title: Inner and outer retinal mechanisms engaged by epiretinal stimulation in normal and rd mice.
abstract: 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 E(Cl) 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 (GABA(a/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.
authors.affiliation: VA Nebraska-Western Iowa Health Care System, USA. emargalit@unmc.edu
authors.forename: Eyal
authors.initials: E
authors.lastname: Margalit
authors.forename: Norbert
authors.initials: N
authors.lastname: Babai
authors.forename: Jianmin
authors.initials: J
authors.lastname: Luo
authors.forename: Wallace B
authors.initials: WB
authors.lastname: Thoreson
mesh_terms: D000818:Animals; D001703:Biophysics; D002118:Calcium / Q000378:metabolism; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D018613:Microscopy, Confocal; D018408:Patch-Clamp Techniques / Q000379:methods; D010852:Picrotoxin / Q000031:analogs & derivatives / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D012160:Retina / Q000473:pathology*; D012162:Retinal Degeneration / Q000145:classification / Q000235:genetics / Q000473:pathology*; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D054830:Sesterterpenes; D013331:Strychnine / Q000494:pharmacology; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology
chemical_list: D002118:Calcium; D018691:Excitatory Amino Acid Antagonists; D058787:GABA-A Receptor Antagonists; D018684:Glycine Agents; D010852:Picrotoxin; D011810:Quinoxalines; D054830:Sesterterpenes; D013331:Strychnine; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C022961:picrotoxinin