No abstract

Intense exogenous noise penetrated the uterus of pregnant sheep and resulted in elevations in ABR thresholds 2 to 3 wk after exposure. In fetuses repeatedly exposed to noise, the middle and apical turns of the cochlea showed greater hair cell damage than found at the same locations in control cochlea. The basal turn of the cochlea was not damaged.

No abstract

The Auditory Brainstem Response (ABR) was recorded from fetal sheep in utero between gestational ages of 111 days and 136 days (Normal gestation is 145 days). The ABR was detected at 111 days gestation (dGA) and morphology of the waveform improved rapidly from 116 to 123 dGA. At 123 dGA, the four vertex-positive peaks were similar to those observed in adult ewes. Thresholds of the ABR to clicks and tone bursts improved rapidly between 111 and 123 dGA. From 123 to 136 dGA, ABR thresholds continued to improve, but at a much slower rate. Latencies for the peaks also decreased during development from 111 to 136 days, with latencies for Waves III and IV showing a greater decrease than latencies for Waves I and II.

No abstract