Establishment Of Hearing Loss Models Of C57BL/6N Mice Induced By Different Types Of Noise And Comparative Morphometry Of Inner Ear Hair Cells Damage

Objective: To establish hearing loss models of C57BL/6N mice induced by different types of noise and explore the effects of different types of noise on hearing function and the relationship with hair cells damage.To provide necessary experimental models and theoretical basis for further study of the pathogenesis of NIHL,gene therapy,hair cells regeneration,and screening of hearing-related protective drugs.Methods: Thirty mice with normal hearing were divided randomly into six groups(n = 5/group): control group,100 dB 3h group,120 dB 3h group,112 dB 3h group,112 dB 6h group,and 112 dB 9h group.Control group is not exposed to noise.100 dB 3h group is exposed to 100 dB SPL white noise for 3h.120 dB 3h group is exposed to 120 dB SPL white noise for 3h.112 dB 3h group is exposed to 112 dB SPL 8-l6 k Hz octave band noise for 3h.112 dB 6h group is exposed to 112 dB SPL8-l6 k Hz octave band noise for 6h.112 dB 9h group is exposed to 112 dB SPL8-l6 k Hz octave band noise for 9h.ABR measurements were performed pre-exposure and 4th days,7th days and 14 th days after noise exposure.The stimulation sounds were click and tone burst,and the detection frequency of tone burst included 4k Hz,8k Hz,16 k Hz and 24 k Hz.After ABR measures,the hair cells were observed and counted.Results: 1.The click and TB 4k Hz thresholds of normal C57BL/6N mice were22.0 ± 33 dB SPL and 17.5 ± 2.5 dB SPL,respectively.The thresholds of TB8 k Hz and TB 16 k Hz were lower than that of click(p < 0.01),which were 15.5 ±1.5 dB SPL and 11.0 ± 2.0 dB SPL,respectively.TB 24 k Hz threshold was higher than click threshold(p < 0.01),which was 33.0 ± 4.6 dB SPL.2.The effects of100 dB white noise exposure for 3h on the click and tone burst thresholds were different.There was no significant effect on the thresholds of click and TB 4k Hz(p > 0.05).The thresholds of TB 8k Hz,TB 16 k Hz and TB 24 k Hz were increased at NE-4d(p < 0.01),among which TB 16 k Hz had the largest threshold shift,followed by TB 8k Hz and TB 24 k Hz.The hearing threshold returned to normal after 7 days of noise exposure.3.After exposure to 120 dB white noise for 3h,the thresholds of click and tone burst at different frequencies increased significantly and did not recover at NE-14 d.The threshold shift of click,TB 8k Hz and TB 24 k Hz has no obvious change at NE-4d,NE-7d and NE-14 d.The largest threshold shift degree of TB 4k Hz and TB 16 k Hz occurred at NE-4d and NE-l4 d,respectively.The threshold shift of TB 4k Hz was similar to that of click,and the threshold shift of TB 8k Hz,TB 16 k Hz and TB 24 k Hz was larger than that of click(p < 0.01).Among them,TB 16 k Hz threshold shift is the largest,TB 8k Hz and TB 24 k Hz threshold shift are the next.And the I wave latency of TB 8k Hz was delayed.4.The mice of 112 dB 3h,6h and 9h groups had almost complete hearing loss after exposure to 8-16 k Hz octave band noise,and the hearing loss was irreversible.5.In the 100 dB 3h group,outer hair cells and inner hair cells in apical,middle and basal turn of the cochlea were arranged neatly,without obvious loss.6.In the 120 dB 3h group,the outer hair cells of apical turn and inner hair cells were not being damaged,the outer hair cells of middle turn were moved slightly,whereas the outer hair cells of basal turn were lost obviously.7.The mice of 112 dB 3h group and 6h group showed no obvious damage to the inner hair cells.In the 112 dB 9h group,the inner hair cells were being damaged,especially in the basal turn.In the addition,the outer hair cells of the mice in 112 dB 3h,6h and 9h group were being damaged seriously.The basal turn was the most damaged,followed by the middle turn.In general,the most serious damage group was the 112 dB 9h group,followed by the6 h group.Conclusion: 1.Temporary threshold shift occur in C57BL/6N mice after 3 hours of exposure to 100 dB white noise and is recovered after 7 days of exposure.Temporary threshold shift is not related to hair cells damage.2.Exposed to 120 dB white noise for 3h cause permanent threshold shift in C57BL/6N mice,but there is still some hearing residual,and the loss of outer hair cells in the basal turn is observed.3.White noise has a greater impact on 8k Hz-24 k Hz hearing.4.Exposure to 112 dB 8-16 k Hz octave band noise for 3h,6h and 9h result in complete hearing loss in C57BL/6N mice,which is irreversible and permanent.With the increase of exposure time,the degree of damage to hair cells increased and the damage range expand.5.Permanent threshold shift is associated with hair cells damage.6.In the noise with the same intensity,8-16 k Hz octave band noise has stronger damage to hearing than white noise.