Cochlear microphonic potentials: A new recording technique

A new instrumentation and a particular method for detecting and recording c ochlear microphonic potentials (CMPs) are de scribed here. The CMPs were re corded in rats by means of pure tones (4,000, 2,000, 1,000, 500, and 250 Hz ) and intraepidermic electrodes; the electrocochleography technique was avo ided. An experimental design that included the use of a glutamatergic agoni st (kainic acid [KA]) and an aminoglycoside antibiotic (kanamycin [KANA]) w as carried out to demonstrate the origin of the recorded potential. Morphol ogical studies showed that KA selectively eliminated the afferent type I de ndrites of the spiral ganglion, while the administration of KANA resulted i n the absence of outer hair cells. When CMPs were recorded after KA adminis tration, no alterations were detected. In contrast, KANA administration res ulted in the absence of any selective electrophysiological activity corresp onding to CMPs. All these results were compared with the recording of the c ompound action potential of the eighth nerve obtained by electrocochleograp hy. These findings and the great specificity of the reproduction of the sou nd stimulus confirm that the CMPs can be recorded by the new equipment.