Clock-Talk: Interactions between Central and Peripheral Circadian Oscillators in Mammals

Dec 20, 2015Cold Spring Harbor symposia on quantitative biology

Communication Between Brain and Body Clocks in Mammals

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Abstract

Nearly all physiological processes in mammals are influenced by a daily rhythm regulated by a central pacemaker in the brain.

The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the central pacemaker for circadian rhythms.
Photons from light are transmitted from the retina to the SCN, helping to synchronize its daily activity.
The SCN coordinates the timing of peripheral organ oscillators through feeding-fasting cycles and other signals.
Feeding-fasting rhythms are identified as the strongest cues for the circadian clocks in peripheral organs in mice and rats.
The SCN influences peripheral clocks through pathways involving the glucocorticoid receptor and serum response factor, independent of feeding cycles.
Body temperature rhythms also play a significant role in regulating peripheral oscillators, mediated by the SCN.

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In mammals, including humans, nearly all physiological processes are subject to daily oscillations that are governed by a circadian timing system with a complex hierarchical structure. The central pacemaker, residing in the suprachiasmatic nucleus (SCN) of the ventral hypothalamus, is synchronized daily by photic cues transmitted from the retina to SCN neurons via the retinohypothalamic tract. In turn, the SCN must establish phase coherence between self-sustained and cell-autonomous oscillators present in most peripheral cell types. The synchronization signals (Zeitgebers) can be controlled more or less directly by the SCN. In mice and rats, feeding-fasting rhythms, which are driven by the SCN through rest-activity cycles, are the most potent Zeitgebers for the circadian oscillators of peripheral organs. Signaling through the glucocorticoid receptor and the serum response factor also participate in the phase entrainment of peripheral clocks, and these two pathways are controlled by the SCN independently of feeding-fasting rhythms. Body temperature rhythms, governed by the SCN directly and indirectly through rest-activity cycles, are perhaps the most surprising cues for peripheral oscillators. Although the molecular makeup of circadian oscillators is nearly identical in all cells, these oscillators are used for different purposes in the SCN and in peripheral organs.

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Clock-Talk: Interactions between Central and Peripheral Circadian Oscillators in Mammals

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