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Kosta P, Iseri E, Loizos K, Paknahad J, Pfeiffer RL, Sigulinsky CL, Anderson JR, Jones BW, Lazzi G. Model-based comparison of current flow in rod bipolar cells of healthy and early-stage degenerated retina. Exp Eye Res 2021; 207:108554. [PMID: 33794197 DOI: 10.1016/j.exer.2021.108554] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 03/04/2021] [Accepted: 03/23/2021] [Indexed: 12/27/2022]
Abstract
Retinal degenerative diseases, such as retinitis pigmentosa, are generally thought to initiate with the loss of photoreceptors, though recent work suggests that plasticity and remodeling occurs prior to photoreceptor cell loss. This degeneration subsequently leads to death of other retinal neurons, creating functional alterations and extensive remodeling of retinal networks. Retinal prosthetic devices stimulate the surviving retinal cells by applying external current using implanted electrodes. Although these devices restore partial vision, the quality of restored vision is limited. Further knowledge about the precise changes in degenerated retina as the disease progresses is essential to understand how current flows in retinas undergoing degenerative disease and to improve the performance of retinal prostheses. We developed computational models that describe current flow from rod photoreceptors to rod bipolar cells (RodBCs) in the healthy and early-stage degenerated retina. Morphologically accurate models of retinal cells with their synapses are constructed based on retinal connectome datasets, created using serial section transmission electron microscopy (TEM) images of 70 nm-thick slices of either healthy (RC1) or early-stage degenerated (RPC1) rabbit retina. The passive membrane and active ion currents of each cell are implemented using conductance-based models in the Neuron simulation environment. In response to photocurrent input at rod photoreceptors, the simulated membrane potential at RodBCs in early degenerate tissue is approximately 10-20 mV lower than that of RodBCs of that observed in wild type retina. Results presented here suggest that although RodBCs in RPC1 show early, altered morphology compared to RC1, the lower membrane potential is primarily a consequence of reduced rod photoreceptor input to RodBCs in the degenerated retina. Frequency response and step input analyses suggest that individual cell responses of RodBCs in either healthy or early-degenerated retina, prior to substantial photoreceptor cell loss, do not differ significantly.
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Affiliation(s)
- Pragya Kosta
- Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT, USA.
| | - Ege Iseri
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA
| | - Kyle Loizos
- Institute for Technology and Medical Systems Innovation (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Javad Paknahad
- Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA
| | - Rebecca L Pfeiffer
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | | | - James R Anderson
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA
| | - Bryan W Jones
- John Moran Eye Center at the University of Utah, Salt Lake City, UT, USA.
| | - Gianluca Lazzi
- Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA; Institute for Technology and Medical Systems Innovation (ITEMS), Keck School of Medicine, University of Southern California, Los Angeles, CA, USA; Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA; Department of Ophthalmology, University of Southern California, Los Angeles, CA, USA.
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