtained from studies of mice that selectively lack 5-HT either in enterochromaffin cells (deletion of tryptophan hydroxylase 1 knockout; TPH1KO) or neurons (TPH2KO) imply that neuronal 5-HT is more important for constitutive gastrointestinal transit than that of enteroendocrine cells. The enteric nervous system of TPH2KO mice, however, also lacks a full complement of neurons; therefore, it is not clear whether slow transit in TPH2KO animals is due to their neuronal deficiency or absence of serotonergic neurotransmission. Neuronal 5-HT promotes the growth/maintenance of the mucosa as well as neurogenesis. Enteroendocrine cell derived 5-HT is an essential component of the gastrointestinal inflammatory response; thus, deletion of the serotonin transporter increases, whereas TPH1KO decreases the severity of intestinal inflammation. Enteroendocrine cell derived 5-HT, moreover, is also a hormone, which inhibits osteoblast proliferation and promotes hepatic regeneration.
  
  
  CONCLUSIONS
  New studies show that enteric 5-HT is a polyfunctional signalling molecule, acting both in developing and mature animals as a neurotransmitter paracrine factor, endocrine hormone and growth factor.
authors.affiliation: Department of Pathology and Cell Biology, Columbia University, College of Physicians and Surgeons, New York, New York, USA. mdg4@columbia.edu
authors.forename: Michael D
authors.initials: MD
authors.lastname: Gershon
mesh_terms: D000818:Animals; D003248:Constipation / Q000378:metabolism* / Q000503:physiopathology; D003967:Diarrhea / Q000378:metabolism* / Q000503:physiopathology; D004759:Enterochromaffin Cells / Q000378:metabolism*; D019858:Enteroendocrine Cells / Q000378:metabolism; D005260:Female; D005769:Gastrointestinal Motility; D041981:Gastrointestinal Tract / Q000378:metabolism* / Q000503:physiopathology; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000503:physiopathology; D043183:Irritable Bowel Syndrome / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D059326:Serotonergic Neurons / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism; D009435:Synaptic Transmission; D014365:Tryptophan Hydroxylase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D050486:Serotonin Plasma Membrane Transport Proteins; D012701:Serotonin; C487801:Tph1 protein, mouse; C487802:Tph2 protein, mouse; D014365:Tryptophan Hydroxylase