Inner and outer retinal mechanisms engaged by epiretinal stimulation in normal and rd mice

• Published in: Visual neuroscience Vol. 28; no. 2; pp. 145 - 154
• Main Authors: MARGALIT, EYAL, BABAI, NORBERT, LUO, JIANMIN, THORESON, WALLACE B.
• Format: Journal Article
• Language: English
• Published: New York, USA Cambridge University Press 01.03.2011
• Subjects: Animals; Biological and medical sciences; Biophysics; Calcium - metabolism; Disease Models, Animal; Electric Stimulation - methods; Electrodes; Evoked Potentials - drug effects; Evoked Potentials - genetics; Evoked Potentials - physiology; Excitatory Amino Acid Antagonists - pharmacology; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - genetics; Experiments; Eye and associated structures. Visual pathways and centers. Vision; Eyes & eyesight; Fundamental and applied biological sciences. Psychology; GABA-A Receptor Antagonists - pharmacology; Glycine Agents - pharmacology; Human subjects; In Vitro Techniques; Mice; Mice, Inbred C57BL; Mice, Mutant Strains; Microscopy, Confocal; Patch-Clamp Techniques - methods; Picrotoxin - analogs & derivatives; Picrotoxin - pharmacology; Quinoxalines - pharmacology; Retina; Retina - pathology; Retinal Degeneration - classification; Retinal Degeneration - genetics; Retinal Degeneration - pathology; Retinal Ganglion Cells - drug effects; Retinal Ganglion Cells - physiology; Retinal Ganglion Cells - radiation effects; Strychnine - pharmacology; Surgical apparatus & instruments; Transplants & implants; Vertebrates: nervous system and sense organs; Veterans; Visual Pathways - drug effects; Visual Pathways - physiology; Electrical stimulation; Retina; rd mouse; Retinal prosthesis; Ganglion cell; Rodentia; Stimulation; Eye; Visual system; Vertebrata; Mammalia; Mouse; Animal
• ISSN: 0952-5238; 1469-8714
• DOI: 10.1017/S0952523810000489

Retinal prosthetic devices are being developed to bypass degenerated retinal photoreceptors by directly activating retinal neurons with electrical stimulation. However, the retinal circuitry that is activated by epiretinal stimulation is not well characterized. Whole-cell patch clamp recordings were obtained from ganglion cells in normal and rd mice using flat-mount and retinal slice preparations. A stimulating electrode was positioned along the ganglion cell side of the preparation at different distances from the stimulated tissue. Pulses of cathodic current evoked action potentials in ganglion cells and less frequently evoked sustained inward currents that appeared synaptic in origin. Sustained currents reversed around ECl and were inhibited by blockade of α-amino-3-hydroxyl-5-methyl-4-isoxazole-proprionate (AMPA)-type glutamate receptors with 2,3-dihydroxy-6-nitro-sulfamoyl-benzo(f)-quinoxaline-2,3-dione (NBQX), γ aminobutyric acid a/c (GABAa/c) receptors with picrotoxinin, or glycine receptors with strychnine. This suggests that epiretinal stimulation activates glutamate release from bipolar cell terminals, which in turn evokes release of GABA and glycine from amacrine cells. Synaptic current thresholds were lower in ON ganglion cells than OFF cells, but the modest difference did not attain statistical significance. Synaptic currents were rarely observed in rd mice lacking photoreceptors compared to normal retina. In addition, confocal calcium imaging experiments in normal mice retina slices revealed that epiretinal stimulation evoked calcium increases in the outer plexiform layer. These results imply a contribution from photoreceptor inputs to the synaptic currents observed in ganglion cells. The paucity of synaptic responses in rd mice retina slices suggests that it is better to target retinal ganglion cells directly rather than to attempt to engage the inner retinal circuitry.