The intestinal microbiota consists of a vast bacterial community that resides primarily in the lower gut and lives in a symbiotic relationship with the host. A bidirectional neurohumoral communication system, known as the gut–brain axis, integrates the host gut and brain activities. Here, we describe the recent advances in our understanding of how the intestinal microbiota communicates with the brain via this axis to influence brain development and behaviour. We also review how this extended communication system might influence a broad spectrum of diseases, including irritable bowel syndrome, psychiatric disorders and demyelinating conditions such as multiple sclerosis.
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The authors' work cited in this paper was supported by the Canadian Institutes of Health Research (CIHR) and the Crohn's and Colitis Foundation of Canada (CCFC). Support to S.M.C. and P.B. was also received from the Nestle Research Center.
Stephen M. Collins and Premysl Bercik are the recipients of a grant from the Nestle Research Centre. Michael Surette declares no competing financial interests.
(5-HT). A neurotransmitter that is produced mainly by the enteroendocrine cells of the gut, where it is an important regulator of gut physiology (particularly motility); however, 10% of 5-HT is found in the central nervous system, where it contributes to mood. 5-HT, also called serotonin, is derived from tryptophan via the formation of 5-hydroxytryptophan.
- Brain-derived neurotrophic factor
A protein that is widely distributed in the nervous system. In the brain, it is found in the hippocampus, amygdala and cortex. It contributes to a range of functions, including memory, mood and learning.
- Core microbiome
The 50–100 bacterial species that are common to the microbiomes of many individuals. Outside of these core species, there is considerable diversity in the microbiome components among healthy subjects.
A compositional change in the microbiota and/or an abnormality in the interactions between the host and the commensal microbiota.
An impairment of brain function, ranging in severity from mild confusion to deep coma. Severe liver disease is a common cause.
(γ-aminobutyric acid). An inhibitory neurotransmitter that is found throughout the nervous system, including in the central and enteric nervous systems.
- Postsynaptic density protein 95
A component of the postsynaptic density, a lattice-like array of proteins that is crucial for synaptic function.
According to the WHO: “Live microorganisms which when administered in adequate amounts confer a health benefit on the host.”
- Specific-pathogen-free mice
Laboratory mice that are free of defined pathogens.
An integral membrane protein of small synaptic vesicles. Initially considered a synaptic marker, it is now thought to have several roles in synaptic function throughout the nervous system.
- Toll-like receptors
Transmembrane proteins that recognize highly conserved molecules of microbial origin and subsequently trigger activation of the innate immune system.
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Collins, S., Surette, M. & Bercik, P. The interplay between the intestinal microbiota and the brain. Nat Rev Microbiol 10, 735–742 (2012). https://doi.org/10.1038/nrmicro2876