Acute exposure to methyl or ethyl alcohol alters auditory function in the rat

Effects of alcohol on audition were studied in the rat by examining the modification of acoustic startle reflexes by pure tone pulses and by gaps in white noise. Systematic inhibition of the startle reflex by variation in pulse intensity provides an objective measure of loudness perception, while variation in gap duration assesses temporal acuity. Groups of rats (n = 8) received four injections of 0.0, 0.25, 1.00, and 2.00 g/kg of either methyl or ethyl alcohol in increasing order at 1-hr intervals. One-half hour after the administration of each dose, loudness perception or temporal acuity was measured. Blood alcohol levels (mM) for the two alcohols obtained in control animals were equivalent following the final dose. Alcohol produced a dose-dependent reduction in baseline startle amplitude that was greater during exposure to ethanol than during methanol. Loudness functions associated with pulse intensity were not diminished by alcohol; however, inhibition produced by a gap in noise was reduced following the highest dose of either alcohol. These data are consistent both with behavioral studies that have suggested that alcohol does not affect loudness perception, and with electrophysiological experiments which indicate that alcohol disrupts temporal relationships along the primary auditory pathway.