| Many accidents lead to global ischemia in clinical emergencies, such as cardiac arrest, drowning, shock, and marked hypotension during cardiopulmonary surgery. Global cerebral ischemia may result in a deficit in spatial learning and memory, cause that the CA1 layer of the hippocampus is very vulnerable to ischemia. In the past decades, a lot of researches attempted to provide protection to ischemia/reperfusion injury, but few treatments can be successfully applied in practice so far.Ischemic postconditioning is a new neuroprotective method, which is a series of rapid intermittent interruptions of blood flow in the early phase of reperfusion, mechanically altering the hydrodynamics of reperfusion. In the field of cardiovascular diseases, ischemic postconditioning has been trying to move from labs to clinical applications, and has achieved fine results in cardiovascular such as in thrombolysis. This may be related to its ability of reducing oxidative stress and inhibiting apoptosis. Recently, it has also been proved that ischemic postconditioning can reduce infarct size after focal brain ischemia and reduce neuronal injury after global cerebral ischemia. However, the underlying protective mechanisms of ischemic postconditioning on ischemia are still not clear, and no papers provide its effects and mechanisms on cognitive and behavioral improvement. On the other side, whether reduce infarct size equal to the protection of neurological function has been questioned by many researches.We adopted global cerebral ischemia model, and chose Morris water maze, Open-field, Neurologic deficit score to evaluate the cognitive and behavioral improvement.Then, causing synaptic plasticity was considered as the base of study and memory, and was very important to normal neurologic function, we suppose that the ischemic postconditioning protection may be based on synaptic plasticity, including morphological plasticity and Long-term potentiation. The N-methyl-D-aspartate (NMDA) receptor is required for LTP and memory, we also examined whether ischemic postconditoning influences NMDA receptor.PART 1 The effect of ischemic postconditioning on behavior and memory in rats after global cerebral ischemiaPurpose : We attempt to investigate the effects of ischemic postconditioning on behavior and memory in rats after global cerebral ischemia for confirm whether ischemic postconditioning result protection of neurological functionMethods:18 SD male rats were randomly divided into sham operated group, global cerebral ischemia group and ischemic postconditioning group. The pullsinelli 4 vessel occlusion was applied to produce the models of global cerebral ischemia reperfusion injury, common carotid arteries (CCA) occlusion with 15min and postconditioning with three cycles, of 15sec release and 15 sec occlusion (15s/15s). 6 rats in each group were evaluated by Morris Maze test for the ability of space learning and memory, gauged by Open-field for functional integrity, Neurologic deficit was evaluated by Neurologic deficit score.Results:(1) The mean escape latency of rats in the ischemic postcondtioning group showed significant short compared with the rats in the cerebral ischemia group in the last 3days (p<0.05) .(2) In the probe test, the number of crossing correct platform of rats in the ischemia group was significantly decreased compared with the sham (p<0.001). The number of crossing correct platform of rats in the postconditioning group was significantly increased compared with the cerebral ischemia group (p <0.05).(3) Open-field score of rats in global cerebral group was significantly increased compared with sham group (p<0.05), and score of rats in ischemic postcondtioning group were significantly decreased compared with cerebral ischemia group at 7d (p<0.05).(4) NDS of rats in global cerebral group was significantly increased compared with sham group (p<0.001), and NDS of rats in ischemic postcondtioning group were significantly decreased compared with cerebral ischemia group (p<0.05).Conclusions : Ischemic postcondtioning improved learning and memory deficit in rats caused by ischemia injury; reduced excessive nervous excitement and neurological deficit caused by cerebral ischemia injury.PART 2 The preservation of ischemic postconditioning related to synaptic plasticity and NMDA receptorPurpose:Causing learning and memory were based on synaptic plasticity, ischemic postconditioning may effect cognitive function by dendritic spine and LTP.NMDA receptors, in particular the NR1 receptor and NR2B receptor, are key protein to LTP, So we investigate the effects of ischemic postconditioning on dendritic spine, LTP, NR1 and NR2B, to explore the mechanism of ischemic postconditioning on the preservation of memory.Methods:72 SD male rats were randomly divided into control group, global cerebral ischemia group and ischemic postconditioning group. The treatment like as before.6 rats in each group were evaluated by golgi stain for morphologic change of neuron. LTP was recorded for the evaluation of function; NR1 mRNA and NR2B mRNA expression of cortex and hippocampus were evaluated by RT-PCR;NR1 protein and NR2B protein expression of cortex were evaluated by immunofluorescence.Results:(1) The density of dendritic spine of rats in ischemia group decreased significantly compared with sham group (p<0.01), and the density of dendritic spine of rats in ischemic postcondtioning group was increased significantly compared with ischemia group (p<0.01).(2) The LTP amplitude and slop in CA1 region of hippocamps of rats in ischemia group was decreased significantly compared with sham group (p<0.01). The LTP amplitude and slop in CA1 region of hippocamps of rats in ischemic postconditioning group was increased significantly compared with ischemia group (p<0.01).(3) NR1 mRNA in the hippocampus and cortex of rats were decreased significantly in ischemia group compared with control group at 72h and 7d after cerebral ischemia-reperfusion (p<0.05). NR1 mRNA in the hippocampus and cortex of rats were increased significantly in ischemic postconditioning group compared with ischemia group at 72h and 7d after cerebral ischemia-reperfusion(p<0.05)(4) NR2B mRNA in the hippocampus and cortex of rats were decreased significantly in ischemia group compared with control group at 72h and 7d after cerebral ischemia-reperfusion (p<0.05). NR2B mRNA in the hippocampus and cortex of rats were significantly increased in ischemic postconditioning group compared with ischemia group at 72h and 7d after cerebral ischemia-reperfusion(p<0.05)(5) NR1 protein and NR2B protein in the cortex of rats in ischemic group were significantly decreased compared with the control group (p<0.01). NR1 protein and NR2B protein in the cortex of rats in ischemic postconditioning group were significantly increased compared with the cerebral ischemia group (p<0.01).Conclusions : Compare with rats of ischemia group, Ischemic postconditioning improved the density of dendritic spines, improved the amplitude and slope of LTP, improved the expression of NR1 and NR2B, that may be one of the important mechanism of cognitive functional protection of ischemic postconditioning. |
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