ABSTRACT
BACKGROUND: Repetitive brief and non-lethal cerebral ischemia can produce cumulative neuronal damage and vascular dementia; however, precisely injured patterns and mechanisms are still unclear. Thalamus is an important structure of learning and memory; meanwhile, it is also one of the selectively vulnerable regions of cerebral ischemia.However, there are a few reports about neuronal damage induced by repetitive cerebral ischemia.OBJECTIVE: To investigate the pathological damage and mechanism of neurons induced by repetitive cerebral ischemia in thalamus.DESIGN: Randomized controlled experimental study.SETTING: Department of Neurology, General Hospital of Chengdu Military Area Command of Chinese PLA.MATERIALS: The experiment was carried out at the Animal Central Laboratory of the Third Military Medical University of Chinese PLA from March to December 1999. A total of 72 healthy male Wistar rats were randomly divided into sham operation group, single cerebral ischemic group,repetitive cerebral ischemic group, MK-801 treatment group and saline group.METHODS: Transient global cerebral ischemia models of rats were established with modified Pulsinelli-4 vessel occluing method for single 15-minute ischemia and repetitive three 5-minute ischemia at hourly intervals,followed by 5 hours, 2 days and 4 days of survival. Rats in sham operation group were not treated with burning vertebral artery and clipping common carotid artery. 45Ca autoradiography and light microscopy were used to determine the calcium accumulation and neuronal pathological changes of thalamus following repetitive cerebral ischemia as compared with single cerebral ischemia. The effects of MK-801, a N-methyl-D-aspartate (NMDA)receptor antagonist, were also examined.MAIN OUTCOME MEASURES: Distribution and degree of calcium accumulation and neuronal damage in the thalamus of rats in each group.RESULTS: Sham-operated rats revealed no abnormal calcium accumulation and neuronal damage in the thalamus. At 5 hours following ischemia,slightly abnormal calcium accumulation was found in the partial thalamus of the repeated ischemic group, and the neuronal damage was also relatively severer than that in the single ischemic group (0.98±0.19, 0.60±0.14, P＞ 0.05). At 2 days after ischemia, obviously abnormal calcium accumula tion and neuronal damage were shown in thalamus, and the degree of calcium accumulation and score of neuronal damage in repeated ischemic group were significantly severer than that in single ischemic group (1.62±0.31, 0.88±0.21, P ＜ 0.01). At 4 days, the thalamus calcium accumulation and neuronal damage were further increased, and also that in repeated ischemic group was significantly severer than that in single ischemic group (1.80±0.21, 1.02±0.23, P ＜ 0.01), especially marked calcium accumulation and cumulative damage were shown in the ventral thalamus. MK-801 significantly relieved the abnormal calcium accumulation and neuronal damage in the thalamus in repeated ischemic group, showing significant protection of thalamus neurons as compared with that in saline-treated group (0.20±0.12, 1.80±0.15, P ＜ 0.01).CONCLUSION: Repetitive non-lethal cerebral ischemia results in an intense cumulative damage in the ventral thalamus, and the excitatory amino acid and Ca2+ may play a major role in it.