Objective Present study aimed to research the mechanism of the use of 0.2% brimonidine tartrate eye drops in the treatment of optic nerve crush injury of rat.MethodsAnimal models of optic nerve crush injury were created in 60 SD female rats by clipping the exposed optic nerve at 2 mm in retrobulbar for 6 seconds with 78 grams of reverse forceps.The successful model was identified as Marcus-gun pupil without bleeding of fundus after operation.The animals were randomly assigned to model group and brimonidine treating group,and another 30 normal SD rats were used as the normal control group.The 0.2% brimonidine tartrate eye drops was topically administered at 2 hours before operation and after operation twice per day in the brimonidine treating group.The retinas from 18 rats were isolated after 3,7,21 days for RGCs counting by H&E staining,and the retinal ultrastructure was examined under the transmission electron microscope.The retinas from the other 72 SD rats (including normal,model and brimonidine groups) were prepared for the detection of bcl-2 and bax using immunohistochemistry l,3,5,7,14,21 days after the operation.ResultsNormal and almost normal retina structure was exhibited in rats of the normal group and brimonidine treating group,but disorder of cellular arragement and decrease of retinal thickness were found in the model rats under the optical microscope.The RGCs counting was significantly different among the three groups from 3 days through 21 days after operation with the considerably declination in the model group and brimonidine treating group compared with the normal control group (P＜0.05-0.01).However,that of the brimonidine treating group was obviously increased in comparison with the model group (P＜0.01).The expression of bax in rat retina was obviously reduced (P＜0.01),but the expression of bcl-2 was increased in brimonidine group compared with the model group from 5 through 7 days after operation (P＜0.01).ConclusionThe 0.2% brimonidine tartrate eye drops has a preventive effect on optic nerve crush injury of rat,and its inhibition on apoptosis is one of the mechanisms.