The Stereological Study On Neurons And Astrocytes In Cerebral Cortex After Cerebral Ischemia-reperfusion In The Rats

In order to study the morphologic changes of neurons and astrocytes in cerebral cortex at various time points after cerebral ischemia-reperfusion,42 male SD rats were selected and randomly divided into seven groups which were control group(C), 6h reperfusion following 15min ischemia group(15m-6),6h reperfusion following 2h ischemia group(2h-6),12h reperfusion following 15min ischemia group(15m-12), 12h reperfusion following 2h ischemia group(2h-12),24h reperfusion following 15min ischemia group(15m-24)and 24h reperfusion following 2h ischemia group(2h-24),each group included six rats.The animal model of cerebral ischemia-reperfusion was made by ligating of the left common carotid artery and clamping of the right common carotid artery by artery clamps for 15min or 2h, followed by 6h,12h,24h of reperfusion separately.The rats were sacrificed and then Nissl staining and immunohistochemistry method were used to observe the morphological change of neurons and astrocytes in hippocampus CA₁,CA₂,CA₃, CA₄,dentate gyrus and parietal cortex under light microscope,and volume density (Vv),surface density(Sv)were measured to evaluate morphologic changes as well according to stereology.The results showed as followed:Nissl staining showed that in ischemia-reperfusion group,a series of morphology changes took place in cerebral cortex.Morphology changes of neurons showed up as early as 15m-6,including cell layer disordered,cells swelled slightly,neuroglial cell proliferated around neurons.As the ischemia-reperfusion time went on,neuron distorted and swelled,Nissl bodies decreased,et al.When it came to 2h-24, intercellular space widened,cell layer got thinner,Nissl bodies even disappeared.GFAP immunohistochemistry showed that as the ischemia-reperfusion time went by,the cell bodies enlarged and the processes exitended.In the 2h-24 group,the positive expression of astrocyte reached peak,astrocytes stained dark and deformed.The Vv,Sv of neurons in cerebral cortex decreased with the extension of reperfusion,there were distinct differences among ischemia-reperfusion groups and control group(P＜0.05;P＜0.01)in hippocampus subregion and dentate gyrus,While in parietal cortex,ischemia-reperfusion groups had distinct differences compared with control group except 15m-6 group. At the same time point after reperfusion,the Vv,Sv of neurons in 2h ischemia groups were less than that of 15min ischemia groups,and there were distinct differences between these two ischemia time at 6h,12h,24h of reperfusion in CA₁ and CA₂ region of hippocampus(P＜0.05),while in hippocampus CA₃,CA₄,dentate gyrus and parietal cortex,the Vv,Sv in 2h ischemia groups had no differences compared with 15min ischemia groups(P＞0.05).The Vv,Sv of astrocytes in 15m-6 groups in all cerebral cortex region had no distinct differences compared with control group(P＞0.05),the Vv,Sv of astrocytes in 15m-12 groups increased significantly in hippocampus CA₁,CA₂,CA₃,dentate gyrus compared with control group(P＜0.05),while there were no distinct differences between 15m-12 groups and control group in parietal cortex(P＞0.05).The Vv,Sv of astrocytes in 15m-24,2h-6,2h-12,2h-24 groups had distinct differences compared with control group(P＜0.05).There were no distinct differences of astrocytes between 2h-6 group and 15m-6 group(P＞0.05)in all cerebral cortex region,there were distinct differences beween 2h-12 and 15m-12 group as well as 2h-24 group and 15m-24 group in hippocampus CA₁,CA₂ and parietal cortex,while in hippocampus CA₃,CA₄,dentate gyrus,there were no differences beween 2h-12 and 15m-12 group as well as 2h-24 group and 15m-24 group.The differences between the Vv and Nv of neurons and astrocytes in different regions of cerebral cortex:there were no differences between CA₁ and CA₂,there were no differences among CA₃,CA₄,dentate gyrus and parietal cortex.The Vv and Nv in CA₁,CA₂ have distinct differences compared with CA₃,CA₄,dentate gyrus and parietal cortex.There were no distinct differences of neurons and astrocytes between the left and right side of the same region in various groups.These results indicated that neurons damage in cerebral cortex aggravated as reperfusion time went on,While astrocytes functioned more actively and were closely related with neurons damage degree.