title: Separate oscillating cell groups in mouse suprachiasmatic nucleus couple photoperiodically to the onset and end of daily activity.
abstract: The pattern of circadian behavioral rhythms is photoperiod-dependent, highlighted by the conservation of a phase relation between the behavioral rhythm and photoperiod. A model of two separate, but mutually coupled, circadian oscillators has been proposed to explain photoperiodic responses of behavioral rhythm in nocturnal rodents: an evening oscillator, which drives the activity onset and entrains to dusk, and a morning oscillator, which drives the end of activity and entrains to dawn. Continuous measurement of circadian rhythms in clock gene Per1 expression by a bioluminescence reporter enabled us to identify the separate oscillating cell groups in the mouse suprachiasmatic nucleus (SCN), which composed circadian oscillations of different phases and responded to photoperiods differentially. The circadian oscillation in the posterior SCN was phase-locked to the end of activity under three photoperiods examined. On the other hand, the oscillation in the anterior SCN was phase-locked to the onset of activity but showed a bimodal pattern under a long photoperiod [light-dark cycle (LD)18:6]. The bimodality in the anterior SCN reflected two circadian oscillatory cell groups of early and late phases. The anterior oscillation was unimodal under intermediate (LD12:12) and short (LD6:18) photoperiods, which was always phase-lagged behind the posterior oscillation when the late phase in LD18:6 was taken. The phase difference was largest in LD18:6 and smallest in LD6:18. These findings indicate that three oscillating cell groups in the SCN constitute regionally specific circadian oscillations, and at least two of them are involved in photoperiodic response of behavioral rhythm.
authors.affiliation: Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo 060-8638, Japan.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Inagaki
authors.forename: Sato
authors.initials: S
authors.lastname: Honma
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ono
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tanahashi
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Honma
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001683:Biological Clocks / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002469:Cell Separation; D005786:Gene Expression Regulation; D008027:Light; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL / Q000502:physiology*; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056950:Period Circadian Proteins; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
chemical_list: D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins