Effects Of Global Cerebral Ischemia-Reperfusion On Expression Of Synaptic Proteins And Morphology Of Microglia

Stroke is a major disease that threatens human health.The structures of neurons can change dramatically after ischemia,but it is unclear how the synaptic proteins change during this process.In addition,microglia are activated after ischemia.The degree of the activation of microglia is closely related to the degree of ischemia and reperfusion.However,how different degrees of ischemia and reperfusion lead to changes in microglial processes has yet to be studied.In this study,a global cerebral ischemia-reperfusion model was established by bilateral common carotid artery ligation surgery.Nissl staining was used to analyze the consistency of neuronal damages in different brain regions under different ischemia and reperfusion conditions.The results showed that there was no significant change in the densities of Nissl bodies in different brain regions after 3 hours of reperfusion following 30 min of BCAL.The density of Nissl bodies in striatum decreased significantly after 3 hours of reperfusion following 3 h of BCAL,and after prolonging the reperfusion time to 3 days,the densities of Nissl bodies in cortex and hippocampus also significantly reduced.Earlier research in the laboratory found that while the dendritic structures of neurons recovered,the dendritic spines also reappeared.We explored whether restoration of dendritic spines affected the expressions of synaptic proteins.The results of immunofluorescence staining showed that the areas and densities of the postsynaptic marker PSD95 puncta and presynaptic marker Syn1 puncta did not change significantly after 30 min of BCAL and 3 hours of reperfusion following 30 min of BCAL.But after 3 h of BCAL and 3 hours of reperfusion following 3 h of BCAL,the density of PSD95 puncta reduced significantly.Furthermore,although the synapses,represented by the colocalization of the Syn1 and PSD95puncta,had no change in area and density after a short period of global cerebral ischemia and reperfusion,their density reduced significantly after a long period of global cerebral ischemia and reperfusion.In addition,quantitative analysis of some synaptic molecules was performed by quantitative PCR.The results showed that the mRNA expressions of most synaptic molecules returned to normal level after 3 hours of reperfusion following 30 min of BCAL.However,the mRNA expressions of some synaptic molecules were significantly lower than normal level after 3hours of reperfusion following 3 h of BCAL.We further explored the effects of different degrees of ischemia and reperfusion on microglia.After confocal imaging of brain coronal slices of transgenic mice(Cx3Cr1^GFP/+),skeleton and Sholl analyses revealed that microglia were activated,a large number of microglial processes retracted and reduced after 3 hours of reperfusion following 30 min of BCAL.With the extension of ischemia time,the reduction was more pronounced.This study found that in different degrees of ischemia models,only prolonged ischemia led to a decrease in the expressions of synaptic proteins.The changes in microglial processes were closely related to the degree of ischemia.Severe stroke led to further disappearance of microglial processes.These conclusions provide a new theoretical basis for the future study of the mechanism of neuronal damage and the connection between neurons and microglia.