This article describes the procedure for creating a calvarial window in an anesthetized mouse, allowing access to the brain for experimental purposes. The method involves careful drilling through the skull while ensuring the animal's stability and safety.
The calvaria is the top part of the skull, which covers and protects the cranial cavity - the hollow space within the skull that encloses the brain. It consists of five bones connected by fibrous tissue called sutures, including the coronal, sagittal, and lambdoid sutures.
To generate a calvarial window for accessing the brain, first, take an anesthetized mouse with its head shaved.
Secure the animal onto a stereotactic unit, stabilizing its skull. Maintain its body temperature using a heating pad.
Then, sterilize the scalp and make a small incision along the central median portion of the cranium.
Subsequently, orient the drill perpendicular to the bregma - the intersection point of the coronal and sagittal sutures.
Position the drill at the intended area, at a suitable distance from the bregma.
Carefully initiate the drill onto the skull, moistening the target site to prevent tissue damage from heat buildup.
Drill with shallow depth through the calvaria to form the calvarial window.
Once the window is created, the mouse can be used for further experimental procedures.
Before beginning the procedure, twist the stage lock on the drill to allow a drill bit adaptor and sterile 1-millimeter drill bit to be inserted into the drill, and manually tighten the bit locks to lock the drill. Attach the drill to the stereotactic frame.
After confirming a lack of response to pedal reflex, place the anesthetized mouse onto the frame, and use the blunt end of a cotton-tip applicator to position the teeth in the trough of the mouthbar.
Press the left ear bar against the medial canthus of the left ear to stabilize the skull, and use the screw on the stereotactic frame to lock the skull into place. Then, secure the other side of the skull with the right ear bar in the same manner.
To make a calvarial window, clean the scalp with three sequential, alternating betadine solution and 70% ethanol scrubs, and use a sterile scalpel to make a 3-millimeter incision through the skin along the central median aspect of the cranium following the sagittal suture line.
Identify and orient the sterile drill bit perpendicular to the bregma, making sure to reset the digital Vernier scale to zero, and move the drill bit 2 millimeters lateral to the sagittal suture and 1 millimeter anterior to the coronal suture.
Move the skin away from the drill, and using the highest speed and paying attention to the landmarks, carefully drill a hole roughly 0.5 millimeters deep through the calvaria, cooling the drill site with drops of sterile saline as necessary.
Once the calvarial window has been made, carefully raise the drill and remove the drill from the stereotactic frame.
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