Abstract:

Past evidence from investigations in which an intense noise was delivered to the fetal hearing mechanism has been contradictory. Some investigations suggest the possibility of a critical period during auditory development when exposure to intense noise may adversely affect auditory function. Other studies have reported no effect of intense noise on the auditory brainstem response of fetal sheep. In one recent experiment, auditory brain-stem response thresholds were recorded in utero from fetal sheep prior to and following an intense broadband noise exposure delivered at a developmental period when the ABR was emerging. The ABR thresholds recorded from the noise-exposed fetuses, when measured over developmental time, were not as sensitive as thresholds obtained from age-matched control fetuses. In a related experiment, sheep were exposed four times to an intense broadband noise and the cochleae were harvested 20 days later for histological analysis. Histological comparisons revealed significant inner and outer hair cell damage in the noise-exposed fetuses. This damage was not observed in control fetuses. These studies provide increased evidence that intense noise delivered to a pregnant ewe can result in alterations of structure and function in the developing auditory system of the sheep fetus.