Interrelationship of brain edema, motor deficits, and memory impairment in rats exposed to focal ischemia.

We investigated the relations of brain edema, ion shifts, motor performance, and memory impairment using a focal ischemia model in rats. Cortical infarction was produced by ligation of the middle cerebral artery and the ipsilateral common carotid artery combined with temporary occlusion of the contralateral common carotid artery for 1 hour. Water content and sodium, potassium, and calcium concentrations were measured until Day 14 after the ischemic insult. Significant edema formation was observed; it peaked on Day 3 (p less than 0.001) and then declined. The tissue sodium concentration changed in a manner similar to that of water content, but the tissue potassium concentration changed in an opposite fashion. Massive accumulation of calcium was detected as early as Day 1 after ischemia (almost four times the normal level). The increased calcium concentration was sustained even up to Day 14. Motor performance examinations performed on Day 3, including inclined plane, balance beam, and prehensile tests, demonstrated significantly reduced (p less than 0.001) motor ability that did recover even by Day 7. Passive avoidance learning was carried out on Day 2, followed by a memory retention test on Day 3. Significant memory dysfunction was observed in ischemic compared with sham-operated rats (p less than 0.001). A high correlation coefficient (r = 0.91, p less than 0.01, n = 13) was obtained between water content and calcium concentration on Day 3. Both the total motor score and the degree of disturbance of the passive avoidance reaction also correlated well with water content.