Circadian Phase Determines Effects of Repeated Ethanol Vapor Exposure and Withdrawal on Body Temperature and Activity Rhythms of Male Mice

Background Physiological responses to acute ethanol (EtOH) injection depend critically on the timing of their administration. Whether daily timing modulates effects of longer intoxication intervals characteristic of alcohol‐dependent humans remains unknown. The present work examines time‐of‐day effects during EtOH exposure and withdrawal measured by locomotor activity (ActLoc) and body temperature (Tb) across multiple rounds of EtOH exposure/withdrawal. Methods Two groups of C57BL/6J mice (n = 8 per group), implanted with radio‐telemeters, were entrained to opposite light–dark periods (14:10 LD cycle) so that their rest/activity cycles were 12 hours apart. Under a 2‐hour skeleton photoperiod animals were simultaneously exposed to 3 daily cycles of EtOH vapor inhalation (14 hours EtOH on) and withdrawal (10 hours EtOH off). During this time, air‐only control groups (n = 4 per group) matched for entrainment were handled in a comparable manner. After the third cycle of EtOH vapor, the animals were left undisturbed for 11 days to recover. The 14‐day protocol was repeated 3 additional times. Results During intoxication, mice exposed to EtOH in the subjective night exhibited greater hypothermia and more overall disruptions in the Tb and ActLoc rhythms. Acute withdrawal induced hypothermia during the subjective night and hyperthermia during the subjective day. Animals in both phases demonstrated significant disruptions in ActLoc during withdrawal. ActLoc had little effect on Tb during EtOH exposure, but it significantly influenced Tb during acute withdrawal. Conclusions The physiological responses of both EtOH exposure and withdrawal differ as a function of time of day. These findings suggest that controlling for the circadian phase of exposure and/or withdrawal may mitigate the severity of symptomatic withdrawal.