Experimental Studies Of Focal Cerebral Ischemic Preconditioning Induced Endogenous Neuroprotection And Inflammatory Mechanisms

Objective To introduce a simple model in vivo of ischemic toleranceinduced by a transient focal cerebral ischemic preconditioning (IPC) in SD rats, to explore the "time window" of endogenous neuroprotection and to evaluate the effectiveness and stability of this model.Methods Step 1: To investigate the optimal "dose" and opportunityof focal IPC for inducing endogenous neuroprotection. Focal-focal IPC model was established by improved suture method of Zea Longa and 5min,10 min and 15min middle cerebral artery occlusion (MCAO) were used for IPC. SD rats were subjected to IPC or sham-surgery (SS) 1, 3, 7, 14, 21and 28 days before 2 h MCAO followed by 22 hours of reperfusion respectively. Neurological deficit scores, infarct volume and pathological injury were evaluated by Menzies method, TTC staining and hematoxylin and eosin staining in each group. Step 2: For evaluating the effectiveness and stability of this model, 10min IPC followed by 3d reperfusion were chosen before 2h MCAO and more samples were investigated according to the results achieved by step 1. In addition to Neurological deficit, infarct volume and pathologicalinjury, brain water content and neuronal apoptosis were evaluated by wet-dry weight method and TUNEL staining respectively.Results1. No neurological impairment resulted from 5 min IPC. Transient Homer's sign and neurological deficit which recovered within 24h were observed occasionally after 10 min and 15 min I PC respectively.2. No infarct resulted from IPC was identified by TTC staining.3. Compared with SS+MCAO group, there was a significant reduction in infarct volume in 10 min and 15 min TPC+MCAO group. No significant difference in infarct volume was observed between 5 min IPC+MCAO group and SS+MCAO group.4. No significant cell injury and necrosis was microscopically identified in HE stained histological sections in 5 min and 10 min IPC group.5.10 min IPC reduced neurological deficits significantly caused by 2h MCAO 1-28 days after IPC. The most satisfying behavioral improvement was observed in animals received IPC 3 days before 2h MCAO.6. Infarct volume was reduced only when IPC was performed l~14days before 2h MCAO. The most significant reduction was observed in animals received IPC 3 days and 7 days before 2h MCAO.7. Based on the results of step 1, lOmin IPC followed by 3d reperfusion were chosen and the model was further established with more animals. There were 16 rats models failed to be made and the odds of success was 81.4%. The majority of death resulted from cerebral hemorrhage and/or subarachnoid hemorrhage occurred within 12h after the second reperfusion.8. Compared with SS+MCAO group, the neurological deficit scores,infarct size, brain water content of ipsilateral and contralateral hemisphere and the number of apoptotic neurons were significantly reduced in IPC+MCAO group.Conclusions1. The result suggested that 1 Omin MC AO may be the optimal EPC "dose" and endogenous neuroprotection induced by focal IPC existed during the period of 1 ~14d after EPC.2. Focal EPC achieved by lOmin MCAO can effectively induce endogenous neuroprotection without any structural injury itself. This model might be a promising tool of research in cerebral ischemic tolerance because of its simplicity, stability and similarity to ischemic stroke in human being.