Changes in extracellular amino acid neurotransmitters and purines during and following ischemias of different durations in the rat cerebral cortex.

The time courses of changes in extracellular levels of the transmitter amino acids, glutamate, aspartate and gamma-aminobutyric acid (GABA), and of the purines, adenosine and inosine, during 20 or 40 min periods of four vessel occlusion rat cerebral ischemia, followed by reperfusion, were investigated using a cerebral cortical cup technique. During a 20 min period of ischemia, superfusate amino acids increased by 10-30-fold and adenosine levels increased five-fold. Reperfusion was followed by the return of amino acids and purines towards pre-ischemic levels. Significantly greater increases in glutamate and aspartate levels were observed during a 40 min ischemia and, in contrast to the 20 min ischemia, the efflux of all compounds remained elevated throughout the 40 min reperfusion period. These results suggest that longer periods of ischemia are associated with increasing degrees of plasma membrane disruption allowing for a greater leakage of intracellular contents. The failure of extracellular levels of amino acids and purines to return towards pre-ischemic levels indicates that cells may be unable to effectively reconstitute their membranes after longer periods of ischemia.