Study On The Degree Of Secondary Functional Injury Of Rat Brain Stem Pyramidal Tract Based On Grip Strength And Motor Evoked Potential

Background and Purpose:In recent years,approximately 60000 people have died and 250000 have been disabled due to road traffic accidents in China.The casualties caused by road traffic accidents constantly threaten the health and safety of the public.The World Health Organization（WHO）reports that the number of deaths and injuries caused by car accidents worldwide has reached 1.35 million annually,with up to 50 million disabled.According to data from the National Bureau of Statistics,head injuries account for a relatively high proportion of traffic injuries,ranging from 25%to 41%.The research on the biomechanical mechanism of craniocerebral impact injury has achieved many practical results.The current evaluation criteria for craniocerebral injury often use parameters such as bleeding,fractures,edema,and soft tissue deformation as descriptive indicators of the severity of craniocerebral injury.These indicators more reflect the morphological changes of neural tissue and are difficult to reflect the functional changes that occur after neuronal axonal injury.In craniocerebral traffic injury,the brain stem is the most common part of the injury.The pyramidal tract passes through the ventral side of the brain stem,which is the most direct way for the cerebral cortex to control the body movement.In the event of a traffic accident,if the pyramidal tract is involved due to brain stem injury,the compound nerve action potential（CNAP）signal transmitted in it will inevitably attenuate or change,and then the downstream motor evoked potential（MEP）signal coupled with this nerve fiber and the grip strength（GS）signal dominated by neuromuscular will attenuate or change.In addition,axonal injury may initially be mild after head injury,but if a cascade reaction occurs subsequently,it may also develop into a more severe secondary brain injury.There are reports that the network structure between neurons after brain injury can be repaired,so using functional brain injury indicators to measure the degree of brain injury should be more accurate and effective.Considering the aforementioned traffic injuries and their current research status,this study,based on the theories and methods obtained by predecessors,takes the brainstem pyramidal tract and its signaling pathway as the research object.Using animal experiments,MEP,and GS correlation research methods,the study investigates the degree of limb disability in rats under different heights of impact induced brain stem pyramidal tract injuries using limb dysfunction signals（GS,MEP）in the brainstem pyramidal tract pathway as the medium,And conduct experiments and analysis on the situation of secondary brain injury,exploring the quantitative relationship between the degree of nerve loading and the degree of functional injury.Research method:The main research methods of this project are as follows:1)Conduct literature research,review the current status of injuries and disabilities caused by traffic accidents,the biomechanical research status of car collisions,the biomechanical mechanisms of brain injury,identification and detection methods of brain stem pyramidal tract injury,and quantitative methods of functional injury,etc.,to determine the research objectives,methods,and research plan of this topic.2)Establish a quantitative injury platform for the brainstem pyramidal tract based on the relevant research parameters of the classic Marmarou model improved by Wayne State University.Establish the behavioral detection method and the electrophysiology detection method of SD rats.3)Explore experimental boundary conditions.In the detection of motor evoked potentials,it is necessary to accurately locate the pyramidal tract of the brain stem for measurement,and analyze the effects of narcotic drugs on behavior and neuro electrophysiology.4)Using a mechanical injury model of the rat brainstem pyramidal tract,traumatic axonal injury（TAI）was induced by striking at heights of 1.25m and 2.25m.Based on the cone bundle strain/strain rate corresponding to the 1.25m and 2.25m impact conditions obtained through finite element simulation in Dr.Runzhou’s literature from Wayne State University,rats were divided into 1.25m group,2.25m group,and undamaged normal control group.GS and MEP signals under different injury conditions were detected and studied to observe the changes in rats before and after injury on the 1st,3rd,5th,7th,14th,28th,and 42nd days.Conclusion:Conclusion 1:Based on the relevant research parameters of the Marmarou model improved by Wayne State University,collision velocity testing was conducted on the mechanical damage model of the rat cone bundle in our research group,ensuring that the collision generated under the impact conditions of 1.25m and 2.25m meets the velocity range given in the paper;The polyurethane foam used in the model has a large difference in elastic modulus,has a nonlinear response,absorbs a lot of energy at the moment of collision,and plays a buffer role.The sponge compression experiment was carried out,and the best foam buffer material was selected by referring to the stress-strain curve in the literature of Dr.Runzhou of Wayne State University to reduce the experimental error.Conclusion 2:Using a combination of SD rat brain stereotaxic locator and brain atlas to accurately locate the position of the pyramidal tract,the MEP stimulation electrode is placed at the front end of the pyramidal tract to measure stable MEP signals.Therefore,the position of the stimulation electrode for MEP measurement at the pyramidal tract site is determined to be at the level of the ventral and binaural regions.By observing the changes in GS and MEP signals in the undamaged normal control group rats within 42 days,it was found that anesthesia had no significant cumulative effect on the changes in GS and MEP signals in rats.Conclusion 3:At a strike height of 1.25m,the strain/strain rate is 0.138/0.285ms^-1;Under the condition of a striking height of 2.25m and a strain/strain rate of0.168/0.283ms^-1,it was found that the maximum GS of the rat GS decreased,the amplitude of the MEP wave decreased,and the incubation period extended.The experimental results showed that the GS and MEP signals of the injured group rats decreased significantly in the early stage of injury,and then gradually recover after three days,reaching the maximum recovery level between 28 and 42 days.The overall recovery trend of the injured group rats was roughly the same.There were significant differences in GS and MEP data between the 1.25m and 2.25m groups of rats and the undamaged normal control group,and there was a high correlation between GS and MEP.As the degree of injury increases,the maximum GS continues to decrease,and the amplitude of MEP waves continues to decrease.In the early stage of injury,the amplitude of MEP waves is significantly reduced due to damage to some nerve fibers and obstruction of signal transmission,resulting in functional impairment of MEP and GS amplitudes;In the later stage of injury,due to the reconstruction of the network between neurons and the reconstruction of signal transduction pathways,the amplitude of MEP and GS gradually recovers.Data analysis shows that in cases of significant damage,the correlation between GS and MEP is stronger,and functional damage is more significant after nerve fiber damage.From the GS-MEP mathematical model,it can be found that in the case of small damage,MEP is more sensitive in the early stage,and small changes can show significant changes in GS,while MEP is not sensitive in the later stage;In cases of significant damage,MEP is relatively sensitive in both the early and late stages.The Degree of Craniocerebral Injury-PSSR（Production of Strain and Strain Rate,PSSR）model constructed in the paper based on experiments can provide data reference for risk assessment of functional brain injury and data support for the formulation of brain injury standards.To sum up,this study established a mechanical injury model of the pyramidal tract in the brain stem of rats,and quantitatively analyzed the degree of functional injury of the pyramidal tract in the brain of rats by using the methods of behavioral and neuro electrophysiology,and preliminarily established the change relationship of GS and MEP with time after injury,including the recovery trend;Established the interrelationships and models of the GS-MEP change process;In addition,the paper preliminarily established a PSSR functional injury degree model of the rat brain stem pyramidal tract under load,which can provide data support for predicting the risk of brain functional injury and formulating injury standards.