STUDY OF CEREBRAL ISCHEMIC TOLERANCE : PART 2 : SUPERDELAYED NEURONAL CHANGES DUE TO CHRONIC HYPOPERFUSION IN AGED ANIMALS

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In order to elucidate the difference of cerebral tolerance to ischemia between aged and young animals, two experimental studies were performed. In experiment A,Sprague-Dawley rats with 2 months of age (young group) and 18 months of age (aged group) were subjected to right middle cerebral artery occlusion. Neuronal changes in teh ipsilateral thalamus were studied at 3 days, 1 week and 2 weeks after occlsuion, respectively. After occlusion, all the animals developed infarction in the ipsilateral cerebral cortex and the lateral caudoputamen. At 3 days after occlsuion, the thalamus was pared in both groups. At 1 week after occlusion, 40% of young animals showed mild neuronal changes in the ipsilateral thalamus, and 60% of aged animals exhibited mild neronal changes in the thalamus. At 2 weeks after occlusion, all the young and aged animals displayd neuronal changes in the ipsilateral thalamus. The extent of changes were more widely spreaded in aged animlas as compared with young animals. I … More n experiment B,mongolian gerbils with 2 months of age (young group) and 18-20 months of age (aged group) were subjected to the occlusion of right internal carotid artery and left external carotid artery. Both groups were further divided into two subgroups, one for cerebral blood flow measurments and the other for histological examinations. After occlusion, 60% of young animals and 70% of aged animals showed severe cerebral blood flow reduction by more than 50%, and the remainders exhibited moderate blood flow reduction by less than 50%. IN both groups, animals with severe reduction all showed ischemic symptoms and died within 3 days after occlusion, whereas those with moderate redcution revealed no ischemic symptoms. Histological examinations were performed in the non-symptomatic animals at 1 week, 1 month and 3 months after occlsuion, respectively. At 1 week after occlusion, none of animals in young and aged groups exhibited-neuronal changes. At 1 month after occlusion, none of animlas in young group exhibited neuronal changes. However, 3 of 9 animals in aged group developed neuronal changes in the cerebral cortex and/or hippocampus CA1 area. At3 months after occlusion, only 1 of 8 animals in young group showed neuronal changes in the hoppocampus CA1 region. On the other hand, 5 of 8 animals in aged group displayd neuronal changes in teh cerebral cortex and/or hippocampus. The results of teh present study suggest that the ages brain is more vulnerable to ischemic insults as compared with the young brain. Moderate hypoperfusion ensuing for a chronic interval may cause cortical and hippocampal neuronal changes in the aged brain. Less