Postprandial Sodium Sensor in the Drosophila Gut

Abstract Sodium is essential for all living organisms. Animals including insects and mammals detect sodium primarily through peripheral taste cells. It is not known, however, whether animals can detect this essential micronutrient independently of the taste system. Here, we report that Drosophila IR76b mutants that were unable to detect sodium1 became capable of responding to sodium after a period of dietary salt deprivation. From a screen for cells required for the deprivation-induced sodium preference, we identified a population of anterior enteric neurons that we named INSO (Internal Sodium Sensing) neurons, that are necessary and sufficient for directing a behavioral preference for sodium. Enteric INSO neurons innervate the gut epithelia mainly through their dendritic processes and send their axonal projections along the esophagus to the brain and to the crop duct. Through calcium imaging and CaLexA experiments, we found that INSO neurons are amiloride-insensitive and respond immediately and specifically to sodium ions. Taken together, we have identified a previously unknown taste-independent sodium sensor that is essential for the maintenance of sodium homeostasis.