Sustained spinal motor activity triggered by direct mechanosensory stimulation in adult Drosophila melanogaster

Abstract

AbstractMost vertebrates and invertebrates such as Drosophila melanogaster are able to move in complex environments due to their ability to integrate sensory information along with motor commands. Mechanosensory structures exist along each leg to assist in motor coordination by transmitting external cues or proprioceptive information to motor centers in the central nervous system.Nevertheless, how different mechanosensory structures engage these locomotor centers and their underlying circuits remains poorly understood. Here, we tested the role of mechanosensory structures in movement initiation by optogenetically stimulating specific classes of leg sensory structures. We found that stimulation of leg Mechanosensory Bristles (MsB) and femoral Chordotonal Organ (ChO) is sufficient to initiate forward movement in immobile animals. We also found that while the stimulation of the ChO depends on the presence of the central brain to trigger forward movement, stimulation of leg MsB could trigger cyclic motor activity independently of central brain circuits. Leg MsB-triggered movement lacks inter-leg and intra-leg coordination, whilst antagonistic muscle activity within joints is preserved. Moreover, we found that the duration of the MsB-induced movement is dependent on the number of excited cells and is specific to leg afferents, since stimulation of MsB in other segments lead to different motor outcomes. This study sheds light on the ability of specific sensory circuits to modulate motor control, including initiation of movement, and how this information can be automatically translated to a motor command by spinal neuronal pathways.