Active ultrasonic vocal communication channel found in Mongolian gerbils through the cochlear microphonics with noise exposure

Mongolian gerbils (Meriones unguiculatus) use ultrasonic vocal communication in frequency range of 22-45 kHz. However, hearing threshold of this frequency range reported has been very high, which is not suited for vocal communication. We examined possible active amplification created by the outer hair cells for frequency range of 22-45 kHz. In this study, we evaluated the amount of active amplification by the cochlear microphonics (CM) combined with temporary damage created by noise exposure. Adult gerbils received surgical implantation of a silver wire electrode on the round window of their cochlea through the middle ear to record CM. They were exposed to broadband noise (0.5 to 45 kHz) at 90 dB SPL for 5 minutes. CMs were recorded for tone bursts of 1 to 45 kHz. The following results were obtained. First, we observed the largest CM reduction immediately after the noise exposure. Second, decrements in CM amplitude depended on frequency. Largest reduction in CM amplitude was observed in frequency range of...