Development of a Porcine Optic Nerve Injury Model

Abstract

Purpose : Visual recovery after traumatic injury to the optic nerve or in degenerative disorders such as glaucoma remains elusive. While rodent studies have shown partially successful neuro-regenerative outcomes, these treatment modalities have not been scaled into well-characterized large animal models. Therefore, the purpose of this study is to characterize the anatomic and physiologic response of the pig optic nerve following traumatic optic nerve injury in order to establish a model for translating these treatments into pre-clinical trials.

Methods : Under anesthesia, lateral canthotomies were performed on female Yucatan mini pigs (Sus scrofa domestica) (10-17 kg), allowing access to approximately 5 mm of the right (OD) retrobulbar optic nerve. Exposed optic nerves were crushed at a bite force of 1.29 N, or 0.92 N for 10 s, then incisions were closed and animals recovered. Baseline ocular assessments including fERG and fVEP were performed prior to nerve crush, then post-operatively at weekly time points until sacrifice. Anterograde axon tracing using intra-vitreal injection of cholera toxin-β subunit (CT-β) conjugated to Alexa Fluor 555 (0.1%) was performed 7 days prior to humane euthanasia. Transcardiac perfusion fixation followed by immediate tissue extraction and post-fixation was performed prior to paraffin-embedding and histological analysis.

Results : Optimal access to the pig optic nerve was accomplished using the lateral canthotomy approach. Application of the 0.92 N aneurysm clip caused 50% compression of the optic nerve and resulted in significant, time-dependent decreases in N1 and P1 fVEP amplitudes (n=3, p<0.05) after two weeks. Retinal function evaluated by fERG did not show statistically significant differences in A/B wave amplitudes or latencies. Additionally, despite clear H&E identification of the crush site, CT-β expression within the optic nerve and lateral geniculate nucleus did not display a significant loss of viable retinal ganglion cell axons at this timepoint.

Conclusions : Our results demonstrate the feasibility of performing an optic nerve crush in a larger animal with the capability of collecting consistent morphologic and functional data. Longer time points or a greater crush force are necessary for capturing anatomic changes with CT-β subsequent to observed functional changes induced by traumatic optic nerve injury.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.