Establishment Of A New Rat Model Of Blast-related Diffuse Axonal Injury

Research Background：Explosive weapons are getting to be the major lethal weaponsin the modern high-tech local wars, and the blast-related traumatic brain injury (bTBI),which is known as the "feature damage" in war has attracted great attention. Blast-relatedtraumatic brain injury with the characteristics of multiple trauma, multi-site damage, andthe combined injury,is the most common form of damage in nuclear weapons, conventionalwarfare, mining, and terrorist attacks. Since Gulf War, milestone of modern high-tech wars,explosive weapons have gradually become the main lethal weapons in modern warfare.Particularly high rare of the head in the site of injury in the explosion, blast injury is themajor head injury class, the TBI in the Gulf War injuries accounted for70-90%of alltraumatic brain injury.Blast brain injury is an important research of modern militarymedicine,Emergency Medicine and trauma medicine.Blast-related traumatic brain injury is a rather complex mixed injury, including theprimary injury (injury caused by blast waves), secondary injury (injury caused byhigh-speed shrapnel and fragments), thirdly injury (injuries caused by the throwing, rotatingand distorting of shock waves or caused by the squeezing in the collision of objects), fourthinjury (damages caused by other non-high-speed injury factors, such as harmful gases, heat,light, etc.), these injury factors often coexist, causing not the brain injury alone, but multiinjury,while the injury of other parts of the body might also affect the evolution of braininjury, making the research contents of the brain injury more varied, complicated anddifficult. There’s no mature and stable animal model of brain blast injury so far, the majorinjury mechanisms include the hydraulic injury, shock tube injury and heavy pound injury.We had designed a pure brain blast injury model with real blasts with the protection of thetrunk at the previous stage, and it was well accepted after the publication, thus laid areliable foundation for this study.Diffuse axonal injury(DAI) is a common cause of the severe disability, vegetative state and death of the patients with traumatic brain injury, and it often get characteristics assevere condition, poor prognosis, treatment difficulties and high mortality rate.Currently, aconsistent understanding of the mechanisms of DAI has been reached, that is linear orangular acceleration is generated due to the external forces at first, then shearing force isgenerated within the brain tissue, resulting in axonal nerve damage or even fracture, andcapillary rip. However, the relationship between DAI and various types of brain injury isstill unclear, no literature has ever reported its occurrence in bTBI.For the study of DAI, scholars have created a variety of animal models, include:①instantaneous rotation injury model: Gennarelli (1982) etc.designed a shearingstress-induced axonal injury model by instantaneous rotation head to cause angularacceleration and generate shearing stress in the brain;②hydraulic shock injury model:Dixon etal conducted studies on axonal injury by drilling on the middle of animal skull andcausing injury to the midline structure with the impact;③pound load injury model:Mamarou, etc.improved the pound load injury model that applied for the research of localcraniocerebral trauma, by placing the rats on foam pads, glue a steel ingot with thegutta-percha on the skull fornix of rat, then caused DAI with weight falling to strike theingot;④complex injury model of rotation and pounding:by combining the instantaneousrotation injury model and the pound load injury model, Hong-Cai Wang caused DAI withinstantaneous linear acceleration and angular acceleration to induce compound injury;⑤acceleration or deceleration injury model: make the whole brain tissue withstand the load ofinertia by the accelerated or decelerated motion, and generate changes of stress in the braintissue, thus resulting in the neurons and fiber injury;⑥stretch injury model: Gennarellietal[8] exerted traction force in vitro directly on the nerve fibers, believing that it can leadto the same injuries caused in the rotation, acceleration or deceleration. There is no realanimal model of DAI blast injury has ever been found to be applied yet.ObjectiveBased on DAI mechanism,a new bTBI model device is going to be manufacture,in orderto make the rat head an instant high-speed swing, resulting in lines or angular acceleration,shear force generated in the brain tissue,and leading to axonal damage and even rupturecapillaries tear,using real explosives blast.The aim of these research is to establish a stableexplosive DAI animal model and so providing a convenient experimental platform for bTBI associated with DAI situation, and open up a new direction to DAI animal model.Methods1. New explosive devices design: Base on rat bTBI model,some reconfigurations aremade,designed the fixed program of rat head,combine of the three parts witch are explosionsource, stress test systems and explosion protected space as a whole, fully consider themodel accuracy, repeatability and portability.2.26adult SD rats with half male and half female weighed150±10g were randomlydivided into the experimental group (n=16) and the control group (n=10).The frontal,parietal and occipital cortex of rats in the experimental group were exposed, and noexposure in the control group, then a self-designed device of rat craniocerebral blast injurywas applied.A paper electric detonator equivalent to400mgTNT exploded to causeinjury.Then a high-speed camera was employed to measure the biomechanical parametersof the sagittal head swing,Physical and behavioral changes are also observed,magneticresonance imaging (MRI) and T2-weighted gradien-techo imaging of head were conductedat2,12,24,48h after craniocerebral injury separately. The rats were sacrificed48h afterinjury for the pathologic examination of brain stem.Results1. A new rat model of blast-related diffuse axonal injury is successfully manufectured;2. The head of rats in the experimental group swung curvedly at the sagittal plane, theswing axis was roughly at the cervical-thoracic junction, with the maximum angularvelocity of about248rad/sec, the maximum angular acceleration of about212krad/sec2;Head MRI indicated the signal changes on the lateral dorsal of upper brain stem in14ratsin experimental group,including6cases associated with the frontal and parietal cortex andcerebellum at the top of the ventrolateral contusion;1case of parietal cortex contusion wasfound in the control group.Morphological features observed by light microscope: retractionball (RB) was detected in14cases of rat brain stem with MRI signal changes, and brainstem was normal in the control group.There were14cases (87.5%) in line with theexplosive DAI diagnosis in experimental group but no DAI rats in the control group,significant difference between the two groups (P <0.05).Conclusions:New rat model of blast-related diffuse axonal injury applications spring tooth hook relatively fixed head, to reduce injury when the head and trunk relative displacement.Tosimulate the possible presence of a real explosion, according to the injury strength andinjury results, we can establish more stable explosive rat DAI model.