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Jasdeep Sabharwal, Cameron S Cowan, Samuel M Wu, ; Characterization of light adaptation induced alterations in mouse retinal ganglion cell spatiotemporal tuning. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1339.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies of adaptation induced changes in the linear receptive field of mouse retinal ganglion cells (GCs) described only modifications in temporal processing for a small population of GCs. We hypothesized that temporal slowing is accompanied by an increase in receptive field size. We further anticipated that the observed shifts will differ between ON and OFF GCs. These observations will help attribute changes in GC space-time tuning to different retinal circuits.
Flat-mount retinal preparation (N=6) from 12-14 week-old dark adapted C57/B6 mice were placed onto a multi-electrode array (MEA) for multicellular recording. Receptive fields (RFs) were mapped at both photopic and scotopic mean light levels using a binary white noise checkerboard stimulus with 50 micrometer checkerboard squares presented at 15 Hz. Spike-triggered averages (STA) were used to identify the average space-time stimulus preceding a spike for our population of GCs (N=216) at each light level. Subsequent model fitting allowed identification of properties for the space-time RF. The differences in properties between the light conditions were compared using a Wilcoxon rank sum test. To identify ON and OFF GCs we used principal components (PC) analysis of the temporal STA at the peak spatial location and clustered cells based on the first two PCs.
At photopic light levels, ON GCs had higher spatial and temporal tuning (p<.001). Their low-pass corner frequencies ranged from 2-4 Hz while OFF GCs had a broader range from 0.2-4 Hz. Switching to scotopic light levels caused a decrease in spatial frequency (67% of GCs) and temporal frequency tuning (94% of GCs). RF center size increased by 3% (p<.05) while low and high-pass corner frequencies decreased by 4 and 1 Hz, respectively (p<.001). Lastly, ON GCs showed a greater decrease in high-pass corner frequencies in scotopic conditions.
We identified spatiotemporal properties of the linear RF from a large population mouse GCs at photopic and scotopic light intensities. These results show that, though there are some general ubiquitous changes when shifting to scotopic conditions, subtypes of GCs show differential modification. Studying these differential changes will shed light on contribution of specific retinal pathways on RGC encoding.
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