Abstract

The N-methyl-D-aspartate (NMDA) antagonists ifenprodil and SL-82,0715 were examined for neuroprotective efficacy against glutamate toxicity of hippocampal neurons in culture. Hippocampal cells were grown on 96-well culture plates for 2 to 3 weeks and then exposed for a 15-min period to glutamate or NMDA. Neurodegeneration was quantified 24 hr after the excitotoxin exposure, by measuring the activity of lactate dehydrogenase leaked into the culture medium by the damaged cells. Glutamate induced a concentration-dependent increase in lactate dehydrogenase that reached 3-fold the activity of control cultures. The NMDA antagonists MK-801 and AP-7 blocked this neurotoxicity when added either during or after the glutamate exposure. Ifenprodil and SL-82,0715 blocked the neurotoxicity only when added during the excitotoxin exposure. Ifenprodil was 3 times more potent than SL-82,0715 in blocking glutamate or NMDA-induced neurotoxicity. Glycine did not reverse the neuroprotective effects of these antagonists. The neuroprotective effect of ifenprodil or SL-82,0715 did not appear to result from actions at alpha-1 adrenergic or sigma receptor sites because the alpha-1 adrenergic antagonist prazosin and the sigma ligands haloperidol, 3-(3-hydroxyphenyl)-N-propylpiperidine) and 1,3-di-o-tolylguanidine) showed no neuroprotective activity. We conclude that ifenprodil and SL-82,0715 protect cultured hippocampal neurons from excitotoxic damage by antagonizing NMDA receptors.