Elevation of the extracellular glutamate concentration in the hippocampus after total cerebral ischemia related to the deterioration of the recovery in EEG and evoked potentials in dogs.

The concentrations of extracellular glutamate (Glu), aspartate (Asp) and glycine (Gly) were measured by microdialysis method in the cortex and hippocampus before, during and after 15 min of total cerebral ischemia in dogs. The correlations between the concentrations of amino acids and the changes in EEG and evoked potentials (EP) after ischemia were evaluated. Total cerebral ischemia was achieved by occluding the ascending aorta and the caval veins. The concentrations of Glu in the hippocampus significantly increased from 1.73 +/- 0.59 (mean +/- SEM) nmol.ml(-1) at pre-ischemia to 5.46 +/- 1.34 (P < 0.05) during ischemia and 14.37 +/- 3.70 (P < 0.01) 0-15 min after ischemia, and returned to the pre-ischemic level 30 min after ischemia. The concentration of hippocampal Glu 0-15 min after ischemia had significant negative correlations with the EEG-EP scores (0 = serious deterioration of electrical function and 6 = normal electrical function) 30 min, 3 hr and 5 hr after ischemia (r = -0.69, P < 0.05 : r = -0.67, P < 0.05 : r = -0.70, P < 0.05, respectively). The increase of the extracellular Glu concentration in the hippocampus immediately after ischemia may aggravate the neurological outcome after total cerebral ischemia.