title: Seasonal encoding by the circadian pacemaker of the SCN.
abstract: The circadian pacemaker of the suprachiasmatic nucleus (SCN) functions as a seasonal clock through its ability to encode day length [1-6]. To investigate the mechanism by which SCN neurons code for day length, we housed mice under long (LD 16:8) and short (LD 8:16) photoperiods. Electrophysiological recordings of multiunit activity (MUA) in the SCN of freely moving mice revealed broad activity profiles in long days and compressed activity profiles in short days. The patterns remained consistent after release of the mice in constant darkness. Recordings of MUA in acutely prepared hypothalamic slices showed similar differences between the SCN electrical activity patterns in vitro in long and short days. In vitro recordings of neuronal subpopulations revealed that the width of the MUA activity profiles was determined by the distribution of phases of contributing units within the SCN. The subpopulation patterns displayed a significantly broader distribution in long days than in short days. Long-term recordings of single-unit activity revealed short durations of elevated activity in both short and long days (3.48 and 3.85 hr, respectively). The data indicate that coding for day length involves plasticity within SCN neuronal networks in which the phase distribution of oscillating neurons carries information on the photoperiod's duration.
authors.affiliation: Department of Molecular Cell Biology, Lab for Neurophysiology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands.
authors.forename: Henk Tjebbe
authors.initials: HT
authors.lastname: VanderLeest
authors.forename: Thijs
authors.initials: T
authors.lastname: Houben
authors.forename: Stephan
authors.initials: S
authors.lastname: Michel
authors.forename: Tom
authors.initials: T
authors.lastname: Deboer
authors.forename: Henk
authors.initials: H
authors.lastname: Albus
authors.forename: Mariska J
authors.initials: MJ
authors.lastname: Vansteensel
authors.forename: Gene D
authors.initials: GD
authors.lastname: Block
authors.forename: Johanna H
authors.initials: JH
authors.lastname: Meijer
mesh_terms: D000818:Animals; D001683:Biological Clocks; D002940:Circadian Rhythm / Q000502:physiology*; D004594:Electrophysiology; D007700:Kinetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000166:cytology / Q000502:physiology; D017440:Photoperiod; D012621:Seasons; D013493:Suprachiasmatic Nucleus / Q000502:physiology*