Acoustic Trauma of Guinea Pigs Caused by 60 Cobalt γ-Ray

Auditory cortical cvokod rcsponse（ACER） and auditory brainstom cvoked response（ABR） were recorded in guinea pigs before and after irradiation of 60Co γ-ray. A single dose ofirradiation on head was 90Gy and 70Gy in two groups, respectively. Two h after irradiation. thethreshold shift was 12. 5 dB and 9 dB, and the ACER （?） post-irradiation amplitude ex-ceeded the maximum pre-irradiation value by 20% and 37%. Six h after irradiation, the thresholdshift increased to 37 dB and the maximum amplitnde decreased to the level of pre-irradiation in70Gy-group. In another group, right auditory bulla arca was irradiated with a total dose of 45Gy ina course of six fractions/two weeks. Fourteen d after irradiation, the threshold shift of ABR was 118dB and the latency of wave I was longer. The amplitude-intensity curve was （?） afterirradiation. Histological observation using scanning （?） showed that only outer hair-cells in the basal coil of the cochlea were （?） 6 h after irrdiation 50Gy-group. Bul 16 hlater, outer, hair cells in all coils of the cochlea were found to be destroyed extensively and inner （?）cells were destroyed slightly. In 45Gy-group, 14 d after irradiation, outer hair cells in all coils of thecochlea were damaged and no inmer hair cell was injured severely.