title: Phase resetting light pulses induce Per1 and persistent spike activity in a subpopulation of biological clock neurons.
abstract: The endogenous circadian clock of the mammalian suprachiasmatic nucleus (SCN) can be reset by light to synchronize the biological clock of the brain with the external environment. This process involves induction of immediate-early genes such as the circadian clock gene Period1 (Per1) and results in a stable shift in the timing of behavioral and physiological rhythms on subsequent days. The mechanisms by which gene activation permanently alters the phase of clock neuron activity are unknown. To study the relationship between acute gene activation and persistent changes in the neurophysiology of SCN neurons, we recorded from SCN neurons marked with a dynamic green fluorescent protein (GFP) reporter of Per1 gene activity. Phase-resetting light pulses resulted in Per1 induction in a distinct subset of SCN neurons that also exhibited a persistent increase in action potential frequency 3-5 hr after a light pulse. By simultaneously quantifying Per1 gene activation and spike frequency in individual neurons, we found that the degree of Per1 induction was highly correlated with neuronal spike frequency on a cell-by-cell basis. Increased neuronal activity was mediated by membrane potential depolarization as a result of a reduction in outward potassium current. Double-label immunocytochemistry revealed that vasoactive intestinal peptide (VIP)-expressing cells, but not arginine vasopressin (AVP)-expressing cells, exhibited significant Per1 induction by light pulses. Rhythmic GFP expression occurred in both VIP and AVP neurons. Our results indicate that the steps that link acute molecular events to permanent changes in clock phase involve persistent suppression of potassium current, downstream of Per1 gene induction, in a specific subset of Per1-expressing neurons enriched for VIP.
authors.affiliation: Department of Physiology, University of Kentucky, Lexington, Kentucky 40536-0084, USA. kuhlman@cshl.edu
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Kuhlman
authors.forename: Rae
authors.initials: R
authors.lastname: Silver
authors.forename: Joseph
authors.initials: J
authors.lastname: Le Sauter
authors.forename: Abel
authors.initials: A
authors.lastname: Bult-Ito
authors.forename: Douglas G
authors.initials: DG
authors.lastname: McMahon
mesh_terms: D000200:Action Potentials; D000818:Animals; D001127:Arginine Vasopressin / Q000032:analysis; D001683:Biological Clocks; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D002940:Circadian Rhythm; D004553:Electric Conductivity; D005786:Gene Expression Regulation; D049452:Green Fluorescent Proteins; D007700:Kinetics; D008027:Light; D008164:Luminescent Proteins / Q000235:genetics; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008822:Mice, Transgenic; D008959:Models, Neurological; D009474:Neurons / Q000737:chemistry / Q000145:classification / Q000502:physiology*; D009687:Nuclear Proteins / Q000235:genetics*; D018408:Patch-Clamp Techniques; D056950:Period Circadian Proteins; D015221:Potassium Channels / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000502:physiology*; D015533:Transcriptional Activation; D014660:Vasoactive Intestinal Peptide / Q000032:analysis
chemical_list: D018797:Cell Cycle Proteins; D008164:Luminescent Proteins; D009687:Nuclear Proteins; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins; D015221:Potassium Channels; D001127:Arginine Vasopressin; D049452:Green Fluorescent Proteins; D014660:Vasoactive Intestinal Peptide