Over 300 million people worldwide suffer from depression. Despite the fact that depression is the leading cause of disability in the world, its biological causes have remained unclear. Recently, several studies have suggested a link between the gut microbiome and mood disorders like depression. The microbiome is an enormously diverse population of bacteria that lives in the intestine, which can affect the host’s digestive, immune, and central nervous systems. Researchers at the Pasteur Institute set out to determine exactly what that link between the microbiome and mood disorders might be. 

To accomplish this, the researchers studied mice with depression caused by chronic stress. They found that when they isolated microbes from the feces of depressed mice and transferred them to healthy mice, the bacteria alone could induce depressive behaviors in the recipients. Then, the researchers analyzed differences in the metabolites found in these mice. They discovered that the depressed mice had lower levels of some metabolites in the blood and in the brain when compared to healthy mice. Specifically, there was a reduction in metabolites called endogenous cannibinoids (eCB), which are normally involved in communicating information between the body and the brain.

Importantly, the researchers showed that they could also reverse depressive behaviors in the mice. They were able to accomplish this in three different ways: by increasing eCB signaling with a drug, feeding the mice a diet high in eCB precursors, or by giving the mice a specific probiotic bacteria. As a result, this study not only helps clarify the link between diet, the gut microbiome, and mood disorders, but also suggests that microbiome-targeted treatments could be used as therapies for mood disorders like depression. 

Lead Author Grégoire Chevalier is a researcher in the Microenvironment and Immunity Unit at the Pasteur Institute in Paris. Gérard Eberl is the head of this Unit and a Professor of Immunology, and Pierre-Marie Lledo is a Professor in the Perception & Memory Unit at the Pasteur Institute. 

Managing Correspondent: Jaclyn Long

Original Article: Effect of gut microbiota on depressive-like behaviors in mice is mediated by the endocannabinoid system

Press Article: Gut microbiota plays a role in brain function and mood regulation

Picture credit: Billion photos / shutterstock.com

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