Gut microbiota by-products circulate in the bloodstream, regulating host physiological processes including immunity, metabolism and brain functions. Scientists from the Institut Pasteur (a partner research organization of Université Paris Cité), Inserm and the CNRS have discovered that hypothalamic neurons in an animal model directly detect variations in bacterial activity and adapt appetite and body temperature accordingly. These findings demonstrate that a direct dialog occurs between the gut microbiota and the brain, a discovery that could lead to new therapeutic approaches for tackling metabolic disorders such as diabetes and obesity. The findings are published in Science.