inducing and monitoring repetitive mild traumatic brain injury (rmtbi) in mice using a modified fluid percussion device

rmTBI Induction in Mice via a Closed-Head Injury Method

Mild TBI, including concussion and sub-concussion, account for the majority of all TBI cases (&#62;80% of all TBI)1. Mild TBI commonly results from falls, traffic accidents, acts of violence, contact sports (e.g., football, boxing, hockey), and military combat2,3. Mild TBI can lead to neurobiological events that affect neurobehavioral functions throughout the patient&#39;s lifetime and increase the risk of neurodegenerative diseases4,5,6. Animal models provide an efficient and controlled means to study mild TBI, with the hope of further enhancing the diagnosis and treatment of mild TBI. Various models for mild TBI have been developed, such as the controlled cortical impact (CCI), weight drop (WD), fluid percussion injury (FPI), and blast-TBI models7,8. No single experimental model can mimic the entire complexity of TBI-induced pathology9,10. The heterogeneity of these models is advantageous for addressing the diverse features associated with mild TBI patients and investigating the corresponding cellular and molecular mechanisms. However, each animal model of TBI has its limitations3, limiting our current knowledge concerning animal mild TBI and their clinical relevance.
The WD and CCI models are utilized to replicate clinical conditions such as cerebral tissue loss, acute subdural hematoma, axonal injury, brain concussion, blood-brain barrier dysfunction, and even coma following TBI3,11,12. The WD model involves inducing brain damage by striking either the dura mater or skull with freely falling weights. The impact of a weighted object upon an intact skull can replicate mixed focal/diffuse injuries; however, this method is associated with poor accuracy and repeatability of the injury site, rebound injury, and a higher mortality rate due to skull fractures3,11,12. The CCI model involves applying air-driven metal to impact the exposed dura mater directly. Compared to the WD model, the CCI model is more accurate and reproducible, but it does not produce diffuse injury due to the small diameter of the impacting tip11. During FPI modelling, the brain tissue is briefly displaced and deformed by percussion. FPI can induce mixed focal/diffuse injury and replicate intracranial hemorrhage, brain swelling and progressive gray matter damage after TBI. However, FPI has a high mortality rate due to brainstem damage and prolonged apnea3,12. The craniotomy involved in conventional WD, CCI, and FPI models can lead to cortical contusion, hemorrhagic lesions, the damage of the blood-brain barrier, immune cell infiltration, glial cell activation, prolonged modeling time, and possible fatal outcomes3,12.
Mild TBI is characterized by a GCS (Glasgow coma scale, GCS) score within the range of 13 to 152. Mild TBI can be either focal or diffuse and is associated with both acute injuries, such as breakdown of cellular homeostasis, excitotoxicity, glucose depletion, mitochondrial dysfunction, blood flow disturbance, and axonal damage, as well as subacute injuries, including axonal damage, neuroinflammation, and gliosis2,3. Despite significant progress in delineating the intricate pathophysiology of TBI, the underlying mechanisms of mild TBI/rmTBI remain elusive and require further investigation9. Given that CHI is the most common type of TBI12, this protocol presents a novel approach to creating a more precisely controlled mouse model of rmTBI using a modified FPI device to perform impact in a thinned-skull window13. By avoiding craniotomy-induced injuries, variable skull thickness and shape-induced inaccuracies, and rebound injury, this approach aims to overcome the main disadvantages associated with the WD, CCI, and FPI models. Applying FPI impact on the thinned-skull window is convenient for evaluating cerebral vessel damage following rmTBI and helps minimize high mortality rates in some models, resulting in a closer resemblance to the clinical features of TBI patients.

Author Spotlight: Optimizing Rodent Models for Investigating the Mechanisms and Rehabilitation in Repeated Mild Traumatic Brain Injury

Modified Mouse Model of Repetitive Mild Traumatic Brain Injury Incorporating Thinned-Skull Window and Fluid Percussion

Traumatic brain injury is a significant health issue for the worldwide population. Our main focus is on the mechanism of TBI and the rehabilitation, with a particular focus on the mild TBI and the neuroprotective effects of access. No single animal models can adequately mimic all aspects of the human TBI due to the complexity of a clinical TBI.Each model has its own advantages and the disadvantages when implemented for TBI research. These challenges necessitate the optimization of animal models. The closed-head injury is a common message for making the rodent models of a repeated mTBI.However, this message is susceptible to many factors, including the impact methods used and the anatomy of the rodent scaffold. In our research, we combine the thinned-skull window and the fluid percussion measures to minimize the inflammation due to the craniotomy and the fluid percussion, and produce a more precise model of our repeated mTBI. Overall, the modified closed-head injury associated to repeated mTBI represents a valuable tour for researchers investigating the underlying mechanism that contribute to focal and diffuse pathological changes in repeated mTBI.

Inducing and Monitoring Repetitive Mild Traumatic Brain Injury (rmTBI) in Mice Using a Modified Fluid Percussion Device

To begin, randomly allocate the mice into either the control or repetitive mild traumatic brain injury group. Acclimate the mice in separate cages one week before the experiment. Carefully inspect the modified fluid percussion device for signs of leakage and ensure that there are no bubbles present within the system.After anesthetizing and trimming the fur on the mouse's head, disinfect the scalp with 75%ethanol. Secure the mouse using non-terminal ear bars in a stereotaxic frame and place an isothermal heating pad underneath to maintain body temperature at 37 degrees Celsius. Carefully clean the surgical area using a saline-soaked cotton swab.After making a 1.5-centimeter incision along the midline of the scalp, use a flat-tipped micro drill bit and a microsurgical blade to create a thin skull window in the right frontal motor cortex. Locate the surgical site at 1.5 millimeters anterior to the bregma and 1.3 to 2.0 millimeters lateral to the midline. Attach an adjusted female Luer lock to the thin skull site.Transfer the mouse from the stereotaxic apparatus to the Impactor platform. Connect the female Luer lock to the male Luer lock at the end of the fluid percussion injury device tubing. To apply fluid percussion injury impact, raise the pendulum to the designated degree along the protractor on the device and release the pendulum using software control, achieving a percussion intensity of approximately two atmospheres.Following the impact, immediately detach the Luer lock connection and transfer the mouse to an isothermal heating pad for recovery. After the second traumatic brain injury, carefully remove the female Luer lock and dental cement. Suture the scalp with tissue adhesive and use flat forceps to pinch the scalp to facilitate the adhesive process.To alleviate post-surgical pain and discomfort, apply a one-to-one mixture of erythromycin and sodium diclofenac ointment to the wound. Finally, transfer the mouse to an isothermal heating pad for recovery. Analysis at seven to 12 days post-injury using the Morris water maze showed that repeated mild traumatic brain injury led to impairments in spatial learning and memory in mice.The open field test conducted at six days post-injury showed no significant impact on the mice's general locomotive abilities, but induced significant anxiety and altered exploratory behavior in repeated mild traumatic brain injury mice. The Y-maze test performed at eight days post-injury revealed impairments in both spatial working and reference memory in repeated mild traumatic brain injury mice.

Research

JoVE Journal

Neuroscience

Mild traumatic brain injury is a clinically highly heterogeneous neurological disorder. Highly reproducible traumatic brain injury (TBI) animal models ...