Before surgery, all guinea pigs were checked to ensure that they had a normal Preyer reflex and no abnormalities in physical appearance. The guinea pigs were anesthetized with a 40-mg/kg ketamine–3- to 5-mg/kg xylazine mixture given intramuscularly. In addition, 0.05 mg/kg of buprenorphine hydrochloride was injected intramuscularly as an analgesic. Two delivery methods were assessed (n = 5 each), using the ventral approach as described. The guinea pig was placed in the supine position. Ventral and paramedian skin incisions were made extending from the jawbone to the collarbone. The jugular vein, submandibular gland, and connective tissue were retracted medially. The tympanic bulla was exposed and opened with forceps, disclosing the cochlea laterally. A small orifice was made in the cochlea bony shell (middle turn), penetrating the scala tympani. In the cochleostomy method, with the use of a microsyringe (Hamilton Company, Reno, Nevada) connected with a 30-gauge needle, 10 μL of the DNA complex solution was injected through the orifice manually over a period of 10 minutes from a microsyringe mounted on a free-standing clamp. The needle was then carefully removed and the orifice was sealed with dental cement on needle retraction to prevent backflow of the vector solution. In the osmotic pump method, a catheter (PUFC-C30-10; Instech Solomon, Plymouth Meeting, Pennsylvania) connected to an osmotic pump (1007D; Alzet, Cupertino, California; flow rate, 0.5 μL/h; reservoir volume, 90 μL; containing 10 μg of DNA complexed with PEI at an N:P ratio of 6) preactivated by overnight incubation at 37°C was inserted into the orifice made in the cochlea bony shell and secured by means of dental cement and a topical tissue adhesive (NEXABAND; Abbott Laboratories, Chicago, Illinois). The osmotic pump reservoir was then inserted subcutaneously under the neck region of the guinea pig. On completion, the cavity in the bulla was sealed with dental cement (Fuji I glass ionomer luting cement; GC America Inc, Alsip, Illinois) and the wound was sutured closed.