Controlled cortical impact is easy to standardize across subjects and experiments and allows for the application of the entire spectrum of traumatic brain injury to precisely defined regions of the brain. Demonstrating this procedure is Mecca Islam, a research technician in my laboratory. This technique remains the most consistent and reproducible form of inducing traumatic brain injury in rodents.
Before beginning the procedure, attach the impacting device to the stereotaxic operating frame. Se the actuating device with the desired biomechanical parameters for the appropriate experimental velocity and well time. Don new personal protective equipment and sterile gloves and confirm a lack of response to toe pinch in the anesthetized experimental mouse.
Use clippers to shave the fur for the surgical site and apply ointment to the animal's eyes. Then place the mouse into the operating theater and prep the shaved skin with three sequential iodine based and alcohol surgical scrubs. To induce a controlled cortical traumatic brain injury, first use a scalpel to make a one centimeter incision along the midline of the scalp to expose the skull.
Retract the scalp from the operative site and identify the sagittal and coronal sutures on the exposed skull. To perform a craniectomy, equip a microdrill with a five millimeter trephine drill bit to activate the drill at maximum speed and apply the bit perpendicular to the skull two millimeters to the left of the sagittal suture and two millimeters rostral to the coronal suture with gentle even pressure. A slight give will be felt when the drill penetrates the skull.
Use forceps and a small gauge hypodermic needle to remove the bone flap, fully exposing the underlying dura mater and rotate the impacter tip into the operative field. Secure the bilateral temporal bones between the miniature ear bars of the stereotaxic frame and lock the incisors within the incisor clamp to create a stable three point hold on the mouse head. Lower the tip until it makes contact with the exposed dura mater.
The contact sensor of the instrument will make an audible tone to alert that contact has been made. Retract the impacting tip from the zero point and lower the impacter position on the stereotaxic frame to set the desired impact depth. Then active the impacter on the actuating device before rotating the device back out of the field to allow the animal to be removed from the frame.
Immediately after the injury, apply direct pressure from a sterile cotton tipped applicator to the skull and injured cortical surface to control any bleeding and use a fresh applicator to dry the skull. Close the scalp over the craniectomy according to standard techniques and administer postoperative analgesia. Then place the animal in the lateral decubitus recovery position in a clean pre-warmed cage with monitoring until full recumbency and measure the body weight every three days throughout the course of the experiment.
Delivery of the injury as demonstrated results in a subdural intraparenchymal and subarachnoid hemorrhage. Histologic evaluation of traumatic brain injury brain tissue sections after severe injury reveals a significant ipsilateral cortical and hippocampal loss as well as contralateral edema and distortion. MR imaging of severely injured brains also demonstrates progressive tissue loss and replacement by cerebra-spinal fluid.
Controlled cortical impact induces a reliable and consistent injury that is capable of producing a wide range of clinically applicable brain injuries. Our controlled cortical impact method generates a murine model of severe traumatic brain injury for behavioral and imaging analysis and produces tissue for molecular and cellular analysis.
