Different serotonergic neurons regulate appetite for sucrose and hunger for proteins

For the organism it is important to replenish internal energy storages selectively and selective appetite for nutrients might uncover internal energy requirements. How is the selective uptake of a specific nutrient regulated? Here we show that in Drosophila melanogaster different sets of serotonergic neurons regulate appetite for sucrose and hunger for proteins. Increased neuronal activity in specific subsets of serotonergic neurons and interfering with serotonin reuptake using a mutated serotonin transporter reduced the appetite for sucrose selectively, but not the hunger for proteins. The insulin receptor together with the serotonin transporter regulates the selective sucrose appetite. We provide evidence that the cellular location of the serotonin transporter depends on the insulin receptor. This mechanism might allow optimizing nutrient intake and in turn might prevent overconsumption by repressing appetite for sucrose. Given the conserved nature of the molecules involved it is likely that the mechanism is conserved in higher organisms.