title: Glycogen synthase kinase 3 regulates photic signaling in the suprachiasmatic nucleus.
abstract: Glycogen synthase kinase 3 (GSK3) is a serine-threonine kinase that regulates mammalian circadian rhythms at the behavioral, molecular and neurophysiological levels. In the central circadian pacemaker, the suprachiasmatic nucleus (SCN), inhibitory phosphorylation of GSK3 exhibits a rhythm across the 24 h day. We have recently shown that GSK3 is capable of influencing both the molecular clock and SCN neuronal activity rhythms. However, it is not known whether GSK3 regulates the response to environmental cues such as light. The goal of this study was to test the hypothesis that GSK3 activation mediates light-induced SCN excitability and photic entrainment. Immunofluorescence staining in the SCN of mice showed that late-night light exposure significantly increased GSK3 activity (decreased pGSK3β levels) 30-60 min after the light-pulse. In addition, pharmacological inhibition of GSK3 blocked the expected light-induced excitability in SCN neurons; however, this effect was not associated with changes in resting membrane potential or input resistance. Behaviorally, mice with constitutively active GSK3 (GSK3-KI) re-entrained to a 6-h phase advance in the light-dark cycle in significantly fewer days than WT control animals. Furthermore, the behavioral and SCN neuronal activity of GSK3-KI mice was phase-advanced compared to WT, in both normal and light-exposed conditions. Finally, GSK3-KI mice exhibited normal negative-masking behavior and electroretinographic responses to light, suggesting that the enhanced photic entrainment is not due to an overall increased sensitivity to light in these animals. Taken together, these results provide strong evidence that GSK3 activation contributes to light-induced phase-resetting at both the neurophysiological and behavioral levels.
authors.affiliation: Departments of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Jodi R
authors.initials: JR
authors.lastname: Paul
authors.affiliation: Department of Vision Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Alex S
authors.initials: AS
authors.lastname: McKeown
authors.affiliation: Departments of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Davis
authors.affiliation: Department of Psychology, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Stacie K
authors.initials: SK
authors.lastname: Totsch
authors.affiliation: Department of Biological Sciences, Kent State University, Kent, OH, USA.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Mintz
authors.affiliation: Department of Vision Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Kraft
authors.affiliation: Departments of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Rita M
authors.initials: RM
authors.lastname: Cowell
authors.affiliation: Departments of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, 35294, USA.
authors.forename: Karen L
authors.identifier: 0000-0003-3813-8577
authors.initials: KL
authors.lastname: Gamble
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D057906:Circadian Clocks / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D008027:Light; D055537:Light Signal Transduction / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009043:Motor Activity / Q000502:physiology; D009474:Neurons / Q000201:enzymology*; D017440:Photoperiod; D012160:Retina / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000201:enzymology*; D046509:Tissue Culture Techniques
chemical_list: D038362:Glycogen Synthase Kinase 3
keywords: circadian; electrophysiology; entrainment; light; mouse