Structure and function of the adult cochlea following prenatal irradiation

The structure and function of the cochlea of the CBA/CBA mouse were analysed after exposure to single doses of gamma irradiation during embryonic development. Pregnant mice were exposed to 0.5, 1 and 2 Gy, respectively, on either the 12th, 13th, or 16th gestational day. Morphological analyses were performed using light microscopy, scanning electron microscopy and transmission electron microscopy while the function was measured with the auditory brainstem response (ABR) technique. The inner and outer hair cells showed pathological changes of sensory hairs and their anchoring in the cuticular plate. Cytocochleogram counting was performed classifying the morphological changes into three different severity degrees of pathology. A dose dependent pattern of irradiation induced pathology was documented. A threshold shift of about 20 dB was found after irradiation with 2 Gy. A flat loss of ABR curves occurred in animals irradiated on the 12th or 16th gestational days. If the fetuses were exposed on the 13th gestational day the high frequencies resulted in more pronounced damage than the middle and low frequencies.