INFLUENCE ON THE COCHLEA OF GUINEA PIG BY LONG TERMED EXPOSURE OF BAND NOISE

OBSERVATIONS BY MEANS OF SURFACE PREPARATION TECHNIQUE

Abstract

Guinea pigs were exposed to the intermittent band noise centered at 4 kKz and 0.5 kHz at intensity of 100 phon for two years (eight hours daily).
Cochlea was prepared in surface specimen. In order to determine the pattern of hair cell loss, cochleogram of the sensory cell population was constructed using light microscope. The results are as follows;
(1) The site of lesions was observed at 10-14 mm distant from the basal end of the cochlea with exposure of 4 kHz for three months.
(2) With 4 kHz exposure for 24 months, collapse of the hair cells occurred at 8.5-14 mm distant from the basal end of the cochlea.
(3) The existence of maximal damage caused by 0.5 kHz exposure was observed at 12-16.5 mm from the basal end.
(4) The cochlea exposed to 0.5 kHz showed patchy change in more extended area.
(5) Hair cell damage caused by exposure to 4 kHz and 0.5 kHz extended towards the base of the cochlea.
(6) Damage started from the first row of outer hair cells and at later stage it extened to the inner hair cells.
(7) It was supposed that the intermittent sound was less injurious than the continuous one.