This article details a surgical procedure for drug delivery to the inner ear of an anesthetized mouse. It outlines the steps for accessing the posterior semicircular canal and administering a drug solution.
Begin with an anesthetized mouse placed in a right lateral position.
Make an incision behind the ear and dissect the underlying muscles to expose the semicircular canals.
Excise a small muscle piece for later use.
Locate the posterior semicircular canal or PSC, a fluid-filled duct within the inner ear.
Make a hole in the middle of the PSC and clean the area.
Take a cannula connected to a drug-filled micro-syringe, which is attached to a syringe pump.
Insert this cannula into the hole on the PSC and move it towards the crus commune, a region where the posterior canal merges with the anterior canal, to access the inner ear.
Inject the drug solution through the cannula into the inner ear, ensuring local drug delivery.
Post-delivery, remove the cannula and place the excised muscle piece into the hole to prevent leakage. Finally, close the incision with sutures.
Begin by placing the anesthetized mouse on a pre-heated electric pad. Set the temperature of the electric pad to approximately 37 degrees Celsius. Cover the animal's eyes with eye ointment, then shave the left postauricular region with an electric animal clipper, and disinfect the skin three times with 75% ethanol.
Next place, the animal in the right lateral position to facilitate surgery on the left ear. Make a one to 1.5-centimeter postauricular incision, three millimeters from the left retroauricular groove. Note, when the root of the pinna is defined as the origin, and the plane parallel to the calvarium as 3 to 9 o'clock, the posterior semicircular canal and the lateral semicircular canal are typically located about three millimeters from the root of the pinna between 2 and 3 o'clock.
Bluntly dissect the muscle covering the temporal bone with micro forceps to expose the posterior semicircular canal and lateral semicircular canal, whose margins are clearly visible as dark stripes in the temporal bone. Then, collect a small piece of muscle with micro-forceps, and let it dry.
Next, make a small hole in the middle portion of the posterior semicircular canal using a 26-gauge needle, such that fluid leakage through the hole indicates successful penetration of the bony wall of the posterior semicircular canal. Enlarge the hole to slightly larger than the diameter of the polyamide tubing.
Then, clean the effusion surrounding the whole of the posterior semicircular canal using a cotton pellet. Insert the tip of the polyamide tubing gently into the posterior semicircular canal towards the crus commune to a depth of one to two millimeters.
Start the injection by pressing the 'Run' button on the pump. After the injection, wait two minutes to allow the reagent to spread. Then, remove the injection cannula, and immediately place the muscle into the hole in the posterior semicircular canal.
Return the separated muscles and subcutaneous tissues together. Suture the incision using a 5-0 suture. Disinfect the incision region with povidone-iodine. Finally, after the surgery is complete, position the animal in the right lateral position on an electric pad preheated to 37 degrees Celsius for recovery.
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