Asian Journal of Physics Vol 30, No 12 (2021) 1689-1696

Theoretical analysis of optogenetic excitation of ON and OFF retinal ganglion neurons

Gur Pyari, Himanshu Bansal and Sukhdev Roy
Department of Physics and Computer Science, Dayalbagh Educational Institute, Agra-282 005, India
Dedicated to Prof D V G L N Rao

Retinal ganglion neurons (RGNs) have a large range of variation in their ionic channel properties and morphologies. In optogenetic retinal prostheses, the variation becomes crucial as the irradiance thresholds and pulse widths to evoke desired firing patterns are highly sensitive to the biophysical properties of targeted neurons. In the present study, a theoretical analysis of optogenetic excitation of ON and OFF RGNs has been presented by formulating morphologically- and biophysically-accurate models of opsin expressing neurons. The study also compares the potential of experimentally studied opsins namely ChR2 and ChrimsonR with a recently discovered opsin named ChRmine, not studied as yet for retinal prostheses. The study reveals that ChRmine is able to evoke spiking upto 112 Hz in OFF RGNs on axonal illumination at 3.6 × 1014 photons mm–2 s–1 i.e., an order of magnitude lower than standard safety threshold at 590 nm of retina. In comparison, to target other parts, both ON and OFF RGNs respond faster on axonal stimulation. Minimum irradiance threshold to evoke high-fidelity spiking under pulsed illumination is lowest on somatic stimulation in ON-RGCs, while it is almost similar on both somatic and axonal stimulation in OFF-RGNs. The study provides a useful insight on how different kinds of RGCs and their different parts respond to optical stimulations. The more detailed biophysical model of opsin-expressing RGNs would be useful in accurately predicting the response of real biological neurons to optogenetic stimulation.© Anita Publications. All rights reserved.
Keywords: Optogenetics, Channelrhodopsin, Retinal prostheses, ChRmine.

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