title: Gut Microbiota-brain Axis.
abstract: OBJECTIVE
  To systematically review the updated information about the gut microbiota-brain axis.
  
  
  METHODS
  All articles about gut microbiota-brain axis published up to July 18, 2016, were identified through a literature search on PubMed, ScienceDirect, and Web of Science, with the keywords of "gut microbiota", "gut-brain axis", and "neuroscience".
  
  
  METHODS
  All relevant articles on gut microbiota and gut-brain axis were included and carefully reviewed, with no limitation of study design.
  
  
  RESULTS
  It is well-recognized that gut microbiota affects the brain's physiological, behavioral, and cognitive functions although its precise mechanism has not yet been fully understood. Gut microbiota-brain axis may include gut microbiota and their metabolic products, enteric nervous system, sympathetic and parasympathetic branches within the autonomic nervous system, neural-immune system, neuroendocrine system, and central nervous system. Moreover, there may be five communication routes between gut microbiota and brain, including the gut-brain's neural network, neuroendocrine-hypothalamic-pituitary-adrenal axis, gut immune system, some neurotransmitters and neural regulators synthesized by gut bacteria, and barrier paths including intestinal mucosal barrier and blood-brain barrier. The microbiome is used to define the composition and functional characteristics of gut microbiota, and metagenomics is an appropriate technique to characterize gut microbiota.
  
  
  CONCLUSIONS
  Gut microbiota-brain axis refers to a bidirectional information network between the gut microbiota and the brain, which may provide a new way to protect the brain in the near future.
authors.affiliation: Department of Neurology, Xuanwu Hospital, Capital Medical University, Beijing 100053, China.
authors.forename: Hong-Xing
authors.initials: HX
authors.lastname: Wang
authors.affiliation: Department of Neurology, Xuanwu Hospital, Capital Medical University, Beijing 100053; Center of Epilepsy, Beijing Institute for Brain Disorders, Laboratory of Brain Disorders, Capital Medical University, Beijing 100069, China.
authors.forename: Yu-Ping
authors.initials: YP
authors.lastname: Wang
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000502:physiology; D002490:Central Nervous System / Q000378:metabolism / Q000502:physiology; D000069196:Gastrointestinal Microbiome / Q000502:physiology*; D041981:Gastrointestinal Tract / Q000382:microbiology; D006801:Humans; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism / Q000502:physiology; D010913:Pituitary-Adrenal System / Q000378:metabolism / Q000502:physiology