All animal experiments were conducted in accordance with protocols approved by the Johns Hopkins Animal Care and Use Committee. Four adult chinchillas (C. laniger, 450–650g) were anesthetized with ketamine/xylazine IM and then treated bilaterally with 0.5cc intratympanic injections of 26.7 mg/mL gentamicin buffered with sodium bicarbonate to pH 7.0. This regimen ablates 3D aVOR responses to head rotation by destroying Type I vestibular hair cells and denuding Type II vestibular hair cells of their stereocilia while leaving a viable population of Type II hair cell bodies and spontaneously firing ampullary and macular nerve fibers subjacent to the endorgan neuroepithelium (Hirvonen et al 2005 (link); Della Santina et al 2005b , 2007b (link), 2010 (link); Lyford-Pike et al 2007 (link); Fridman et al 2010 (link)).
For animal restraint during testing, a post was affixed to the animal’s skull using dental cement. For prosthetic electrical stimulation, each chinchilla was implanted with four pairs of electrodes. One pair was placed within or near each of the three semicircular canal ampullae, while the last pair served as reference electrodes and was implanted in the neck musculature. Electrodes consisted of Teflon™ coated 10% iridium/90% platinum wires of diameters ranging from 25um to 125um (Medwire, Sigmund Cohn Corp, Mount Vernon, NY). Distal ends of each wire were stripped 200 μm from the end. Electrode wires of 25 μm diameter were flamed to form a ball on the distal end in order to increase the contact area of the electrode-perilymph interface. This was necessary to avoid electrode corrosion and nerve injury that would otherwise occur during passage of stimulus currents (Robblee and Rose 1990 ).
For animal restraint during testing, a post was affixed to the animal’s skull using dental cement. For prosthetic electrical stimulation, each chinchilla was implanted with four pairs of electrodes. One pair was placed within or near each of the three semicircular canal ampullae, while the last pair served as reference electrodes and was implanted in the neck musculature. Electrodes consisted of Teflon™ coated 10% iridium/90% platinum wires of diameters ranging from 25um to 125um (Medwire, Sigmund Cohn Corp, Mount Vernon, NY). Distal ends of each wire were stripped 200 μm from the end. Electrode wires of 25 μm diameter were flamed to form a ball on the distal end in order to increase the contact area of the electrode-perilymph interface. This was necessary to avoid electrode corrosion and nerve injury that would otherwise occur during passage of stimulus currents (Robblee and Rose 1990 ).
