Phase–Response Curve for Ethanol: Alterations in Circadian Rhythms of Temperature and Activity in Rats

Abstract

Circadian rhythms of core body temperature and general activity in Sprague–Dawley rats were monitored for 21 days using remote radiotelemetry to examine acute and sustained effects of 0 (saline) 1.0, and 2.0 g/kg ethanol injections administered at four different times of day. Ethanol produced dose-dependent and statistically significant hypothermia and hypoactivity when injected at 0100, 0700, 1300, and 1900 h; however, the magnitude of the hypothermic effect was greatest at the 1900-h injection time. Cosinor analyses revealed persistent alterations in both activity and temperature rhythms, which lasted for at least 48 h postinjection. Ethanol significantly shortened the period of activity rhythms when injected in either 1.0 or 2.0 g/kg doses at 0700 and 1300 h, and produced similar period-shortening effects on temperature rhythms at 1300 and 1900 h. The acrophase of the activity rhythm was significantly phase delayed by 1.0 g/kg ethanol at 0700 h, while the acrophase of temperature was significantly phase advanced by 2.0 g/kg ethanol at 0100 h, but significantly phase delayed by the same dose administered at 1300 h. A statistically significant and dose-dependent reduction in the amplitude of the body temperature rhythm was observed at the 1900-h administration time. There were no differences in the MESOR (Midline Estimating Statistic of Rhythm; i.e., rhythm-adjusted mean value) of either temperature or activity circadian rhythms as a function of ethanol treatment at any dose.