Evolution of CM, SP and AP during etacrynic acid intoxication in the guinea pig

During etacrynic acid intoxication in the guinea pig, patterns of click-evoked compound electrocochleographic responses are similar to those observed in Menière and retro-cochlear human pathologies. Using high frequency tone bursts, SP, CM and AP were studied after intracardiac injection of etacrynic acid. The evolution of SP precedes that of CM and AP. Its change in polarity could be related to that reported for EP by Bosher et al. (1973). While during the recovery period SP overshoots (after 90 min), CM and AP increase more slowly (up to about 7 days) and in most cases AP amplitudes do not exceed 70-80% of their original value (25 days). N1, when present, keeps its classical pattern durint the entire evolution, whatever its amplitude and latency variations are. The early positive peak or negative shift observed in click-evoked human pathological electrocochleography can therefore be identified as SP. Thus this response is the indication of the presence of hair cells and of the impairment of the nerve fibre stimulation or response.