Abstract

The present study explored the neuroprotective efficacy of delayed manipulations performed after completion of an excitotoxic insult. Many cultured murine cortical neurons that would otherwise die after exposure to 500 microM N-methyl-D-aspartate (NMDA) or glutamate could be rescued by the late addition of NMDA antagonists to the bathing medium. D-2-Amino-5-phosphonovalerate (D-APV), MK-801 (5-methyl-10, 11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine maleate) and dextrorphan all produced concentration-dependent neuroprotection, with EC50 about 10, 0.3 and 3 microM, respectively, and similar efficacy. The fraction of the doomed neuronal population that could be rescued depended on the time interval between washout of NMDA and antagonist addition, starting at a maximum of 40 to 80% with immediate addition, and decaying to zero after 30 min. D-APV only needed to be present for 30 min for near maximal protection. The ability of NMDA antagonists to rescue doomed neurons was not mimicked by several other drugs: 1 mM gamma-D-glutamyl-aminomethyl sulfonate, 1 mM L-glutamate diethyl ester, 10 microM 6-nitro-7-cyano-quinoxaline-2,3-dione, 1 mM secobarbital, 100 microM diphenylhydantoin, 10 microM nifedipine or 3 microM tetrodotoxin. The broad spectrum glutamate antagonist kynurenate had a protective action similar to that of D-APV, but when added to D-APV did not improve neuroprotection. Neurons could also be rescued by the delayed removal of extracellular calcium for 30 min after exposure to NMDA. In contrast, replacement of sodium with choline actually enhanced resultant neuronal damage.(ABSTRACT TRUNCATED AT 250 WORDS)