Channelrhodopsin mediated retinal ganglion cell responses in the living macaque

Abstract

Purpose : Optogenetics offers the prospect of vision restoration following photoreceptor degeneration by conferring light sensitivity to postreceptoral retinal neurons. Channelrhodopsin mediated activity in primate retinal ganglion cells (RGCs) has been demonstrated in ex-vivo preparations but not in the living primate. We assess channelrhodopsin mediated responses in the intact macaque by optically recording from RGCs expressing both a channelrhodopsin (ChrimsonR) and a calcium indicator (GCaMP6s).

Methods : AAV2-CAG-G-CaMP6s and AAV2-CAG-ChrimsonR-tdTomato were co-injected into the vitreous of two normal male macaques (M. fascicularis). Adaptive optics scanning light ophthalmoscopy (AOSLO) of GCaMP fluorescence (ex. 488 nm, em. 520/35 nm) was performed while 561 nm drifting gratings were presented at 0.2Hz and 1-5 cycles/deg. Stimuli were stabilized to compensate for the effects of eye motion. Recordings were made at 6, 7, and 19 weeks following injection. Response amplitude and phase were quantified by temporal Fourier analysis.

Results : GCaMP6s and ChrimsonR were co-expressed in RGCs in a ring around the foveal center. We demonstrated that RGCs could be driven in either of two ways, either through the normal photoreceptor pathway or through direct stimulation of ChrimsonR in the RGCs themselves. These pathways can be distinguished using the lateral displacement of the RGCs from the photoreceptors that drive them. The possibility that stray light scattering on foveal photoreceptors generated the response when the stimulus was delivered directly to the RGCs was ruled out by the spatial variation across the RGC array of the temporal phase of RGC responses.

Conclusions : We observe ChrimsonR mediated calcium activity in the foveal RGCs of living macaques. While optogenetic vision restoration has been successfully achieved in the living mouse, demonstrating this in primates is an important step toward deployment in humans. Non-invasive optical recording from RCGs allows longitudinal monitoring and direct observation of vision restoration in the retinal circuitry of the living primate.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.