Effects of exposure to an augmented acoustic environment on auditory function in mice: roles of hearing loss and age during treatment.

The effects of exposure to an augmented acoustic environment (AAE) on auditory function were evaluated in mouse strains that exhibit various degrees and time courses of progressive hearing loss (BXD-22, BXD-12, BXD-16, BXD-14, BALB/cJ), and in normal-hearing CBA/CaJ mice. Beginning at age 25 days, mice were exposed 12 h every night to a 70 dB SPL broadband noise AAE. The AAE was maintained for at least 30 days in each strain. Same-strain control mice were age-matched and maintained under normal vivarium acoustic conditions. The auditory brainstem response (ABR), acoustic startle response amplitude, and prepulse inhibition (PPI) were used to assess the auditory system. Exposure to the AAE resulted in improved auditory performance (better PPI, lower ABR thresholds) when hearing impairment was present, but not when hearing was normal. The ameliorative effects occurred irrespective of a mouse's age at the onset of hearing loss, as long as initiation of AAE treatment preceded the occurrence of severe hearing loss. If AAE treatment was delayed beyond such a point, loss of threshold sensitivity progressed as usual, although PPI could still benefit. Finally, AAE treatment can slow, but not prevent, the occurrence of severe genetically determined hearing loss.