This article describes a method for measuring blood flow in the middle cerebral artery (MCA) of anesthetized mice using a laser Doppler probe. The procedure involves surgical exposure of the MCA and careful placement of the probe to ensure accurate readings of blood flow.
The middle cerebral artery, or M-C-A, is a prominent brain vessel that supplies oxygenated blood to the cerebrum.
To measure the blood flow within the MCA, place an anesthetized mouse in the prone position. Make a small incision on the scalp between the left ear and the left eye to locate the temporal skull bone. Cut the adjacent muscle layers and retract them to visualize the MCA beneath the skull bone.
Position the probe holder containing the laser Doppler probe over the MCA. This step allows the probe to be implanted close to the artery. Apply surgical glue to restrain the probe in its position. Using more glue, close the skin around the implanted probe and cover the wound site.
Connect the probe to a laser Doppler device. The probe focuses a laser beam at a particular frequency on a narrow region of the MCA. Subsequently, the red blood cells flowing in the artery absorb the laser beam.
Being in motion, these cells scatter the laser, causing a Doppler shift—an apparent change in the frequency of the emitted waves. The detector captures these minute frequency shifts to measure blood flow within the artery.
Prepare a holder for the laser Doppler probe by cutting the tip of a 10-microliter pipette tip. Once the mouse is completely anesthetized, place it in a prone position in the operation area. Gently insert the rectal probe to monitor the temperature throughout the surgical procedures. After disinfecting the surgical site, cut the scalp between the left ear and the eye to expose the skull bone.
Next, cut and retire the temporal muscle to visualize the multiple cerebral arteries or MCA beneath the skull. Fix the outer part of the tip, holding the laser Doppler probe or fiber on top of the left MCA with glue, and close the skin so that the skin is glued, as well. Apply two to three drops of hardener glue to speed up the process. Make sure that the laser Doppler fiber is not glued and can be easily removed from the tip holder at any time.
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