title: Optic nerve transection: a model of adult neuron apoptosis in the central nervous system.
abstract: Retinal ganglion cells (RGCs) are CNS neurons that output visual information from the retina to the brain, via the optic nerve. The optic nerve can be accessed within the orbit of the eye and completely transected (axotomized), cutting the axons of the entire RGC population. Optic nerve transection is a reproducible model of apoptotic neuronal cell death in the adult CNS (1-4). This model is particularly attractive because the vitreous chamber of the eye acts as a capsule for drug delivery to the retina, permitting experimental manipulations via intraocular injections. The diffusion of chemicals through the vitreous fluid ensures that they act upon the entire RGC population. Moreover, RGCs can be selectively transfected by applying short interfering RNAs (siRNAs), plasmids, or viral vectors to the cut end of the optic nerve (5-7) or injecting vectors into their target, the superior colliculus (8). This allows researchers to study apoptotic mechanisms in the desired neuronal population without confounding effects on other bystander neurons or surrounding glia. An additional benefit is the ease and accuracy with which cell survival can be quantified after injury. The retina is a flat, layered tissue and RGCs are localized in the innermost layer, the ganglion cell layer. The survival of RGCs can be tracked over time by applying a fluorescent tracer (3% Fluorogold) to the cut end of the optic nerve at the time of axotomy, or by injecting the tracer into the superior colliculus (RGC target) one week prior to axotomy. The tracer is retrogradely transported, labeling the entire RGC population. Because the ganglion cell layer is a monolayer (one cell thick), RGC densities can be quantified in flat-mounted tissue, without the need for stereology. Optic nerve transection leads to the apoptotic death of 90% of injured RGCs within 14 days postaxotomy (9-11). RGC apoptosis has a characteristic time-course whereby cell death is delayed 3-4 days postaxotomy, after which the cells rapidly degenerate. This provides a time window for experimental manipulations directed against pathways involved in apoptosis.
authors: Department of Surgery, University of Toronto, Ontario, Canada.
authors: Mark M
authors: MM
authors: Magharious
authors: Philippe M
authors: PM
authors: D'Onofrio
authors: Paulo D
authors: PD
authors: Koeberle
references: Gene Ther. 1999 Oct;6(10):1759-67
references: 10516726
references: Neurosci Lett. 1991 Jun 10;127(1):108-12
references: 1881605
references: J Neurosci. 1994 Jul;14(7):4368-74
references: 8027784
references: Restor Neurol Neurosci. 2001;19(1-2):19-27
references: 12082226
references: Prog Retin Eye Res. 2003 Jul;22(4):483-543
references: 12742393
references: Exp Eye Res. 1992 Jul;55(1):101-17
references: 1383017
references: J Neurobiol. 1993 Jan;24(1):23-36
references: 8419522
references: Invest Ophthalmol Vis Sci. 1995 Apr;36(5):774-86
references: 7706025
references: Trends Neurosci. 2000 Oct;23(10):483-90
references: 11006465
references: Neuroreport. 1998 Oct 5;9(14):3165-70
references: 9831445
references: Neuroscience. 2004;125(4):903-20
references: 15120851
references: Brain. 2005 Mar;128(Pt 3):550-8
references: 15659426
references: J Neurobiol. 2004 Apr;59(1):162-80
references: 15007834
references: J Neurosci. 1988 Jan;8(1):265-80
references: 2448429