Automated measurement of Proboscis Extension Response (PER) in Drosophila

PER stimulated by flash of blue light to the legs

To get the fly to respond it has a light sensitive pigment (a channelrhodopsin) encoded in the sense cells that detect sugar. Thus the cells that detetct sugar now also detect a flash of light. This means we can deliver a very precise stimulus to the fly, and know exactly when it will start to respond. This permits the automation of the measurement of the proboscis extension movement. The green dot shows the movement of the tip of the proboscis as calculated by our assay. The faint red line shows the calculated outline of the proboscis.

click the Image to start the Movie

This means we can measure, in an unbiased way, if the flies respond to the stimulus, if they complete the proboscis extension in a single movement, or if they make multiple movements and show tremor. We have found that flies with mutations related to PD show abnormal proboscis extension responses, including slower movement, failure to respond, incomplete movement and tremor. Flies fed with L-DOPA show dyskinesias (rapid and uncoordinated responses). All these observations mean that these flies make an excellent model of Parkinson's. Here is the response of the fly shown in the video.

picture of the trace calculated at the proboscis extends

Technical details

Video recorded at 162 frames per second with a Point Grey Grasshopper3 camera, by Raul Stein, Chris Elliott and Laurence Wilson, 2017

Optogenetic tool: Gr5a-GAL4 > UAS-ReachR