Bioelectric correlates of kanamycin intoxication

Young guinea pigs were given a series of subcutaneous injections of kanamycin (400 mg/kg body weight for 8-14 days) and after at least a two-week waiting period various electrical responses from the cochlea were measured. After the experiments the cochlea was perfused with osmic acid, surface preparations were used to obtain sensory (hair) cell counts, and cochleograms were prepared. In this report the relationship between the various electrical in dices of cochlear function (cochlear microphonic: CM. summating potential: SP, and whole nerve action potential: AP) and the degree and configuration of sensory cell damage is discussed. The electrode potentials were obtained with the differential electrode technique and localized CM and SP responses were collected from the first and often the third cochlear turns. Both the differential (DIF) and the average (AVE) SP components were studied. The results reveral that the CM production of inner hair cells alone is about 30-40 dB below that of the outer hair cells, and there is a 90° phase difference between the CM outputs of the two groups. The low intensity segment of the AP input-output function is missing in these cases, while they achieve near normal magnitude at high intensities. The inner hair cells apparently do not produce a positive DIF SP component