Mechanically-evoked spike responses of pentascolopidial chordotonal organs of Drosophila larvae

Stretch-sensitive ensembles of neurons in insects, known as Chordotonal organs (COs), function in proprioception, the detection of sound and substrate vibrations. Here we characterize the mechanical sensitivity of the lateral pentascolopidial CO (lch5) of Drosophila larvae to establish its postulated role in proprioception. We developed a physiologically realistic method to replicate proprioceptive input to lch5 by pulling the apodeme (tendon) to which the tips of the neurons attach. We found that lch5 sensory neurons respond transiently with a short latency to the velocity-component of stretch displacements and the release of stretch (relaxation). The mechanosensory mutant inactive, has a decreased response to mechanical stimuli and a lower overall spontaneous spike rate. Finally, we simulated the input that lch5 receives during crawling and observed spikes coincident with the start, middle and end of each peristaltic body contraction. We provide the first characterization of proprioceptive feedback in Drosophila larvae and firmly establish the proprioceptive function of lch5 in larval locomotion. Summary statementWe have characterized the spiking responses of the pentascolopidial chordotonal organ of 20 Drosophila larvae to mechanical stimuli and reveal a clear role in proprioception.