Quantitative And Qualitative Analyses Of The Nerve Fiber Layer Degeneration After Optic Nerve Axotomy In Adult Mice.

Abstract

Purpose: : To analyze the degenerative events taking place in the nerve fiber layer of the mouse retina after optic nerve transection or optic nerve crush.

Methods: : Adult albino Swiss male mice were used for this study. The left optic nerve was intraorbitally transected (IONT) or crushed (IONC). The right eyes were used as controls. Three, seven, fourteen and ninety days post-lesion (dpl), retinas were dissected as whole flat mounts (n=6-8 per time point and lesion). Retinal ganglion cells (RGCs) axons, i.e. the nerve fiber layer, were detected by immunodetection of the highly phosphorylated heavy subunit of the neurofilament triplet (pNFH). Retinas were photographed under an epifluorescence microscopy. The aberrant expression of pNFH after axotomy was qualitatively studied, and the number and distribution of RGCs expressing high or low levels of pNFH in their somas assessed (pNFH+RGCs).

Results: : In control retinas, pNFH is only expressed in the central and medial retina, in fascicles of RGC axons converging towards the optic disc. These axons are rectilinear and uniformly labeled. After both lesions, this expression pattern changes dramatically and thus, 3 days later, pNFH signal is already observed in the retinal periphery and in the RGCs somas. As the time post-lesion increases, pNFH intra-axonal deposits are observed, reaching their maximum at day 14 post-lesion. By day 90 post-lesion, only few axons remain in the retina. In both lesions the number of pNFH+RGCs reaches its highest at 3 dpl.

Conclusions: : Axonal damage to mice RGCs induces a change in the expression pattern of pNFH which is similar in appearance to the one reported for rat (Parrilla-Reverter et al., Vis.Res, 49 (2009): 2808-2825). However, in mice appearance of pNFH+RGCs occurs earlier. In addition, while in rat the course of the ganglion cell layer degeneration was qualitatively and quantitatively different for IONT and IONC, in mice both lesions trigger a similar response.

Keywords: ganglion cells • retina • nerve fiber layer