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Background: Evidence supports a role for the circadian system in alcohol use disorders, but the impact of adolescent alcohol exposure on circadian timing later in life is unknown. Acute ethanol (EtOH) attenuates circadian photic phase‐resetting in adult, but not adolescent, rodents. However, nearly all studies have focused on males and it is unknown whether this adolescent‐typical insensitivity to EtOH persists into adulthood after adolescent drinking. Methods: Circadian activity was monitored in C57BL/6J mice receiving adolescent intermittent EtOH (AIE) exposure (15% EtOH and water every other day throughout adolescence) or water alone followed by 24 days wherein EtOH was not available (washout). Mice then received a challenge dose of EtOH (1.5 g/kg, intraperitoneal) or saline 15 minutes prior to a 30‐minute phase‐delaying light pulse and then were released into constant darkness (DD). To control for possible phase‐shifting by EtOH challenge alone, a separate group of mice underwent AIE exposure (or water‐only) and washout and then received an EtOH or saline injection, but did not receive a light pulse prior to DD. Results: Striking sex differences in nearly all measures of circadian photic entrainment were observed during adolescence but AIE effects were subtle and few. Only EtOH‐naïve adult male mice showed attenuated photic phase‐shifts with EtOH challenge, while all other groups showed normal phase‐resetting responses to light. AIE‐exposed females showed a persistent delay in activity offset. Conclusions: Adult male AIE‐exposed mice retained adolescent‐like insensitivity to EtOH‐induced suppression of photic phase‐resetting, suggesting AIE‐induced "lock‐in" of an adolescent behavioral phenotype. Adult AIE‐exposed females showed delayed initiation of the rest phase. Our results also indicate that intermittent EtOH drinking has subtle effects on circadian activity in mice during adolescence that differ from previously reported effects on adult males. The observed sex differences in circadian activity, EtOH consumption and preference, and responses to EtOH challenge merit future mechanistic study. Differential effects of adolescent drinking on circadian rhythms in adult mice. A) Adult female mice showed persistent delays in activity offset after exposure to adolescent intermittent ethanol (AIE), perhaps reflecting increased latency to sleep. B) Adult male mice with prior AIE exposure showed persistent insensitivity to acute ethanol‐induced attenuation of circadian phaseresetting to light. These data suggest that adolescent drinking affects circadian rhythms differently between the sexes, and may ultimately play a sex‐dependent role in motivation to drink in adulthood. [ABSTRACT FROM AUTHOR]

Background Growing evidence supports a central role for the circadian system in alcohol use disorders, but few studies have examined this relationship during adolescence. In mammals, circadian rhythms are regulated by the suprachiasmatic nucleus, a biological clock whose timing is synchronized (reset) to the environment primarily by light (photic) input. Alcohol (ethanol [EtOH]) disrupts circadian timing in part by attenuating photic phase-resetting responses in adult rodents. However, circadian rhythms change throughout life and it is not yet known whether EtOH has similar effects on circadian regulation during adolescence. Methods General circadian locomotor activity was monitored in male C57BL6/J mice beginning in adolescence (P27) or adulthood (P61) in a 12-hour light, 12-hour dark photocycle for ~2 weeks to establish baseline circadian activity measures. On the day of the experiment, mice received an acute injection of EtOH (1.5 g/kg, i.p.) or equal volume saline 15 minutes prior to a 30-minute light pulse at Zeitgeber Time 14 (2 hours into the dark phase) and then were released into constant darkness (DD) for ~2 weeks to assess phase-resetting responses. Control mice of each age-group received injections but no light pulse prior to DD. Results While adults showed the expected decrease in photic phase-delays induced by acute EtOH, this effect was absent in adolescent mice. Adolescents also showed baseline differences in circadian rhythmicity compared to adults, including advanced photocycle entrainment, larger photic phase-delays, a shorter free-running (endogenous) circadian period, and greater circadian rhythm amplitude. Conclusions Collectively, our results indicate that adolescent mice are less sensitive to the effect of EtOH on circadian photic phase-resetting and that their daily activity rhythms are markedly different than those of adults. [ABSTRACT FROM AUTHOR]