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Cameron Baker, Janette Tang, Mike Berry, Ehud Isacoff, John Gerard Flannery; ChR2 Stimulation in Müller cells Modulates the Retinal Light Response. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4194.
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© ARVO (1962-2015); The Authors (2016-present)
Müller cells are the principle glia cells of the retina. Responsible for homeostasis, waste removal, and nutrient delivery, these macroglia cells support their highly specialized neuronal neighbors. Beyond these maintenance roles, Müller glia can potentially augment neuronal communication through their role in neurotransmitter reuptake. Like astrocytes, Müller glia take up excess, and potentially toxic, neurotransmitters (e.g. glutamate) via ion exchange transporters. Müller glia maintain a high membrane potential of -80 mV to support their ion exchange transporters like GLAST and GLT-1. We hypothesize that biasing this membrane potential can inhibit neurotransmitter reuptake systems, modulating the surrounding retinal neuronal light response.
We expressed the canonical ChR2 or a bi-stable point mutant, C128S, in mouse retinal Müller cells via intravitreal injection of ShH10-Y445F, an Müller cell specific AAV capsid previously developed in our group by directed evolution. Mouse retinal light reponses were measured by electroretinogram (ERG) and multielectrode array (MEA).
ERG recordings demonstrate a depressed B-wave from retinas expressing ChR2 in Müller cells. We hypothesized that if ChR2 attenuates the membrane potential of Müller cells and inhibits glutamate uptake, we should observe this as a depression of the B-wave amplitude with no change to the A-wave. We indeed found the B-wave for the ChR2-Müller retina to be reduced, and the A-wave remained unaltered.MEA recordings using the bi-stable ChR2(C128S) show a recoverable decreased OFF response after ChR2 stimulation. The bi-stable ChR2(C128S) treated retinas display different channel kinetics than the canonical ChR2. After light stimulation, ChR2(C128S) remains open for ~ 5 minutes. Retinas were exposed to low white light stimulation and then bright activating ChR2 light. Low light stimulation after ChR2(C128S) stimulation showed a decreased OFF response that was able to recover.
This electrophysiological data shows neuronal perturbation due to ChR2 stimulation in Müller glia, demonstrating the glial capability to modulate its neuronal neighbors.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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