Circadian timed wakefulness at dawn opposes compensatory sleep responses after sleep deprivation in Octodon degus

The circadian timing system in mammals is thought to promote wakefulness an d oppose sleep drive that accumulates across the activity phase in diurnal and nocturnal species. Whether the circadian system actively opposes compen satory sleep responses in mammals with episodes of alertness consolidated a t dawn and dusk is unknown. In the present study, an interaction between ci rcadian timed arousal at dawn and compensatory sleep responses after sleep deprivation (SD) was examined in Octodon degus, a hystricomorph rodent with crepuscular episodes of wakefulness. Recovery sleep was compared after 6 h ours and 12 hours of SD ending at either CT 21 or 12, just before the dawn, and just after the dusk crepuscular episodes of consolidated wakefulness, respectively. Total sleep time and NREM sleep after SD increased proportion ally to the amount of sleep loss; however, compensatory sleep responses aft er SD were attenuated at CT 23, a circadian time when a crepuscular event o f wakefulness occurs in this species. EEG slow-wave activity (SWA) and body temperature levels in the first two hours after 6 and 12 hours of SD endin g at CT 12 were similar. However, both were significantly higher than after 12 hours of SD ending at CT 21, suggesting factors other than the amount o f prior wake duration can influence SWA levels. This study provides evidenc e that the circadian arousal system opposes compensatory sleep responses at dawn by actively promoting wakefulness in this species.