Effects of chronic ethanol ingestion on mid-latency auditory evoked potentials depend on length of exposure

We hypothesized that chronic ethanol ingestion is associated with modifications in components of mid-latency auditory evoked potentials (MAEPs). To test this, male Long-Evans rats were administered 10% ethanol in drinking water as the sole fluid source for 3, 6, or 9 months. MAEPs were obtained and compared to age-matched control groups. MAEPs were obtained from additional rats after 4 weeks of abstinence. Data were obtained for varying frequencies (4, 8, 16, 24, 32 kHz) and intensities (65, 75, 85 dB SPL). Three months of ethanol exposure was associated with increased latencies and amplitudes of Na and Pa. MAEP components recovered and returned to control values after 4 weeks' abstinence following 3 months of EtOH exposure. Few significant differences were observed in the ethanol-treated or abstinent group after 6 month's exposure. However, 9 months of ethanol exposure revealed a significant increase in latencies and decrease in amplitudes of both Na and Pa components. After 4 weeks of abstinence, the Na and Pa component peak latencies appeared earlier than age-matched controls. The Na and Pa peak amplitudes were slightly greater than the ethanol-treated group; however, they did not recover to control values. These findings suggest that chronic ethanol consumption may produce time-dependent structural and/or neurochemical alterations in substrates for cortical information processing, which may be irreversible. In the present paradigm, this irreversibility may occur after 6 or more months of ethanol intake, and may be detected with the use of MAEPs.