Rebound hyperthermia follows ethanol-induced hypothermia in rats

We have recently described a telemetry/microcomputer system to monitor core temperatures in rats. We implant a miniature transmitter (Mini-mitter) into the peritoneal cavity of the rat, allowing us to obtain temperatures around the clock without handling the animals or disturbing the light-dark cycle. In the present study we describe the temperature effects of ethanol doses ranging from 2 to 6 g/kg. Baseline temperatures were collected for 2 days before drug was administered. Subsequent computer analysis then allowed us to compare experimental results in each animal with its own baseline temperature to allow for individual and circadian temperature differences. In preliminary studies we observed the well-known dose-dependent hypothermic effect of ethanol. However, by observing animals continually over 4 days we also observed a period of rebound hyperthermia beginning at about the time of complete ethanol elimination and persisting for several days. During this period daytime temperatures remained at the normally high night-time level. This may be evidence of a mild abstinence syndrome, or alternatively, may be due to a disruption of the normal circadian temperature rhythm.