Connectomics Reveals a Feed-Forward Swallowing Circuit Driving Protein Appetite

Nutrient state shapes not only what animals eat, but how they eat it. We lack circuit-level mechanisms explaining how gustatory and internal state information regulates feeding at the motor control level. In Drosophila, protein deprivation prolongs protein-specific feeding bursts, yet the detailed motor mechanisms underlying this change remain unknown. Using EM connectomics, we identified a feed-forward pathway from proteinsensitive gustatory receptor neurons to swallowing motor neurons. At its core is the Sustain neuron, which coordinates multiple swallowing motor neurons to move food efficiently through the cibarium and pharynx. This nutrient-dependent facilitation of swallowing sustains long feeding bursts, directly linking internal state to the temporal structure of the feeding motor program. Our findings reveal how a dedicated sensorimotor circuit translates physiological need into precise motor control to drive nutrient-specific feeding appetite and highlights the power of combining EM connectomics with experimental circuit dissection.