SIMULTANEOUS BLOCKADE ON NON-NMDA IONOTROPIC RECEPTORS AND NMDA RECEPTOR-ASSOCIATED IONOPHORE PARTIALLY PROTECTS HIPPOCAMPAL SLICES FROM PROTEIN-SYNTHESIS IMPAIRMENT DUE TO SIMULATED ISCHEMIA

A large body of evidence exists to demonstrate that excitatory amino a cids (EAA) and their receptors are involved in the pathophysiological mechanisms linking several acute brain insults, such as cerebral ische mia, to neuronal degeneration and death. Accordingly, the use of EAA r eceptor antagonists can be beneficial in attenuating or preventing the neuronal irreversible damage subsequent to various neuropathological syndromes. We have investigated the effect of 15 min of simulated isch emic conditions, i.e., oxygen/glucose deprivation, on hippocampal slic es preparation measuring, as neurotoxicity indexes, both the amino aci ds efflux in the incubation medium, detected by HPLC, and the inhibiti on of protein synthesis, evaluated as H-3-Leucine incorporation into p roteins. Accumulation of neurotransmitter amino acids was measured in the medium during the ''ischemic'' period. Glutamate increased 30-fold over the basal level while aspartate was sevenfold and GABA 12-fold h igher than in normal conditions. After a reoxygenation period of 30 mi n, the rate of protein synthesis of hippocampal slices subjected to '' ischemia'' was reduced to 35-50% of controls. The non-competitive NMDA antagonist MK-801 (100 mu M) and the competitive NMDA antagonist CGP 39551 (100-250 mu M) as well as the non-NMDA receptor antagonists NBQX (100 mu M) and AP3 (300 mu M) were unable to counteract the metabolic impairment when they were present alone in the incubation fluid durin g simulated ''ischemia.'' An incomplete, but highly significant (p < 0 .001), protection from protein synthesis impairment was achieved in th e presence of an equimolar concentration (100 mu M) of MK-801 and NBQX . A similar protective effect could be reproduced using 100 mu M NBQX in concomitance with a high Mg++ (20 mM) voltage-dependent block of th e NMDA receptor-associated channel but not exposing the slices to a NB QX (100 mu M) and CGP 39551 (100-250 mu M) mixture. The recovery of pr otein synthesis in the presence of the MK-801/NBQX effective combinati on was not paralleled by a detectable decrease in the amount of amino acids released in the incubation medium during the ''ischemic'' period . Taken together, the present data allow new insights into neurotoxici ty-mediating mechanisms, suggesting that multiple additive processes a re involved and that antagonists acting at different sites on excitato ry amino acid receptor subtype can show different neuroprotective pote ncy. (C) 1995 Wiley-Liss, Inc.