Pathological Changes And Mechanism Of Glial Cells In Chronic Injury Of Intraorbital Optic Nerve In Rabbit

BACKGROUND: It's a focus topic whether optic nerve (ON) can regenerate after injuried. Nowadays, acute injury of ON has been researched deeply while reports of studys on chronic injury of ON were scarce. Orbital tumor may induce chronic injury on ON by long period of oppression and patients may suffer from optic functional disturbance. It's greatly significant of repairing damaged ON to functional reconstruction in order to enhance patients'living quality after tumour extirpation. The pathologic mechanism and process of chronic injury of ON in which glial cells play importment parts should be identified so as to undertake the project to promote the regeneration of damaged ON.OBJECTIVE: To establish animal model of optic nerve injury by chronic intraorbital oppression analogue orbital tumour so as to investigate the changes of RGCs and glial cells in different stages as well as to elucidate the pathomechanism of glial cells for the purpose of searching for the suitable microenvironment to repair injuried ON in orbit.METHODS: Disregarding sex, 24 matured rabbits were medially divided into 6 groups randomly: control group (sham opration), group A (oppressed for 2 weeks), group B (oppressed for 2 weeks then decompressed for 2 weeks, 2+2w), group C (oppressed for 4 weeks), group D (oppressed for 4 weeks then decompressed for 4 weeks, 4+4w) and group E (oppressed for 8 weeks). We established mammal model by implanting a sacculus of 2ml volume into right orbit of rabbit along the lateral side of ON and infusing increasing dose of contrast medium in the sacculus along with time extention. FVEP, CT scaning and fundus photograph were used after operation. Eyeballs involving ON were obtained to evaluate the damage using light microscope after HE staining and mRNA was extracted to analyze the changes of gene expression compared with the control group in vitro after execution.RESULTS:1. FVEP: Shape of FVEP (P1, N1 and P2) diversed obviously and irregular figures appeared with the compression extension. Latence prolonged and amplitude cut down. The changes of FVEP had no statistical significance when oppressed 2 weeks (P>0.05). But after 4 weeks the changes were obvious (P<0.05) and more manifest after 8 weeks (P<0.01). Disposal with decompression for 4 weeks after oppression for 4 weeks had a positive sense to FVEP (P<0.01).2. HE staining: (1)Retina: Retina in sham operation group had no marked changes but gentle dropsy. After ON oppressed for 2 weeks till 4 weeks, retina just attenuated lightly. Nuclei in retina layers were sparse and disorder after 8 weeks'oppression. Population of nuclei augmented and lined up in order with retina thickening in decompression groups (2+2w or 4+4w). (2)ON: Sham operation group had no marked changes. After oppressed for 2 weeks, cells in ON decreased and fasciculi arranged disorderly with fiber membrane broken. In 4 weeks group cells increased but fasciculi still in disorder. In 8 weeks groups there were a deal of nuclei rambled in ON and fasciculi were unsharp. Decompression groups showed deranged fasciculi with augmented cells.3. Immunohistochemistry: Content of GFAP in ON was higher than contrast group after oppressed for 2 weeks and 4 weeks and remained in high level even after 8 weeks. Decomppression groups had a cut down in GFAP's level but still higher than contrast group.4. Apoptosis detection: The increase of apoptosis cells in RGCs layer of retina had a direct correlation with the extention of oppression on ON.5. Gene detection: Expressions of CNTF and GAP-43 were low in normal rabbit ON but had up regulations when ON oppressed for 2 weeks. The changes were more obvious and had a direct correlation with the damage aggravation. The expressions had down regulations after decompressed for 2 weeks and 4 weeks but still higher than contrast group.CONCLUSION: This study established animal model of chronic injury of intraorbital ON in rabbit by implanting a sacculus into orbit and infusing increasing dose of contrast medium in the sacculus along with time extention analogue orbital tumor. The conclusions were summarized bellow after undertaking research:1. The mammal model of chronic oppression of ON in rabbit was successfully established for the further study of searching for the protective measure and therapy to damaged ON in clinic.2. FVEP is convient and easy in monitoring vision because it objectively reflect the injury on visual pathway. It can be used in research on chronic injury of intraorbital ON in rabbit.3. RGCs degenerated and disorded with ON fibers decreased and retina attenuated as well result in functional impairment after ON damaged. The changes were obvious in the wake of injury aggravation. Retina and ON had certain degree ability of self repairment after decompression.4. Glial cells degenerated and decreased after ON oppressed. Reactive hyperplasia in glial cells emerged which had positive significance to promote RGCs survival and regeneration in early stage but became barricade after hyperplasia unduly.5. It's may give a hope to develop a new way to cure damaged ON by controling the reaction of glial cells and confining its hyperplasia.