Developmental changes of susceptibility to temporary threshold shift in hamsters

Abstract

The magnitude of temporary threshold shift (TTS) and the time course of recovery of TTS were studied in young hamsters. Animals aged 15, 28, 40, 55, or 85 days were anesthetized with urethane and a sound speculum was sealed around the left tympanic ring. Evoked potentials in response to tone bursts were recorded from an electrode in the right inferior colliculus and thresholds for detecting the computer-averaged neural response were measured before and for 100 min after a 10 minute presentation of a continuous tone (3 kHz, 110 dB SPL), Mean threshold shifts at 4 kHz, 1 min post-exposure, were 16, 35, 41, 28, and 25 dB in the 15-, 28-, 40-, 55-, and 85-day-old groups respectively. Threshold shifts recovered within 100 min in 15- and 85-day-old animals, but required considerably longer to recover in the other age groups. The data suggest that young hamsters pass through a critical period of susceptibility to TSS. Consideration of the development of normal thresholds suggests that the critical period may be dependent on developmental changes within the cochlea. [Work supported by the Deafness Research Foundation.]