2023-12-11 10:02:56
A study involving Inserm shows that the vagus nerve which connects the intestine and the brain determines the occurrence of depression induced by abnormalities in the intestinal microbiota.
An article to be found in Inserm magazine n°58
The association between depression and intestinal dysbiosis is no longer in doubt. Various studies have in fact proven that people suffering from depression present anomalies in the composition of their intestinal microbiota, that is to say imbalances between populations. bacteria that naturally colonize their digestive system. Some are in deficit and others, on the contrary, are in excess. Furthermore, transferring the truncated flora from an individual suffering from depression to another healthy person is enough to trigger depression in the latter, confirming a causal link. Until then, the biological mechanism underlying this association remained enigmatic.
A joint study by Inserm, the Pasteur Institute and the CNRS shows the involvement of the vagus nerve. The latter is the most extensive in the body. “ It connects the brain to different organs including the digestive system and thus constitutes a direct anatomical link between the two. In addition, intestinal bacteria are found near this nerve and impact its activity, explains Eleni Siopi, first author of this work. And this nerve is connected to brain regions involved in managing emotions. »
A gut-brain decoupling
This body of evidence led researchers to test the role of this nerve in gut-brain communication in depression. To do this, they carried out transfers of microbiota from mice suffering from this disease to other, healthy ones, presenting an unaffected vagus nerve or, on the contrary, severed in the abdomen (vagotomy). “ This transfer procedure is common in the laboratory to induce depression in recipient animals. This results in a loss of interest, curiosity, motivation, or even apathy during simple exercises. », specifies Eleni Siopi. This is also what the team observed in control mice. On the other hand, in those who underwent vagotomy, the transfer of microbiota did not induce depression. “ The effect is very significant since all of the animals concerned were protected from the disease. Vagotomy caused a decoupling of the intestine and the brain which was sufficient to preserve the subjects from the depressive state caused by intestinal dysbiosis. », Clarifies the researcher.
If these discoveries allow us to better understand this mechanism in depression, they also open the way to therapeutic perspectives. “ Stimulating the vagus nerve through meditation or even massages might strengthen the effect of treatments thanks to better stress control. In addition, modulating the activity of specific proteins or molecules of the vagus nerve might help combat the severity or recurrence of depression in patients, hopefully Eleni Siopi. Currently, only a third of patients are effectively relieved by medications, which means that additional solutions are expected. », she concludes.
Eleni Siopi carried out this work at the Necker-Enfants Malades Institute (unit 1151 Inserm/CNRS/Université Paris Cité), Paris
E. Siopi et al. Gut microbiota changes require vagus nerve integrity to promote depressive-like behaviors in mice. Mol Psychiatry., 2 mai 2023 ; doi : 10.1038/s41380-023–02071-6
Author: AR
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