Abstract
Purpose :
Detecting movement reliably under dim light conditions is critical for rodents to navigate their environment. Direction selective ganglion cells (DSGCs) in the retina encode information about movements across a broad range of light levels and relay this information to the brain. Previous work has shown that adaptation to low, rod-activating light levels, differentially tunes responses of ON-OFF DSGCs (ooDSGCs), such that superior direction preferring ooDSGCs exhibit broad tuning while ooDSGCs preferring other directions exhibit narrow tuning. Here, we sought to identify other functional asymmetries between the populations of ooDSGCs.
Methods :
We used multielectrode array to measure spiking responses of hundreds of retinal ganglion cells in ex vivo retina. Retinas from wild-type mice (C57BL/6J) and conditional knockout mice with Cx36 mediated gap-junctions eliminated specifically in superior ooDSGCs (FACx), were used for experiments. Sparse white noise, dim flashes and moving grating visual stimuli at different light levels were presented, and spiking responses were measured under control condition and condition where GABA receptors were pharmacologically inhibited. Spike sorting was performed using custom written JAVA script.
Results :
We found that the absolute sensitivity of superior ooDSGCs is tenfold higher than other ooDSGC subtypes. The higher sensitivity could be explained partly by a larger receptive field size and a difference in GABA mediated inhibition, between superior and non-superior ooDSGCs. Blocking GABA-ergic inhibition largely eliminated the difference in the threshold responses across ooDSGC subtypes. Using conditional knockout mice, we found that gap junction coupling did not significantly contribute to the absolute sensitivity difference between the ooDSGC subtypes. GABA-ergic inhibition was also found to mask the OFF responses of ooDSGCs under scotopic conditions.
Conclusions :
This study reveals a functional asymmetry between different types of ON-OFF direction selective retinal ganglion cells (ooDSGCs), near the absolute threshold of vision. This asymmetry arises primarily because of different amounts of GABA mediated inhibition on superior versus non-superior ooDSGC subtypes.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.