Two-photon calcium imaging from head-fixed Drosophila during optomotor walking behavior

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Abstract
This technique allows functional imaging of neurons in head-fixed Drosophila while the fly walks on an air-supported ball. Using a genetically encoded calcium sensor, the activity of motion-sensitive neurons in the fly optic lobe was recorded while the flies were presented with visual stimuli. Activity in these cells correlated with robust optomotor behavior in the walking flies. Drosophila melanogaster is a model organism rich in genetic tools to manipulate and identify neural circuits involved in specific behaviors. Here we present a technique for two-photon calcium imaging in the central brain of head-fixed Drosophila walking on an air-supported ball. The ball's motion is tracked at high resolution and can be treated as a proxy for the fly's own movements. We used the genetically encoded calcium sensor, GCaMP3.0, to record from important elements of the motion-processing pathway, the horizontal-system lobula plate tangential cells (LPTCs) in the fly optic lobe. We presented motion stimuli to the tethered fly and found that calcium transients in horizontal-system neurons correlated with robust optomotor behavior during walking. Our technique allows both behavior and physiology in identified neurons to be monitored in a genetic model organism with an extensive repertoire of walking behaviors.