Low-frequency hearing loss in prenatally stressed rats

We investigated the possibility that hearing thresholds are altered in prenatally stressed rats raised in a normal auditory environment. Pregnant dams were assigned randomly to prenatally stressed and control groups. Half of the dams were subjected to the mild stressors of handling, exposure to a novel cage and saline injection at random times during lights-on daily. The hearing thresholds of young adult male offspring were assessed by recording auditory-evoked brainstem responses to 0.5, 1, 2, 4, 8, 16, 32 and 64 kHz pure tones. The resultant audiograms showed that prenatally stressed offspring had significantly higher hearing thresholds than control animals at 1, 2 and 4 kHz (t-tests, P<0.05). The threshold shifts caused by prenatal stress averaged 7.7 dB across frequencies. We conclude that prenatal stress causes low-frequency hearing loss, possibly due to increased vulnerability to noise-induced hearing loss, accelerated cochlear degeneration and/or disrupted cochlear development.