Learning and memory ability and its mechanism in rats with focal cerebral ischemia induced by two filament-occluded methods / 中国康复理论与实践

ABSTRACT

ObjectiveTo explore the difference of learning and memory function between permanent cerebral ischemia and ischemia-reperfusion rat models by filament-occluded method after three weeks of natural recovery, and to observe the changes of brain structure. MethodsA total of 21 SPF male Sprague-Dawley rats were randomly divided into sham group (n = 7), permanent ischemia group (n = 7) and ischemia-reperfusion group (n = 7). The latter two group underwent left middle cerebral artery occlusion, and the ischemia-reperfusion group was reperfused after 90 minutes of ischemia. All the rats were tested with Morris Water Maze 16 to 22 days after modeling, to record escape latency in the navigation experiment, as well as first latency, platform quadrant swimming time ratio and distance ratio, boundary swimming time ratio and distance ratio, average speed, and the swimming path in the space exploration experiment. On the 22nd day after modeling, four rats with similar Longa scores in each group were scanned by magnetic resonance by diffusion tensor imaging, to measure the fractional anisotropy (FA) of cerebral ischemic cortex, striatum, hippocampus and their corresponding contralateral regions, to calculate ratio of FA (rFA); as well as the volume of infarct (VI) and ratio of VI (rVI). ResultsFor navigation experiment, the escape latency decreased in all the groups with the time (F = 36.202, P < 0.001), but it was not significant for the permanent ischemia group (F = 4.004, P > 0.05). The escape latency was longer in the permanent ischemia group than in the other two groups at each time points (P < 0.05). For space exploration experiment, the boundary time ratio and distance ratio were more in the permanent ischemia group and the ischemia-reperfusion group than in the sham group (P < 0.017), and the first latency was longer in the permanent ischemia group than in the sham group (P < 0.017). The swimming path of ischemia-reperfusion group and sham operation group was better than that of the permanent ischemia group. FA and rFA in left cortex and striatum were less in the permanent ischemia group and the ischemia-reperfusion group than in the sham group (P < 0.05), while FA and rFA of left cortex and FA of left striatum were less in the permanent ischemia group than in the ischemia-reperfusion group (P < 0.05). The VI and rVI were larger in the permanent ischemia group than in the ischemia-reperfusion group (t > 4.185, P < 0.01). FA and rFA of left cortex and striatum correlated with escape latency, boundary time ratio and distance ratio (|r| > 0.498, P < 0.05). The VI and rVI correlated with escape latency and boundary time ratio (|r| > 0.538, P < 0.05). ConclusionCognitive impairment is more severe in the rat model of permanent cerebral ischemia, which may relate to the larger damage of structure of nerve fibers in ischemic cortex and striatum, and larger infarct size.