Biologists have learned how gut microbes affect appetite and temperature

When certain intestinal bacteria invade the rest of the body, the immune system catches them,

focusing on fragments of cell wallsmicroorganisms known as muropeptides. The detection of such elements is ensured by the Nod2 protein, which covers the cells of the “first line of defense”. Scientists have suggested that similar proteins can be found in brain cells.

The researchers used two groupsgenetically modified mice: the first had the genes responsible for the production of Nod2 turned off, and the second produced fluorescent labels that helped to understand in which cells this protein was created.

Experiments have shown that mice with blockedsynthesis of Nod2 gained excess weight with age. Biologists believe that because food can stimulate microbes in the gut, more murapeptides enter the outer cells during meals. At the same time, in mice without Nod2, such molecules are not captured, and the brain does not know about saturation.

The researchers fed the second group of miceradioactive muropeptides. Within an hour, traces of such cells were found in the brains of mice. The scientists note that Nod2 is indeed produced in the mouse brain, and that muropeptides can get there within hours of reaching the intestines.

The authors of the work say that Nod2 is apparentlyaffects not only digestion, but also performs other functions. Older female mice lacking this protein in their brains had higher body temperatures and typically spent three times less time building a burrow to keep warm.

Metabolic control through the gut-brain axis. Source: Ilana Gabanyi et al., Science

Over the past 20 years, other studies havea connection has been found between the intestines and the rest of the body, including in humans. Scientists have shown that certain gut microbes are associated with conditions such as depression, multiple sclerosis, and immune system disorders. However, until now it has not been clear how the gut and the brain communicate.

Biologists say their experiments showmechanism by which bacteria can control the brain. However, this is only the first study in mice, and in the future, scientists plan to confirm their hypothesis in other animals. In addition, it is still not clear which function of the protein is primary - the immune response or communication with the brain.

“The same molecule that warns ourthe immune system that something is wrong can be used by the nervous system as a signal to regulate key survival processes such as food intake and temperature control,” says Juan Escobar, an evolutionary biologist who was not involved in the study.

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