Hangover hyperthermia in rats: relation to tolerance and external stimuli.

The recent finding of rebound hyperthermia in rats on the day after a single IP injection or oral intubation of ethanol was confirmed. In our studies, body temperature measured by rectal probe was significantly decreased for 8 h after 2.5 g/kg ethanol IP and was then significantly elevated 16-24 h after injection; increased vocalization during handling at 24 h was also found. However, rats isolated in a sound-attenuation chamber with remote temperature measurement showed no hyperthermia even though they were hypothermic during intoxication. The results do not support the hypothesis that rebound hyperthermia was caused by either a disruption of circadian rhythms, or by a mild abstinence syndrome alone. Instead, it appears that external stimuli, perhaps related to stress or associated with ethanol administration, are necessary on the day after a moderate dose of ethanol to produce the hyperthermia. Like hangover in humans, hyperthermia was reduced in rats made tolerant to ethanol: both the hypothermia and the rebound hyperthermia were significantly lower on the day after the 12th alternate-day ethanol injection than after the first injection. The aftereffects in rats of acute intoxication are, by definition, hangover signs, and they resemble hangover in humans in several ways, but their relevance as an animal model of hangover remains to be determined.