From the WUSTL Newsroom…
New research sheds light on how the rhythms of daily life are encoded in the brain. Scientists at Washington University School of Medicine in St. Louis have discovered that different groups of neurons, those charged with keeping time, become active at different times of day despite being on the same molecular clock.
The findings are published in Science.
Life on Earth follows the rising and setting of the sun. Daily cycles have been found in animals, plants, fungi and even bacteria. For humans, sleeping and waking as well as hormone levels, body temperature and cognitive performance, follow a daily cycle.
“The influence of our circadian rhythms can be substantial – for example, some of us are night owls and others are morning larks,” said senior investigator Paul Taghert, PhD, professor of neuroscience. “It’s important to understand how such fundamental timing information is translated into actual neuronal signals in the brain that control daily rhythms, including rhythmic behavior.”
The biological control for these daily cycles is known as the circadian clock. In animals, a master circadian clock in the brain helps coordinate most of these body rhythms, including the sleep-wake cycle.
The biochemical basis of the circadian clock has been conserved through evolution. It involves a small number of “clock proteins” whose levels go up and down in a controlled manner once a day.
But scientists long have puzzled over how some circadian-controlled behaviors and physiological changes that occur two or more times a day correspond to the once-daily rise and fall of clock proteins. The fruit fly Drosophila, for example, is behaviorally active twice a day, in the morning and evening.
Taghert, along with graduate student Xitong Liang and Timothy Holy, associate professor of neuroscience, asked how one biochemical peak in clock proteins could lead to two distinct peaks of activity at different times of day. They wondered whether the neuronal time-keeping circuit produces a single daily signal or generates multiple signals throughout the day.
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