Measuring Seasonal Time within the Circadian System: Regulation of the Suprachiasmatic Nuclei by Photoperiod

Jun 11, 2005Journal of neuroendocrinology

How the body’s internal clock tracks seasons by adjusting its main time-keeping center based on day length

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Abstract

Photoperiod may regulate the core molecular clock mechanism in mammals.

The suprachiasmatic nuclei (SCN) in the hypothalamus serve as the master circadian clock in mammals.
Circadian rhythms are synchronized with environmental light cycles, incorporating both daily and seasonal time.
Recent models suggest that specific core 'clock genes' may be linked to morning or evening phases of the light/dark cycle.
Debate exists regarding the validity of associating particular genes with morning and evening phases.
The article reviews evidence supporting photoperiodic regulation of circadian clock function and discusses alternative explanatory models.

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Day-length (photoperiod) is the primary environmental signal used to synchronise endogenous rhythms of physiology and behaviour. In mammals, the suprachiasmatic nuclei (SCN) of the hypothalamus house the master circadian clock. The SCN incorporate photoperiodic information and therefore measure both daily and seasonal time. Over the past decade, there have been significant advances in the understanding of the molecular basis of circadian clocks. It is now becoming apparent that the core molecular clock mechanism is itself regulated by photoperiod, although there is currently debate as to how this occurs. One recent model proposes that distinct groups of core 'clock genes' are associated with either morning or evening phases of the daily light/dark cycle. However, the validity of associating particular genes to morning and evening has been questioned. This article reviews the evidence for photoperiodic regulation of circadian clock function and then discusses alternative models that may explain the available data.

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Measuring Seasonal Time within the Circadian System: Regulation of the Suprachiasmatic Nuclei by Photoperiod

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