[The study of the high sensitivity to noise trauma in the inner ear mimetic aging model]

Use the inner ear mimetic aging model which has been established by our research institute, investigate its sensitivity to noise trauma and the possible role of mitochondrial DNA deletions.

Thirty-two Wistar rats of 2 months old were randomly divided into four groups. In group A, D-galactose was subcutaneously injected at dose of 150 mg/kg weigh per day for 8 weeks, after that these rats were exposed to 110 dB SPL noise 4 hours each day, for 2 days. Group B were given normal saline (NS) injected at dose of 150 mg/kg weigh per day for 8 weeks,also given noise exposure as that of group A. Group C were give D-galactose without noise exposure. Group D were given normal saline (NS) without noise exposure. The thresholds of auditory brainstem response (ABR) were measured 2 weeks after stopping of noise exposure. And T-SOD and MDA of the inner membranous labyrinthine tissue were measured. Nest polymerase chain reaction (Nest PCR) were used to identify the mtDNA common deletion (CD), and PCR products were sequenced in the meantime.

The elevation of the mean ABR thresholds in group A was higher than that in group B, and the difference had statistic significance (P < 0.01). The reduction of T-SOD in group A was obvious, while the level of MDA was greatly increased. The difference in the levels of T-SOD and MDA between group A and group B had statistic significance (P < 0.01). The detection rate of mtDNA 4834 deletion were as follows: group A 87.5% (7/8); group B 12.5% (1/8); group C 75.0% (1/8); group D 0(0/8).

The rat in the inner ear mimetic aging model are hypersensitive to noise exposure, and mtDNA4834 deletions in the inner ear may play an important role in it.