Prevention of retinal ganglion cell swelling by systemic brimonidine in a rat experimental glaucoma model

Background: The objective of this study was to evaluate the neuroprotective effect of brimonidine on retinal ganglion cells in rats with elevated intraocular pressure and to characterize the subpopulation of cells that can be rescued, as well as assess the effect of this drug on retinal ganglion cell soma size. Methods: Episcleral vein cauterization was used to increase intraocular pressure for 5 weeks on left eyes, considering right eyes as intrinsic controls in all cases. All the animals were then given weekly intraperitoneal injections, the experimental group receiving brimonidine, and the control group were administered only phosphate-buffered saline. Surviving retinal ganglion cells were quantified and their area and distribution measured by retrograde labelling with fluorogold. Results: Brimonidine administered systemically has a neuroprotective effect on retinal ganglion cells, which is unrelated to its capacity to lower intraocular pressure. It prevents the increase of cell size that is associated with stages prior to cell death. This phenomenon is particularly evident in the zones of the retina most susceptible to the damage caused by glaucoma (middle and periphery). Conclusion: This effect of preventing retinal ganglion cell swelling can be considered as a new marker to study neuroprotection from antiglaucomatous drugs in the early stages of neurodegeneration in glaucoma.