title: Varying photoperiod in the laboratory rat: profound effect on 24-h sleep pattern but no effect on sleep homeostasis.
abstract: To assess the influence of the photoperiod on sleep regulation, laboratory rats were adapted to a long photoperiod (LPP; 16:8-h light-dark cycle, LD 16:8) or a short photoperiod (SPP; LD 8:16). The electroencephalogram (EEG) and cortical temperature (TCRT) were continuously recorded for a baseline day, a 24-h sleep deprivation (SD) period, and a recovery day. Data obtained previously for LD 12:12 served for comparison. Whereas the photoperiod exerted a prominent effect on the 24-h sleep pattern, the 24-h baseline level of sleep and the response to SD were little affected. Recovery from SD was characterized by a marked rise in rapid eye movement sleep, a moderate rise in non-rapid eye movement sleep, and an initial enhancement of EEG slow-wave activity followed by a decrease below baseline. The amplitude and phase of the "unmasked" 24-h component of TCRT did not differ between LPP and SPP. Computer simulations demonstrated that the changes of TCRT and EEG slow-wave activity can be largely accounted for by the sequence of the vigilance states. We conclude that the photoperiod does not affect the basic processes underlying sleep regulation.
authors.affiliation: Institute of Pharmacology, University of Zürich, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Franken
authors.forename: I
authors.initials: I
authors.lastname: Tobler
authors.forename: A A
authors.initials: AA
authors.lastname: Borbély
mesh_terms: D000818:Animals; D001143:Arousal; D001831:Body Temperature; D002540:Cerebral Cortex / Q000502:physiology; D002940:Circadian Rhythm; D006706:Homeostasis; D008297:Male; D009043:Motor Activity / Q000502:physiology; D017440:Photoperiod; D051381:Rats; D017207:Rats, Sprague-Dawley; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000502:physiology