Exposure to an augmented acoustic environment alters auditory function in hearing-impaired DBA/2J mice

The effects of exposure to an augmented acoustic environment (AAE) on auditory function were evaluated using DBA/2J (DBA) mice, a strain that exhibits high-frequency hearing loss beginning around the time of weaning/adolescence (between 3-4 weeks of age) and becoming severe by 2-3 months of age. Mice were exposed 12 h per night for 10 nights to a 70 dB SPL broad-band noise AAE at one of three age periods ranging from the onset of hearing loss (25-35 days of age) to more severe degrees of hearing loss (35-45 days and 45-55 days); control mice did not receive the AAE. C57BL/6J (C57) mice of the same ages provided normal-hearing. age-matched mice in both exposed and control conditions. The auditory brainstem response (ABR), acoustic startle response amplitude, and prepulse inhibition (PPI) were used to assess the auditory system. The AAE had significant effects on DBA mice, but had no effect on normal-hearing C57 mice. For the most part, AAE exposure resulted in improved auditory performance in DBA mice (better PPI, lower ABR thresholds, bigger startle amplitudes). However, the age of the mice and/or severity of hearing loss proved to be an important variable; improvement of PPI occurred only when the AAE was initiated later in the course of hearing loss (35 days of age or older); in contrast to this, beneficial effects on ABR thresholds occurred only when the AAE was initiated early in the course of hearing loss (< 45 days of age).