We propose to impart light sensitivity directly onto normally non-photosensitive neurons in a diseased retina. While inherited retinal degenerations have many genetic causes at their source, one common theme is the eventual apoptotic death of photoreceptor cells. In most cases, the remaining inner retinal neurons survive long after rods and cones are lost. Central to our goal is the use of novel rhodopsins that allow for precise optical control of neural activity with visible light. Channelrhodopsin-2 is a photosensitive cation channel that allows for neural excitation in response to blue light. A functional converse is Halorhodopsin, a photo- sensitive chloride pump that silences neural activity with yellow light. These rhodopsins use retinoids as their chromophore and directly modulate activity without accessory protein cascades or exogenous chemicals. We hypothesize that if initiated in the appropriate cell subtype, light-driven excitation and inhibition may re- create the ON and OFF-center visual information streams normally present in the retina. These parallel information streams are largely responsible for allowing contrast sensitivity and high acuity. Specific delivery to the desired ON or OFF-center cell population is not trivial, and we propose to approach this by a combination of transcriptional targeting along with viral gene transfer methods. Patch clamp electrophysiology combined with raster scanning stimuli will be integral to the project for both evaluating the specificity of transgene targeting and in characterizing the photocurrents generated from networks of these neurons. Finally, we hope to understand if a photosensitive inner retina can transmit functional information to higher visual centers in a disease model with simple behavioral tools. Using these combined neuroengineering and electrophysiological approaches, we aim to determine if selective photo-excitation and inhibition of ON and OFF pathway inner neurons can confer useful light sensitivity to the injured retina.
Gene therapy is a highly promising method for attempting to restore vision in diseases that cause photoreceptor loss, and imparting light sensitivity directly to surviving retinal neurons may be one approach. We hope to understand the potential for converting non-photosensitive neurons into photosensors and apply this knowledge toward the future development of a retinal prosthetic.
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|Stradleigh, Tyler W; Ogata, Genki; Partida, Gloria J et al. (2011) Colocalization of hyperpolarization-activated, cyclic nucleotide-gated channel subunits in rat retinal ganglion cells. J Comp Neurol 519:2546-73|
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