| Objective: Brain edema is one of the main pathological manifestations after cerebral ischemia.Studies have indicated that aquaporin-4(AQP4)plays an important role in the formation and development of brain edema after cerebral infarction.Little is known about the correlation between magnetic resonance diffusion weighted imaging(MRI-DWI)and AQP4 expression in stage of the reperfusion following acute cerebral ischemia.The present study aimed to observe the dynamic changes of cerebral ischemia reperfusion in rats by DWI,to analysis the relationship between the expression of AQP4 and apparent diffusion coefficient(ADC)in brain damage zone,and investigate the relationship between the expression of AQP4 and ischemic brain edema.Methods:1 Eighty SD male rats were randomly divided into 8 groups,weight of rats among 270-300 g,respectively for cerebral ischemia reperfusion 1h group,3h group,6h group,12 h group,1d group,3d group,7d group and sham group.The right middle cerebral artery ischemia reperfusion(MCAO/R)model in the rats was induced by the intraluminal suture method.2 The Longa Zea score was used to evaluation the neurological function of the rats in the MCAO/R group and sham group.3 Coronal sections were performed with Philips Achieva 3.0-tesla whole-body MR scanner in the sham group and ischemia reperfusion at different time points.All rats were underwent T1 WI,T2WI and DWI scanning.The ADC map was reconstructed on the workstation,and the DWI signal intensity,ADC value and the relative apparent diffusion coefficient(rADC)value of each rat was calculated.4 Rats were sacrificed and the cerebral ischemic tissues were examinedfor histopathology.Measure the infarct volume at each time point by2,3,5-Triphenyltetrazolium chloride(TTC)staining.5 The morphological changes were observed by HE staining at different reperfusion time points(12h,1d,3d,sham).6 The expression of AQP4 protein in brain tissue at different reperfusion time points(12h,1d,3d,sham)was determined by immunohistochemistry method,and measured the mean optical density(MOD)to evaluate the degree of staining.Results:1 There were no neurological deficits in sham group,the neurological function score was 0.Compared to the sham-operated group,all the ischemic groups have significantly neurological deficits indicated by higher Longa score(P<0.05).The rats showed neurological deficits in 1h after cerebral ischemia reperfusion,left limb weakness,muscle tension decreased,the left circle and not eating.The neurological deficits were significantly severer in3h-1d,and showed contra lateral tumble on 1d.Oral intake was started on3-7d,and the severity of the neurological deficits was reduced.The neurological function score on the 1h group was significantly higher than that of sham group(P<0.05),but there was no significant difference among 3h-1d.The neurological deficits improved slightly in the 3d,the neurological function score in the 7d was significantly lower than that of in the 1d(P<0.05).2 No abnormal signal was detected on DWI and ADC maps in the sham group.The DWI showed high signal in striatum,and the ADC value of the corresponding part was decrease on 1h after MCAO/R.The high signal area in DWI and the signal intensity increased gradually from 1h to 1d,decreased gradually from 3d to 7d.The rADC value took on a firstly decreasing and then increasing,reached the lowest at 6h,which began to rise on 12 h and decreased on 1d(P<0.05).The rADC value began to increase on 3d.There was no significant difference between sham group and 7d group(P>0.05).The rDWI-SI increased continuesly from 1h to 1d,reached its peak on 1d,began todecrease on 3d,the rDWI-SI at 7d group was still higher than that of in sham group.3 In sham operated group,there were no obvious abnormalities in the structure of the hippocampus and the cortex,the cell structure was complete,the nucleus was stained dark blue,the cytoplasm was abundant,and the chromatin was homogeneous.At 12 h after MCAO/R,it has been observed that some dense staining cells,cytoplasmic vacuoles formed,and nuclear nuclear pyknosis in the hippocampus and cortex of ischemic side,but cell arrangement was acceptable.The ischemic neuronal injury aggravated on the first day,cell arrangement disordered,cell gap widened,a large number of cytoplasmic vacuoles and nuclear condensation were seen on the first day,the cytoplasmic vacuoles of the hippocampus was reduced slightly.4 The white dying area was not found in sham group and whole brain was stained red.The model group rats showed white staining area in the right striatum and the surrounding cortex at 1h,staining area gradually expanded from 1h to 1d,including the right basal ganglia and frontotemporal cortex,the range on 3-7d was smaller than that of on 1d.The infarct volume increased gradually from 1h to 1d,and which was increased rapidly at 6h-1d.The infarct volume reached a peak on 1-3d group and decreased on 7d,but still higher than that of 6h group(P<0.05).The ischemic brain edema volume of model group increased gradually from 1h to 1d,reached a peak at 1d group,began to decrease at 3d group,decreased significantly at 7d group.5 The expression of AQP4 in the hippocampus and cortical area was very little in sham group.AQP4 positive staining cells were found in cortex and hippocampus in the side of ischemia at 12 h group,12h-3d the AQP4 mean optical density value increased gradually over time,reached the peak at 3d group.The AQP4 expression levels of three groups were significantly higher than those in the sham group(P<0.05).6 The nerve function score was positively correlated with the rDWI-SI of basal ganglia in the model group(r=0.503,P=0.000),the infarct volume and the volume of edema was positively correlated with the rDWI in themodel group(r=0.542,P=0.001.r=0.740,P=0.000).7 The cerebral edema volume of rats and AQP4 expression level of cortex in the side of ischemic showed a positive correlation at 12 h,1d and 3d groups(r=0.642,P<0.05),and also positively related to the MOD value of the AQP4 expression level of hippocampus(r=0.605,P<0.05).The rADC value of basal ganglia and AQP4 expression levels of cortex and hippocampus in the side of ischemia showed a positive correlation at three groups(r=0.542,P=0.037.r=0.655,P=0.008).Conclusion:1 Magnetic resonance diffusion weighted imaging and ADC value have a high specificity and sensitivity on the changes of cerebral ischemia reperfusion injury,it had a intuitive value on the dynamic change of ischemia reperfusion injury.2 Brain edema volume,rADC value and the expression level of AQP4 showed a correlation,the brain edema volume and the expression level of AQP4 increased significantly between 12 h and 1d,the edema volume began to decrease,but the expression level of AQP4 was significantly increased between 1d and 3d.This suggested that AQP4 in the acute phase(12h-1d)was likely to participate in the formation of brain edema after ischemia and reperfusion,in the subacute phase(1d-3d)may prevented brain edema from further aggravate,removed excess water on the brain.3 Combining DWI with histological examination,the systematic deep study on the AQP's expression sites,function and regulating mechanism may provide a new diagnostic idea and treatment method for the treatment of brain edema. |
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