Assessment Of The Neuro-optic Protection Of Benztropine In A Rat Model Of Non-anterior Ischemic Optic Neuropathy

Objective1.To establish a rat model of non-anterior ischemic optic neuropathy(rNAION).2.To evaluate the time-course of ultrastructural optic nerve(ON)damage in rNAION model.3.To investigate the neuro-optic protection of intraperitoneal injection of benztropine in rNAION model.Methods1.After intravenous infusion with Rose Bengal(RB)as the photosensitizing agent,rNA10N was induced by illuminating the ON head with 532nm green laser(n=10).Rats in normal control group underwent no interventions(n=10).Changes of the fundus including ON and retina was observed with funduscope.Transmission electron microscopy(TEM)was performed to assess rNAION-induced histologic changes in the ON.After labeling retinal ganglion cells(RGCs)by stereotactic injections of 4%Fluoro Gold(FG)into the superior colliculus,the animals were sacrificed,and retinas were mounted flat in a masked fashion.2.The rats were randomly divided into 5 groups:1-week(n=5),2-week(n=6),4-week(n=4),8-week(n=5)model group and the normal control group(n=5).At 7,14,28 or 56 days post-injury,the NAION rats were sacrificed.The ultrastructure of optic nerve was investigated with TEM.3.Animals were randomly divided into 3 groups:benztropine treatment group(n=8),phosphate buffer saline(PBS)treatment group(n=8),and normal control group(n=8).Rats either received benztropine(intraperitoneal injection,10mg/kg)or PBS daily for 3weeks.4 weeks after modeling,the number of surviving RGCs was measured by RGC staining using retrograde labeling of PG.Results1.3 days after rNAION-induced,the optic disc was swollen.The edema of ON resolved on day 7.And after 4 weeks,the ON atrophied.At day 28,the density of RGC axons decreased apparently on TEM.At the same time,extensive reactive gliosis was observed.Retrograde labeling with PG revealed that rNAION resulted in RGCs loss.2.ON TEM,the amount of RGC axons decreased slightly 1 week after modeling.After 2 weeks,RGC axons loss was more obvious,and reactive gliosis was observed.4 weeks after,obvious degenerative change was observed including axonal loss and glial scar.At day 56,few normal axons could be found,most of the myelin sheath degenerated.3.Both the ultrastructural damage of RGC axons and RGCs cell loss were reduced in the benztropine treatment group under TEM and fluorescence microscope compare to the PBS treated group.Conclusions1.The rNAION model resembles the histologic and clinical characteristic of NAION patients.Therefore,the model is appropriate for the following research.2.The damage of axons aggravates gradually.The best treatment time is within 2 weeks after modeling.3.Benztropine has neuro-optic protection on rNAION in our pilot study.