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Ben Sivyer, Shandiz Tehrani, Katherine Delf, Diana C Lozano, William Cepurna, Tiffany Choe, Elaine C. Johnson, John C Morrison; EARLY MORPHOLOGICAL AND PHYSIOLOGICAL SIGNS OF NERVE DEGENERATION IN LIVING RETINAL GANGLION CELLS FOLLOWING OPTIC NERVE TRANSECTION.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1879.
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© ARVO (1962-2015); The Authors (2016-present)
We seek to better understand the early cellular mechanisms underlying retinal ganglion cell (RGC) degeneration following optic nerve injury. In this study, we examined morphological changes and recorded electrophysiological responses from RGCs using whole-mounted rat retina following optic nerve transection (ONT).
Following ONT, rats were dark-adapted overnight, anesthetized using intraperitoneal ketamine & xylazine, and were sacrificed at 3 time points (24 hours, 2 weeks, and 3 weeks post-ONT). The retina was immediately removed from the eye under infrared illumination and placed in a recording chamber containing Ames medium maintained at 35-37°C. RGCs were examined by differential interference contrast optics. Extracellular and whole-cell patch clamp recordings were made from individual RGCs in response to light stimuli.
At all time points following ONT, RGCs contained high-contrast punctate accumulations (vesicles) 1.1 ± SD 0.3 µm diameter (n = 11 cells from 3 animals) present in both the soma and the initial axon compartments and in axon bundles beyond the axon initial segment. The number of vesicles within each RGC was more numerous at later time points. Targeted patch-clamp recordings from vesicle-containing RGCs revealed that all vesicle-containing RGCs showed physiological signs of degeneration: either depolarized resting membrane potentials (Vrest = -46 ± 4 mV, n = 9 cells from 3 animals) and/or spontaneous somatic spikelets, which resemble dendritic spikes (6.0 ± 1.3 mV, t rise 1.3 ± 0.7 ms, t-decay 6.6 ± 1.0 ms n = 3 cells from 2 animals).
These results suggest that: vesicle accumulation is an early sign of ONT-mediated degeneration and may even be present earlier than 24 hours following ONT. Physiological signs of degeneration are present as early as 24 hours following ONT. Determining the content of these vesicles, and the mechanisms underlying early physiological changes will provide further information on the early events of RGC degeneration and in various optic neuropathies, including glaucoma.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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