Video 3. Drosophila R1-R8 photoreceptors contract photomechanically in vivo, moving back-to-front inside each observed ommatidium.
We utilized the optical cornea-neutralization technique with antidromic deep-red (740 or 785 nm peak) illumination to observe deep pseudopupils (photoreceptor rhabdomeres that align with the observer’s viewing axis) in the Drosophila eye. High-speed video captures fast rhabdomere movements to bright orthodromic blue-green flashes (470 + 535 nm peaks). The panels show: left, R1-R7 photoreceptor rhabdomere tips moving rapidly back-to-front and returning slower to each 10 ms flash, delivered repeatedly every second; right, the cross-correlated horizontal (blue) and vertical (red) components as the time series of this movement. Grey vertical lines indicate each flash. The rhabdomere movement is caused by the photomechanical photoreceptor contractions (not by muscle activity). These in vivo movements are large, here 1.7 µm from dark-adapted rest-state; causing up to five degree transient shift in the R1-R6 photoreceptors receptive fields (Appendix 7). Note average diameter of R1-R6 rhabdomeres is 1.7 µm (Appendix 5). The high-speed video rate was 500 frames/s. Video playback slowed down and down-sampled to reveal the contractions, which otherwise would be too fast to see with a naked eye.