The effect of noise trauma following training exposures in the mouse

The effect of moderate level acoustic stimulation, or 'training', on a subsequent high intensity noise exposure was studied in CBA/Ca mice. Eight groups of mice were exposed to a variety of training paradigms as well as different intensity traumatic exposures. We sought a combination which would result in the maximum protective effect from acoustic trauma as measured by the auditory brainstem responses. Using a narrow band noise centered at 4.5 kHz, we investigated the effects of a 10-day 'interval' training regimen, allowing a rest period between successive training exposures, as well as several continuous training exposures. These training paradigms were followed by a 24 h traumatic noise exposure (also centered at 4.5 kHz) at one of three intensities, 107, 110, or 117 dB SPL which induce a temporary, a moderate, or a severe permanent threshold shift, respectively. In none of these trained groups was a protective effect demonstrated at any time up to one month following a subsequent traumatic noise exposure. Several groups demonstrated higher compound threshold shifts after the traumatic noise exposure compared to controls. After a recovery period of 4 weeks nearly all trained groups demonstrated a tendency toward higher permanent threshold shifts than the control, untrained, animals. While no protective effect was demonstrated, examination of the threshold shifts following the training periods and after the traumatic noise exposures raised interesting questions for future investigation regarding the inherent resistance to noise induced threshold shifts in the mouse.