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Tiffany Choe, Carla Abbott, Kendra Young, Brad Fortune; Longitudinal Measurements In Vivo of Retinal Nerve Fiber Layer Thickness (RNFLT) and Retinal Ganglion Cell (RGC) Density after Optic Nerve Transection (ONT) in Rat. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4849.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the relationship between RNFLT and RGC density measured in vivo after unilateral ONT.
Eighteen adult male Brown-Norway rats were studied. All procedures were performed under anesthesia (ketamine:xylazine:acepromazine, 55:5:1 mg/kg IM). Two baseline measurements of peripapillary RNFLT were obtained by SDOCT (Spectralis, Heidelberg Engineering) then repeated weekly for 1 month after either unilateral ONT (N=11) or sham surgery (N=7). RGCs were labeled by retrograde transport from the superior colliculus of fluorescently conjugated cholera toxin B (CTB) 48 hours prior to surgery (N=15; bilateral saline injections in N=3 ONT controls). RGC density measurements were obtained by confocal scanning laser ophthalmoscopy (Spectralis) at baseline (1 hour prior to surgery) and weekly for 1 month (N=15). Fluorescence microscopy of whole-mount retinae was performed post mortem to measure RGC density and to evaluate reactivity of microglia (anti-Iba1) and astrocytes (anti-GFAP). Statistics included two-way ANOVA for repeated measures with Bonferroni corrected post-hoc comparisons and Deming linear regression.
RNFLT decreased after ONT (p<0.0001) by 16%, 28% and 34% at weeks 2, 3 and 4. RGC density decreased after ONT (p<0.0001) by 24%, 69%, 84% and 91% at weeks 1, 2, 3 and 4. In vivo measures of RNFLT and RGC density were strongly correlated (R=0.83, p<0.0001). RGC density measured in vivo at week 4 and post mortem by microscopy were strongly correlated (R=0.92, p<0.0001). RNFLT and RGC density did not change in sham operated or their fellow control eyes and there was no difference between these groups for post mortem RGC density (p=0.62). In the fellow eyes of the ONT-operated group that had bilateral CTB labeling of RGCs, RNFLT increased by 24%, 68% and 49% at weeks 2, 3 and 4 (p<0.0001), but it did not change in fellow ONT-eyes that did not receive CTB. Microgliosis was clearly evident in the RNFL of the ONT-fellow eyes that had CTB, far exceeding that observed in eyes of any other group. Astrocyte changes were not observed in any group.
In vivo measurements of RNFLT and RGC density are strongly correlated and can be used to monitor longitudinal changes after optic nerve injury. Microgliosis occurred in fellow eyes of ONT operated rats if CTB was used to label their RGCs, causing increased RNFLT.
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