Separating morning and evening in the circadian clock of mammals

June 24, 2005

Work by researchers at the universities of Aberdeen and Nottingham suggest an anatomical basis for the adaptation of the mammalian circadian clock to changing day-length.
Endogenous circadian clocks ensure that temporal patterns of physiology and behavior predict environmental changes determined by the Earth’s rotation and orbit of the Sun. Such clocks are synchronized by the daily light-dark cycle.

A key question for circadian biologists concerns the way in which seasonal changes in day-length alter the behavior of circadian clocks over the course of the year. One idea for which evidence has accumulated is that circadian clocks contain coupled “morning” and “evening” oscillators that are separately synchronized to dawn and dusk.

In the new work, published in this week’s issue of Current Biology, Dr David Hazlerigg and colleagues considered the possibility that distinct populations of neurons within the principal mammalian circadian clock (the suprachiasmatic nuclei of the hypothalamus, SCN) might constitute these different oscillators. By measuring gene-expression rhythms in the SCN of hamsters held on different day-lengths, they were able to show that cells in the caudal region of the SCN synchronize their gene-expression rhythms to dawn and, when the day-length is increased, exhibit earlier peak expression relative to midday.

The researchers also report a lesser, but opposite, response in cells in another group of neurons, the rostral SCN. Hence, synchronous gene expression across the SCN may be a hallmark of short-day acclimation, whereas regional de-synchrony increases on long days.

Further studies are needed to discern whether this phenomenon translates into distinctive day-length-induced changes in rhythmic output from different regions of the SCN. Abnormalities in the adaptation of the SCN to changing day-length may underlie the development of seasonal affective disorder (SAD) in humans.

Source: University of Aberdeen

Explore further: Disrupting the brain's internal clock causes depressive-like behavior in mice

Related Stories

Chronobiology—internal clocks in synch

October 14, 2016

Ludwig II of Bavaria is a particularly striking example of how differently people's internal clocks can tick. Historical sources tell us that the monarch usually carried out his government business at night and slept during ...

Brain's biological clock stimulates thirst before sleep

September 28, 2016

The brain's biological clock stimulates thirst in the hours before sleep, according to a study published in the journal Nature by researchers from the Research Institute of the McGill University Health Centre (RI-MUHC).

Central and peripheral signals set the circadian liver clock

January 30, 2007

Anyone who has experienced jet lag will understand the importance of a smooth-running circadian clock. Crossing time zones decouples our biological rhythms from the natural cycle of light and dark we’re used to. We perceive ...

Recommended for you

Samsung to disable Note 7 phones in recall effort

December 9, 2016

Samsung announced Friday it would disable its Galaxy Note 7 smartphones in the US market to force remaining owners to stop using the devices, which were recalled for safety reasons.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.