Neurovascular Unit Mechanism Of Neuropathological Changes After Repeated Mild Traumatic Brain Injury

ObjectiveTraumatic brain injury(TBI)is a risk factor for neurodegenerative diseases,and current research conclusions on the effect of repeated mild traumatic brain injury(r-mTBI)on neurodegenerative diseases are still controversial.Neurodegenerative diseases are mainly manifested by the accumulation of misfolded protein aggregates in the brain,neuroinflammation,axonal and synaptic dysfunction,neuronal loss,and behavioral and cognitive disorders.Previous studies on brain neuropathology and behavioral cognitive changes after r-mTBI have different results,and the effect of r-mTBI on neurodegenerative diseases is still incomplete,and its pathological changes and related mechanisms still need to be studied.This study aims to clarify the neuropathological and behavioral cognition changes in the rat model of r-mTBI at different time points after the injury,and to further study its mechanism on the neurovascular unit.MethodsThe 12-week-old Sprague-Dawley(SD)rats were used to construct the r-mTBI model,through animal behavior experiments,including open field,balance beam,screen test,sucrose preference test,and object recognition test to detect the neurological function and cognitive changes of animals after r-mTBI;At the tissue level,use optical microscope(HE staining)to detect the overall pathological changes of the brain tissue,and use transmission electron microscope(TEM)to detect the changes in the ultrastructure of the neurovascular unit;Finally,at the molecular level,use immunohistochemistry and Opal multiple immunofluorescence detecte the expression and their positional relationship of A β 1-42,p-Tau,IBA-1 positive microglia,GFAP positive astrocytes,MAP-2 positive neurons and axons.Results1.Selecting 12-week-old male SD rats to construct the r-mTBI model,then the rats were scored by the neurological function score,which shows that there is acute neurological damage;2.On the 15 th day and the 6th month after r-mTBI,the rats were subjected to a sucrose preference test,and no depression was detected in the rats;object recognition test was carried out on the rats at the 6th month after r-mTBI,which shows that the memory of r-mTBI rats was impaired;3.After cerebral perfusion of r-mTBI rat,use hematoxylin-eosin staining to observe the pathological changes of rat cerebral tissue,no bleeding,contusion were observed;and measure the thickness of cortex and corpus callosum at DPI 6 m,which became thinner;4.At the molecular level,use immunohistochemistry experimental technology detecte the expression of MAP-2,GFAP,IBA-1,p-Tau,A β 1-42 in the brain tissue of r-mTBI rats;The expression of MAP-2,GFAP,IBA-1,p-Tau,and Aβ1-42 in the brain tissue of r-mTBI rats was detected by immunohistochemistry experimental technology.It was observed that the continuous activation of microglia and increased expression of p-Tau and Aβ1-42 then returned to normal in the acute phase of injury,loss of MAP-2 positive neurons,continuous activation of microglia and increased expression of p-Tau and Aβ1-42 in the chronic phase of injury;5.Using Opal multiple immunofluorescence technology to co-localize MAP-2,GFAP,IBA-1,p-Tau,Aβ1-42 in the brain tissue of r-mTBI rats,we observe and analyze that p-Tau may be produced by neurons and phagocytosed by microglia,Aβ1-42 may be produced in neurons and metabolized through BBB;6.Observation of the ultrastructure of the axon and neurovascular unit of r-mTBI rats by transmission electron microscopy.The results showed that there was axonal injury in the acute phase and the capillary in NVU was compressed and deformed by swollen astrocytes ends.In the chronic phase of the injury,the axonal injury recovers to a certain extent,but the NVU structure is seriously damaged.ConclusionsAll in all,in the early stage of r-mTBI,the expression of p-Tau and Aβin rat brain tissues increased temporarily,microglia continued to activate and proliferate,axons were damaged,and capillaries were compressed and deformed;in the late stage of injury,p-Tau,A β expression increased again,microglia continued to activate,neurons were lost,cortex and corpus callosum became thinner,NVU structure was destroyed,and memory impairment in rats.