Science reports:

With more microbes than cells in our body, it’s not surprising that bacteria and other invisible “guests” influence our metabolism, immune system, and even our behavior. Now, researchers studying mice have worked out how bacteria in the mammalian gut can ping the brain to regulate an animal’s appetite and body temperature—and it involves the same molecular pathway the immune system uses to detect bacterial pathogens.

“It’s quite an important finding,” says Antoine Adamantidis, a neuroscientist at the University of Bern who was not involved with the work. “Our life depends on food intake, and this is one more [thing] that bacteria can [influence].”

Over the past 20 years, researchers have uncovered connections between the human gut and the rest of the body. They have linked certain intestinal microbes to conditions such as depression, multiple sclerosis, and immune system disorders; they have also documented nervous system connections between the gut and the brain. But researchers have been hard pressed to understand exactly how gut microbes—or the molecules they make—influence the brain.

When certain gut bacteria infiltrate the rest of the body, our immune system picks up on them by sensing fragments of their cell walls, known as muropeptides. Our molecular detectors for these muropeptides, proteins called Nod2, coat the surfaces of cells involved in the body’s first line of defense. Ilana Gabanyi, a neuroimmunologist at the Pasteur Institute, wanted to know whether these molecular detectors also exist in the brain’s nerve cells. [Continue reading…]