Study by the Institut Pasteur: The effect of the intestinal microbiota on depressive behavior is mediated by the endocannabinoid system
A 2005 study by the University of Saskatchewan in Canada had already shattered the myth. Today, researchers at the Institut Pasteur have found that changes in the bacterial population in the gut lead to lower endocannabinoid levels and depression in mice. The microbiota influences depressive behavior and neurogenesis. In other words, bacteria in the gut play a role in the endocannabinoid system and the functioning of the brain.
This could be the pathway, at least in part, that links microbiota dysbiosis to mood disorders, which in turn can affect the composition of the gut microbiota through physiological adjustments and modulation of the immune system.
In the present study, researchers explored the mechanisms by which dysbiosis of the gut microbiota contributes to brain dysfunctions and behavioral abnormalities associated with depressive states. Chronic stress is recognized as a major risk factor for depression, and most animal models of depressive behavior rely on chronic stress or the manipulation of stress-sensitive brain circuits. Using UCMS as a mouse model of depression, we showed that, upon transplantation to naive hosts, the microbiota of UCMS mice reduced adult hippocampal neurogenesis and induced depressive behaviors.
The study supports the concept that dietary or probiotic interventions could be effective levers in the therapeutic arsenal to fight against depressive syndromes associated with stress
In scientific terms, the data shows that chronic stress-induced microbiota dysbiosis affects lipid metabolism and eCB generation, leading to decreased signaling in the eCB system and reduced adult neurogenesis in the hippocampus.
Scientists have found that changes in the bacterial population in the gut caused by chronic stress can lead to depressive behaviors in mice. However, they also found that the whole process is moderated by the endocannabinoid system and cannabinoid receptors which are the primary target of THC.
In the new study from the Institut Pasteur in Paris, France, researchers wanted to find out how an imbalance of trillions of bacteria in the gut plays a role in brain function and mood regulation.
Bacterial cells in the body are ten times more numerous than human cells and most of them live in the intestine. Research has increasingly shown that healthy gut microbiota contributes to normal brain function.
“Depression is the leading cause of disability around the world. Recent observations have revealed an association between mood disorders and alterations in the gut microbiota ”, the new study reads.
The gut microbiota makes about 95% of serotonin, the key hormone that stabilizes our mood, according to the American Psychological Association.
The microbiota influences depressive behaviors and neurogenesis
In mice exposed to chronic stress, researchers found that disturbed levels of gut microbiota resulted in reduced lipid metabolites, also known as endocannabinoids. This led to a lack of endocannabinoids in the hippocampus, a key region of the brain involved in the formation of memories and emotions, and resulted in depressive-like behaviors.
Scientists gathered these results by studying the gut microbiota of healthy mice and mice with mood disorders.
“It is surprising to note that the simple transfer of the microbiota from an animal suffering from mood disorders to a healthy animal was enough to cause biochemical changes and give the latter depressive-type behaviors”, explains Pierre. -Marie Lledo, author of the study and head of the Perception and Memory unit at the Institut Pasteur.
Researchers identified certain species of bacteria that were significantly reduced in mice with mood disorders. One of these is L. plantarum, which is commonly found in many fermented foods. Scientists found that oral treatment of this bacteria restored normal endocannabinoid levels and reduced depressive-like behaviors in mice.
Using specific bacteria could be a promising method to restore a healthy microbiota and treat mood disorders more effectively, the researchers say.
The study suggests that these bacteria could be used as antidepressants, in treatments known as psychobiotics. However, more research and human clinical trials are needed to back up these claims.