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P. Lagali, D. Balya, G. Awatramani, T. Muench, D. Kim, C. Cepko, B. Roska; Retinal Repair by Circuit-Specific Intervention With Channelrhodopsin - Part I. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4877. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To induce photosensitivity in ON bipolar cells of retinas with photoreceptor degeneration, thereby bypassing the requirement of the photoreceptor cells and rescuing retinal function.
A mammalian expression construct encoding a light-activated cation channel, channelrhodopsin-2 (ChR2), fused to a yellow fluorescent protein tag, and driven by an ON bipolar cell-specific enhancer element found within the mouse GRM6 gene promoter was engineered. The expression construct was delivered to the inner retinal cells of wild-type and rd1 mice by subretinal injection followed by in vivo electroporation. ChR2 expression in electroporated retinas was analyzed by immunohistochemistry and confocal microscopy. Photosensitivity of ChR2-expressing bipolar cells and post-synaptic visual signal transduction was tested electophysiologically by whole-cell patch clamp recordings of retinal ganglion cells in the electroporated retinas.
In the electroporated retinas, expression of ChR2 was observed exclusively in retinal ON bipolar cells. ChR2 expression was stable for at least 6 months post-injection in both wild-type and rd1 retinas. Approximately equal numbers of rod and cone bipolar cells were targeted, and all subtypes of cone bipolar cells were represented in the ChR2-expressing bipolar cell population. Electrophysiological analysis of post-synaptic retinal ganglion cells demonstrated that ChR2 activation can elicit both transient and sustained ganglion cell responses. In addition, both excitatory and inhibitory ganglion cell responses were observed in the electroporated rd1 retinas that are similar to photoresponses in wild-type mouse retinas.
ChR2 delivery to and activity in retinal ON bipolar cells can restore photoresponsiveness to rd1 retinas in which endogenous photoreceptors have degenerated. The diversity of retinal ganglion cell responses observed suggests that the functional integrity of different parallel visual processing pathways in the inner retina is maintained well after the photoreceptor cells are lost.
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