Optogenetic Approaches to Restore Vision and to Analyse Neural Circuits in the Retina

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The introduction of microbial opsins is a promising approach to restore light sensitivity in retinal degenerative diseases. The goal of this project is to express a red-light sensitive channelrhodopsin-variant in ON-bipolar cells of the primate retina, ex vivo by using a viral vector. Here, we will focus on the ON-bipolar cells of the central retina (ON-midget BPCs). A key feature of these cells is that they receive synaptic input from single cone photoreceptors, and these signals are then transmitted to single ganglion cells (midget RGCs). This one-to-one connectivity is an important anatomical prerequisite for the foveal high-acuity vision in primates, including humans. By using optogenetic stimulation of ON-midget BPCs we will trigger light-response in connected ganglion cells which will be analysed with electrophysiology. In particular, we will determine their receptive field properties which will provide important information about the potential spatial resolution that can be achieved with this optogenetic approach. In a parallel project, we will develop a tandem-construct, composed of a chlorid-pump/sensor that will allow for simultaneous manipulation and observation of intracellular chloride concentrations. Cell-type specific expression of this construct will enable to control the intracellular chloride concentration of these cells in a quantitative manner (ratiometric sensor), in order to investigate the impact of transient inhibition on local neuro-circuits. Therefore, we will use a custom-made setup that allows to stimulate retinal cones with patterned light at visible wavelengths, combined with 2-photon induced optogenetic (holographic) stimulation and 2-photon imaging.