Correction to Supporting Information for Smyllie et al., Temporally chimeric mice reveal flexibility of circadian period-setting in the suprachiasmatic nucleus

GABA is a principal neurotransmitter in the hypothalamic suprachiasmatic nucleus (SCN) that contributes to intercellular communication between individual circadian oscillators within the SCN network and the stability and precision of the circadian rhythms. GABA transporters (GAT) regulate the extracellular GABA concentration and modulate GABAA receptor (GABAAR)-mediated currents. GABA transport inhibitors were applied to study how GABAAR-mediated currents depend on the expression and function of GAT. Nipecotic acid inhibits GABA transport and induced an inward tonic current in concentration-dependent manner during whole cell patch-clamp recordings from SCN neurons. Application of either the selective GABA transporter 1 (GAT1) inhibitors NNC-711 or SKF-89976A, or the GABA transporter 3 (GAT3) inhibitor SNAP-5114, produced only small changes of the baseline current. Coapplication of GAT1 and GAT3 inhibitors induced a significant GABAAR-mediated tonic current that was blocked by gabazine. GAT inhibitors decreased the amplitude and decay time constant and increased the rise time of spontaneous GABAAR-mediated postsynaptic currents. However, inhibition of GAT did not alter the expression of either GAT1 or GAT3 in the hypothalamus. Thus GAT1 and GAT3 functionally complement each other to regulate the extracellular GABA concentration and GABAAR-mediated synaptic and tonic currents in the SCN. Coapplication of SKF-89976A and SNAP-5114 (50 µM each) significantly reduced the circadian period of Per1 expression in the SCN by 1.4 h. Our studies demonstrate that GAT are important regulators of GABAAR-mediated currents and the circadian clock in the SCN. NEW & NOTEWORTHY In the suprachiasmatic nucleus (SCN), the GABA transporters GAT1 and GAT3 are expressed in astrocytes. Inhibition of these GABA transporters increased a tonic GABA current and reduced the circadian period of Per1 expression in SCN neurons. GAT1 and GAT3 showed functional cooperativity: inhibition of one GAT increased the activity but not the expression of the other. Our data demonstrate that GABA transporters are important regulators of GABAA receptor-mediated currents and the circadian clock.

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Astrocytic Modulation of Neuronal Activity in the Suprachiasmatic Nucleus: Insights from Mathematical Modeling

Journal of Biological Rhythms ◽

10.1177/0748730420913672 ◽

2020 ◽

Vol 35 (3) ◽

pp. 287-301

Author(s):

Natthapong Sueviriyapan ◽

Chak Foon Tso ◽

Erik D. Herzog ◽

Michael A. Henson

Keyword(s):

Circadian Rhythm ◽

Suprachiasmatic Nucleus ◽

Neuronal Activity ◽

Clock Genes ◽

Rhythmic Activity ◽

Neuronal Population ◽

Circadian Period ◽

Circadian Oscillators ◽

Bidirectional Interactions ◽

The Impact

The suprachiasmatic nucleus (SCN) of the hypothalamus consists of a highly heterogeneous neuronal population networked together to allow precise and robust circadian timekeeping in mammals. While the critical importance of SCN neurons in regulating circadian rhythms has been extensively studied, the roles of SCN astrocytes in circadian system function are not well understood. Recent experiments have demonstrated that SCN astrocytes are circadian oscillators with the same functional clock genes as SCN neurons. Astrocytes generate rhythmic outputs that are thought to modulate neuronal activity through pre- and postsynaptic interactions. In this study, we developed an in silico multicellular model of the SCN clock to investigate the impact of astrocytes in modulating neuronal activity and affecting key clock properties such as circadian rhythmicity, period, and synchronization. The model predicted that astrocytes could alter the rhythmic activity of neurons via bidirectional interactions at tripartite synapses. Specifically, astrocyte-regulated extracellular glutamate was predicted to increase neuropeptide signaling from neurons. Consistent with experimental results, we found that astrocytes could increase the circadian period and enhance neural synchronization according to their endogenous circadian period. The impact of astrocytic modulation of circadian rhythm amplitude, period, and synchronization was predicted to be strongest when astrocytes had periods between 0 and 2 h longer than neurons. Increasing the number of neurons coupled to the astrocyte also increased its impact on period modulation and synchrony. These computational results suggest that signals that modulate astrocytic rhythms or signaling (e.g., as a function of season, age, or treatment) could cause disruptions in circadian rhythm or serve as putative therapeutic targets.

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Temporally chimeric mice reveal flexibility of circadian period-setting in the suprachiasmatic nucleus

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1511351113 ◽

2016 ◽

Vol 113 (13) ◽

pp. 3657-3662 ◽

Cited By ~ 38

Author(s):

Nicola J. Smyllie ◽

Johanna E. Chesham ◽

Ryan Hamnett ◽

Elizabeth S. Maywood ◽

Michael H. Hastings

Keyword(s):

Gene Expression ◽

Suprachiasmatic Nucleus ◽

Feedback Loops ◽

Chimeric Mice ◽

Pacemaker Cells ◽

Daily Behavior ◽

New Perspective ◽

Circadian Behavior

The suprachiasmatic nucleus (SCN) is the master circadian clock controlling daily behavior in mammals. It consists of a heterogeneous network of neurons, in which cell-autonomous molecular feedback loops determine the period and amplitude of circadian oscillations of individual cells. In contrast, circuit-level properties of coherence, synchrony, and ensemble period are determined by intercellular signals and are embodied in a circadian wave of gene expression that progresses daily across the SCN. How cell-autonomous and circuit-level mechanisms interact in timekeeping is poorly understood. To explore this interaction, we used intersectional genetics to create temporally chimeric mice with SCN containing dopamine 1a receptor (Drd1a) cells with an intrinsic period of 24 h alongside non-Drd1a cells with 20-h clocks. Recording of circadian behavior in vivo alongside cellular molecular pacemaking in SCN slices in vitro demonstrated that such chimeric circuits form robust and resilient circadian clocks. It also showed that the computation of ensemble period is nonlinear. Moreover, the chimeric circuit sustained a wave of gene expression comparable to that of nonchimeric SCN, demonstrating that this circuit-level property is independent of differences in cell-intrinsic periods. The relative dominance of 24-h Drd1a and 20-h non-Drd1a neurons in setting ensemble period could be switched by exposure to resonant or nonresonant 24-h or 20-h lighting cycles. The chimeric circuit therefore reveals unanticipated principles of circuit-level operation underlying the emergent plasticity, resilience, and robustness of the SCN clock. The spontaneous and light-driven flexibility of period observed in chimeric mice provides a new perspective on the concept of SCN pacemaker cells.

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Harmine Lengthens Circadian Period of the Mammalian Molecular Clock in the Suprachiasmatic Nucleus

Biological and Pharmaceutical Bulletin ◽

10.1248/bpb.b14-00229 ◽

2014 ◽

Vol 37 (8) ◽

pp. 1422-1427 ◽

Cited By ~ 10

Author(s):

Daisuke Kondoh ◽

Saori Yamamoto ◽

Tatsunosuke Tomita ◽

Koyomi Miyazaki ◽

Nanako Itoh ◽

...

Keyword(s):

Suprachiasmatic Nucleus ◽

Molecular Clock ◽

Circadian Period

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Corrigendum: Circadian Chimeric Mice Reveal an Interplay Between the Suprachiasmatic Nucleus and Local Brain Clocks in the Control of Sleep and Memory

Frontiers in Neuroscience ◽

10.3389/fnins.2021.740799 ◽

2021 ◽

Vol 15 ◽

Author(s):

Elizabeth Susan Maywood ◽

Johanna Elizabeth Chesham ◽

Raphaelle Winsky-Sommerer ◽

Nicola Jane Smyllie ◽

Michael Harvey Hastings

Keyword(s):

Suprachiasmatic Nucleus ◽

Chimeric Mice ◽

Local Brain

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Different Roles for VIP Neurons in the Neonatal and Adult Suprachiasmatic Nucleus

Journal of Biological Rhythms ◽

10.1177/0748730420932073 ◽

2020 ◽

Vol 35 (5) ◽

pp. 465-475 ◽

Cited By ~ 1

Author(s):

Cristina Mazuski ◽

Samantha P. Chen ◽

Erik D. Herzog

Keyword(s):

Suprachiasmatic Nucleus ◽

Daily Activity ◽

Locomotor Behavior ◽

Circadian Period ◽

Circadian Gene ◽

Daily Rhythms ◽

Apoptotic Pathway ◽

Adult Mice ◽

Genetic Deletion

The suprachiasmatic nucleus (SCN) drives circadian rhythms in locomotion through coupled, single-cell oscillations. Global genetic deletion of the neuropeptide Vip or its receptor Vipr2 results in profound deficits in daily synchrony among SCN cells and daily rhythms in locomotor behavior and glucocorticoid secretion. To test whether this phenotype depends on vasoactive intestinal polypeptide (VIP) neurons in the SCN, we ablated VIP SCN neurons in vivo in adult male mice through Caspase3-mediated induction of the apoptotic pathway in cre-expressing VIP neurons. We found that ablation of VIP SCN neurons in adult mice caused a phenotype distinct from Vip- and Vipr2-null mice. Mice lacking VIP neurons retained rhythmic locomotor activity with a shortened circadian period, more variable onsets, and decreased duration of daily activity. Circadian hormonal outputs, specifically corticosterone rhythms, were severely dampened. In contrast, deletion of neonatal SCN VIP neurons dramatically reduced circadian gene expression in the cultured SCN, mimicking the effects of global deletion of Vip or Vipr2. These results suggest that SCN VIP neurons play a role in lengthening circadian period and stimulating the daily surge in glucocorticoids in adults and in synchronizing and sustaining daily rhythms among cells in the developing SCN.

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