Spatial memory disturbance after focal cerebral ischemia in rats.

We investigated the impairment of retention of spatial memory in rats with chronic focal cerebral ischemia, and examined the correlation between this impairment and pathological outcomes. A preoperative acquisition trial of the Morris water-maze task was performed twice a day for 14 successive days, and then the middle cerebral artery (MCA) was occluded. A retention trial was performed 8 weeks after MCA occlusion. Escape latency and swimming path length to the platform were significantly increased in MCA-occluded rats compared with those of sham-operated rats, and these deficits significantly correlated with massive shrinkage of the brain. Retention latency of a passive avoidance task, which was trained preoperatively, was also significantly shortened in MCA-occluded rats compared with that in sham-operated rats. These results suggest that chronic focal cerebral ischemia causes prolonged spatial memory disturbance in rats and is associated with pathological changes, and that this rat model may be useful for assessing not only anterograde but also retrograde amnesia caused by focal cerebral ischemia.