title: Rapid resetting of the mammalian circadian clock.
abstract: The suprachiasmatic nuclei (SCN) contain the principal circadian clock governing overt daily rhythms of physiology and behavior. The endogenous circadian cycle is entrained to the light/dark via direct glutamatergic retinal afferents to the SCN. To understand the molecular basis of entrainment, it is first necessary to define how rapidly the clock is reset by a light pulse. We used a two-pulse paradigm, in combination with cellular and behavioral analyses of SCN function, to explore the speed of resetting of the circadian oscillator in Syrian hamster and mouse. Analysis of c-fos induction and cAMP response element-binding protein phosphorylation in the retinorecipient SCN demonstrated that the SCN are able to resolve and respond to light pulses presented 1 or 2 hr apart. Analysis of the phase shifts of the circadian wheel-running activity rhythm of hamsters presented with single or double pulses demonstrated that resetting of the oscillator occurred within 2 hr. This was the case for both delaying and advancing phase shifts. Examination of delaying shifts in the mouse showed resetting within 2 hr and in addition showed that resetting is not completed within 1 hr of a light pulse. These results establish the temporal window within which to define the primary molecular mechanisms of circadian resetting in the mammal.
authors.affiliation: Department of Anatomy, University of Cambridge, Cambridge CB2 3DY, United Kingdom.
authors.forename: J D
authors.initials: JD
authors.lastname: Best
authors.forename: E S
authors.initials: ES
authors.lastname: Maywood
authors.forename: K L
authors.initials: KL
authors.lastname: Smith
authors.forename: M H
authors.initials: MH
authors.lastname: Hastings
mesh_terms: D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D006224:Cricetinae; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017403:In Situ Hybridization; D008027:Light; D008297:Male; D008647:Mesocricetus; D051379:Mice; D008813:Mice, Inbred ICR; D010766:Phosphorylation; D010775:Photic Stimulation; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D013493:Suprachiasmatic Nucleus / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D016760:Proto-Oncogene Proteins c-fos