EXTRACELLULAR NEUROACTIVE AMINO-ACIDS IN THE RAT STRIATUM DURING ISCHEMIA - COMPARISON BETWEEN PENUMBRAL CONDITIONS AND ISCHEMIA WITH SUSTAINED ANOXIC DEPOLARIZATION

Changes in the extracellular levels of excitatory and inhibitory amino acid transmitters were studied in the rat striatum during penumbral i schaemia using intracerebral microdialysis. Effects of penumbral foreb rain ischaemia were compared with those of ischaemia with sustained an oxic depolarisation and K+ (100 mM). Comparisons were also made betwee n different groups of animals at 2 and 24 h after dialysis probe impla ntation. The K+ stimulus did not provoke any release of excitatory ami no acids in the 24-h group, probably reflecting a decrease of function al synapses adjacent to the probe. During 30 min of penumbral ischaemi a, excitatory amino acids did not reach critical concentrations in the extracellular fluid, and increases in levels of inhibitory/modulatory amino acids were similar. On the other hand, severe transient ischaem ia resulted in massive synchronous release of many neuroactive excitat ory and inhibitory compounds, in both the 2- and 24-h groups. These an d other data suggest that changes during severe ischaemia may arise fr om both neurotransmitter and metabolic pools. It is concluded that isc haemic damage in the penumbra may not be related to extracellular neur oactive amino acid changes generated within this region.