Chronic study on the neuronal excitability of the cochlear nuclei of the cat following electrical stimulation.

To examine the safety of auditory brainstem prosthesis, the cat cochlear nuclei were implanted and stimulated chronically with bipolar surface electrodes using charge-balanced biphasic current pulses at rates of 250 pulses/s. The stimulation was continuous 16 h/day for up to 12 weeks. The electrically-evoked auditory brainstem response (EABR) was used to monitor neuronal excitability of the cochlear nuclei following the chronic electrical stimulation. The body weight, respiration, and body temperature of the cats were monitored throughout the experiment. The amplitudes and latencies of the EABR waves were measured fortnightly and compared before, during and after the electrical stimulation. The results showed that the respiration, body weight and body temperature of the cats remained within normal limits during the chronic stimulation. During the stimulation, no change was found in the EABR waveform, but a decreased threshold and wider dynamic range were observed after the stimulation. There was no significant change in the amplitudes and latencies of the EABR waves after stimulation. The present findings suggest that chronic bipolar electrical stimulation with surface electrodes at rates of 250 pulses/s is safe for neuronal excitability of the cochlear nuclei in the cat.