Abstract
Methods for recording the cochlear potentials, i. e., electrocochleogram (ECoG) and the auditory brain stem response (ABR) in unrestrained rats were developed. The electrodes for recording the ECoG and ABR were implanted chronically in the vicinity of the round window membrane and on the epidural surface at the lower margin of the parietal bone, respectively. The ECoG and ABR were recorded simultaneously on unrestrained rats using a slip ring which allows the rat free movement without twisting the cables. Latencies of each component of the ABR were compared with those of the ECoG, and binaural interaction was also checked by unilateral puncture of the tympanic membrane. The early components of the ABR, which corresponded to the ECoG, were related to the homolateral cochlea, while the late components to the contralateral cochlea. The amplitudes and latencies of the ECoG were reproducible for 3-4 weeks and those of the ABR for 6 weeks. These results indicate that this recording technique for ECoG and ABR is useful for evaluating the ototoxicity of drugs in unrestrained rats.
