Retinotopic Responses in the Visual Cortex Elicited by Epiretinal Electrical Stimulation in Normal and Retinal Degenerate Rats
Purpose: Electronic retinal prostheses restore vision in people with outer retinal degeneration by electrically stimulating the inner retina. We characterized visual cortex electrophysiologic response elicited by electrical stimulation of retina in normally sighted and retinal degenerate rats. Methods: Nine normally sighted Long Evans and 11 S334ter line 3 retinal degenerate (rd) rats were used to map cortical responses elicited by epiretinal electrical stimulation in four quadrants of the retina. Six normal and six rd rats were used to compare the dendritic spine density of neurons in the visual cortex. Results: The rd rats required higher stimulus amplitudes to elicit responses in the visual cortex. The cortical electrically evoked responses (EERs) for both healthy and rd rats show a dose-response characteristic with respect to the stimulus amplitude. The EER maps in healthy rats show retinotopic organization. For rd rats, cortical retinotopy is not well preserved. The neurons in the visual cortex of rd rats show a 10% higher dendritic spine density than in the healthy rats. Conclusions: Cortical activity maps, produced when epiretinal stimulation is applied to quadrants of the retina, exhibit retinotopy in normal but not rd rats. This is likely due to a combination of degeneration of the retina and increased stimulus thresholds in rd, which broadens the activated area of the retina. Translational Relevance: Loss of retinotopy is evident in rd rats. If a similar loss of retinotopy is present in humans, retinal prostheses design must include flexibility to account for patient specific variability.
Additional Information© 2018 The Authors. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. Received: 12 February 2018; Accepted: 24 August 2018; Published: 31 October 2018. The authors thank Drs. Artin Petrossians and Curtis Lee for the high-surface area Pt/Ir thin film coating used with some stimulation electrodes in this study; Prof. Michael Jakowec for advice and assistance for performing the golgi stain portion of the study; and Fernando Gallardo and Lina Flores for assistance during the animal surgeries. A subset of the results in this study have been reported55,56 previously. Supported by the National Science Foundation Grant numbers CBET-1353018 and CBET-1343193, and an unrestricted departmental grant to the USC Department of Ophthalmology from Research to Prevent Blindness. Disclosure: K. Nimmagadda, None; J.D. Weiland, high surface area Pt/Ir electrodes (F).
Published - i2164-2591-7-5-33.pdf
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