Development of a Traumatic Optic Neuropathy Model Induced by Blunt Force Trauma

Abstract

Purpose : To establish a reproducible and reliable rat model of indirect traumatic optic neuropathy (ITON) induced by blunt force trauma, characterized by a high specificity in replicating the progression of axonal membrane damage while ensuring no mortality.

Methods : Male Brown Norway rats received closed-head blunt force trauma five times from a pneumatically controlled cortical impactor near the bony orbit cavity without any overt damage to the surrounding tissue structures. Optic nerves were harvested 2 weeks and 4 weeks post-injury to assess structural changes and microglial activation. Immunohistological analysis was employed to assess myelin thickening as a marker of axonal damage, and its validation was conducted using Stimulated Raman Scattering (SRS) microscopy. Morphological changes indicative of the microglial response to injury along the optic nerve were observed, accompanied by inflammation tracked by CD68 immunostaining.

Results : Our trauma model generated a concussive trauma to the intra-orbital segment of the optic nerve. We observed an early and statistically significant increase in the thickening of individual axonal membranes (p< 0.0001) compared to age matched sham animals. Imaging based evaluation of lipids in the optic nerve by label free stimulated Raman scattering SRS microscopy revealed significant changes in signal intensity in 2850 cm⁻¹, primarily indicating CH2 symmetric stretching, reflecting axonal membrane myelin lipid variation. A progressive transition of the microglial population from ramified morphology (M2) to ameboid/phagocytic (M1) was observed with time. A temporal progression of increase in CD68 immunopositive microglia (p<0.01) was observed along the optic nerve tract.

Conclusions : We have created a progressive axonal damage ITON model that confers no mortality and skull fracture. This model produces quantifiable axonal myelin thickening as a response to inflammation and attempts to repair the nerve fibers. However, the structural alterations within the optic nerve were observed as early as two weeks as an adaptive mechanism to enhance the insulation and support of the damaged nerve fibers within the optic nerve. This blunt force trauma model will be useful for determining the molecular and cellular pathophysiology of ITON, addressing progressive axonal damage and testing therapeutics.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.