There is a growing understanding of the importance of the gut microbiota in influencing brain function, behaviour and mental health.
This understanding started with studies into irritable bowel syndrome, which linked the gut-brain axis and the microbiota with stress-related illness, and has now been extended to include other brain disorders such as autism, schizophrenia and Parkinson’s disease.
What is the Microbiota-Gut-Brain Axis?
The microbiota-gut-brain axis includes the central nervous system (CNS), the endocrine-immune system, the hypothalamus-pituitary-adrenal (HPA) axis, the autonomic nervous system, the enteric nervous system (ENS) and the gut microbiota. This axis allows two-way communication where signals from the brain can influence the GI tract and signalling from the gut affects brain function. The ways in which the microbiota communicates with the brain are now being identified and include the vagus nerve, gut hormone signaling, the immune system, tryptophan metabolism and through microbial metabolites, including short chain fatty acids. This is an evolving area of research, which is growing quickly and it is hoped will generate insights into new treatments for a range of neuro-developmental and neuro-degenerative disorders.
How can Microbiota positively effect the Brain?
Germ-free mice and antibiotics have been used extensively in studying the impact of the microbiota on the brain and key changes in neurotransmitter systems and their receptors have been shown in a variety of different brain regions. These include the cerebellum and hippocampus, which showed changes in gene expression, and the amygdala, which is critical for social behaviour and anxiety. In addition, human research has shown that the composition of the microbiota influences an individual’s behaviour. As well as functional GI disorders, changes in the microbiota-gut-brain axis have been linked to non-GI brain disorders, including anxiety, depression, multiple sclerosis, Alzheimer’s disease, Parkinson’s disease and autism.
 Dinan TG & Cryan JF 2017 Gut instincts: microbiota as a key regulator of brain development, ageing and neurodegeneration. J Physiol 595.2:489-503
 Cerdo T et al 2017 Probiotic, Prebiotic and Brain Development. Nutrients 9 1247
 Foster JA et al 2016 Gut Microbiota and Brain Function: An Evolving Field in Neuroscience. Int J Neuropsychopharmacol 19(5):1-7