The microglia response to electrical overstimulation of the retina imaged under a transparent stimulus electrode

Alula R Yohannes; Christopher Y Jung; Katherine I Shea; Wai T Wong; Alexander Beylin; Ethan D Cohen

doi:10.1088/1741-2552/abda0a

The microglia response to electrical overstimulation of the retina imaged under a transparent stimulus electrode

J Neural Eng. 2021 Mar 1;18(2). doi: 10.1088/1741-2552/abda0a.

Authors

Alula R Yohannes¹, Christopher Y Jung², Katherine I Shea³, Wai T Wong⁴, Alexander Beylin⁵, Ethan D Cohen¹

Affiliations

¹ Division of Biomedical Physics, Office of Science and Engineering Labs, Center for Devices and Radiological Health, Food and Drug Administration, White Oak Federal Research Labs, Bldg. 62 Rm 1204, Silver Spring, MD 20993-0002, United States of America.
² University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, United States of America.
³ Division of Applied Regulatory Science, Center for Drug Evaluation and Research, Food and Drug Administration, White Oak Federal Research Labs, Silver Spring, MD 20993-0002, United States of America.
⁴ National Eye Institute, Laboratory of Retinal Cell and Molecular Biology, National Institute of Health, 6 Center Drive, Bethesda, MD 20814, United States of America.
⁵ Office of Health Technology 1, Office of Product Evaluation and Quality, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD 20993-0002, United States of America.

PMID: 33418555
DOI: 10.1088/1741-2552/abda0a

Abstract

Objective.We investigated using the morphological response of retinal microglia as indicators of tissue damage from electrical overstimulation by imaging them through an optically transparent stimulus electrode.Approach.To track the microglia, we used a transgenic mouse where the microglia expressed a water soluble green fluorescent protein. The clear stimulus electrode was placed epiretinally on the inner limiting membrane and the microglia layers were imaged using time-lapse confocal microscopy. We examined how the microglia responded both temporally and spatially to local overstimulation of the retinal tissue. Using confocal microscope vertical image stacks, the microglia under the electrode were imaged at 2.5 min intervals. The retina was overstimulated for a 5 min period using 1 ms 749μC cm^-2ph^-1biphasic current pulses and changes in the microglia morphology were followed for 1 h post stimulation. After the imaging period, a label for cellular damage was applied to the retina.Main results.The microglia response to overstimulation depended on their spatial location relative to the electrode lumen and could result in three different morphological responses. Some microglia were severely injured and became a series of immotile ball-like fluorescent processes. Other microglia survived, and reacted rapidly to the injury by extending filopodia oriented toward the damage zone. This response was seen in inner retinal microglia outside the stimulus electrode edge. A third effect, seen with the deeper outer microglia under the electrode, was a fading of their fluorescent image which appeared to be due to optical scatter caused by overstimulation-induced retinal edema.Significance.The microglial morphological responses to electrical overstimulation injury occur rapidly and can show both direct and indirect effects of the stimulus electrode injury. The microglia injury pattern closely follows models of the electric field distribution under thinly insulated disc electrodes.

Keywords: confocal microscopy; electrode; microglia; retinal prosthesis; stimulation.

MeSH terms

Animals
Electric Stimulation / methods
Electrodes
Green Fluorescent Proteins / genetics
Mice
Mice, Transgenic
Microglia*
Retina* / physiology

Substances

Green Fluorescent Proteins