Developmental Exposure to Aroclor 1254 Produces Low-Frequency Alterations in Adult Rat Brainstem Auditory Evoked Responses

Developmental exposure of Long—Evans rats to 0, 1, 4,or 8 mg/kg/day Aroclor 1254 (A1254) from Gestational Day 6 throughPostnatal Day 21 produces an elevated behavioral threshold fora 1-kHz tone. Brahistem auditory evoked responses (BAERs) wereassessed in a subset of these animals (about 1 year old) usingfiltered clicks at 1 (65 and 80 dB SPL), 4 (60 and 80 dB SPL),16 (40 and 80 dB SPL), and 32 (40 and 80 dB SPL) kHz. Aroclor1254 decreased BAER amplitudes at 1 and 4 kHz, but not at 16or 32 kHz. A dose-related decrease in the baseline-to-peak P_1Aamplitude was observed for the 1-kHz (80-dB) stimulus. Dosesof 1, 4, or 8 mg/kg/day A1254 decreased the peak-to-peak amplitudeof both P_1AN₁ and P_1BN₁ for a 1-kHz (80-dB) stimulus. Dosesof 4 and 8 mg/kg/day A1254 decreased the peak-to-peak amplitudeof N₁P₂ and P₂N₂ for a 4-kHz (60-dB) or 1-kHz (80-dB) stimulus.At 8 mg/kg/day, A1254 also increased the latency of peak P₄at 1 kHz (65 dB). The decreases in peak P_1A amplitudes are consistentwith a dysfunction of the cochlea and/or auditory nerve. Together,the data confirm that developmental exposure of rats to A1254produces a permanent low- to mid-frequency auditory dysfunctionand suggest a cochlear and/or auditory nerve site of action.