This article details a surgical procedure for inducing facial nerve injury in a rat model. The methodology emphasizes careful dissection and identification of key anatomical structures to ensure successful nerve transection.
Begin with an anesthetized rat and shave the surgical area.
Place a gauze roll under the rat's neck to enhance exposure to the surgical field.
Disinfect the site with antiseptic.
Position the rat under a stereomicroscope.
Make a small incision behind the ear and dissect the superficial connective tissue.
Use a retractor to access the underlying tissues.
Identify the anterior digastric muscle, a type of jaw muscle. Spread this muscle to expose its tendon.
Adjust the retractor to reveal the facial nerve's trunk.
Dissect the nerve inferiorly to ensure clear accessibility for inducing injury.
Grasp the epineurium, a thin tissue layer overlying the nerve, and cut the target nerve at the desired site to create a transection injury.
Then, rinse the wound with saline, dry it, and suture the incision.
The rat model with a facial nerve injury is now ready for further studies.
After confirming a lack of response to toe pinch, apply ointment to the eyes of the rat, and shave the surgical area. Establish a method for rat identification, and place a roll of gauze under the neck.
Disinfect the exposed skin with three alternating chlorhexidine and 70% ethanol scrubs, and place the rat under a stereomicroscope. Manipulate the ipsilateral ear in an anterior-posterior direction to determine the natural folding of the postauricular skin. Use a number 15 blade to make a two to three-millimeter incision in the postauricular crease.
The planning and the placement of the incision are the most critical steps for ensuring reliable identification of the facial nerve while minimizing the wound size.
Bluntly dissect through the immediate subcutaneous fascia, and place a micro-Weitlaner retractor to enhance the tissue exposure. Identify the anterior digastric muscle as it travels in an inferior to superior direction towards its insertion along the skull base. Spread gently through the muscle belly along the muscle insertion point to reveal the tendon of the anterior digastric belly.
The tendon will appear as a filmy white process emanating from the muscle with a solid insertion onto the skull base. After identification of the anterior digastric muscle and its tendon, adjust the Weitlaner retractor to further retract the muscle belly.
The exposed region is the three-dimensional space in which the main trunk of the facial nerve lies. Dissect along the nerve in an inferior direction, distally from the exit of the stylomastoid foramen. For a simple transaction, grasp the immediate epineurium overlying the nerve with fine-toothed forceps, and use sharp micro-scissors to cleanly transect the nerve at the desired point with a single cut.
After the experimental injury has been delivered, irrigate the wound with sterile saline, and dry the tissue with sterile gauze, before closing the skin incision according to institutional guidelines.
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