title: Moody microbes or fecal phrenology: what do we know about the microbiota-gut-brain axis?
abstract: BACKGROUND
  The microbiota-gut-brain axis is a term that is commonly used and covers a broad set of functions and interactions between the gut microbiome, endocrine, immune and nervous systems and the brain. The field is not much more than a decade old and so large holes exist in our knowledge.
  
  
  CONCLUSIONS
  At first sight it appears gut microbes are largely responsible for the development, maturation and adult function of the enteric nervous system as well as the blood brain barrier, microglia and many aspects of the central nervous system structure and function. Given the state of the art in this exploding field and the hopes, as well as the skepticism, which have been engendered by its popular appeal, we explore recent examples of evidence in rodents and data derived from studies in humans, which offer insights as to pathways involved. Communication between gut and brain depends on both humoral and nervous connections. Since these are bi-directional and occur through complex communication pathways, it is perhaps not surprising that while striking observations have been reported, they have often either not yet been reproduced or their replication by others has not been successful.
  
  
  CONCLUSIONS
  We offer critical and cautionary commentary on the available evidence, and identify gaps in our knowledge that need to be filled so as to achieve translation, where possible, into beneficial application in the clinical setting.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada. forsytp@mcmaster.ca.|McMaster Brain-Body Institute, St. Joseph's Healthcare, Hamilton, Ontario, Canada. forsytp@mcmaster.ca.|Firestone Institute for Respiratory Health, St. Joseph's Healthcare, Hamilton, Ontario, Canada. forsytp@mcmaster.ca.
authors.forename: Paul
authors.initials: P
authors.lastname: Forsythe
authors.affiliation: Department of Psychiatry & Behavioural Neurosciences, McMaster University, Hamilton, Ontario, Canada.|McMaster Brain-Body Institute, St. Joseph's Healthcare, Hamilton, Ontario, Canada.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kunze
authors.affiliation: Department of Pathology & Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.|McMaster Brain-Body Institute, St. Joseph's Healthcare, Hamilton, Ontario, Canada.
authors.forename: John
authors.initials: J
authors.lastname: Bienenstock
mesh_terms: D001921:Brain / Q000502:physiology; D017615:Enteric Nervous System; D005243:Feces; D000069196:Gastrointestinal Microbiome; D041981:Gastrointestinal Tract; D006801:Humans; D015213:Neuroimmunomodulation
keywords: Antibiotic; Enteric Nervous system; Germ free; Microbiome; Vagus