Immunohistochemical and electrophysiological analysis of rat retinas after subretinal implantation of photovoltaic arrays

Abstract

Purpose: Network-mediated retinal stimulation by subretinal prostheses may depend on a functional retinal interface. Excessive glial scarring or the loss of inner retinal neurons at the implant site could reduce or eliminate implant-evoked signaling. In this study, immunohistochemical evaluation of the inner retina was compared to electrophysiological recordings of implant-evoked responses in the superior colliculus (SC) to assess signal transmission and retinal health after implantation of photovoltaic arrays (PVAs) in the transgenic S334ter-3 rat model of retinitis pigmentosa.

Methods: Silicon-based PVAs were implanted monocularly into the subretinal space of S334ter-3 rats at 7 or 12 weeks of age. In an intact animal preparation at 18 to 27 weeks post-implantation, arrays were stimulated with IR light (905 nm) at locations on the implant surface and evoked responses were mapped across the dorsal surface of the SC. Immediately after, animals were sacrificed and eyes were enucleated, fixed, and processed for immunohistochemistry. Retinal sections were labeled with primary antibodies against ChAT, PKCα, and GFAP with fluorescent secondary antibodies and visualized with confocal microscopy. The morphology of cells in regions immediately contacting the PVA was compared with areas adjacent to and distant from the implant site.

Results: In most implanted animals, PVA-evoked responses were recorded in the SC. PKCα and ChAT labeling showed preservation of rod bipolar cells and cholinergic amacrine cells, respectively, in and around the implant site. In fully subretinal implantations, amacrine cell lamination patterns were well-maintained in the IPL. Similarly, rod bipolar cells were robustly labeled, and their axon terminal locations were consistent across the retina. GFAP labeling was widespread in all retinal areas, indicating a general glial reaction, but showed little or no additional glial scarring at the implant site.

Conclusions: PVA-evoked responses in the SC indicate that the implanted degenerate retina is still able to pass signals to higher visual structures. That rod bipolar and cholinergic amacrine cells exhibit well-preserved morphology indicates that they should be able to contribute to retinal signal transmission. Glial reactivity is uniform across the retina and is unlikely to interfere with signaling.

Keywords: 688 retina • 554 immunohistochemistry • 508 electrophysiology: non-clinical