Effect Of Cerebrovascular Distribution On Microglial Activation And Neuronal Injury After Stroke In Mice

Under physiological condition,the cerebral activity is a considerable energy consuming process.The distribution and structure of cerebrovascular provides the specific needs for energy in each brain region.Maintaining the cerebral function and homeostasis relies on the interaction between microglia,neurons and cerebrovascular.Ischemic stroke is caused by cerebrovascular obstruction or embolism,which leads to glial cell activation,neuronal structural and functional damage,and tissue edema.Our previous studies have found that microglial activation and neuronal injury in different brain regions have shown regional differences after ischemia.However,whether the distribution difference of cerebrovascular is related to the differences in injury regions has not been clearly studied.Therefore,in this study,fluorescence protein vascular labeling technology,combined with tissue staining,immunofluorescence staining,confocal imaging and other technologies were used to compare the degree of microglia activation,neuron injury and astrocyte response in different brain regions after global cerebral ischemia reperfusion,and to analyze the relationship between vascular distribution in different brain regions,microglia activation and neuron injury.The spatio-temporal relationship between blood vessels and microglia activation at different time after ischemia reperfusion was also initially explored.The results showed that there were significant differences in the distribution of blood vessels,distribution of microglia and structure in different brain regions.Among them,the vascular length density in the cortex was 0.39 m/mm~3,which was significantly higher than that in the striatum,callosum and hippocampus,while the microglia density in the cortex was 274.2/mm~2,which was also higher than that in the callosum and hippocampus;the vascular length density in each brain region was positively correlated with the microglia density.To investigate the effect of stroke on vascular distribution in different brain regions,we evaluated the changes in vascular distribution in the cortex,striatum,callosum and hippocampus in the bilateral common carotid artery ligation model.The results revealed that ischemia-reperfusion resulted in vascular loss in all brain regions.The vascular loss rate in the striatum was 69.5%,which was significantly higher than that in the cortex and hippocampus.Subsequently,we further evaluated the activation and differences of microglia in different brain regions.Rate of microglia density changed was significantly higher in the CA1 region than in the cortex,striatum and callosum,while the volume of microglia in the striatum decreased by 63.4%,with a significantly higher degree of volume change than in the cortex and callosum.Following that,we also analyzed the changes in neuronal density in each brain region after stroke and found that neuronal density in the striatum was reduced by 59.2%compared to normal mice.Finally,we compared the activation levels of astrocytes in different brain regions after stroke,and find that astrocyte activation was significantly higher in the striatum than in the cortex,callosum,and hippocampus.Based on the facts mentioned above,we concluded that the rate of vascular loss in different brain regions after ischemia-reperfusion correlated with changes in the density of microglia in that brain region.Meanwhile,the rate of vascular loss in different brain regions is related to the change of microglia cell density.The vascular structure in brain regions with low vascular density and more capillaries is more susceptible to ischemic injury.In addition,in the MCAo reperfusion model,at 3 d of reperfusion,the aggregation of activated microglia around the infarcted tissue with vascular distribution;at 7 d of reperfusion,activated microglia entered the infarct center,and the density of microglia in the area with vascular distribution gradually recovered.Our results indicate that vascular distribution correlates with microglia density in both healthy and ischemic brain.We speculate that the differences in the distribution of blood vessels after stroke are one of the reasons for the differences in the damaged areas of different brain regions,and that the interaction between vascular and activated microglia can change the distribution of microglia during injury recovery.In conclusion,our study explains the reason of brain region differences in ischemic stroke injury from the perspective of vascular structure,and also provides a new reference for studying the interaction between blood vessels and microglia cells after reperfusion.