Mg2+ reduces N-methyl-D-aspartate neurotoxicity in embryonic chick neural retina in vitro.

N-Methyl-D-aspartate (NMDA) is a potent neurotoxin that affects cells in the inner layers of the embryonic chick retina exposed in vitro. After exposure of the embryonic day 12 neural retina to 0.5-10.0 mM NMDA for 30 min, 50-80% of the cells in the inner region of the inner nuclear layer and 50-100% of the cells in the ganglion cell layer were hypochromatic. When retinas were incubated with Mg2+ (0.5-10.0 mM) for 15 min and then incubated with Mg2+ and NMDA (0.5 mM) for 30 min, the NMDA effect in the inner layers was dramatically reduced but not abolished. Removal of Mg2+ before NMDA exposure produced retinas as seriously affected as retinas not exposed to Mg2+. Studying the effects of NMDA inhibitors, such as Mg2+, may help elucidate the mechanism of the cytotoxic events that occur in the retina in response to certain excitatory acidic amino acids.