Gut microbiota plays role in brain function, mood regulation

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A healthy gut microbiota contributes to normal brain function, according to a new study published in the journal Nature Communications.

The bacterial population in the gut, known as the gut microbiota, is the largest reservoir of bacteria in the body. Research has increasingly shown that the host and the gut microbiota are an excellent example of systems with mutually beneficial interactions. Recent observations also revealed a link between mood disorders and damage to the gut microbiota, including a correlation between the gut microbiota and the efficacy of an antidepressant medication. Some of the mechanisms governing depression, the leading cause of disability worldwide, remained unknown.

Using animal models, researchers recently discovered that a change to the gut microbiota brought about by chronic stress can lead to depressive-like behaviors, by causing a reduction in lipid metabolites in the blood and the brain. These lipid metabolites, known as endocannabinoids, coordinate a communication system in the body which is significantly hindered by the reduction in metabolites. Gut microbiota plays a role in brain function and mood regulation, the researchers said.

Endocannabinoids bind to receptors that are also the main target of tetrahydrocannabinol, the most widely known active component of cannabis. The scientists discovered that an absence of endocannabinoids in the hippocampus, a key brain region involved in the formation of memories and emotions, resulted in depressive-like behaviors.

The researchers obtained these results by studying the microbiotas of healthy animals and animals with mood disorders. Additionally, the scientists identified some bacterial species that are significantly reduced in animals with mood disorders. They then demonstrated that an oral treatment with the same bacteria restored normal levels of lipid derivatives, thereby alleviating the depressive-like behaviors. These bacteria could therefore serve as an antidepressant, the researchers said.

"This discovery shows the role played by the gut microbiota in normal brain function," said Gérard Eberl, PhD, joint last author of the study, in a statement. “If there is an imbalance in the gut bacterial community, some lipids that are vital for brain function disappear, encouraging the emergence of depressive-like behaviors. In this particular case, the use of specific bacteria could be a promising method for restoring a healthy microbiota and treating mood disorders more effectively.”