The dynamic change of Brn-3a expression in retina of chronic high intraocular pressure rat

Abstract

Background Brn-3a is a newly discovered specificity marker for retina ganglion cells(RGCs).It is well-known that RGCs damage is a important pathological basis of hypertension-visual disorder.But the study concerning expression of Brn-3a in RGCs in glaucoma eye is still rately.Objective The purpose of this work was to investigate the changes of Brn-3a expression in model eye with chronic high intraocular pressure(IOP) and its relation with morphology of retina and the expression of Brn-3a in chronic ocular hypertension rats.Methods Thirty-five clean adult SD rats were randomly divided into normal control group(5 rats) and model group(30 rats).Experimental chronic ocular hypertension models were induced unilaterally in the left eyes of 30 health adult SD rats by cauterizing super-scleral veins,and the conjunctival incision was made in the right eyes as sham operative group.The operated rats were subdivided into 6 groups according to the examination time points and 6 rats for each group.IOP was measured with Tono-Pen tonometer before and after 30 minutes,1,3,7,14,28 day after surgery respectively.The rat models were sacrificed in 1,3,5,7,14,28 days after operation by excessive anesthesia method,and retinal section was prepared for the histopathological examination and the RGCs were counted using Nissl staining method.Expression of Brn-3a in RGCs was detected by immunohistochemistry.This experimental complied with the Regulations for the Administration of Affair Concerning Experimental Animals by State Science and Technology Commission.Results The IOP was significantly raised from 30 minutes to 28 days after operation in model eyes with the top IOP( 34.46±4.65 )mmHg in the 30 minutes after operation,showing statistically significant differences in various time groups ( F =95.631,P =0.001 ) and different eyes ( F =287.473,P =0.001 ).Compared with sham operative group,the IOP were elevated from 1 day through 14 days after operation ( q =18.418,15.261,10.987,6.931,4.975,2.962,P ＜ 0.05 ).The numbers of RGCs were ( 29.08 ± 1.98 ) in the normal control group and decreased gradually by 3.17％,7.84％,14.60％,22.40％ in 1,7,14,28 day after surgery in the model eyes with the considerable differences in comparison with normal eyes ( t =5.943,8.034,15.023,17.004,19.371,P ＜ 0.05 ).Immunochemistry revealed that Brn-3a was specially expressed in the RGCs layer and the positive RGCs for Brn-3a were evidently decreased as the prolong of high IOP duration ( F =127.583,P =0.000 ).Conclusions Chronic glaucoma model can be successfully established using Shareef-Sharma method.The loss of RGCs is associated with the high lOP duration.The expression level of Brn-3a is a reliable index of high-IOP-induced damage of optical nurve. Key words: Glaucoma/model; Ocular hypertension; Retinal ganglion cell; Brn-3a