Changes of electrocochleography in regional difference of labyrinthine lesion by argon laser irradiation

Abstract

Investigation of both striae and cochlear nerve lesion in guinea pigs were performed indirectly through the cochlear wall by means of argon laser irradiation. The changes of AP, CM and SP measured by the round window recording were investigated both after one hour and also after one month in the same animals. The following results were obtained.1. There was no electrocochleographic correlation at the power 80 to 100mw irradiation between the apical and basal turn. However, in the cases of a high power irradiation such as 600mw at the apical turn, the irradiated region showed disappearance of the outer hair cells, and AP threshold was extremely increased and AP out-put potential was reduced. The CM responses below 0.5kHz were almost disappeared.2. An one hour after the stria vascularis irradiation the out-put potentials of AP, CM and SP were reduced with the increase of irradiation power. However, after one month a well developed AP out-put potential was observed with intensive sound stimulus, even though the AP threshold was increased. Some animals of a low power irradiation showed a higher out-put potential than that of the control value.3. In the cases of irradiation of the cochlear nerve, even a full month later the AP showed a lower out-put potential at intensive sound stimulus, but the threshold was relatively stable as compared with the out-put potential.The above results indicate an interesting finding in view of the difference between cochlear and retro-cochlear lesion.