Athletes absorb several hundred mild traumatic brain injuries (mTBI)/concussions every year; however, the consequence of these on the brain is poorly understood. Therefore, an animal model of single and repetitive mTBI that consistently replicates clinically relevant symptoms provides the means to advance the study of mTBI and concussion.
The overall goal of this mouse model of traumatic brain injury or TBI, is to create a reliable and reproducible method for examining the mechanisms that underlie concussive and sub-concussive brain injury. This method facilitates the investigation of key questions in the mouse TBI field such as, what are the physiological changes that occur in the brain after single or repeat concussion. The main advantage of this technique is that the injury device is specifically designed to allow repetitive head impacts without the risk of skull fracture or structural brain damage.
Before beginning the procedure, turn on the compressed air and initialize the high velocity pneumatic impactor to a pressure setting of 861.85 kilo pascals. Calibrate the machine to the desired velocity and dwell time. Place the gel filled base, such that the mid line is perpendicular to the trajectory of the impactor tip and record the weights of all of the mice to be used.
Next, transfer and anesthetize the mouse to the MTBI apparatus, placing the head on the gel pad with the skull perpendicular to the impactor tip and tape over the mouse head, to create a flat surface and to ensure the ears are away from the impact site. Lower the polytetrafluoroethylene impactor tip to align with the sagittal mid line in the center of the head, just behind the eyes. The impator tip is 10 millimeters in diameter and will cover the majority of the head area.
Adjust the impactor until it is just touching the surface of the mouse's head. Then, retract the tip and manually dial down the required deflection depth to 7.5 millimeters. Now, arm the data acquisition control system and to press the trigger button to impact the mouse's head.
Immediately after the final impact, transfer the mouse to the bench top in the supine position, without the nose cone and use a stopwatch to measure the latency of the return of righting reflex to determine the loss of consciousness time and the time to return, of spontaneous ambulation. Upon recovery to normal behavior, return the animal to its home cage. The return of the righting reflex time, is an acute neurological evaluation of injury severity that can be used to quantify the loss of consciousness after MTBI.
For example, animals that receive a single MTBI, demonstrate significantly increased loss of consciousness and ambulation times, compared to sham animals. In repeat injury paradigms, loss of consciousness and ambulation times are significantly increased on all of the testing days. IBA one staining for microglia and macrophages reveals changes in experimental mouse inflammatory profiles, after repeat MTBI, compared to single MTBI or sham animals.
Repeat MTBI animals display a strong IBA one immunoreactivity that is limited to the optic tract, with no evidence of gray matter inflammation in the cortex, hippocampus or other brain areas. Once mastered, this technique can be done in five minutes if it is performed properly.
