The Neural Origination Of Acoustically Evoked Short Latency Negative Response (ASNR) In Guinea Pigs

Objectives:To establish a model of acoustically evoked short latency negative response (ASNR) in guinea pigs, a model of profound hearing loss with normal saccular function. Combination of stereotaxic and electrolytic methods was applied to define the nucleus generating ASNR, the vestibular nucleus or the cochlear nucleus.Methods:24 healthy guinea pigs were employed in the experiment, which were randomly divided into control group (8 subjects) and deafened group (16 subjects). Each animal experienced auditory brainstem response (ABR) test. A quick treatment was employed for deafened group consisting of a subcutaneous injection of kanamycin at a dose of 400mg/kg followed by an intravenous injection of ethacrynic acid at a dose of 40mg/kg one hour later. The animals were performed ABR test 7～10 days after the drug administration. According to the presence of ASNR, the deafened group was further divided into ASNR group and non-ASNR group. The vestibular nucleus and cochlear nucleus were destroyed by electrolytic lesion respectively, followed by ABR test. The animals were perfused through the ascending aorta, the brainstems were removed, tissue fixation, paraffin embedment, sequential sections and Nissl's staining were made, consequently the lesioned structures were verified through microscope.Results:In deafened group, ASNR was elicited in 10 ears (31.3%), the threshold was 120-130dB SPL with mean of 124.5±4.69 dB SPL. Its latency range was 1.70ms-2.68ms with mean of 2.18±0.31ms. The mean latency of threshold was 2.26±0.23ms. ASNR was erased by electrolytic lesion to the vestibular nucleus but it still existed after the same procedure to the cochlear nucleus.Conclusions:It is clear that ASNR is originated from the vestibular nucleus but not the cochlear nucleus.