Inner Ear Morphology Study Of Acoustically Evoked Short Latency Negative Response Model In Guinea Pigs

Objective: We describe an ASNR model by high intensity click stimuli in guinea pigs. It is reported that the presence of ASNR was consistent with VEMP and not correlated with caloric test, suggesting that ASNR and VEMP are both originated from saccule. This study is to establish a model of profound sensory hearing loss in guinea pigs. In order to prove vestibular origin of ASNR, through techniques of stretched preparation, light microscope and scanning electron microscope, the inner ears are observed on basal membrane, saccule, utricle and ampulla canalis semicircularis.Methods: Each animal experienced ABR to remove abnormal auditory perception guinea pigs. 50 healthy guinea pigs were employed in experiment and divided into two groups randomly, normal group (14 subjects) and deafened group (36 subjects). There are 30 subjects deafened by Ka-Ea; 6 subjects by GM among the deafened group. Ka-Ea deafened: subcutaneous injection of Ka at a dose of 400mg/kg, one hour later by a Jugular vein injection of Ea acid at a dose of 40mg/kg. GM deafened: only treated with GM (i.m., 120mg/kg/d) for 14 days. Animals were left for at least ten days after treatment and then received ABR/ASNR test. The deafened group were further divided into three groups, ASNR group,non-ASNR group and non- profound hearing loss group by presence of ABR/ASNR. All the guinea pigs were killed at scarified the end of the experiment. The Corti organ,macula sacculi,macula utriculi and crista ampullaris were observed by light microscope, scanning electron microscope and stretched preparation.Results: Ka-Ea deafened: ASNR was elicited in 26 ears (57.8%), the threshold of ASNR was110-125 dB SPL, the mean of threshold was 121.73±4.46 dB SPL. Its latency was 1.80-2.08ms. The mean latency of threshold was1.93±0.07 ms. GM deafened: ASNR was elicited in one ears (10 %). The stretched preparation results: In normal control sample, outer and inner hair cells of basement membrane line up in order with eumorphism . Parts of cells are absent, which are outer hair cells in the main in non- profound hearing loss group sample. In ASNR group and non-ASNR group sample, all of hair cells disappear almost completely. But there are remaining few cells of ASNR group sample with abnormal ASNR wave. Vestibular terminal organ, cell density of macula saccule,macula utriculi and crista ampullaris in normal control sample,non- profound hearing loss group sample,ASNR group sample,non-ASNR group sample diminished by turns. There is no difference in normal and ASNR group control sample about cell density of macula saccule. Other statistics comparison is significant. The med of Ka-Ea deafened is better for making ASNR animal model than GM deafened.Conclusions: ASNR was recorded in sensory hearing loss guinea pigs. The med of Ka-Ea deafened is better for making ASNR animal model than GM deafened. Morphological studies suggest that ASNR originate from the saccule. The presence of ASNR is dependent on saccular function and independent on cochlear,utricle and semicircular canal, but remnant cochlear function may diminish amplitude of ASNR.