EFFECT OF ANOXIA ON EXCITATORY AMINO-ACIDS IN BRAIN-SLICES OF RATS AND TURTLES - INVITRO MICRODIALYSIS

Using in vitro microdialysis, we tested the hypothesis that anoxia-ind uced release of excitatory amino acids is greater in adult rat brain t han in turtle brain. Ten minutes of anoxia produced significant elevat ion of glutamate (from 0.39 +/- 0.03 to 0.90 +/- 0.18 muM dialysate, m eans +/- SE, P < 0.05), aspartate (from 0.28 +/- 0.12 to 1.20 +/- 0.49 muM, P < 0.05), glycine, and alanine in the rat brain slice. During r eoxygenation, alanine and glycine returned toward baseline values, whe reas aspartate and glutamate remained elevated. In contrast, prolonged anoxia (60 min) in the turtle brain slice resulted in only minimal in crease in aspartate (from 0.06 +/- 0.01 to 0.09 +/- 0.02 muM, P < 0.05 ) and, interestingly, a decrease in glutamate (from 0.50 +/- 0.11 to 0 .33 +/- 0.09 muM, P < 0.05). Levels of glycine, alanine, and taurine w ere unchanged. We conclude that oxygen deprivation causes marked incre ase in excitatory amino acids in the anoxia-sensitive rat brain slice, while oxygen deprivation for an even longer period of time in the tur tle brain slice produces substantially less change. We speculate that the difference in sensitivity to anoxia between rat and turtle is at l east partly attributable to the major difference in interstitial level s of excitotoxic amino acids during oxygen deprivation.