Overview

The Circadian Clock

Life on Earth is dominated by predictable changes in the environment, as we cycle through day and night. Almost all life on Earth has evolved internal time-keeping machinery to make the most of these changes. These 24-hour rhythms are termed circadian, and the timing system, the circadian clock (often referred to as the body clock).

In vertebrates the central clock, which receives light input to allow synchronisation to the light-dark cycle, is in the brain, in a cluster of nerve cells called the suprachiasmatic nucleus (SCN).

The sleep-wake cycle is the most familiar 24-hour cycle, but involves more than the SCN. Sleep is a highly complex state arising from an interaction between multiple brain regions, neurotransmitter pathways and hormones, none of which are exclusive to the generation of sleep.

Other major changes occur as we transition from the fed state, during wakefulness, to the fasted state, during sleep. These changes require a major change in energy handling. During the day we store energy from food in the liver, and in fat; and during the night these energy stores are used to maintain body function. These changes are controlled by the clock.

Many human diseases show striking changes in severity through the day; for example asthma is typically worse in the early hours of the morning, and patients with rheumatoid arthritis report more joint pain and stiffness on waking. Many commonly used medicines work by regulating pathways in the body that change with time of day, making time of use an important consideration.

Sleep and Circadian Rhythm Disruption

Sleep and Circadian Rhythm Disruption (SCRD) occurs when our natural circadian rhythms are pushed out of sync. Small changes in brain function can have a big impact on sleep, and disrupted sleep leads to health problems ranging across increased stress hormones, heart disease, weight abnormalities, reduced immunity, increased risk of cancer, and emotional and cognitive problems.

Our new data suggests that parallel brain pathways might be affected in these diseases and in sleep disturbance. We plan to further this understanding and use it to develop new approaches to correct abnormal sleep, so improving the broader health problems and quality of life for sufferers.