Immunohistochemical changes in rat retinas at various time periods of elevated intraocular pressure

Purpose: To study alterations in different retinal cell types associated with retinal ganglion cell (RGC) death after elevation of intraocular pressure (IOP) in rats. Methods: IOP was elevated by episcleral vein cauterization of the rat left eye. The right unoperated eye was kept as the control. IOP was measured when rats were awake. The animals were euthanized after one week (n=4) and five weeks (n=4). Their eyes were enucleated, postfixed, cryoprotected, and embedded in optimal cutting temperature (OCT) medium. Cryosections of the retina were cut at 14 mu m thickness and processed for immunocytochemistry with 15 antibodies that specifically stain different retinal cell types. The distribution and intensity of the label was analyzed by comparing sections of control and glaucomatous retinas obtained from identical locations. Results: The amount of amacrine cells identified by calcium binding proteins and choline acetyltransferase antibodies decreased after five weeks of elevated IOP. By using the anti-protein kinase C-alpha antibody, we were able to label a subpopulation of rod bipolar cells in control retinas but not in retinas that had elevated IOP. No changes were found in RGCs labeled with brain derived neurotrophic factor when comparing control and glaucomatous retinas. Glial fibrillary acidic protein and vimentin expression in glial cells increased after one week of elevated IOP. Conclusions: After one week of elevated IOP and before the onset of RGC death, it was evident that inner retinal cells showed remarkable changes in their molecular expression.