Making Feeding Decisions in the Drosophila Nervous System

Feeding is one of the most fundamental activities of animals. Whether an animal will eat or not depends on sensory cues concerning nutrient availability and quality as well as on its growth, hormonal and metabolic state. These diverse signals, which originate from different regions of the body and act on different time scales, must be integrated by the nervous system to enable an appropriate feeding response. Here, we review recent studies in Drosophila melanogaster larvae that aim to elucidate the central circuits that underlie food intake, based on a serial section electron microscopic volume of an entire central nervous system. We focus on the comprehensive mapping of the synaptic connections between the sensory inputs and motor outputs of the larval feeding system. The central feeding circuit can be organized into a series of parallel pathways that connect a given set of input and output neurons. A dominant circuit motif is that of a monosynaptic sensory-motor connection upon which a series of polysynaptic paths are superimposed. The interneurons of the different parallel paths receive slightly different sets of sensory inputs, which enable flexibility in the selection of feeding motor outputs.