This article describes a method for targeted delivery of substances to the brain in anesthetized mice by bypassing systemic circulation. The technique involves manipulating the common carotid artery and external carotid artery to infuse a test substance directly into the brain parenchyma.
Take an anesthetized mouse with an exposed common carotid artery or CCA, which bifurcates into the external carotid artery or ECA and the internal carotid artery or ICA.
Tightly suture the distal ECA, place a loose knot near the bifurcation, then clip the CCA and ICA to restrict blood flow.
Incise the ECA, then insert a capillary connected to a syringe containing the test substance.
Advance the capillary between the bifurcation and the CCA clip, then secure it by tightening the proximal ECA knot.
Remove the ICA clip and infuse the substance for targeted delivery to the brain while bypassing systemic circulation.
The substance crosses the blood-brain barrier to reach the brain parenchyma.
Once the ECA and ICA are exposed, use forceps to place a segment of 1 centimeter nylon suture under the external carotid artery, then place a second 1 centimeter segment. Then tie a permanent knot at the highest point possible of the ECA.
At the lowest point possible of the ECA immediately above the CCA bifurcation, tie a looser removable knot. Then use vessel clips to close the CCA at the lowest possible point and to close the ICA.
Properly closing the internal carotid artery before making a small cut in the external carotid artery will prevent bleeding.
Now, using microdissection spring scissors, make a 2-millimeter cut in the ECA between the two knots.
It is important to keep the cut small, as a large cut will cause leaking of the substance to be infused.
Assemble the infusion system by attaching 6 inches of capillary tubing to a tuberculin syringe containing 250 microliters of the substance to be infused. Then gently insert the tip of the capillary tubing into the incision in the ECA. Keep advancing the tip until it reaches midway between the bifurcation and the clip on the CCA.
Tie down the lower ECA knot. Verify that the knot is loose enough to allow capillary fluidity and tight enough to prevent leaking. Then, remove the clip from the ICA. Gently apply pressure to the syringe piston, allowing substance infusion at approximately 10 microliters per second.
Following infusion of the test substance, place the clip back on the ICA. Gently remove the capillary tubing, then tie down the lower ECA knot completely. Remove the clip from the ICA and the CCA. Then remove the retractor or tissue hooks and pillow.
Clean the area to be sutured with sterile saline and then close the incision using nylon sutures. After administering an approved anti-inflammatory agent and analgesic to alleviate postoperative discomfort, place the animal in a cage on a heating pad for at least one hour and monitor recovery.
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