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EH Hu, SA Bloomfield; Modulation of Correlated Spike Activity of Alpha Ganglion Cells in the Rabbit Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1942.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the effects of light adaptation on the correlated spike activity of alpha ganglion cells (α-GCs). Methods: Dual, simultaneous extracellular recordings were made sequentially from arrays of neighboring α-GCs under infrared illumination in the superfused, flattened rabbit retina-eyecup preparation. One cell in each array was then injected with Neurobiotin to assess tracer coupling. Adaptational conditions of the retina were maintained with calibrated background lights. Results: Under all adaptational states, nearest neighbor off-center α-GCs showed correlated spontaneous and light-evoked spike activity. Cross-correlograms consisted of two short latency peaks at ± 1-2 msec separated by a trough at 0 msec. In the dark-adapted retina, about 25% of α-GC neighbors once-removed showed correlated light-evoked spike activity, but no correlated spontaneous spike activity. In the light-adapted retina, the fraction of α-GC neighbors once-removed showing correlated light-evoked activity increased to 45%, but we found no change in the synchrony of spontaneous spiking. We also found a significant increase in the extent and intensity of tracer coupling of α-GCs in light-adapted vs. dark-adapted retinas. In contrast, under all adaptational states, neighboring on-center α-GCs never showed short-latency correlations for either spontaneous or light-evoked spike activity. Instead, cross-correlations of light-evoked activity from neighboring on-center α-GCs showed a single, broad 100 msec-wide peak centered at 0 msec, indicative of common synaptic inputs. Consistent with the lack of short latency spike synchrony, on-center α-GCs never showed tracer coupling. Conclusions: The difference between the correlated spike activities of on- and off-center α-GCs reflects their different coupling patterns: neighboring off-center α-GCs are electrically coupled, whereas on-center α-GCs are not. In dark-adapted retinas, off-center α-GC coupling is localized to nearest neighbors and diminishes with distance. Light adaptation increases the extent of coupling to the second ring of neighboring off-center α-GCs, thereby synchronizing their light-evoked spike activity. However, light adaptation does not effect the correlations between the spontaneous spike activity of α-GCs.
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