Brain-stem auditory evoked potentials in the rat: effects of gender, stimulus characteristics and ethanol sedation

Rat BAEPs varied significantly as a function of gender and ethanol sedation as well as stimulus intensity and repetition rate. All BAEP wave latencies decreased and amplitudes increased with increasing stimulus intensity. Contrary to the prevailing view, the I-IV interpeak latency changed significantly as a function of stimulus intensity. In terms of repetition rate, all BAEP wave latencies increased and amplitudes decreased with increasing repetition rate. Male rats, compared to females, had significantly longer latencies for several BAEP components and interpeak latencies as well as smaller wave II amplitudes across a broad range of stimulus intensities. Males, compared to females, also had longer BAEP wave IV latencies and I-IV interpeak latencies at a slow stimulus repetition rate (8 clicks/sec) but shorter wave IV and I-IV latencies at a fast repetition rate (120 clicks/sec). These gender-dependent differences indicate that male and female rat BAEP data should not be combined indiscriminantly. Ethanol sedation had a statistically significant effect on the I-IV interpeak latency that was judged to be largely independent of core temperature changes. This finding suggests that while sedatives and anesthetics used to immobilize animals may have apparently minor temperature-independent effects on BAEP latencies, these effects can be statistically significant.