Temporal Profile of Cortical Injury Following Ischemic Insult Just Below and at the Threshold Level for Induction of Infarction: Light and Electron Microscopic Study

Summary

By unilaterally occluding the carotid artery of Mongolian gerbils twice for 10 min, with an interval of 5 h, we affected ischemic insults of just below or at the threshold level needed to induce infarction in cerebral cortex that had been sectioned coronally at the level of the infundibulum or at the chiasma. The temporal profile of cortical tissue injuries was compared by light- and electron microscopy at 15 min, 5 h, 12 h, 24 h, 4 days and 7 days following both intensities of the above insults. We have found that:

• 1. Following ischemic insults just below the threshold level to induce infarction, only disseminated selective neuronal necrosis (DSNN) progresses. Following ischemic insults of threshold level to induce infarction, DSNN develops first, followed by an evolution to a gradually enlarging infarcted focus.

• 2. Swelling, glycogen accumulation and an increase in the size and number of mitochondria are observed in astrocytes associated with DSNN, and no astrocytic necrosis is found.

• 3. When astrocytic cell processes degenerate and perivascular end-feet disappear, the cortical tissue demonstrates infarction

• 4. Astrocytes appear to protect against post-ischemic neuronal and cortical tissue injuries. A therapeutic window exists to rescue the cortical tissue evolving from DSNN to infarction.

• 5. Surviving astrocytes proliferate, extending and widening their cell processes, which are rich in astrocytic fibrils. The processes are intercalated among the neuropil and surround blood vessels as astrocytic end-feet.