CREPUSCULAR RHYTHMS OF EEG SLEEP-WAKE IN A HYSTRICOMORPH RODENT, OCTODON-DEGUS

Sleep-wake circadian rhythms are well documented for nocturnal rodents , but little is known about sleep regulation in diurnal or crepuscular rodent species. This study examined the circadian sleep-wake rhythms in Octodon degus by means of electroencephalogram (EEG) analysis. Reco rdings were made from animals housed with or without running wheels in the cages. In a 24-h light-dark (LD) cycle (LD 12:12), sleep and wake patterns were highly fragmented under both conditions except for crep uscular timed episodes of waking. Without running wheels, sleep bout l engths averaged 3.7 +/- 0.1 min, and total sleep time was 37.6 +/- 3.7 % per 24 h. Although the percentage of total wakefulness was similar d uring the light phase (63.4 +/- 2.4%) and dark phase (61.5 +/- 2.8%), measures of locomotor activity (LMA) and body temperature were general ly greater during the day than during the night. Without running wheel s, EEG slow wave activity (SWA) in nonrapid eye movement (NREM) sleep exhibited a circadian waveform that was elevated only during the light phase. SWA peaked at Zeitgeber Time 7 (ZT 7) (several hours after the dominant waking episode at ZT 23), then declined across the later hal f of the light phase and into the dark phase. Voluntary wheel running- did not alter daily total sleep time, the duration of average sleep bo uts, or maximum sleep bouts, but it increased the episode of waking, L MA, and body temperature at ZTs 11-12. Under these conditions, NREM sl eep and SWA exhibited crepuscular patterns, with elevated SWA during t he day and night. Although Octodon degus exhibited no strong preferenc e for sleep during the light or dark phase, these data suggest that in this species homeostatic sleep responses (indicated by SWA) are gated by the dominant crepuscular episode(s) of waking and can be influence d by wheel running.