Begin with an immobilized, anesthetized mouse with a shaved head.
Apply an eye ointment and disinfect the scalp with iodine.
Remove the excess iodine, and cover the mouse with a surgical drape.
Make a midline incision to expose the skull and clean the wound.
Mark a circle on one side of the skull, targeting the brain cortex.
The cortex contains motor and sensory neurons crucial for signal transmission between the brain and the body.
Drill through the skull bone over the marking in a circular fashion, then remove the bone flap to expose the cortex.
Position a sterilized impactor probe over the exposed area. Hit the probe over the tissue to deliver high pressure.
This pressure induces trauma in the brain cortex, disrupting the motor and sensory neurons and impairing signal transmission.
Clear the wound and suture it. The mouse model with traumatic brain injury is ready for further experiments.
To perform a unilateral craniectomy, confirm a lack of response to toe pinch in the anesthetized mouse, and secure the mouse in a stereotaxic frame. Apply antibiotic ophthalmic ointment to the eyes with a sterile cotton swab, and iodine-based solution to the shaved scalp area. Remove the iodine with 70% ethanol, and cover the animal with a fenestrated surgical drape.
Make a 1.5 to 2-centimeter midline incision on the scalp, and use sterile cotton swabs to clean the wound and to clear the fascia left of the midline at bregma. Use an impactor probe to identify the craniectomy site, and set the x equals 0, y equals 0 stereotaxic reference point to bregma. Adjust the probe laterally to two millimeters left of the midline. Use a fine tip surgically safe marker to landmark a five-millimeter diameter circle around the presumptive impact area.
Raise and rotate the impactor out of position and complete the 5-millimeter circle. Briefly return the impactor into position to verify accuracy of the 5-millimeter circle. Then, raise and rotate the impactor out of position, and use a high-speed rotary micromotor kit hand tool equipped with a round tip of 0.6 or 0.8-millimeter bird drill bit to make an open hole in the skull at 70% to 80% maximum speed. Apply light pressure to the skull while drilling along the 5-millimeter circumferential outline to thin this border, and use forceps to lift the resulting bone flap.
Drilling through suture lines may present additional difficulty as the bone is interrupted and requires additional pressure. Blood vessels may be in close association, and therefore bleeding events are likely.
To induce a mild controlled cortical impact injury, clean the impactor probe with a sterile alcohol prep pad, and move the impactor probe back into position over the exposed cortex. Lower the probe until it touches the dura mater surface, and mark this position as z equals 0. Withdraw the piston, and move to z equals minus 1 millimeter, and discharge the piston to impact the cortex. Immediately raise the piston and move the arm out of position, and irrigate the cortex with a generous volume of saline, and use simple interrupted stitches and 5-0 silk suture to close the scalp incision.
