Circadian entrainment is a fundamental property by which the period of the internal biological clock is entrained by recurring exogenous signals, such that the organism's endocrine and behavioral rhythms are synchronized to environmental cues. In mammals, a master clock is located in the suprachiasmatic nuclei (SCN) of the hypothalamus and may synchronize circadian oscillators in peripheral tissues. Light signal is the dominant synchronizer for master SCN clock. Downstream from the retina, glutamate and PACAP are released and trigger the activation of signal transduction cascades, including CamKII and nNOS activity, cAMP- and cGMP-dependent protein kinases, and mitogen-activated protein kinase (MAPK). Of non-photic entrainment, important phase shifting capabilities have been found for melatonin, which inhibits light-induced phase shifts through inhibition of adenylate cyclase (AC). Multiple entrainment pathways converge into CREB regulation. In turn, phosphorylated CREB activates clock gene expression.

Organismal Systems; Environmental adaptation

Bos taurus (cow) [GN:bta]

PMID:17646042

Brown TM, Piggins HD

Electrophysiology of the suprachiasmatic circadian clock.

Prog Neurobiol 82:229-55 (2007)
DOI:10.1016/j.pneurobio.2007.05.002

PMID:19109992

Dickson L, Finlayson K

VPAC and PAC receptors: From ligands to function.

Pharmacol Ther 121:294-316 (2009)
DOI:10.1016/j.pharmthera.2008.11.006

PMID:20664079

Golombek DA, Rosenstein RE

Physiology of circadian entrainment.

Physiol Rev 90:1063-102 (2010)
DOI:10.1152/physrev.00009.2009

PMID:16217123

Dubocovich ML, Markowska M

Functional MT1 and MT2 melatonin receptors in mammals.

Endocrine 27:101-10 (2005)
DOI:10.1385/ENDO:27:2:101

PMID:20605968

Dubocovich ML, Delagrange P, Krause DN, Sugden D, Cardinali DP, Olcese J

International Union of Basic and Clinical Pharmacology. LXXV. Nomenclature, classification, and pharmacology of G protein-coupled melatonin receptors.

Pharmacol Rev 62:343-80 (2010)
DOI:10.1124/pr.110.002832

PMID:19449447

Hardeland R

Melatonin: signaling mechanisms of a pleiotropic agent.

Biofactors 35:183-92 (2009)
DOI:10.1002/biof.23

PMID:12700026

Golombek DA, Ferreyra GA, Agostino PV, Murad AD, Rubio MF, Pizzio GA, Katz ME, Marpegan L, Bekinschtein TA

From light to genes: moving the hands of the circadian clock.

Front Biosci 8:s285-93 (2003)

PMID:17586087

Mertens I, Husson SJ, Janssen T, Lindemans M, Schoofs L

PACAP and PDF signaling in the regulation of mammalian and insect circadian rhythms.

Peptides 28:1775-83 (2007)
DOI:10.1016/j.peptides.2007.05.005

PMID:15813931

Kim DY, Choi HJ, Kim JS, Kim YS, Jeong DU, Shin HC, Kim MJ, Han HC, Hong SK, Kim YI

Voltage-gated calcium channels play crucial roles in the glutamate-induced phase shifts of the rat suprachiasmatic circadian clock.

Eur J Neurosci 21:1215-22 (2005)
DOI:10.1111/j.1460-9568.2005.03950.x

PMID:15016477

Agostino PV, Ferreyra GA, Murad AD, Watanabe Y, Golombek DA

Diurnal, circadian and photic regulation of calcium/calmodulin-dependent kinase II and neuronal nitric oxide synthase in the hamster suprachiasmatic nuclei.

Neurochem Int 44:617-25 (2004)
DOI:10.1016/j.neuint.2003.09.005

PMID:11294753

Ferreyra GA, Golombek DA

Rhythmicity of the cGMP-related signal transduction pathway in the mammalian circadian system.

Am J Physiol Regul Integr Comp Physiol 280:R1348-55 (2001)
DOI:10.1152/ajpregu.2001.280.5.R1348

PMID:15930378

Butcher GQ, Lee B, Cheng HY, Obrietan K

Light stimulates MSK1 activation in the suprachiasmatic nucleus via a PACAP-ERK/MAP kinase-dependent mechanism.

J Neurosci 25:5305-13 (2005)
DOI:10.1523/JNEUROSCI.4361-04.2005

PMID:10446325

Hamada T, Niki T, Ziging P, Sugiyama T, Watanabe S, Mikoshiba K, Ishida N

Differential expression patterns of inositol trisphosphate receptor types 1 and 3 in the rat suprachiasmatic nucleus.

Brain Res 838:131-5 (1999)
DOI:10.1016/S0006-8993(99)01719-9

PMID:10208575

Diaz-Munoz M, Dent MA, Granados-Fuentes D, Hall AC, Hernandez-Cruz A, Harrington ME, Aguilar-Roblero R

Circadian modulation of the ryanodine receptor type 2 in the SCN of rodents.

Neuroreport 10:481-6 (1999)

PMID:11086993

Fang M, Jaffrey SR, Sawa A, Ye K, Luo X, Snyder SH

Dexras1: a G protein specifically coupled to neuronal nitric oxide synthase via CAPON.

Neuron 28:183-93 (2000)
DOI:10.1016/S0896-6273(00)00095-7

PMID:12573527

Takahashi H, Umeda N, Tsutsumi Y, Fukumura R, Ohkaze H, Sujino M, van der Horst G, Yasui A, Inouye ST, Fujimori A, Ohhata T, Araki R, Abe M

Mouse dexamethasone-induced RAS protein 1 gene is expressed in a circadian rhythmic manner in the suprachiasmatic nucleus.

Brain Res Mol Brain Res 110:1-6 (2003)
DOI:10.1016/S0169-328X(02)00543-0

PMID:17167088

Cheng HY, Dziema H, Papp J, Mathur DP, Koletar M, Ralph MR, Penninger JM, Obrietan K

The molecular gatekeeper Dexras1 sculpts the photic responsiveness of the mammalian circadian clock.

J Neurosci 26:12984-95 (2006)
DOI:10.1523/JNEUROSCI.4253-06.2006