Serotonin phase-shifts the mouse suprachiasmatic circadian clock in vitro

The suprachiasmatic nuclei (SCN) of mammals contain a circadian clock that synchronizes behavioral and physiological rhythms to the daily cycle of light and darkness. We have been probing the biochemical substrates of this endogenous pacemaker by examining the ability of treatments affecting cyclic nucleotide-dependent pathways to induce changes in the phase of oscillation in electrical activity of rat SCN isolated in brain slices. Our previous work has shown that daytime treatments that stimulate cAMP-dependent pathways induce phase shifts of the SCN pacemaker in vitro but treatments during the subjective night are without effect. In this study we report that the phase of SCN oscillation is reset by treatments that stimulate cGMP-dependent pathways, but only during the subjective night. Thus, the nocturnal period of SCN sensitivity to cGMP is in antiphase to the diurnal period of sensitivity to cAMP. These results suggest that cAMP and cGMP affect the SCN pacemaker through separate biochemical pathways intrinsic to the SCN. These studies provide evidence that changing biochemical substrates within the SCN circadian clock may underlie some aspects of differential temporal sensitivity of mammals to resetting stimuli.

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Evidence for a central role of transcription in the timing mechanism of a circadian clock

AJP Cell Physiology ◽

10.1152/ajpcell.1996.271.5.c1646 ◽

1996 ◽

Vol 271 (5) ◽

pp. C1646-C1651 ◽

Cited By ~ 16

Author(s):

S. B. Khalsa ◽

D. Whitmore ◽

B. Bogart ◽

G. D. Block

Keyword(s):

Circadian Clock ◽

Phase Shifts ◽

High Concentration ◽

Marine Mollusc ◽

Transcription Inhibitors ◽

Light Pulses ◽

Pulse Experiment ◽

Sensitive Phase ◽

Transcription Inhibitor

The retinal circadian clock in the isolated in vitro eye of the marine mollusc Bulla gouldiana exhibits a phase-dependent requirement for transcription. The transcription-sensitive phase extends through most of the subjective day and therefore is substantially longer than the previously reported translation-sensitive phase. Lower concentrations of transcription inhibitors yield a significant dose-dependent lengthening of circadian period. Clock motion can be stopped by a high concentration of the transcription inhibitor 5,6-dichlorobenz-imidazole riboside (DRB) when applied during the sensitive phase; after withdrawal of the inhibitor, motion resumes from the phase at which it was stopped. In a double-pulse experiment, phase shifts to light pulses applied after DRB pulses, and not during the translation-sensitive phase, indicate that the inhibition of transcription has immediate effects on the phase of the clock. These data suggest that DRB-induced phase shifts are independent of translation, which implies that the rate of transcription itself plays a significant role in the mechanism underlying the generation of the circadian cycle.

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Cocaine modulates pathways for photic and nonphotic entrainment of the mammalian SCN circadian clock

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00602.2011 ◽

2012 ◽

Vol 302 (6) ◽

pp. R740-R750 ◽

Cited By ~ 21

Author(s):

J. David Glass ◽

Allison J. Brager ◽

Adam C. Stowie ◽

Rebecca A. Prosser

Keyword(s):

Circadian Clock ◽

Receptor Antagonist ◽

Serotonin Receptor ◽

Activity Rhythm ◽

Phase Shifts ◽

Phase Delay ◽

Phase Advance ◽

Regulatory Pathways ◽

Circadian Phase

Cocaine abuse is highly disruptive to circadian physiological and behavioral rhythms. The present study was undertaken to determine whether such effects are manifest through actions on critical photic and nonphotic regulatory pathways in the master circadian clock of the mouse suprachiasmatic nucleus (SCN). Impairment of SCN photic signaling by systemic (intraperitoneal) cocaine injection was evidenced by strong (60%) attenuation of light-induced phase-delay shifts of circadian locomotor activity during the early night. A nonphotic action of cocaine was apparent from its induction of 1-h circadian phase-advance shifts at midday. The serotonin receptor antagonist, metergoline, blocked shifting by 80%, implicating a serotonergic mechanism. Reverse microdialysis perfusion of the SCN with cocaine at midday induced 3.7 h phase-advance shifts. Control perfusions with lidocaine and artificial cerebrospinal fluid had little shifting effect. In complementary in vitro experiments, photic-like phase-delay shifts of the SCN circadian neuronal activity rhythm induced by glutamate application to the SCN were completely blocked by cocaine. Cocaine treatment of SCN slices alone at subjective midday, but not the subjective night, induced 3-h phase-advance shifts. Lidocaine had no shifting effect. Cocaine-induced phase shifts were completely blocked by metergoline, but not by the dopamine receptor antagonist, fluphenazine. Finally, pretreatment of SCN slices for 2 h with a low concentration of serotonin agonist (to block subsequent serotonergic phase resetting) abolished cocaine-induced phase shifts at subjective midday. These results reveal multiple effects of cocaine on adult circadian clock regulation that are registered within the SCN and involve enhanced serotonergic transmission.

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HIV protein, transactivator of transcription, alters circadian rhythms through the light entrainment pathway

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00179.2005 ◽

2005 ◽

Vol 289 (3) ◽

pp. R656-R662 ◽

Cited By ~ 19

Author(s):

J. P. Clark ◽

Christopher S. Sampair ◽

Paulo Kofuji ◽

Avindra Nath ◽

Jian. M. Ding

Keyword(s):

Nmda Receptor ◽

Circadian Rhythms ◽

Circadian Clock ◽

Glutamate Release ◽

Phase Shifts ◽

Channel Blockers ◽

Light Entrainment ◽

Transactivator Of Transcription

Patients infected with the human immunodeficiency virus (HIV), and other mammals infected with related lentiviruses, exhibit fatigue, altered sleep patterns, and abnormal circadian rhythms. A circadian clock in the hypothalamic suprachiasmatic nucleus (SCN) temporally regulates these functions in mammals. We found that a secretary HIV transcription factor, transactivator of transcription (Tat), resets the murine circadian clock, in vitro and in vivo, at clinically relevant concentrations (EC50= 0.31 nM). This effect of Tat occurs only during the subjective night, when N-methyl-d-aspartate (NMDA) receptor [d-2-amino-5-phosphonovaleric acid (0.1 mM)] and nitric oxide synthase ( NG-nitro-l-arginine methyl ester, 0.1 mM) inhibitors block Tat-induced phase shifts. Whole cell recordings of SCN neurons within the brain slice revealed that Tat did not activate NMDA receptors directly but potentiated NMDA receptor currents through the enhancement of glutamate release. Consistent with this presynaptic mechanism, inhibitors of neurotransmission block Tat-induced phase shifts, such as tetrodotoxin (1 μM), tetanus toxin (1 μM), P/Q/N type-calcium channel blockers (1 μM ω-agatoxin IVA and 1 μM ω-conotoxin GIVA) and bafilomycin A1(1 μM). Thus the effect of Tat on the SCN may underlie lentiviral circadian rhythm dysfunction by operating as a disease-dependent modulator of light entrainment through the enhancement of excitatory neurotransmission.

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