title: Distinct Firing Properties of Vasoactive Intestinal Peptide-Expressing Neurons in the Suprachiasmatic Nucleus.
abstract: The suprachiasmatic nucleus (SCN) regulates daily rhythms in physiology and behavior. Previous studies suggest a critical role for neurons expressing vasoactive intestinal peptide (VIP) in coordinating rhythmicity and synchronization in the SCN. Here we examined the firing properties of VIP-expressing SCN neurons in acute brain slices. Active and passive membrane properties were measured in VIP and in non-VIP neurons during the day and at night. Current-clamp recordings revealed that both VIP and non-VIP neurons were spontaneously active, with higher firing rates during the day than at night. Average firing frequencies, however, were higher in VIP neurons (3.1 ± 0.2 Hz, day and 2.4 ± 0.2 Hz, night) than in non-VIP neurons (1.8 ± 0.2 Hz, day and 0.9 ± 0.2 Hz, night), both day and night. The waveforms of individual action potentials in VIP and non-VIP neurons were also distinct. Action potential durations (APD50) were shorter in VIP neurons (3.6 ± 0.1 ms, day and 2.9 ± 0.1 ms, night) than in non-VIP neurons (4.4 ± 0.3 ms, day and 3.5 ± 0.2 ms, night) throughout the light-dark cycle. In addition, afterhyperpolarization (AHP) amplitudes were larger in VIP neurons (21 ± 0.8 mV, day and 24.9 ± 0.9 mV, night) than in non-VIP neurons (17.2 ± 1.1 mV, day and 20.5 ± 1.2 mV, night) during the day and at night. Furthermore, significant day/night differences were observed in APD50 and AHP amplitudes in both VIP and non-VIP SCN neurons, consistent with rhythmic changes in ionic conductances that contribute to shaping the firing properties of both cell types. The higher day and night firing rates of VIP neurons likely contribute to synchronizing electrical activity in the SCN.
authors.affiliation: Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO.
authors.forename: Tracey O
authors.initials: TO
authors.lastname: Hermanstyne
authors.affiliation: Department of Biology, Washington University, St. Louis, MO.
authors.forename: Carrie L
authors.initials: CL
authors.lastname: Simms
authors.affiliation: Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO National Center for Complementary and Alternative Medicine, NIH 35 Convent Drive Building 35A, Room 1E-410, Bethesda, MD 20892, USA.
authors.forename: Yarimar
authors.initials: Y
authors.lastname: Carrasquillo
authors.affiliation: Department of Biology, Washington University, St. Louis, MO.
authors.forename: Erik D
authors.initials: ED
authors.lastname: Herzog
authors.affiliation: Departments of Developmental Biology and Medicine, Washington University School of Medicine, Saint Louis, MO jnerbonne@wustl.edu.
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Nerbonne
mesh_terms: D000200:Action Potentials; D000818:Animals; D002940:Circadian Rhythm; D051379:Mice; D009474:Neurons / Q000502:physiology*; D017440:Photoperiod; D051239:Receptors, Vasoactive Intestinal Peptide, Type II / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000166:cytology* / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000235:genetics / Q000378:metabolism*
chemical_list: D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D014660:Vasoactive Intestinal Peptide
keywords: SCN; VIP neuropeptide; action potential waveforms; circadian rhythms; membrane excitability; rhythmic firing