Disturbance of retention of memory after focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE The purpose of this study was to investigate the behavioral changes, in particular retention of memory, after focal cerebral ischemia in rats. METHODS Ischemia was produced by permanent occlusion of the left middle cerebral artery (MCA). For quantitative behavioral analysis, one-trial passive avoidance response and active avoidance response with the discrete lever-press avoidance procedure were observed. One group of animals was trained once to learn the passive avoidance task 1 day before surgery. The response latency was examined 4 and 14 days after surgery. The second group was trained to learn the active avoidance task for 2 weeks before surgery. The avoidance rate was examined 3 and 14 days after surgery. RESULTS The MCA-occluded group showed significant failure of memory retention in both of these tasks (P < .01). The nonoperated group and sham-operated group showed no definite memory failure. CONCLUSIONS Retention of memory in the passive avoidance response and the active avoidance response was disturbed after left MCA occlusion in the rat. These results strongly suggest that this model can be used to assess memory disturbance after focal cerebral ischemia.