Heart rate orienting and respiratory sinus arrhythmia development in rats exposed to alcohol or hypoxia.

The effect of alcohol exposure and hypoxia on the heart rate orienting response and RSA development was studied in preweanling rats. Rats were artificially reared from postnatal days 4 through 12 and either exposed to alcohol (5 g/kg/day) or hypoxia (two 15-min episodes/day) from postnatal days 4 to 10. Control groups consisted of artificially reared and normally reared rats not exposed to alcohol or hypoxia. The heart rate and respiration was recorded at baseline and during repeated exposures to auditory and visual stimuli every other day from postnatal day 13 through 21. The hypoxia group showed an enhanced heart rate orienting response to the auditory stimuli on postnatal days 17 and 19 compared to the other three groups, which did not differ from each other. The baseline interbeat interval increased over this period of time and there was a large increase in respiratory sinus arrhythmia from postnatal day 15 to 21. The alcohol and hypoxia rats showed significantly less of an increase in respiratory sinus arrhythmia on postnatal days 19 and 21. All rats showed a greater response to the auditory stimuli than to the visual stimuli on postnatal days 17 and 19 and all groups showed equivalent habituation to both stimuli within a session. The results suggest that respiratory sinus arrhythmia and the heart rate response to stimuli may not be strongly related during this developmental stage in the rat and that hypoxia but not alcohol exposure alters attentional processes for auditory stimuli as measured by the heart rate orienting response.