Estrogen treatment and age effects on auditory brainstem responses in the post-breeding Long-Evans rat

The auditory brainstem response (ABR) was recorded from 20-month-old Long-E vans hooded female rats to determine if latency reductions occur from estro gen replacement. The ABR in these post-breeding age rats was also examined for reductions in response latencies as a function of adult age. Tone pip s timuli (8 and 40 kHz) were presented at 21, 51, or 81 s(-1). Aging control and ovariectomized animals showed slower response latencies for waves Ib-VI than young adults for 8 and 40 kHz stimulation at 21 s(-1). Increased stim ulus rate resulted in longer latencies for all waves at 20 months. In contr ast to hormone treatment effects in young adults, ABR latencies in post-bre eding age estrogen-treated animals were not reduced, consistent with a gene ral decrease in CNS responsiveness to estrogen steroids associated with age . The results also suggest that sensorineural modifications in the auditory system which prolong ABR latencies can occur early in the aging process of adult female subjects.