Surgery

Rats were anesthetized with sodium pentobarbital (50 mg/kg, i.p.), and all surgeries were conducted in sterile conditions under a surgical microscope. The hair on the top of the head was shaved, and the rat was placed in a stereotaxic frame. Ophthalmic cream was applied to the corner of both eyes to prevent drying damage. An anterior-posterior 15-mm skin incision was made at midline of the head. The infraorbital muscle was gently dissected from the bone until the orbit could be gently retracted. A piece of gelfoam or a tiny cotton ball was packed into the orbital cavity to minimize bleeding. The infraorbital nerve can be seen deep within the orbital cavity, lying in the infraorbital bony fissure. The infraorbital nerve was dissected free from the bone at its most rostral extent in the orbital cavity, and a single 2-mm length of chromic gut suture (4-0) was inserted between the infraorbital nerve and the maxillary bone. In the sham operation control group, only skin incision and muscle dissection were performed. The nerve was not touched, and no chromic gut suture was inserted. All skin incisions were sutured with 4-0 nylon non-absorbable monofilament.