Pathological changes of the rat retina in response to elevated intraocular pressure

Purpose. To investigate the retinal pathology of elevated intraocular pressure (IOP) in a rodent model on a macroelectrophysiologic (ERG), netirochemical and histological l.evel. Methods. Elevated IOP was induced unilaterally in the rat eye by cauterizing three episcleral veins. After 14 days of elevated IOP, scotopic ERGs were recorded simultaneously from both eyes of anesthetized rats using corneal contact lens electrodes, hnmunocjtochemical procedures were used to stain frozen sections of the experimental retinas for glutamate and connexin 50. The contralateral retina served as control. Identity of connexins was confirmed in Western imrnunoblots. Results. The elet'troretinogram of the experimental eye showed a markedly decreased a-wave amplitude and a prolongation of the b-wave implicit time. Immunocytochemical procedures showed the following retinal changes following elevated IOP: (1) The optic disc showed strong excavation. (2) ConnexinSO, which is found in retinal Müller cells and astrocyies is overexpressed compared to the control, particularly in the ganglion cell- and nerve fiber layer. (3) Glutamate-like immunoreactivhy becomes diffuse, in that the typical trilaminar banding pattern in the IPL is no longer visible and. in addition, ganglion cells appear swollen and display an uneven labeling across the entire soma and primary processes. Most significantly, prominent glutamate labeling is present in Müller cells. Conclusions. The changes observed in the rat retina in response to elevated IOP are consistent with the present knowledge of the retinal pathology of glaucoma in human and primate models.