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M.K. Guyton, B. Rohrer, C. Crosson, N.L. Banik; Neurodegeneration Of The Optic Nerve Occurs In Eae, An Animal Model Of Optic Neuritis. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):563.
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Purpose: Optic neuritis, inflammation and demyelination of the optic nerve, is one of the most common features of multiple sclerosis (MS), an autoimmune disorder of the central nervous system and in human patients results in a reduction in the amplitude of the b–wave of single flash electroretinogram (ERG) of the affected eye, indicating a decrease in retinal function. Previously, we have demonstrated that the neutral proteinase calpain is upregulated in both infiltrating inflammatory and glial cells of the optic nerve (ON) in experimental allergic encephalomyelitis (EAE), an animal model of MS and optic neuritis after onset of clinical symptoms (tail weakness, paralysis) of disease. Demyelination, axonal damage, and increased cell death also occur in EAE after disease onset and this increase is thought to be associated with increased calpain activation. Thus, we hypothesize that neurodegeneration occurs in the ON of animals with EAE. Methods: EAE was induced in Lewis rats by a subcutaneous injection of Complete Freund’s Adjuvant plus guinea pig spinal cord (200 mg/ml) and myelin basic protein (280 µg/ml) followed two hours later by an intraperitoneal injection of pertussis toxin (20 µg/ml). ON samples were collected before (day 8) and after (day 11) disease onset for immunohistochemical analysis of pathophysiological changes. Dark–adapted single flash ERGs were recorded before (days 6 and 8) and after (day 12) onset of disease to examine retinal function. Results: Pathophysiological changes in ON of EAE rats compared to controls included increased calpain expression at days 8 and 11. Upregulation of dephosphorylated neurofilament protein (deNFP) at days 8 and 11 and increased TUNEL staining at day 8 in EAE ON were also demonstrated, indicating that axonal damage (deNFP) and cell death (TUNEL) corresponded with increased calpain expression. Electron microscopy also confirmed that many axons were damaged in EAE ON compared to control. Finally, ERG a– and b–waves were significantly decreased in EAE animals on day 12 but not on day 6 or 8, suggesting that retinal function was not altered until after onset of clinical symptoms. Conclusion: These data indicate that neurodegerative changes occur in the ON of EAE rats before retinal function is compromised and correlate with increased in calpain expression. Studies are in progress to determine if treatment with calpain inhibitors will diminish the neurodegeneration of the ON in EAE rats and thus, restore retinal function. Support Contributed By: NIH–NINDS (31622).
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