Study Of Low-Frequency High-Intensity Noise On Damage And Mechanism Of Inner Ear In Bama Pigs

Objective Establish bama pigs animal model of low frequency high intensity stationary noise-induced hearing loss. By Auditory Brainstem Response(ABR) test/observing behavioral change/observing vestibular organ and hair cell surface structure/immunohistochemistry and fluorescent antibody technique of Caspase-3 on bama pigs, understand morphological changes of inner/outer hair cell surface and vestibular organ structure, changes of hearing, apoptotic factor expression on inner ear. Observe preliminary bama pigs hearing impairment characteristics after intense low-frequency sound, investigate mechanisms of the damage produced.Methods 8 bama pigs were randomly divided into a normal control group(2pigs) and experimental groups(6 pigs),and Auditory Brainstem Response(ABR) were tested before experiment for all, Experimental groups(6 pigs) were randomly divided into immediate group,36h group,84h group(2 pigs per group),and then were exposed to intense low frequency noise at the level of 142dBSPL,50Hz for 5 min. Observe behavioral change and Auditory Brainstem Response(ABR) were tested again before cochlear were collected along points. Observe hair cell surface structure and vestibular organ with scanning electron microscope (SEM).The control group were not exposed to the noise, with other conditions the same as the experimental groups. The expression of Caspase-3 on spiral organ/stria vascularis/spiral ganglion were observed through immunohistochemistry, and confirm the expression on cochlea cytoplasmic by fluorescent antibody technique.Judg the hair cell loss rate by cell counting to determine cell death.Results 8 bama pigs(16 ears) the average ABR threshold of before exposure was 91.25±10.72dBSPL, ABR thresholds were not elicited after exposure to the noise at the level of 142dBSPL,50Hz for 5 min. Reversable behavior changes occurred when the swine were exposed and stimulated by intense low-frequency noise, howerve, it has no apparente changes of ethology after exposure. Normal otolith and cillia on saccule/utricle were saw in experimental groups. Scanning electron microscopy showed inner/outer hair cell ballooning, outer hair cell stereocillia fusion and sporadic deletion in the immediate group;36h group showed inner/outer hair cell ballooning,outer hair cell scattered stereocillia; 84h group showed missing inner/outer hair cell in basal turn, the middle and apical turn showed inner/outer hair cell missing stereocillia and greater damage in the third row. The hair cell surface structure showed greater damage in basal and middle turn than apical turn. Different parts of Bama pigs show positive expression of Caspase-3 in two ways, as time prolonged after exposure, the positive expression of Caspase-3 gradually weakened. Immediate group and 36h group, compared with control group, shows apparent disorder of three outer hair cell's arrangement and level; and 84h group through fluorescent antibody technique lose outer hair cell, and only inner hair cell are visible.ConclusionABR thresholds were raised after exposure to the noise at the level of 142dBSPL, 50Hz. The inner ear structure appeared apoptosis and mechanical damage. The hearing-loss of obama pig after intense low-frequency is in line with the noise intensity. Apoptosis can be induced in the hair cell as well as spiral ganglion.