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Y. Guo, S. L. Bernstein; Amacrine Cell Loss Does Not Occur in Moderate Mouse rAION Induction. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5916.
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We previously demonstrated that optic nerve infarct results in isolated retinal ganglion cell (RGC) death in the rodent model of Non-arteritic ischemic optic neuropathy (rAION). This effect does not result in direct damage to other neuronal cell layers in the retina, but displaced amacrine cell interneurons in the RGC layer, and Cholinergic amacrine cells in the inner nuclear layer were not directly evaluated. We wanted to further determine whether the severity of rAION-induced RGC loss directly impacts survival of amacrine cells in both RGC and inner nuclear (INL) layers.
We utilized a transgenic mouse containing cyan fluorescent protein (CFP) under control of a Thy-1 promoter that results in isolated RGC-CFP expression. rAION was induced as previously described (n=8) and with identical parameters. Slit lamp exam was used to observe the retina at 1-3 days post induction. 30 days post rAION induction, we evaluated CFP expression directly and ChAT positive cells with confocal analysis and whole-mount immuno-fluorescent staining. This was performed using anti-choline acety transferase (ChAT) immuno-staining to identify amacrine cells in the RGC layer and INL.
All induced retinae had different degree of retinal paleness and optic disc edema, subjectively ranging in a scale from 1- 4(+). There is a loss of CFP positive cells corresponding to RGC loss 30 days post rAION induction. We found that there is no significant loss of ChAT positive cell when the CFP loss is less than 50%. However in cases of branch retinal vein or artery occlusion, where there was demonstrable retinal edema or pallor, there were both severe loss of CFP (+ cells), combined with ChAT (+) cell loss in both RGC layer and INL.
Mice far more than rats, have variable responses to induction with standardized rAION parameters. This difference is likely due to the known variability of the optic nerve vasculature in mice. Differences in induction can be estimated with the level of severity of the post induction edema and retinal paleness at 1-3days via slit lamp exam. In moderate rAION induction, there is only RGC loss, without amacrine cell loss at late stage.
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