Meeting Abstract
Extracellular electroretinograms (ERGs), which measure the neuronal response of the retina to light stimuli, have been widely used to examine proper functioning of photoreceptors. ERGs have shown deficiencies resulting from the knockdowns of the gliogenic transcription factor pros in Drosophila melanogaster Semper cells, which are eye-intrinsic glial cells that reside adjacent to the photoreceptors. In contrast, Semper-cell specific knockdown of the transcription factor dPax2 showed no deficiency, even though histologic analysis revealed highly disrupted eye morphology in such flies. In the preceding study, ERGs were measured in response to individual light pulses. Here, we developed two additional extensive light stimulation protocols: the “flicker fusion frequency” test and the “extended sequence” test. In the former test, flickering light stimuli of different frequencies were presented until we found the “fusion frequency” for which photoreceptors respond to the flickering pulses as if they were one prolonged pulse. In the “extended sequence” protocol, multiple repetitions of short light pulses were presented over several minutes to evaluate if photoreceptors were able to sustain consistent responses. Using these protocols, we revealed that Semper-cell knockdowns of dPax2 showed a significant weakening of responses to later-presented light stimuli in the extended sequence. Our evidence suggests that photoreceptors in these knockdowns may not be able to maintain efficient energy supply from their associated Semper cells, and hence proper dPax2 function also appears to play a role in homeostatic support for the photoreceptors. Our findings highlight the importance of characterizing physiological performance under a variety of different stimulus protocols.
