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

为了阐明老龄动物和幼龄动物脑缺血耐受性的差异，我们进行了两项实验研究。实验A采用2月龄（幼龄组）和18月龄（老年组）的Sprague-Dawley大鼠进行右侧大脑中动脉闭塞。分别在闭锁后3天、1周和2周观察同侧丘脑神经元的变化。闭塞后，所有动物在同侧大脑皮层和外侧尾核发生梗死。阻断后3 d，两组均切除丘脑。闭塞后1周，40%的幼龄动物同侧丘脑出现轻度神经元变化，60%的老年动物丘脑出现轻度神经元变化。闭塞后2周，所有幼龄和老年小鼠同侧丘脑均出现神经元变化。与幼龄动物相比，老年动物的变化程度更为广泛。实验B选取2月龄（幼龄组）和18-20月龄（老年组）的蒙古沙鼠进行右颈内动脉和左颈外动脉闭塞实验。两组进一步分为两个亚组，一组进行脑血流量测量，另一组进行组织学检查。闭塞后，60%的幼龄动物和70%的老年动物表现出严重的脑血流减少，减少幅度超过50%，其余动物表现出中度的脑血流减少，减少幅度小于50%。在两组中，严重复位的动物均出现缺血性症状，并在闭塞后3天内死亡，而中度复位的动物未出现缺血性症状。无症状动物分别于闭塞后1周、1个月和3个月进行组织学检查。闭塞后1周，年轻组和老年组均未出现神经元变化。术后1个月，幼龄组动物无神经元变化。然而，老年组9只动物中有3只在大脑皮层和/或海马CA1区出现神经元改变。闭塞后3个月，幼龄组8只动物中只有1只海马CA1区出现神经元改变。另一方面，老年组8只动物中有5只在大脑皮层和/或海马中出现神经元变化。本研究的结果表明，与年轻人相比，老年人的大脑更容易受到缺血性损伤。持续一段时间的中度灌注不足可能导致老年大脑皮层和海马神经元的改变。少

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