[Fluctuation of nucleic acid activity in the organ of corti resulting from noise exposure].

Using histochemical technique, changes of nucleic acid activity in the cochlea resulting from white noise exposure were investigated. Forty-eight guinea pigs were used for this experiment. The results obtained were as follows: 1. The first sign of pathological changes in the organ of Corti due to exposure to white noise occurred in the outer hair cells. Temporary high metabolic rates of DNA were observed in the nuclei of the outer hair cells immediately after exposure to white noise at 110 db sound-pressure level for 10 minutes. The nuclei of the outer hair cells appeared pyknositic in most cases. Chromatin granules were not always clear. DNA activities had low rates between 3 days and 7 days after exposure. However, they recovered completely from low rates on 14th day after exposure. 2. DNA activities in the cuter hair cells immediately after exposure to white noise at 120 db for 5 minutes increased temporarily, while they had low rates. The activities recovered on 21st day after exposure. 3. Pyknosis and decreased clearness of chromatin granules in the nuclei of the outer hair cells appeared in all cases after exposure to white noise at 120 db for 10 minutes. At that time, DNA activities increased temporarily, then they had also low rates. Only the half of the animals were allowed to recover for 21 days after exposure. 4. Recovery pattern of DNA activities in the outer hair cells exposed to white noise at 130 db for 3 minutes was almost the same as that in the outer hair cells ex-