A Repetitive Concussive Head Injury Model in Mice

The overall goal of this procedure is to set up a repetitive concussive mouse model using a traditional impact system. These mice can help answer key questions in the mild traumatic brain injury, or TBI, modeling field about the impact of concussion on brain function. The main advantage of this technique is that electronic magnet impact system can be simply operated, and the process be controlled for delivering the impacts.

Begin by attaching a custom-made silicon rubber-coated metal tip, to an electromagnetic stereotaxic impact device, taking care that the flat bottom of the coated tip is parallel to the surface of the impact device probe tip. Next, place an anesthetized mouse in the prone position on a heating pad, and confirm a lack of response to toe pinch. Then, use a hair trimmer to completely shave the head, and apply ointment to the animal's eyes.

When the animal is ready, preset the velocity of the impact device to four meters per second, and the dwell time to 240 milliseconds on the control box. Place a soft heating pad under the animal's body, to keep the body temperature near 39 degrees Celsius. Then, use the blunt end ear bars to mount the mouse in the stereotactic frame in the prone position.

Use the Z driver to lower the impact tip close to the mouse's head. Move the X and Y drivers midway to the target coordinates, above the sagittal suture, to adjust the flat impact nine-millimeter diameter tip, taking care that one edge of the impact tip is vertically parallel to an imaginary horizontal line drawn between the two ears. To correctly set the impact depth, first set the X and Y channels on the digital stereotaxic control panel to zero, to make sure that there is no shift of the impact center after switching the tips.

Then move the additional probe tip to the impact site of the mouse's brain. Manually adjust the X and Y drivers to move the probe tip to the center of the impact area, and clip a contact sensor to the tail. Use the Z driver to move the impacter down until the probe tip touches the surface of the impact site, and set the Z channel on the stereotaxic control panel to zero.

Then, use the X and Y drivers to manually move the impact tip back to the impact area, until the X and Y drivers are zero. Then move the Z drive down until the control panel is showing the Z driver is at 4.00. And move the retract switch on the control box to retract the actuator.

Now click the impact switch on the control box to trigger an impact with a deformation depth of four millimeters, and use a timer to measure the time from the impact until the mouse's first breath. Then, transfer the animal to a warm pad with monitoring until it is fully recovered. To set up repetitive injury, give the mice additional injuries on days four, seven, and 10, after the initial injury.

An impact on the center of the head causes short-term unconsciousness, as defined by a transient termination of breathing. The brains exhibit normal morphology, with no obvious structural lesions or tissue damage from the impact observed histologically. In response to TBI, astrocytes are known to undergo certain changes, including activation, proliferation, or reactive gliosis.

Indeed, in the corpus callosum of repetitive concussive head injury mouse brains, obvious signs of astrocyte activation can still be observed at seven days after the last impact. Further, ferritin immuno-positive cells can be detected in the mouse cortex one day after the last impact, until at least seven days, suggesting that multiple impactions may result in cortical microbleeds. Once mastered, this technique can be completed in 15 minutes, if it is performed properly.

While attempting this procedure, it's important to remember to correctly position the impact side of the mouse brain. After its development, this technique paved the way for research in the field of TBI, to explore mild TBI effect, diagnosis and the potential treatment in model athletes. After watching this video, you should have a good understanding of how to set up a repetitive concussive mouse model, using a traditional impact system.