Glutamate extracellular accumulation is an early event in
brain ischemia triggering excitotoxic neuron damage. We have investigated how to control the
glutamate efflux from human cerebrocortical slices superfused in conditions simulating an acute ischemic insult (
oxygen and
glucose deprivation). The efflux of previously accumulated [3H]
D-aspartate or endogenous
glutamate increased starting 18 min after exposure to
ischemia and returned almost to basal values in 6 min reperfusion with standard medium. Superfusion with Ca2+-free,
EGTA (0.5 mM)-containing medium or with medium containing
tetrodotoxin (TTX; 0.5 microM) inhibited the
ischemia (24 min)-evoked [3H]
D-aspartate efflux by about 50% and 65%, respectively. The
ischemia (24 or 36 min)-evoked efflux of [3H]
D-aspartate or endogenous
glutamate was reduced at least 40% by the
adenosine A(2A) receptor antagonist
SCH 58261 (1 microM); the compound was effective when added up to 15 min after exposure to
ischemia. No effect of
SCH 58261 on the
ischemia-evoked [3H]
D-aspartate was found in Ca2+-free,
EGTA-containing medium. To conclude, a significant component of the
ischemia-evoked
glutamate efflux in human cerebrocortical slices seems to occur by a vesicular-like mechanism. Endogenously released
adenosine is likely to activate A(2A) receptors that enhance vesicular-like
glutamate release during
ischemia; A(2A) receptor antagonists would deserve consideration for their neuroprotective potential.