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Eyal Margalit, Sylvie Sim, Robert Szalewski, Lee Johnson, Wallace Thoreson; Extracellular recording of multiple retinal ganglion cells during epiretinal vs. subretinal electrical stimulation of isolated mouse retina with a high resolution stimulation device. Invest. Ophthalmol. Vis. Sci. 2013;54(15):346.
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© ARVO (1962-2015); The Authors (2016-present)
To compare response patterns and electrical receptive fields (ERF) of retinal ganglion cells (RGCs) evoked by epiretinal vs. subretinal electrical stimulation (epi vs. sub) of isolated mouse retina with a novel stimulation device.
Retinae were isolated from 4-12 week old normal (C57BL6J) mice, and positioned ganglion cell down (epi ), or up (sub), over a stimulation device with 3200 electrodes (Naval Research Laboratory, Washington DC) that is capable of stimulating single or multiple electrodes. Extracellular recording was performed from multiple RGCs using an array of sixteen recording electrodes (Alfa Omega, Alpharetta, GA).
46 and 59 RGCs were recorded during epi and sub, respectively. The thresholds for spikes evoked by stimuli increased with the square of distance between the stimulating electrode and the target cell. Three response patterns were observed: a burst of activity immediately after stimulation (Type I cells, Jensen and Rizzo- 2008), delayed bursts beginning >25 ms later (Type II), or a combination of both (Type III). Type I responses were produced more often by epi (83%) than sub (53%). Conversely, delayed responses observed in Type II and Type III cells were evoked more frequently by sub (18/59 cells, 31%) than epi (7/46 cells, 15%). Inhibitory responses were also observed more often with sub (17%) than epi (2%). These differences were significant (p=0.0012, chi-square test). In addition, the response delay was shorter for epi vs. sub (p=0.0009, chi-square test). ERF was defined as a stimulating array’s surface area that can successfully stimulate spikes in a given RGC in either epi or sub. The area (in mm2) of ERFs obtained for short latency responses reflecting direct activation was smaller with sub (Type I 0.239+0.151, N=11; Type II 0.362+0.238, N=31) than epi (0.461+0.524, N=7; 0.733+0.773, N=38). The difference in the ERF size between epi vs. sub was significant (p=0.0052, ANOVA).
The greater frequency of delayed and inhibitory responses suggests that sub stimulation is more effective at activating intraretinal circuits than epi stimulation. The differences in epi vs. sub ERFs’ areas can be largely explained by the greater distance between stimulating electrodes and recorded RGCs due to the interposed retina in the sub configuration.
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