Establishment of a cochlear injury model using bone-conducted ultrasound irradiation in guinea pigs and investigation on peripheral coding and recognition of ultrasonic signals.

The cochlea of guinea pigs was irradiated with different frequencies of bone-conducted ultrasound (BCU) at a specific dose to induce cochlear hair cell-specific injuries, in order to establish frequency-related cochlear hair cell-specific injury models. Cochlear near-field potentials were then evoked using BCU of different frequencies and intensities to explore the peripheral coding and recognition of BCU by the cochlea. The inner ears of guinea pigs were irradiated by 30 kHz at 100 db and 80 kHz at100 db BCU for 6h to create frequency-related, ultrasound-specific cochlear injury models. Then, 30 kHz and 80 kHz BCU of different intensities were used to evoke auditory brainstem response (ABR) thresholds, compound action potential (CAP) thresholds, and action potential (AP) intensity-amplitude input-output curves in the normal control group and the ultrasonic cochlear injury group. This allowed us to explore the coding and recognition of BCU frequencies and intensities by cochlear hair cells. Immunofluorescence assay of outer hair cell (OHC) Prestin and inner hair cell (IHC) Otofelin was performed to verify the injury models. Irradiation of guinea pig inner ears by 30 kHz and 80 kHz BCU at a specific dose induced hair cell injuries at different sites. Irradiation with low frequency BCU mainly induced OHC injury, whereas irradiation with high frequency BCU induced IHC injury; moreover, IHC injury was more serious than OHC injury. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the normal control group. The 30 kHz-evoked ABR threshold was significantly higher in the 30 kHz ultrasonic cochlear injury group compared to the 80 kHz ultrasonic cochlear injury group. The difference in the 80 kHz-evoked ABR thresholds were not significant between the 30 kHz and 80 kHz ultrasonic cochlear injury groups. The click- and 30 kHz-evoked AP intensity-amplitude curves for the 30 kHz ultrasonic cochlear injury group indicate that the AP amplitude evoked at the same intensity was higher in the 30 kHz-evoked group than the click-evoked group. The spatial positions of cochlear hair cells in guinea pigs had a coding function for the frequencies of low-frequency ultrasound. OHCs have an amplification effect on the coding of low-frequency ultrasonic intensities. The peripheral perception of high frequency BCU may not require the participation of cochlear hair cells.

Investigation of cochlear hair cells and the perception of ultrasound signals in guinea pigs.

We established a specific ultrasound frequency-dependent model of cochlear injury using bone conduction ultrasounds in the inner ear of guinea pigs at 50 kHz and 83 kHz, to explore the effects of bone conduction ultrasound in the cochlea. To establish a unilateral cochlear damage model, the unilateral cochlea was destroyed. The control group consisted of 50 kHz and 83 kHz bone conduction ultrasounds in unaltered guinea pigs. In each group, cerebral blood oxygenation level dependent (BOLD) effects were determined by functional magnetic resonance imaging (fMRI). The cochlear outer hair cell motor protein, Prestin, and the microfilament protein, F-Actin, were detected. We found that bone conduction ultrasound irradiation at 50 kHz and 83 kHz on the guinea pig inner ear for six hours leads to hair cell damage. Furthermore, low frequency bone conduction ultrasound induces major damage to outer hair cells, while high frequency ultrasound damages both internal and external hair cells. fMRI analysis of cerebral BLOD effects revealed an affected cerebral cortex region of interest (ROI) of 4 and 2, respectively, for the normal control group at 50 kHz or 83 kHz, and 2 for the 83 kHz bone conduction ultrasound cochlear injury group, while 50 kHz bone conduction ultrasound failed to induce the cortical ROI within injury model. Results reveal that the spatial location of guinea pig cochlear hair cells determines coding function for lower ultrasound frequencies, and high frequency bone conduction ultrasound may affect the cochlear spiral ganglion or cranial nerve nucleus in bone conduction ultrasound periphery perception.

Establishment of a Gentamicin Cochlear Poisoning Model in Guinea Pigs and Cochlear Nerve Endings Recognition of Ultrasound Signals.

BACKGROUND Aminoglycosides, a type of gram-negative antibacterial, are broad-spectrum antibiotics that are highly potent and have satisfactory therapeutic efficacy in the treatment of life-threatening infections. Our study aimed to establish a gentamicin-induced cochlear injury model and to investigate the cochlear nerve endings' recognition of ultrasound signals. MATERIAL AND METHODS A guinea pig cochlear injury model was established by intraperitoneal injection of gentamycin. Auditory brainstem response (ABR) and fMRI an affected cerebral cortex region of interest (ROI) of the cerebral cortex blood oxygenation level dependent (BOLD) effect was induced by bone-conducted ultrasound. Immunofluorescence was used to detect expression of Prestin in outer hair cells, Otoferlin in inner hair cells, and cochlear hair cell microfilament protein (F-Actin). RESULTS For 30-35 KHz bone-conducted ultrasound, the induction rate of ABR threshold or ROI in the control group and the cochlear injury group was 40% and 0%, respectively, and for 80-90 KHz the induction rate was 20% and 20%, respectively. Gentamicin poisoning induced downregulation of expression of Prestin in cochlear outer cochlea, and Otoferlin and F-Actin in cochlear hair cells in different regions. CONCLUSIONS Gentamicin poisoning can cause different degrees of damage to cochlea hair cells in different regions. Guinea pigs with gentamicin poisoning can recognize high-frequency ultrasonic signals.