急性眼压升高所致视网膜、视神经及视交叉胶质细胞的早期反应

摘要

背景 中枢神经系统以及视网膜中的胶质细胞与神经元关系十分紧密,胶质细胞在神经元损伤和修复过程中发挥着重要作用.急性眼压升高引起的视网膜、视神经及视交叉各部位胶质细胞的早期反应特点以及其与视神经损伤的关系目前尚不清楚. 目的 探讨大鼠视网膜、视神经及视交叉的胶质细胞对急性高眼压的早期反应,同时观察神经前体细胞标志物巢蛋白( nestin)在反应性胶质细胞中的表达. 方法 成年雌性Wistar大鼠9只,分为正常对照组3只和急性高眼压组6只,急性高眼压组大鼠采用右眼前房灌注生理盐水的方法升高大鼠眼压至110 mmHg,持续60 min.于术后第3天和第7天用过量麻醉法处死各组动物各3只,摘出眼球分离视神经和大脑标本,并制作冰冻切片.利用Nissl染色的方法测量高眼压眼视网膜内层厚度,观察视网膜和视交叉的大体形态.用βⅢ-tubulin免疫荧光染色法标记视神经内的视网膜神经节细胞(RGCs)轴突,用胶质纤维酸性蛋白(GFAP)和nestin双重标记显示视网膜、视神经及视交叉的胶质细胞反应,并对两组结果进行比较.结果 正常大鼠的视网膜、视神经以及视交叉内均可见到一定量的GFAP阳性胶质细胞,但nestin的表达量很低.急性眼压升高后的第3天,视网膜内丛状层厚度明显变薄,RGCs数目较损伤前减少约46％.视网膜内胶质细胞GFAP的表达显著增加,细胞突起由神经纤维层伸展至整个视网膜,增生的胶质细胞内可见nestin的明显表达.视神经内RGCs轴突发生变性样改变,GFAP阳性胶质细胞内nestin的表达较眼压升高前明显增加.同损伤眼相对应的一侧视交叉的横断面积减小,出现大量星状GFAP和nestin共表达的胶质细胞.以上改变在眼压升高后第7天更趋明显.结论 急性眼压升高早期即可引起RGCs的丢失及轴突的变性,视觉神经元改变的同时伴随胶质细胞的反应,增生的胶质细胞表达神经前体细胞的标志物.视网膜与视神经和视交叉的改变在时间上具有一定的同步性.%Background Glial cells perform specialized function in many aspects of the development,homeostasis,and function of neurons.Retinal ganglion cells (RGCs)and glia interactions are critically important in glaucomatous neurodegeneration.However,the precise mechanisms of glial activation and ganglion cells damage are still remained unclear. Objective This study was to assess the early responses of glial cells in the retina,optic nerve and optic chiasm in rat models of acute high intraocular pressure (IOP),and to examine the expression of nestin,a neuronal progenitor marker,in the reactive glias. Methods Acute high IOP of 110 mmHg was induced in the right eyes of 6 clean adult female Wistar rats by infusing normal saline solution into the anterior chamber for 60 minutes.Three normal matched Wistar rats were used as controls.The rats were sacrificed by overanaesthesia and sections of retina,optic nerve and optic chiasm were collected on 3 days and 7 days after the injection.Rat retina was examined by Nissl staining to illustrate the gross structure changes.Loss of axons of RGCs in the optic nerve was assessed by immunostaining of β Ⅲ-tubulin.Double labeling of glia] fibrillary acidic protein (GFAP) and nestin was performed in sections of retina,optic nerve and optic chiasm to evaluate the glial responses.The use of the animals complied with Statement of Animal Ethic Committee of Peking University Third Hospital. Results In control rats,GFAP-positive glial cells were observed in the retina,optic nerve and optic chiasm,where only weak positive response for nestin was noticed.Three days after acute IOP elevation,thickness of inner plexus form layer was significantlydecreased in comparison with the control rats.A loss of 46％ RGCs was found in the rats with ocular hypertension.Obvious increase of GFAP expression was displayed in the retina,and processes of GFAP-positive glia cells extended into outer retina accompanied with significant up regulation of nestin.Axons in the optic nerve demonstrated a tendency of degeneration.Nestin expression increased significantly in the GFAP-positive glias in the optic nerve.Cross-sectional area of optic chiasm corresponding to the injured retina decreased relative to its countcrpart.Astrocyte like GFAP and nestin-colabeled glials were observed in this part of optic chiasm.The pathological changes of the retina,optic nerve and optic chiasm in hypertensive eyes aggravated on 7 days. Conclusions Acute ocular hypertension induce early onset of RGCs loss and axon degeneration.Neuronal injury is accompanied with glial reaction.Reactive glial cells express neuronal progenitor markers.The structural changes of the optic nerve and optic chiasm occur simultaneously with the high IOP.