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Max Eickenscheidt, Peter Fromherz, Günther Zeck; Capacitive Stimulation of Retinal Neurons in Epiretinal and Subretinal Configuration. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2591.
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Electric stimulation of the retina aims for partial restoration of visual function in blind patients. The long-term stability of the electrode-tissue interface represents a technological challenge. Stimulation electrodes have been therefore isolated with a thin layer of titanium oxide. Here, we demonstrate the feasibility of capacitive stimulation of different classes of retinal neurons using a multi-capacitor array. We further investigate how neuronal types can be selectively stimulated.
The isolated rabbit retina is stimulated using an array of 400 capacitive stimulation electrodes. The stimulation sites can be combined to arbitrary areas ranging from 2500 µm2 to 1 mm2. Monophasic capacitive current pulses of different polarity (cathodal and anodal), of variable amplitude (0.5 - 50 mA/cm2) and of variable duration (0.1 - 100 ms) are applied to the retina. Retinal portions are interfaced in either epiretinal or subretinal configuration to the capacitor array. The stimulation of action potentials in retinal ganglion cells (RGCs) is confirmed using an extracellular tungsten electrode.
In epiretinal configuration cathodal current pulses elicit a complex spike burst in RGCs. Using pharmacological blockers we assign the spike with the shortest latency to a direct RGC stimulation, the intermediate burst (blocked by CNQX) to bipolar cell stimulation while the spike burst with the longest latency (blocked by L-AP4) is caused by photoreceptor stimulation. Stimulation with elongated capacitive electrodes (0.1 x 1 mm) confirms the spike assignment: direct RGC stimulation is achieved near the soma, whereas bipolar cell and photoreceptor stimulation is achieved in the RGC receptive field area. In the subretinal configuration anodal current pulses elicited a similar spike burst as detected for cathodal, epiretinal pulses.
Capacitive stimulation of three neuronal classes (photoreceptors, bipolar cells, ganglion cells) is feasible in the isolated rabbit retina using low current densities (1-3 mA/cm2). The capacitor array allows selecting optimal patterns that maximize the probability of stimulating target cell classes.
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