Glucocorticoid Rapidly Enhances NMDA-Evoked Neurotoxicity by Attenuating the NR2A-Containing NMDA Receptor-Mediated ERK1/2 Activation

Glucocorticoid (GC) has been shown to affect the neuronal survival/death through a genomic mechanism, but whether or not it does through a nongenomic mechanism is unknown. Using a previously identified GR-deficient primary hippocampal neuron culture, we show here that a 15-min coexposure of N-methyl-d-aspartate (NMDA) with corticosterone at a stress-induced level significantly enhances neuronal death compared to NMDA alone. This enhancing effect of GC can be mimicked by the BSA-conjugated corticosterone, which is plasma membrane impermeable and cannot be blocked by RU38486 spironolactone. Furthermore, using a calcium-imaging technique, we found that B could increase both the percentage of neurons showing a significant increment of intracellular free calcium ([Ca2+]i) due to NMDA stimulation and the amplitude of [Ca2+]i increment in the individual responsive cells. Interestingly, this boosting effect of GC on [Ca2+]i increment could be blocked by the NMDA receptor subunit 2A (NR2A)-specific antagonist [(R)...