Astrocytic Function Assessed from 1-14C-Acetate Metabolism after Temporary Focal Cerebral Ischemia in Rats

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Abstract
Astrocytes play many roles essential for normal brain activity. The ability of these cells to recover after temporary focal cerebral ischemia is likely to be one important determinant of the extent of brain dysfunction and tissue damage. We have assessed astrocytic function based on the incorporation of radiolabel from 1-14C-acetate into glutamine at 1 hour of recirculation after middle cerebral artery occlusion for 2 or 3 hours in rats. There were marked differences in the response between subregions within the tissue subjected to ischemia, but the overall pattern of changes was similar after each ischemic period. The striatum, which forms part of the severely ischemic focal tissue during arterial occlusion, showed a large (44% to 68%) decrease in glutamine labeling compared with equivalent tissue from the contralateral hemisphere. In contrast, 14C-glutamine content was not significantly altered in perifocal tissue in the cerebral cortex, which was subjected to more moderate ischemia. Cortical focal tissue also was not significantly affected, but the response was much more variable between rats. In these brain subregions, the extent of recovery of the 14C-acetate metabolism after ischemia was not a good predictor of the likelihood of subsequent infarct development. Interestingly, a similar pattern of responses persisted when recirculation was extended to 4 hours. These results indicate that many astrocytes, particularly in the cortex, remain viable and capable of at least some complex oxidative metabolism during the first few hours of recirculation.