Frequency discrimination in rats exposed to noise as juveniles

- We analyzed frequency discrimination in adult rats exposed to noise as juveniles.
- We recorded and evaluated prepulse inhibition of the acoustic startle reflex.
- In exposed animals discrimination was altered at moderate intensities (70 dB SPL).
- Altered discrimination was found even in rats with normal hearing thresholds.
- Deficit in exposed rats disappeared at higher intensities (85-90 dB SPL).

Sound exposure during the early postnatal period can significantly influence the function of the auditory system in rats during adulthood. In the present study, rat pups (strain Long-Evans) were exposed to broad-band noise at 125 dB SPL for 8, 12 or 25 min on postnatal day 14 and then at the age of 3-5 months their frequency discrimination at 4 and 16 kHz was assessed using a modified method of the prepulse inhibition of the acoustic startle reflex. In all groups of exposed rats, an altered frequency discrimination of the tonal stimuli was observed, in comparison with controls, at 70 dB SPL. A worsening of frequency discrimination was observed even in animals exposed for 8 min, the auditory thresholds of which were almost identical to that of control animals. The individual auditory thresholds did not correlate with frequency discrimination. The difference in frequency discrimination between the exposed and control animals disappeared at 85-90 dB SPL. Our data suggests that brief noise exposure during the critical period of development results in the altered frequency discrimination at moderate sound intensities in adult rats, which may appear even in individuals with normal hearing thresholds.