Susceptibility to N-Methyl-D-Aspartate toxicity in morphological and functional types of cat retinal ganglion cells

Background: To examine whether different types of retinal ganglion cells (RGCs) in the cat retina have different survival rates when exposed to N-methyl-d-aspartate (NMDA). Methods: NMDA injury was induced by intravitreal administration of NMDA at fi nal concentrations of 0.2, 0.4, 0.6, and 0.8 mM. The total number of surviving RGCs and their distribution were counted by retrograde labeling with a fl uorescent dye. Measurements of the proportions of the main RGC types (alpha, beta, and neither alpha nor beta cells) were obtained by using intracellular injections of Lucifer yellow. Results: The mean percentage of surviving RGCs in the NMDA-injected retina was reduced to 59.4% (0.2 mM NMDA), 35.8% (0.4 mM), 10.8% (0.6 mM), and 14.1% (0.8 mM). At 0.2 mM, the survival rate of alpha cells was reduced to 56%, but that of beta cells remained at 81%. At 0.8 mM, the survival rate of alpha cells was 19%, while beta cells rapidly decreased to 9.9%. No difference was detected in NMDA vulnerability between ON- and OFF-center RGCs. Conclusions: Different RGC types display different susceptibilities to NMDA injury. A specifi c examination of the functions of different types of RGCs would be helpful in detecting retinal excitotoxicity such as in chronic retinal ischemia. Jpn J Ophthalmol 2010;54:156-162