Abstract
Purpose:
Retinal ganglion cell (RGC) health is of broad interest, given its role in glaucoma. RGCs die after optic nerve section (ONS) in the chick. As toxins can cause cell loss, but may also result in increased mitotic activity, this study was undertaken to characterise the retinal cellular events induced by ONS.
Methods:
One eye of day old chicks underwent ONS surgery while the other eye underwent sham surgery (control). To characterise the time course of cell loss, retinal thickness was measured using high frequency A-scan ultrasonography prior to and up to 7 days post-ONS. Cell loss from the ganglion cell layer (GCL) was assessed in eyes enucleated from 3 to 14 d post-ONS. Retinas were sectioned at 12 µm. Terminal deoxytransferase-mediated deoxyuridine triphosphate nick end labeling was used to detect apoptotic cells. 4’-diamidino-2-phenylindole was used to stain cell nuclei. To assess mitotic activity, 5-bromo-2-deoxyuridine (BrdU) was injected intravitreally 4h before enucleation. Retinal thickness was measured prior to enucleation on days 1 to 8 post-ONS. Sections were labeled with anti-BrdU. Retinal thickness and cell numbers in the GCL were compared as a function of surgery and time.
Results:
Retinas began thinning at 3d post-ONS and were significantly thinner by 7d (p<0.0001) and the number of cells in the GCL decreased over time in ONS-eyes (p<0.0001). However, no equivalent changes were detected in control eyes (p=0.1018, p=0.1481, respectively). Apoptosis was detected in ONS- but not in control eyes, peaking at 5d post-ONS (21.05±8.26%; p<0.0002 for all time points). The retinas of ONS-eyes without BrdU showed early thickening, peaking at 3d post-ONS (p<0.0001) while those with BrdU showed a similar but not significant time course (p=0.1077); no equivalent changes were detected in control eyes for either group. In ONS-eyes no mitotic activity was detected until 3d post-ONS (3.58±2.63 cells/mm; p=0.8846), with a plateau from day 4 (average of 15.13±4.89 cells/mm; p≤0.0175) to day 7, and no detectible activity thereafter (p=1.0000). No proliferation was ever found in control eyes.
Conclusions:
ONS-related cell death is mediated at least in part by apoptotic mechanisms, contributing to retinal thinning. Mitotic activity is induced in the retina post-acute damage (ONS) but does not fully account for early retinal thickening, which may reflect volumetric changes in the globe secondary to choroidal thickening.
Keywords: 688 retina •
695 retinal degenerations: cell biology •
687 regeneration