Poster Session: Optogenetic Stimulation and Calcium Imaging of Single Ganglion Cells in the Living Macaque Fovea.

Abstract

The perceptual roles of most retinal ganglion cell (RGC) classes are controversial in part because we lack a paradigm for measuring the perceptual consequences of activating cells of only one class in the living primate eye. Recent success in classifying single RGCs with in vivo calcium imaging and in vivo optogenetic activation of RGCs en masse now bring such a paradigm within reach. As a first step, we demonstrate the optogenetic stimulation of single foveal RGCs in the living macaque. RGCs in an anesthetized female macaque were stimulated and imaged using adaptive optics scanning light ophthalmoscopy. Co-expression of ChrimsonR and GCaMP6s was achieved via intravitreal injection of a viral vector. On each trial, a targeted soma was exposed to four, 12.5 µm diameter flashes of 0.8 second duration. Targets were limited to those RGCs with at least a 20 µm separation from their nearest neighbors. The GCaMP responses to the flash of both targeted and nearby cells were imaged and the ΔF/F for each soma's response was averaged over the flashes. The ΔF/F values were used to calculate z-scores for each cell's response. Five cells were found to have responded significantly (z-score > 3.5) with no significant response from their neighbors. We can directly activate single RGCs in the living eye and measure the resulting calcium signal, the first step toward a method to measure the sensations produced by individual RGCs in the awake behaving monkey.