Modality-specific impairments in response habituation following postnatal binge ethanol

The rate of habituation of the heart rate orienting response (OR) to both olfactory and auditory cues was examined in subjects neonatally exposed to ethanol. Subjects were administered 5.25 g/kg/day ethanol in a binge-like manner on either postnatal days (PDs) 4-9 or 10-15. Controls were given sham intubations. Ethanol exposure had no effect on the form or magnitude of the heart rate OR; all subjects exhibited a monophasic bradycardia to the olfactory and auditory cues. However, ethanol treatment severely affected the rate of response habituation to an olfactory cue, regardless of the timing of that exposure. Ethanol treatment on either PDs 4-9 or 10-15 resulted in a failure of animals to show complete heart rate response habituation. For the auditory cue, rate of response habituation was unaffected by ethanol treatment. These results indicate that response habituation deficits in a postnatal model of human fetal-alcohol exposure are modality specific. The response habituation paradigm may be useful for studying mechanisms of short-term recognition memory deficits following early alcohol exposure, although modality of the test stimulus needs to be taken into account. The results suggest that central nervous system structures affected by ethanol may be specific to those involved in olfactory processing, such as the olfactory bulb or hippocampus.