title: Photic regulation of clock systems.
abstract: Circadian rhythms in physiology and behavior provide a selective advantage by enabling organisms to anticipate rhythmic changes in their environment. These rhythms are based upon a molecular clock generated via an intracellular transcriptional-translational feedback loop involving a number of key clock genes. However, to be of practical use, circadian rhythms need to be entrained to the external environment. In mammals, the primary signal for entrainment is light detected by the photoreceptors of the eye. Research on the mechanisms of photic entrainment has identified a novel photoreceptor system in the retina, consisting of photosensitive retinal ganglion cells expressing the photopigment melanopsin. Light input from these retinal photoreceptors reaches the master circadian pacemaker in the suprachiasmatic nuclei (SCN) via the retinohypothalamic tract, where it then interacts with the molecular clock to bring about entrainment. This chapter focuses on the retinal photoreceptors mediating entrainment, and how light information from the retina is transmitted to the SCN, before detailing recent advances in our understanding of how the molecular clock within the SCN is regulated by light input. Finally, the primary assays that have been used to measure photic entrainment are described.
authors.affiliation: Sleep and Circadian Institute (SCNi), Nuffield Department of Clinical Neurosciences (Nuffield Laboratory of Ophthalmology), University of Oxford, Oxford, United Kingdom.
authors.forename: Steven
authors.initials: S
authors.lastname: Hughes
authors.affiliation: Sleep and Circadian Institute (SCNi), Nuffield Department of Clinical Neurosciences (Nuffield Laboratory of Ophthalmology), University of Oxford, Oxford, United Kingdom.
authors.forename: Aarti
authors.initials: A
authors.lastname: Jagannath
authors.affiliation: Sleep and Circadian Institute (SCNi), Nuffield Department of Clinical Neurosciences (Nuffield Laboratory of Ophthalmology), University of Oxford, Oxford, United Kingdom.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Hankins
authors.affiliation: Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom. Electronic address: russell.foster@eye.ox.ac.uk.
authors.forename: Russell G
authors.initials: RG
authors.lastname: Foster
authors.affiliation: Nuffield Laboratory of Ophthalmology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom. Electronic address: stuart.peirson@eye.ox.ac.uk.
authors.forename: Stuart N
authors.initials: SN
authors.lastname: Peirson
mesh_terms: D000818:Animals; D001683:Biological Clocks; D002940:Circadian Rhythm; D006801:Humans; D008027:Light; D017299:Rod Opsins / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D000099210:Melanopsin
chemical_list: D017299:Rod Opsins; D000099210:Melanopsin
keywords: Entrainment; Light; Melanopsin; Retina; Suprachiasmatic nuclei; pRGC