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Jianmin Luo, Bronson J. Boosalis, Wallace B. Thoreson, Eyal Margalit; A Comparison Of Optical And Electrophysiological Methods For Recording Retinal Ganglion Cells During Electrical Stimulation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4936.
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© ARVO (1962-2015); The Authors (2016-present)
Electrophysiological activity of surviving retinal ganglion cells (RGCs) in retinal degenerative diseases can be evoked by electrical stimulation. We compared the pros and cons of three electrophysiological and imaging techniques to study responses of retinal neurons to epiretinal electrical stimulation.
In mouse and salamander retina, patch clamp techniques were used for recording spikes and synaptic currents, and sodium (CoroNa Green-AM) and calcium (Fluo4-AM) dyes were used to map intracellular Na+ and Ca2+ changes respectively. Retinal neurons were stimulated using epiretinal metal electrodes (50~100 kΩ). Patch clamp recordings were performed using retinal slices (RS) and flatmount retina (FM). Imaging experiments were performed using RS and a spinning disk confocal microscope.
Electrical stimulation evoked both rapid (spikes) and slower synaptically-mediated currents in RGCs. Spikes were evoked in 67% (8 cells) of salamander RGCs in FM, 68% (13 cells) of salamander RGCs in RS, 76% (38 cells) of mouse RGCs in FM, and 72% (8 cells) of mouse RGCs in RS. Synaptic currents were observed in 41% (5 cells) of salamander RGCs in FM, 32% (6 cells) of salamander RGCs in RS, 36% (13 cells) of mouse RGCs in FM, and 23% (3 cells) of mouse RGCs in RS. The ability of stimulation to evoke spikes in the majority of RGCs suggested the possibility to map depolarizing activity in RS using a Na+ dye. However, stimulation failed to evoke detectable Na+ responses. We confirmed stimulation efficacy by Na+ imaging while recording electrophysiologically. Synaptically-mediated currents were observed in many RGCs suggesting the possibility of detecting of presynaptic Ca2+ increases in the IPL. However, RS rarely showed Ca2+ increases in response to electrical stimulation.
Electrophysiological recording shows more sensitivity than Na+ or Ca2+ imaging techniques and is thus superior for mapping RGC responses to electrical stimulation. The paucity of Ca2+ responses during epiretinal stimulation is consistent with a limited risk for Ca2+-mediated cell damage during electric stimulation.
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