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Peter D Lukasiewicz, Robert Purgert; Two Patterns of Spatial Tuning Occur in ON Ganglion Cells and Change with Ambient Illumination. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3241.
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© ARVO (1962-2015); The Authors (2016-present)
Ganglion cells (GCs) extract spatial information from visual scenes for transmission to the brain. They do so via their antagonistic center-surround receptive fields, mediated by cone bipolar cells (CBC) (center) and horizontal cells (HC) and amacrine cells (AC) (surround). The relative roles of horizontal and amacrine cell surround signaling are unknown. In this study, we assessed the center and surround contributions within ON GCs at different ambient illuminations.
Mouse ON GC light responses were recorded with whole cell voltage-clamp techniques in thick retinal slices. Center and surround contributions were assessed by clamping at ECl to isolate CBC inputs. AC and HC surround contributions were blocked by GABAR antagonists and HEPES, respectively. Visual stimuli were drifting sine wave gratings displayed atop rod-saturating backgrounds. Response data were fit with a difference-of-Gaussians model to derive the magnitudes and spatial extents of inputs. GCs were filled with dye for morphological characterization.
Light-evoked inputs were measured from the same ON GC. All cells had strong CBC input, and weak HC input. However, the magnitude of amacrine cell input varied with ON GC type: cells ramifying near the mid inner plexiform layer (IPL) had strong AC input and spatial tuning, while cells ramifying in proximal IPL had weak AC input and spatial tuning. Increased ambient illumination eliminated differences between the mid and proximal IPL cells; both GC types showed significant AC input and spatial tuning.
Our findings show that there are two classes of ON GCs that exhibit distinct patterns of visual spatial processing at dim ambient illumination, suggesting a functional division in encoding spatial stimuli. The differences are attributed to the distinct strengths of amacrine cell input. These differences were eliminated when ambient illumination increased. We previously reported that two classes of cone BCs show similar spatial tuning and illumination dependence, suggesting that spatial tuning properties are present in cone BCs and then transmitted to GCs.
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