Dynamic Recovery Of Cerebral Blood Flow After Traumatic Brain Injury In Mice And Its Correlation With The Repair Of Brain Injury

Objective: Cerebrovascular injury is an important pathophysiological process of traumatic brain injury(TBI).Its structural destruction and dysfunction participate in the pathogenesis,development and repair of TBI,and are closely related to secondary injury,such as cerebral blood flow(CBF)changes,hemorrhage,edema and blood-brain barrier(BBB)destruction.After acute brain injury,the vascular network and vascular complexity of the lesion decreased.However,these studies focused on the central area of brain injury in the acute stage,and there were few studies on the cerebrovascular changes in the recovery and surrounding areas.CBF is an important index to evaluate vascular function.Most patients with TBI can observe the decrease of local or global CBF after injury,which further leads to ischemic brain injury,which is the main cause of death after craniocerebral injury.However,there are few studies on the relationship between vascular structure and CBF.Although CBF will return to normal in a few weeks,early intervention and reasonable regulation of CBF may improve the prognosis of patients with TBI.Therefore,the purpose of this study is to explore the dynamic changes of CBF after TBI by laser speckle imaging and its correlation with vascular morphology in the process of vascular repair.Methods: 1.The moderate TBI mice model by controlled cortical impact(CCI)was established.2.The dynamic changes of cortical CBF in hyperacute phase(24 hours),acute phase(3 days),subacute phase(3 weeks)and convalescent phase were monitored in vivo laser speckle imaging after TBI.3.In order to quantify the morphological changes of blood vessels in the periphery of injury after TBI,the brain sections of model mice were stained with immunofluorescence,the cerebral vascular structure was shown by confocal imaging,and the peripheral area around the injury was selected for vascular morphological analysis by Angio Tool.4.The motor coordination ability of mice was analyzed by behavioral experiments including rotating rod,string suspension assay,ledge assay.5.IBM SPSS Statistics 21.0 was used to analyze the correlation between CBF and motor function injury and recovery in mice after TBI.Results: 1.After the TBI model of mice was made with precision cortical impactor,the brain tissue showed hemorrhage and contusion.The coronal section of the brain tissue was used to evaluate the brain injury area,which confirmed that the brain injury was limited to the cortex without affecting the hippocampus,which reached the standard of moderate TBI model in mice.2.During the hyperacute period,TBI not only significantly decreased the CBF of the injured site in mice,but also caused significant changes in the CBF around the injury and even on the contralateral side of the injury.The CBF around the injury and the contralateral side of the injury decreased continuously immediately after TBI,and decreased by 64.8% at 10 min after TBI.Then the CBF began to recover slowly,and basically returned to the normal level at 120 min after TBI,and remained stable in a certain range.3.The CBF in the injured area of mice decreased significantly in the hyperacute and acute phase of TBI with a decrease of 69.8%、62.9% and 67.8%respectively,6-hour,the 1st day and the 3rd day after TBI,and began to recover on the3 rd day after TBI.The CBF recovered similarly to the level of the contralateral on the14 th day after TBI,and remained at the normal perfusion level until 35 days after TBI.4. The results of immunofluorescence staining showed that the vascular morphology in the periphery of brain injury in mice changed significantly after TBI,that is,the vascular density and total vascular length in the peripheral area of injury in mice increased significantly,but decreased at 3 days after injury,and the number of vascular branches increased significantly on the 1st day and 14 th day after TBI.The diameter of blood vessels decreased on the 1st day after injury,but increased significantly on the 3rd day after TBI.5.The results of rotating rod in mice showed that TBI caused motor coordination dysfunction in mice,especially on the 3rd day,then the motor ability recovered gradually,and basically returned to the normal level after 28 days.The results of string suspension assay and ledge assay showed that the forelimb muscle strength and limb coordination of mice were significantly impaired on the 1st day after TBI,and basically recovered on the 14 th day after TBI.6.The results of Pearson correlation analysis showed that there was a significant positive correlation between CBF and motor function in mice after TBI.Then using Pearson linear correlation analysis,it was found that there was a linear correlation between the two groups of variables(F = 124,P =0.0004).The linear regression equation of Pearson is Y = 1.307X-5.744.Conclusion: TBI leads to vascular damage,structural damage,decreased CBF and motor dysfunction.The vascular morphology around the injury first appeared the increase of vascular density,length,diameter and complexity of vascular network,which would be maintained for a long time,and then the CBF gradually recovered.With the excessive proliferation of blood vessels and the recovery of blood flow,the motor function gradually recovered.After vascular morphological reactive hyperplasia,accelerating the recovery of CBF may promote the recovery of neurological function.This study provides a direction for exploring the mechanism of cerebral blood perfusion defect and vascular repair and regeneration.