Rabbit retinal ganglion cell survival after optic nerve section and its effect on the inner plexiform layer

Abstract

Structural modifications of the inner retina were studied after optic nerve section (ONS) in the rabbit. Retinal ganglion cells (RGC) were labelled by injection of Fast Blue into the optic nerve, and counted under fluorescent light in control retina and retina 7, 14, 21 and 26 days post-axotomy. Studies on retinal cross-sections were also performed. For this purpose, retinal sections were stained with haematoxylin–eosin and immunohystochemistry for α1 and β2/β3 sub-units of the GABA A receptors. One week after axotomy, there was no significant loss in the number of ganglion cells with respect to control counts (1086±173 cells mm −2 in the visual streak and 119±46 cells mm −2 in the periphery, mean± sd, n=5). At 14 days post-axotomy, 271±46 cells mm −2 remained in the visual streak and 33±6 cells mm −2 in the periphery, corresponding to a mean survival of 27%. The number of ganglion cells decreased further on the following days, reaching 7·54% 1 month after ONS. A significant reduction in the thickness of the inner plexiform and ganglion cell layers was also observed in retinal cross-sections. Immunocytochemical studies show a remarkable disorganization of the layer stratification in the inner plexiform layer (IPL). We conclude that after ONS, RGC death occurs mainly between 7 and 14 days post-axotomy and a progressive death up to 26 days, causing a decrease in the thickness of the IPL and subsequent disorganization of its layers.