Echolocation frequency alteration, and hearing loss induced by an ototoxic drug in the echolocating bat Hipposideros...

Noise exposure increases the level of reactive oxygen species (ROS) in the outer hair cells (OHCs) of the cochlea, which subsequently damages OHCs and causes noise-induced hearing loss. However, increasing evidences have shown that echolocating bats can maintain their auditory sensitivity after intense noise exposure, indicating that they have a strong capacity to clear ROS, or that noise exposure does not increase ROS levels in the cochlea of the animals. To differentiate between these possibilities, the constant frequency-frequency modulation bats, Hipposideros pratti, were intraperitoneally injected with the ototoxic drug Kanamycin, which increases ROS levels in the cochlea of other mammalian species. The results showed that Kanamycin application efficiently altered the echolocation frequency, shifted the auditory brainstem response threshold, and damaged the OHCs, suggesting that echolocating bats were sensitive to ototoxic drugs. Therefore, H. pratti does not seem to be able to clear ROS efficiently, and the decreased susceptibility to noise exposure of echolocating bats might be due to the failed increasement of ROS levels in their cochleae by the noise exposure. Furthermore, our data also showed that the precision of resting frequency (RF) was greatly decreased after the auditory sensitivity was impaired by Kanamycin application, suggesting that the precision of the RF was dependent on the auditory feedback. These findings could provide insights to understand the adaptation mechanisms of the auditory system of echolocating bats to intense sound environments.