Various environmental compounds have been shown to affect the development of organisms leading to long-lasting alterations of adult function. Polychlorinated biphenyls (PCBs) are a group of industrial compounds which were used in numerous applications. Due to their persistence and accumulation in food chains, elevated levels of PCBs are still found in humans and animals. Developing organisms exhibit a particular sensitivity to PCBs. PCB-induced effects on thyroid hormone and retinoids are among the most pronounced effects. Since thyroid hormones and retinoids regulate the development of the auditory system, we examined brainstem auditory evoked potentials (BAEPs) in rats after perinatal exposure to PCBs. Rat dams were orally treated with purified PCB180 or PCB52 during gestation and/or after delivery. There were six dose levels, ranging from 0 to 1000 mg/kg (PCB180, total dose) or 0 to 3000 mg/kg (PCB52, total dose). These PCB congeners were highly purified to exclude effects of dioxin-like contaminants. BAEPs were recorded in male and female offspring at the age of approximately 7 months. Animals were sedated with ketamine and xylazine during the measurements. Clicks and tone pips, ranging from 0.5 to 16 kHz, were used to elicit BAEPs. Sound pressure levels (SPL) were varied to examine BAEP thresholds. Also, latencies of wave II and IV were determined. Results were analyzed with general linear models (GLM) to determine significant dose-response relations. There were slight to moderate effects of purified PCB180 on BAEPs of female offspring in the low frequency range. Significant linear dose-response relations were found for thresholds at 0.5 kHz and 4 kHz and for latency of wave IV at 0.5 kHz (p<0.05). Alterations in males were not significant (p>0.05), with the exception of a small prolongation of wave II latency after stimulation with clicks at 70 dB. In contrast, PCB52 resulted in threshold elevations in the frequency range from 0.5 to 8 kHz (p<0.05) which were particularly pronounced in male offspring. In addition, there marked elevations of wave II latency at 0.5 to 2 kHz in males (p<0.05). These results show that exposure to highly purified PCBs during development impairs auditory function in adulthood and that these effects cannot be attributed to dioxin-like contaminants.

(Supported by the EU commission, ATHON, contract FOOD-CT-2005-022923).