Meeting Abstract
Fruit flies have tiny colour receptors, which are stochastically distributed across the retina. Sharp-electrode electrophysiology from these cells is therefore unfeasible and Drosophila visual pigments have yet to be fully characterised in vivo. Previous findings suggest that fly inner and outer photoreceptors are involved in both colour discrimination and achromatic motion detection. Furthermore, colour-opponent processing has been demonstrated between inner R7-R8 photoreceptor pairs (UV-blue/ UV-green). In this study, we first characterised the spectral sensitivity of D. melanogaster photoreceptors in vivo. We used the electroretinogram (ERG) method on blind norpA mutants with selectively recovered photoreceptor activity and tested the effect of screening pigment and dietary carotenoids on photoreceptor response. We report that the peak sensitivity of Rh6 is shifted by 90 nm from green (510 nm) to red (600 nm) when measured in its native receptor and with wild-type screening pigment. Our findings can be explained by both a blue-absorbing filter and long wavelength light leakage through the screening pigment. Secondly, we measured to what extent spectral sensitivity is refined by opponent processing, by recovering activity in photoreceptor pairs. We saw no evidence of opponent processing between R7 and R8 photoreceptor pairs at the level of the photoreceptors. However, between inner and outer receptors we observed a signal boost, suggesting a feedback mechanism in the medulla. The neural route for this signal boost will be the focus of ongoing experiments.
