title: Causes and consequences of hyperexcitation in central clock neurons.
abstract: Hyperexcited states, including depolarization block and depolarized low amplitude membrane oscillations (DLAMOs), have been observed in neurons of the suprachiasmatic nuclei (SCN), the site of the central mammalian circadian (~24-hour) clock. The causes and consequences of this hyperexcitation have not yet been determined. Here, we explore how individual ionic currents contribute to these hyperexcited states, and how hyperexcitation can then influence molecular circadian timekeeping within SCN neurons. We developed a mathematical model of the electrical activity of SCN neurons, and experimentally verified its prediction that DLAMOs depend on post-synaptic L-type calcium current. The model predicts that hyperexcited states cause high intracellular calcium concentrations, which could trigger transcription of clock genes. The model also predicts that circadian control of certain ionic currents can induce hyperexcited states. Putting it all together into an integrative model, we show how membrane potential and calcium concentration provide a fast feedback that can enhance rhythmicity of the intracellular circadian clock. This work puts forward a novel role for electrical activity in circadian timekeeping, and suggests that hyperexcited states provide a general mechanism for linking membrane electrical dynamics to transcription activation in the nucleus.
authors.affiliation: Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, New Jersey, United States of America.
authors.forename: Casey O
authors.initials: CO
authors.lastname: Diekman
authors.forename: Mino D C
authors.initials: MD
authors.lastname: Belle
authors.forename: Robert P
authors.initials: RP
authors.lastname: Irwin
authors.forename: Charles N
authors.initials: CN
authors.lastname: Allen
authors.forename: Hugh D
authors.initials: HD
authors.lastname: Piggins
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Forger
mesh_terms: D000818:Animals; D056926:CLOCK Proteins / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D003198:Computer Simulation; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D051379:Mice; D008959:Models, Neurological; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015203:Reproducibility of Results; D013493:Suprachiasmatic Nucleus / Q000166:cytology* / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D020746:Calcium Channels, L-Type; D056926:CLOCK Proteins; D002118:Calcium