The overall goal of surgical labyrinthectomy in the rat is to study the vestibular system and vestibular compensation processes. This method can have acute complications regarding the vestibular compensation process of the vestibular function loss. The main advantage of this technique is that it is a simple labor and rapid method.
Generally, individuals new to this method will struggle to preserve the stapes artery. Because the stapes artery is close to the drilling site. Begin by covering autoclaved surgical instruments with a sterile pad and disinfect the operating area with seventy percent ethanol.
After anesthetizing the rat using an institutionally approved method, place the rat on a warming pad set at 42 degrees Celsius. Apply lubricant eye ointment to both eyes of the rat to prevent eye dryness while under anesthesia. Place the rat on its right side.
Then, shave the fur over the surgical area, and disinfect the site with seventy percent ethanol. Place a sterile drape and maintain sterile conditions during the surgery. Inject one percent lidocaine hydrochloride subcutaneously into the left retroauricular area.
Then, after using a number fifteen scalpel blade to make a five centimeter retroauricular incision, use iris scissors to separate the muscle and fascia and expose the external auditory canal. Then, slightly open the external auditory canal and widely expose the tympanic membrane. Use forceps to remove the tympanic membrane and the ossicles except for the stapes.
Use iris scissors or the number fifteen blade to detach the muscles on the lambdoidal ridge. Use a drill fitted with a two point one millimeter cutting and two point one and one point four millimeter diamond burr, to drill the tympanic bulla bone around the point of exit of the facial nerve at low speed. Take a moment to identify the stapedial artery.
This is the single most critical step. Careful handling of the drill is essential. Be careful not to damage the stapedial artery during the drilling process.
Continue drilling the vestibule superior to the stapedial artery, and expose the round window and the bony lateral semicircular canal. Open the lateral semicircular canal near its ampulla, then continue drilling in the plane of the lateral semicircular canal, to drill the ampulla of the superior semicircular canal. Use an eighteen gauge or twenty-two gauge needle to aspirate the contents of the vestibule.
Then inject and aspirate one cubic centimeter of one hundred percent ethanol three times. Close the muscles and the skin in two layers with simple interrupted sutures. Monitor the rat and keep it warm until it wakes.
Once the rat regains sternal recumbancy, return it to the housing room. Spontaneous barrel rolling was evident in a Sprague-Dawley rat that underwent labyrinthectomy two days prior. It could be evoked by light touch in the early recovery phase.
Spontaneous nystagmus was also present in the post-labyrinthectomy rat. After watching this video, you should have a good understanding of the anatomy of the middle ear and labyrinth. Once mastered, this technique can be done in twenty minutes if it is performed properly.
