Depression is a mental disorder that affects more than 264 million people of all ages worldwide.
Understanding its mechanisms is vital for the development of effective therapeutic strategies.
In a new study, researchers found that an imbalance in the gut bacterial community can cause a reduction in some metabolites, resulting in depressive-like behaviors.
These findings also showed that healthy gut microbiota contributes to normal brain function.
The research was conducted by scientists from the Institut Pasteur, Inserm, and the CNRS.
The bacterial population in the gut, known as the gut microbiota, is the largest reservoir of bacteria in the body.
Research has shown a link between mood disorders and damage to the gut microbiota.
The team previously identified a correlation between the gut microbiota and the efficacy of fluoxetine, a molecule frequently used as an antidepressant.
But some of the mechanisms governing depression, the leading cause of disability worldwide, remained unknown.
In the study, the scientists discovered that a change to the gut microbiota brought about by chronic stress can lead to depressive-like behaviors, in particular by causing a reduction in lipid metabolites (small molecules resulting from metabolism) in the blood and the brain.
These lipid metabolites, known as endogenous cannabinoids (or endocannabinoids), coordinate a communication system in the body which is strongly hindered by the reduction in metabolites.
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.
They also identified some bacterial species that are strongly reduced in animals with mood disorders.
They then demonstrated that 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. Such treatments are known as “psychobiotics”.
This discovery shows the role played by the gut microbiota in normal brain function.
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.
One author of the study is Pierre-Marie Lledo, Head of the Perception and Memory Unit.
The study is published in Nature Communications.
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