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 audit ory function were evaluated in mouse strains that exhibit various degrees a nd 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, m ice were exposed 12 h every night to a 70 dB SPL broadband noise AAE. The A AE was maintained for at least 30 days in each strain. Same-strain control mice were age-matched and maintained under normal vivarium acoustic conditi ons. The auditory brainstem response (ABR), acoustic startle response ampli tude, 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 h earing was normal. The ameliorative effects occurred irrespective of a mous e's age at the onset of hearing loss, as long as initiation of AAE treatmen t preceded the occurrence of severe hearing loss. If AAE treatment was dela yed 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. (C) 2000 Elsevier Science B.V. All rights reserved.