A new study from the University of Surrey and the University of Roehampton has found that the neuroactive potential of bacteria living in the human gut is associated with levels of key chemicals in the brain, adding fresh human evidence to the science of the gut-brain axis.
What the researchers found
Published in Molecular Psychiatry, the research examined 61 healthy young women aged 17-25. The team used proton magnetic resonance spectroscopy to measure GABA and glutamate in three brain regions, while stool samples were analysed using shotgun metagenomic sequencing to identify the genetic capacity of gut microbes to carry out metabolic processes involving neuroactive compounds.
The study found that the relationship between the gut microbiome and brain chemistry was not uniform across the brain. Different microbial pathways were associated with GABA, glutamate and excitatory/inhibitory balance in different regions, including the inferior occipital gyrus, the anterior cingulate cortex and the dorsolateral prefrontal cortex. Associations were also reported between specific gut microbial pathways and self-reported anxiety, depressive symptoms and sleep quality.
Why the findings matter
Researchers said the results provide human evidence that links microbial functions in the gut with neurochemistry in the brain, moving beyond much of the earlier evidence that came from animal and preclinical research. The authors stressed, however, that the findings show associations rather than cause and effect, and that the study was cross-sectional. They also noted that the research measured the genetic potential of the microbiome rather than directly measuring the metabolites produced by the bacteria.
Professor Kathrin Cohen Kadosh said the work is notable because it allows scientists to look at the gut microbiome and brain chemistry in the same living people, while Dr Nicola Johnstone said the study connected microbial genes in the gut, neurochemistry in the brain and psychological measures in the same participants.
What comes next
The researchers said the findings point to more specific biological pathways that can now be investigated further. For now, the study suggests that the gut-brain axis may be more regionally specific and biologically complex than a single pathway acting uniformly across the brain.
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