| Objective: To establish the models of thrombotic cerebral ischemia and ischemic postconditioning in tree shrews,and to observe the the MRI characteristics,including plain, diffusion weighted imaging(DWI) and gadolinium-diethylenetriaminepenta-acetate (Gd-DTPA) enhanced scan,and to explore the value of MRI for monitoring thrombotic cerebral ischemia and ischemic postconditioning, which may provide a theoretical basis for clinical application and experimental evidence.Methods:The thrombotic cerebral ischemia were induced by photochemical reaction in tree shrews to establish the ischemic models,and at4h after ischemia ischemic postconditioning were established by3repeated cycles of occlusion of the right carotid arteries5min,and reperfusion5min.3.0T MR imaging was performed after4h,24h,48h and72h after ischemia, to observe the change characteristics of thrombotic cerebral ischemia. The data were measured on the workstation including the volume of abnormal signal on the DWI and T2WI images, the values of relative signal intensity (rSI) on the T1WI and T2WI images, the relative apparent diffusion coefficient(rADC) on the ADC images and the signal intensity(SI) on the enhanced images of the lesion center and marginal area. The changes of the cells and cortical infarct size in the different regions were observed between cerebral ischemia group and ischemic postconditioning group through HE staining,2,3,5-triphenyltetrazolium chloride(TTC) staining, respectively. Results:There were no abnormalities in MRI and TTC in the sham group at all time points. In the ischemia group,the signal changes were observed at4h and the signal relative value of the central area at24h was the largest, which had a significant difference in comparison with4h,48h and72h(P<0.05). Moreover, the signal relative values were no significant difference in different time points between the ischemia group and the ischemic postconditioning group(P>0.05). In the ischemia group, the rADC value decreased in the different parts of the lesions and decreased to about57.63%in the central area at4h, remained relative low level in24h. However, the rADC value in the central area significantly increased at48h and72h, which had significant difference at4h,24h,48h and72h(P<0.05). The rADC values were no significant difference at each time point in the central area between the ischemia group and the ischemic postconditioning group (P>0.05). In the ischemia group, the rADC value in the marginal area decreased from4h to24h and decreased to about66.16%in24h. However, the rADC value increased after24h, which were significant difference in comparison with at4h,48h and72h(P<0.05). In the ischemic postconditioning group, the rADC values in the marginal area gradually increased from4h to72h. Compared with ischemic group, at each time point, the rADC values of the ischemic postconditioning group was statistically different at24h,48h (P<0.05) and no significant difference at4h,72h (P>0.05). In the ischemic group, the rADC value at4h had statistically significant between the lesion center and marginal area (P <0.05), however, there were no significant difference at24h,48h,72h (P>0.05).Compare the volume of infarct area measured by TTC and high signal on DWI, there was statistically significant at4h (P<0.05), however, there were no significant difference at24h,48h and72h(P>0.05). In the ischemia group, the largest volume(83.5±9.2mm3)of cerebral ischemic lesion showed at24h. The largest volume at4h had significant difference in comparison with24h,48h and72h (P<0.05). In the ischemic postconditioning group, the volume of cerebral ischemic lesion showed no significant increase from4h(64.9±6.8mm3) to24h(69.1±5.7mm3). There had no significant difference at the different time (P>0.05). The lesions of all the animal between the ischemia group and ischemic postconditioning group showed abnormal enhancement after injection Gd-DTPA at different time points. SI increase rate at24h in the ischemia group was higher than the other time points, which was significant difference compared with that of4h,48h and72h (P＜0.05). The volume on enhanced images was lower than on T2WI images, which had significant difference (P<0.05). Compared SI increase rate in the ischemia group with the ischemic postconditioning group, there were significant difference at24h,48h and72h (P<0.05), which the latter was lower than the former. Light microscopy showed neurons shrinkage in the central area after4hour-ischemia and swelling between ischemic tissue and normal tissue edema, and ischemic penumbra neurons swelling and pyknosis, parts of the endovascular platelet accumulation and thrombosis. After24hour-ischemia, ischemic core tissue dissolved, showing the loose network structure and the demyelination of neurons, pyknosis were obviously observed by light microscopy. Moreover, after48and72hour-ischemia, eosinophilic neurons appeared, which made the whole cells be stained red.Conclusion:MRI may be useful to reflect the pathological evolution process at different time points after ischemia of the thrombotic cerebral ischemia animal models and evaluate the effects of ischemic postconditioning. The infarcted volume of ischemic postconditioning group was smaller than ischemic group, combined with semi-quantitative parameter rADC value, through which the cause may be supposed to save the penumbra. In the ischemic postconditioning group, SI increase rate after enhance was lower than the ischemic group, which may be considered to decrease the damage to the blood-brain barrier. Objective:To establish the models of thrombotic cerebral ischemia and ischemic postconditioning in tree shrews,and to observe the SPIO-enhanced MRI characteristics, compared with Prussian blue staining and anti-IL-1β and anti-ED-1by double immunofluorescence staining,and to explore the value of the SPIO-enhanced MRI for monitoring thrombotic cerebral ischemia and ischemic postconditioning, which may provide a theoretical basis for clinical application and experimental evidence.Methods:The thrombotic cerebral ischemia were induced by photochemical reaction in tree shrews to establish the ischemic models,and at4h after ischemia ischemic postconditioning were established by3repeated cycles of occlusion of the right carotid arteries5min,and reperfusion5min. SPIO was injected at4h,24h and48h after ischemia and3.0T MR imaging was performed at24h after injection and to observe the characteristics of SPIO-enhanced MRI.The T2WI rSI were measured on the workstation on the T2WI images.By showed The morphology and location of iron particle in the lesion was detected by Prussian blue staining.The invasion of macrophages after cerebral ischemia in the lesion was observed with anti-IL-1β and anti-ED-1by double immunofluorescence staining laser scanning confocal microscopic examination. Results:There were no abnormalities in MRI in the sham group at all time points. In the ischemia group,the low signal changes in the ischemic lesions were observed at24h after injection and the patterns of the low signal were identical at24h,48h and72h after injected SPIO at4h.The T2WI rSI at24h,48h and72h after injected SPIO at4h had a significant difference in comparison with plain scan(P<0.05).The T2WI rSI had no significant difference among24h,48h and72h after injected SPIO at4h(P>0.05). The patterns of the low signal were identical at48h and72h after injected SPIO at24h.The T2WI rSI at48h and72h after injected SPIO at24h had no significant difference in comparison with plain scan(P>0.05).The T2WI rSI at72h after injected SPIO at48h had no significant difference in comparison with plain scan(P>0.05).In the ischemic postconditioning group,the T2WI rSI at24h,48h and72h after injected SPIO at4h were higher than in the ischemia group and there were a significant difference between the groups (P<0.05). The T2WI rSI at48h and72h in the ischemic postconditioning group after injected SPIO at24h had no significant difference in comparison with the ischemia group(P>0.05). The T2WI rSI at72h in the ischemic postconditioning group after injected SPIO at48h had no significant difference in comparison with the ischemia group(P>0.05). The iron particles were mainly located within the cells in the vascular lumens by Prussian blue staining at24h after ischemia. The iron particles were mainly located in the cells out of the vascular lumens at72h. The numbers of the iron particles at24h and48h after ischemia were lower than at4h.The numbers of the iron particles in the ischemic postconditioning group were lower than in the ischemia group.There were a large number of ED-1positive microglia/macrophages detected by double immuno-fluorescence staining laser scanning confocal microscopic examination in the surrounding area of the infarct at24h after ischemia. While the number of microglia/macrophages at48h and72h is less than at24h.But there were many large macrophages around the lesions at72h. The IL-1β expression can be seen at24h after ischemia which was stained with ED-1. The numbers of ED-1and IL-1B positive cells at24h after ischemia in the ischemic and postconditioning groups were more than at48h and72h (P<0.05). The numbers of ED-1and IL-1B positive cells at48h after ischemia in the ischemic and postconditioning groups were more than at72h (P<0.05). The numbers of ED-1and IL-1β positive cells at24h and48h after ischemia in the ischemic groups were more than and in the postconditioning group(P<0.05). The numbers of ED-1and IL-1β positive cells at72h after ischemia in the ischemic groups had no significant difference in comparison with the ischemic postconditioning group(P>0.05).Conclusion: Microglia/macrophages involved in the pathological process of ischemic brain injury in the acute phase of thrombotic infarction animal models.In vivo SPIO-Enhanced MRI imaging can be used for monitoring of macrophage invasion situation of acute thrombotic cerebral ischemia induced by photochemical reaction in tree shrews.Ischemic postconditioning can reduce cerebral ischemia microglia/macrophage invasion and expression of inflammatory mediators. SPIO-enhanced MRI can monitor the changes in the acute phase inflammatory response after cerebral ischemia postconditioning in vivo. |
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