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A. Stett, D. Schwenger; Spatial Sensitivity of Ganglion Cells in RCS Rat Retina to Subretinal Electrical Stimulation With Line Electrodes . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3170.
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© ARVO (1962-2015); The Authors (2016-present)
Subretinal implants aim at activation of the neuronal network in degenerated retinas by electrical stimulation of the distal retina. In order to investigate the receptive field of ganglion cells that is sensitive to spatial extended electric stimulation we applied ex vivo methods with explanted retinas from blind rats.
Retinas were explanted from the enucleated eyes from RCS rats (age: 90 days and older) and adhered to microelectrode arrays (MEA) with the photoreceptor side down. For electrical stimulation with anodic voltage impulses (duration: 500 µs, amplitude up to 3 V) we used an array of line electrodes (length 1 mm, width 10 µm, interelectrode distance10 µm, TiN). The retinal response was measured from individual ganglion cell bodies with a glass pipette (Stett et al., Vision Research 40:1785–1795, 2000) and analyzed with respect to the lateral distance of the stimulated line electrode to the recorded ganglion cell. To identify electrically activated intraretinal signal paths we added Dopamine (1 mM) and high concentrations of Mg2+ (10 mM) to the bath ringer to de–couple amacrine cells and to suppress synaptic transmission.
Ganglion cells responded to subretinal stimulation with line electrodes with a complex spatio–temporal activity pattern. Temporal ON and OFF responses could be measured when the stimulating line electrode ran through a well–defined field surrounding the ganglion cell bodies. These receptive fields have sharp borders with a transition from no response to half–maximal response within 40 µm. The width of the corresponding spatial sensitivity profile within the borders was in the range between 100 µm and 400 µm (median of full width at half maximum: 190 µm, n= 13). Administration of Dopamine led to a significant decrease of the diameter of the receptive field. The threshold charge density for stimulation with a line electrode running through the centre of the receptive field of ganglion cells was 89 µC/cm² (median, n= 28).
In the partly degenerated neuronal network of the RCS rat retina capabilities for lateral signal processing are present and can be activated by electrical input with an accuracy of less than 0,2° angle of vision. We conclude that in blind retinas the receptive–field–organization is accessible to electrical stimulation with subretinal implants.
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