Unilateral Cochlear Ablation in Mice

Male B57BL/6 mice (postnatal 8-week-old) were used in the present study. All anesthetic, surgical, and postsurgical procedures used in this study, as well as animal care, were approved by the Institutional Animal Care Committee of Seoul National University of Korea (IACUC No. 15-0204-C2A4). The mice were divided into three groups: control, SSD-4-week, and SSD-8-week. The control group (postnatal 8-week-old, n = 9) mice were subjected to MEMRI immediately. The SSD-4-week group underwent left-side cochlear ablation surgery and recovered for 4 more weeks until MEMRI study (postnatal 12-week-old, n = 11). The SSD-8-week group recovered for 8 weeks after left cochlear ablation surgery before MEMRI study (postnatal 16-week-old, n = 11) (Figure 1).
The mice were anesthetized with an intraperitoneal injection of a mixture of Zoletil (30 mg/kg) and xylazine (5 mg/kg). All cochlear ablation surgeries were conducted unilaterally on the left ear. After the fur was shaved behind the left ear, a postauricular incision was made. The otic bulla was dissected with care to preserve the facial nerve. A small opening was made in the otic bulla, and the cochlea was visualized. The cochlea was punctured with a 26-gauge needle and was irrigated with kanamycin through the perforation three times. Then, the opening in the cochlea was closed with glue, and a subcutaneous 4.0 Vicryl suture was added. Hearing levels were confirmed before MEMRI acquisitions in all mice groups using the auditory brainstem response (ABR) (SmartEP, Intelligent Hearing Systems, Miami, FL, USA) as described previously [5 (link)]. The ABR results are presented in Table 1. The average ABR thresholds of the deaf side were 81.36 (standard deviation (SD) = 10.02) dB SPL and 80.00 (SD = 10.00) dB SPL for SSD-4-week and SSD-8-week groups, respectively.