Modeling Repetitive Concussive Head Injuries in a Mouse Model

Begin by attaching the impact tip and probe tip to an impact device.

Next, secure an anesthetized mouse in a stereotaxic frame.

Position the impact tip between the interfrontal and lambdoid sutures, vertically aligned with an imaginary horizontal line between the ears.

Zero the X and Y channels on the stereotaxic control panel to prevent impact center shift when switching the tips.

Manually move the probe tip to the impact center and lower it to touch the impact site. Clip a contact sensor to the mouse's tail.

Zero the Z channel, then reposition the impact tip until X and Y are zero and Z reads minus four.

Apply the impact at a specific velocity.

Measure apnea—the time from the impact to the mouse's first breath—to determine the injury severity.

Allow the mouse to recover.

Repeat the impact at specified intervals. Repeated impacts rupture blood vessels in the brain, causing microbleeds and triggering astrocyte activation, mimicking a mild human-like concussion.

Begin by attaching a custom-made silicone 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 4 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 9-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 impactor 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 showing the z driver is at negative 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 4 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.