On the relationships of high-frequency hearing loss and cochlear pathology to the acoustic startle response (ASR) and prepulse inhibition of the ASR in the BXD recombinant inbred series

The measurement of the acoustic startle response (ASR) and prepulse inhibition (PPI) of the ASR in many inbred strains of mice, including C57BL/6 and DBA/2, may be complicated by age-related high-frequency hearing loss (HFHL) and the associated cochlear pathology. Willott and Erway (1998) have recently reported on the age-related changes of the acoustic brain response in the BXD recombinant inbred (RI) series. Based on these data, the RI series was divided into three groups: juvenile-, intermediate-, and adult-onset HFHL. Each of these groups was tested using paradigms which varied the frequency or intensity of the auditory startle and prepulse stimuli. The results obtained in adolescent mice (6-8 weeks) demonstrate that ASR performance is independent of HFHL; there was no group-dependent decline in the ASR amplitudes for high-frequency stimuli. The expected effect of HFHL on PPI is to increase the salience of the still-audible tones. In response to a white-noise prepulse stimulus, the PPI in the juvenile-onset group (which shows marked HFHL at 6 weeks) was similar to that in the adult-onset group. However, when the prepulse stimulus was a pure tone, the juvenile group showed a decrease in salience across all frequencies tested (5-20 kHz). The data point out the need for carefully constructing auditory tasks in the BXD RI series, to avoid the confounding effects of HFHL.