Hypoxia-Induced Activation of N-methyl-D-aspartate Receptors Causes Retinal Ganglion Cell Death in the Neonatal Retina

It is well established that hypoxia causes excess accumulation of glutamate in developing neural tissues. This study aimed to elucidate the mechanism by which glutamate can cause retinal ganglion cell (RGC) death through the N-methyl-D-aspartate (NMDA) receptors (NR) in the developing retina. One-day-old Wistar rats were exposed to hypoxia for 2 hours and then killed at different time points. Normal age-matched rats were used as controls. NR1, NR2A-D, and NR3A messenger RNA and protein expression showed significant increases over control values, notably at early time points (3 hours to 7 days) after the hypoxic exposure, and immunoexpression of NR1, NR2A-D and NR3A on retinal ganglion cells (RGCs) was enhanced in hypoxic rats and this was confirmed in cultured hypoxic RGCs. Ca2+ influx in cultured RGCs was increased after hypoxic exposure, and the intracellular Ca2+ concentration was suppressed by MK-801. Mitochondrial permeability transition pore opening, mitochondrial/cytosolic cytochrome c, and cytosolic caspase-3 expression levels were significantly increased in the hypoxic RGCs. These increases were reversed by MK-801, suggesting that the NMDA receptor subunits in the retina respond rapidly to the hypoxia-induced glutamate overload that leads to the cascade of events that result in RGC death.