Sensory modalities relevant for the walking behavior of adult Drosophila melanogaster. Cesar S. Mendes¹, Imre Bartos², Turgay Akay³, Szabolcs Marka², Richard Mann¹. 1) Columbia University, Dept. Biochemistry and Molecular Biochemistry, , New York, NY; 2) Columbia University Dept. of Physics New York , NY; 3) Columbia University Dept. of Neurological Surgery, New York, NY.

   Coordinated walking in vertebrates and multi-legged invertebrates such as the fruit fly Drosophila melanogaster requires a complex neural network. This network is comprised of motor neurons, Central Pattern Generators and sensory neurons. CPGs produce rhythmic outbursts, without input from the central brain that target leg motor neurons. Critical to this network, sensory neurons constantly report the position and load of each of the leg segments and the terrain conditions. The fruitfly somatic system bears distinct classes of sensory neurons that report distinct proprioceptive parameters and environmental cues. Identify the components and understand the relevance of each one of these sensory components is critical to unravel the circuit regulating the walking behavior. To detect disturbances in the walking circuit of the fruit fly, we developed a high-speed optical imaging system that allows us to track footprints and the flys body as it walks freely on a flat surface. A custom analysis software allows us to quantify many parameters exhibited by walking flies, such as step timings, footprint positions and left-right coordination. With this method as readout, we used a combinatorial expression system to perform loss and gain of function experiments targeting different classes of leg sensory neurons. Surprisingly, we find that inactivation of proprioceptive feedback in the leg led to deficient step precision, but interleg coordination and the ability to execute a tripod gait were unaffected. Moreover, different sensory modalities display speed-dependent requirements indicating that CPGs generate the primary set of instructions required for walking. Finally, we investigate how external sensory cues influence walking. Interestingly, antenna removal affected several gait parameters, possibly through gravity-sensitive neurons.