Alternating Current-Evoked Oto-Acoustic Emission

Abstract

Guinea pigs were anesthetized with urethane (1.2g/kg i.p.), and an alternating current at a frequency of Fc was fed into the scala media at the 2nd turn of the cochlea through a glass micropipet or plutinum microelectrode, and a pure tone at a frequency of Ft (Ft>Fc) was delivered to the ear canal with a hermetically attached earphone. The sound in the ear canal was picked up with a probe tube microphone. The frequency power spectrum analysis of the sound showed components at Ft±Fc in addition to Fc and Ft, as if the oscillation of Ft interacted with the Fc vibration in the cochlea, so as to be amplitude-modulated. The powers of the sidebands at Ft±Fc were decayed reversibly by frocemide (20mg i.a.) and the sidebands were disappeared irreversibly after loud noise exposure. Cardiac arrest suppressed genaration of the sidebands immediately, and their magnitudes became below the noise floor after 60-90min. The amplitude-modulation could not be deteted in kanamycin-treated (400mg/kg/day i.m. for 14days) animals.