title: Colour as a signal for entraining the mammalian circadian clock.
abstract: Twilight is characterised by changes in both quantity ("irradiance") and quality ("colour") of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue-yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Lauren
authors.initials: L
authors.lastname: Walmsley
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Lydia
authors.initials: L
authors.lastname: Hanna
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Josh
authors.initials: J
authors.lastname: Mouland
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Franck
authors.initials: F
authors.lastname: Martial
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Alexander
authors.initials: A
authors.lastname: West
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Smedley
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: David A
authors.initials: DA
authors.lastname: Bechtold
authors.affiliation: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Ann R
authors.initials: AR
authors.lastname: Webb
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Lucas
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Brown
mesh_terms: D000818:Animals; D057906:Circadian Clocks / Q000502:physiology*; D003116:Color; D051379:Mice; D018345:Mice, Knockout; D010775:Photic Stimulation; D017299:Rod Opsins / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin