[Electrocochleographic changes in guinea pigs immunized with type II collagen]

Electrocochleograms (ECoGs) were assessed in guinea pigs with cochlear impairment induced by immunization with type II collagen. Action potential (AP) tuning curves (TCs) were studied using a forward masking technique. Not only AP TCs, but the intensity function of APs and summating potentials (SPs) were assessed. The results were as follows: 1) The TCs displayed the normal pattern in all animals, and the Q10dB values of the curves were within the normal range. 2) Abnormal changes in AP, such as threshold elevation, decrease in amplitude and prolongation of latency were observed. 3) Decreases in +SP were observed in eight of ten animals, but no negative SPs were observed. 4) All animals exhibited degeneration of spiral ganglion cells on light microscopy, despite the preservation of normal hair cells. 5) Levels of antibody against type II collagen were much higher than in controls. This suggests that the normal pattern of TCs may have been the result of only minor hair cell damage. The cause of the decrease in +SP, however, is unknown. Further investigation should be performed to resolve this question. In addition, there may be differences in immune reaction from animal to animal.