Abstract 1064 Poster Session II, Sunday, 5/2 (poster 52)

Fetal asphyxia (FA) may account for a significant number of patients suffering from long-term neurodevelopmental impairment, including hearing loss. The anatomical development of the rat vestibulocochlear system cochlea is believed to be complete by the day 17 of gestation (E17), 80% of full term gestation, and normal physiological measurements can be obtained at postnatal day 16. However, most animal models and research focus on near term or full term animals. The aim of this work was to study the impact of FA on hearing. For this, pregnant Lewis rats were subjected to a midline laparotomy at E17. The uterine and the ovarian arteries were clamped with non traumatic removable clamps for 75 minutes. After reperfusion, the uterine horns were placed back intra-abdominally and the abdominal wall was closed. The pups of the asphyctic group (group 1, n=5) were born vaginally at term date. Control groups were either sham operated (group 2, n=5) or untreated (group 3, n=5). At 6 months of age, the 3 groups of rats were anesthesized by xylazine 1 mg/kg sc and ketamine 50 mg/kg im. 2f1-f2 distortion product otoacoustic emissions (DPOAE) and click-evoked auditory brainstem response (ABR) interpeak latenties and thresholds were registered in normothermic conditions.

Compared to the results obtained in the untreated group, all measurements appeared unaltered in both the asphyctic and the sham operated group.

Discussion: During the first weeks of life, the rat has an extreme sensitivity to environmental stimuli and ototoxic agents and asphyxia in this period is a recognized risk-factor for hearing loss. Theoretically, the prenatal asphyctic insult was severe and long enough to produce long lasting hearing impairment. However, hearing remained intact in the adult rat. Several hypothesis, including absence of damage as well as full recovery, need further research to explain normal hearing after FA in the rat.