Abstract
Purpose: :
Significant loss of retinal ganglion cells (RGCs) occurs 2-4 weeks following optic nerve crush injury in mice. We measured visual acuity using the optokinetic reflex (OKR) and pupillary responses by pupillometry following optic nerve crush to determine whether visual dysfunction precedes RGC loss and to evaluate the utility of these parameters for assessing visual decline in a mouse model of optic nerve injury. Mice were treated with a potential neuroprotective drug to further examine whether visual measures could be used to assess for protection of RGCs.
Methods: :
Baseline pupillometry and OKR testing was performed on ten 8-12-week-old C57BL/6 mice prior to stereotactic retrograde labeling of RGCs with Fluorogold injection. One week later, the left optic nerve of each mouse was crushed 1-2 mm behind the globe for 10 seconds using fine forceps. 1000 mg/kg SRT501 (an activator of the SIRT1 NAD-dependent deacetylase that has previously been found to prevent RGC loss during experimental optic neuritis) or vehicle was administered to each animal via oral gavage following the crush injury and continued daily for three weeks. All mice underwent weekly pupillometry and OKR testing until harvest of retinas and optic nerves on day 21 post-crush. RGC numbers were assessed by fluorescent microscopy of retinal whole mounts.
Results: :
Optic nerve crush induced significant functional damage that correlated with severely decreased visual acuity in the affected eye as measured by OKR even at one week following the injury. Pupillometry readings in the traumatized eye were also significantly decreased by week one following optic nerve crush. By three weeks post-crush, RGC numbers were significantly decreased relative to non-injured eyes. However, SRT501 treatment did not improve RGC number or visual function in this model.
Conclusions: :
This experiment demonstrates that the injury to optic nerve axons induced by mechanical crush results in rapid decline in visual acuity as measured by OKR and pupillometry, with vision loss preceding the known timing of RGC loss. The data suggest SRT501 may not prevent visual decline or RGC loss in this model of optic nerve damage, implying that the molecular mechanism or degree of injury in this model may be significantly different than in experimental optic neuritis. OKR and pupillometry are useful measures of visual function that allow assessment of optic nerve damage over time in mouse models of optic nerve injury and may be useful for evaluating disease modifying therapies.
Keywords: optic nerve • ganglion cells