ABSTRACT
Objective To investigate the effect of intense low frequency noise on the different hearing functions and hair cell damage in bama pigs.Methods Thirteen bama pigs were randomly divided into a normal control group (3 pigs) and an experimental group (10 pigs).The pigs in experimental group were randomly divided into 50 Hz subgroup (5 pigs) and 70 Hz subgroup (5 pigs).The 50 Hz subgroup was exposed to intense low frequency noise at 167～170 dB SPL,50 Hz for 30 min,and the 70 Hz subgroup was exposed to intense low frequency noise at 164 dB SPL,70 Hz for 30 min.Auditory brainstem response(ABR) and distortion product otoacoustic emission (DPOAE) were performed before and after noise exposure.The cochlear were collected and the inner ear morphology changes were studied.Results Before the experiment,the ABR threshold of the pig was 20～50 dB SPL,and the average of 50 Hz group was 33.5±9.4 dB SPL,the average of the 70 Hz group was 34.0±4.6 dB SPL.The level of the above 3 000 Hz DPOAE could be elicited.But they were not elicited after the exposure to the noise.The inner ear structures were damaged.The DAPI showed hair cell missing.Conclusion ABR and DPOAE were elevated after noise exposure.The auditory system of bama pigs had irreversible damages.Hair cells damaged were given priority to with necrosis,and the higher the level of intense low frequency noise,the more serious the damage to the hair cell.
ABSTRACT
Objective To investigate the effects of intense low frequency noise on expression of caspase -3 in bama pigs ,and observe the death of cochlea hair cell .Methods 8 bama pigs were randomly divided into a normal control group(2 pigs) and experimental groups(6 pigs) .Auditory brainstem responses(ABR) were tested before the experiment .The control group was the same as the experimental groups except noise exposure .The experimental group was randomly divided into immediate group ,36 h group ,and 84 h group(2 pigs per group) .They were ex-posed to intense low frequency noise at 142 dB of 50 Hz for 5 min according to the three time points .ABR were test-ed again before the cochlea were collected at different time points .The expression of caspase -3 was studied through immunohistochemistry and immunofluorescence ,hair cell loss rate by counting to determine cell death .Results The average ABR threshold of 8 bama pigs(16 ears) before the exposure was 61 .25 ± 10 .72 dB nHL .ABR thresh-olds were not elicited after exposure to the noise .Different parts of bama pigs showed positive expression of caspase -3 in two ways .As time prolonged after exposure ,the positive expression of caspase -3 gradually weakened .The im-mediate group and 36 h group ,compared with the control group ,showed the apparent misplace of three out hair cells in the arrangement and levels .The 84 h group through immunofluorescence lost out hair cells ,and only inner hair cells were visible .Conclusion ABR thresholds were elevated after noise exposure .The procedure of hair cell nucleus damage and caspase-3 expression is different ,and the noise can induce opening apoptotic program of spiral ganglion .