Elevation of intraocular glutamate levels in rats with partial lesion of the optic nerve

Background: Acute partial lesion of the rat optic nerve, although not a model for glaucoma, mimics some of the features of the disease. Objective: To learn whether degeneration of rat optic nerve fibers and death of their retinal ganglion cells induced by an acute partial lesion are associated with elevated levels of glutamate, known to occur in the eyes of humans and monkeys with glaucoma. Materials and Methods: Rat optic nerve was subjected to a partial crush injury. Aqueous humor samples were aspirated from the anterior and posterior aqueous chambers at specified times and their amino acid contents were determined by means of highperformance liquid chromatography. Results: Three and 7 days after injury, intraocular glutamate and aspartate levels were found to be significantly higher than in normal or sham-operated-on eyes, and returned to normal by day 14, Conclusions: Degeneration of the optic nerve, induced by a mechanical injury of the axons, leads to intraocular elevation of glutamate and aspartate levels. These results illustrate that the model of the partial optic nerve lesion exhibits another feature typical of a long-term optic neuropathy, such as glaucoma.