Food and the circadian clock

In the December 1st issue of Genes & Development, Dr. Ueli Schibler and his team at the University of Geneva in Switzerland report on their exciting discoveries about how the body sets its own time. It has long been known that a region in the brain connected to the eyes resembles a central pacemaker, organizing periods of wake and sleep. In addition, this main clock is thought to regulate local clocks in peripheral organs, such as in the digestive tract. In turn, these presumably remote-controlled clocks switch on or off the expression of food processing enzymes.

To investigate this hierarchy, Dr. Schibler's group used mice, animals that are typically active at night. If the mice experienced a regular day / night lighting scheme and were offered food around the clock, they ate almost all their meals during the night, indicating that the central clock stimulated by light can regulate feeding behavior. Then the mice were kept at the same lighting scheme but fed exclusively either during the day or during the night. Interestingly, if the mice were offered their food only during the day, the expression of digestive proteins in the liver was shifted completely to the daytime, while the expression pattern of the central clock in the brain did not change at all. This exciting result indicates that the peripheral clocks can become independent and even override the central clock.

This result also demonstrates that the central clock either does not response to the feeding schedule or that the stimulus by light is stronger than the stimulus via food. To discriminate between these two possibilities, the mice were kept in permanent darkness and offered food only during the period which they had been experiencing as daytime. Results showed that again, the central clock was not influenced by the feeding pattern even in the absence of light, indicating that the central clock is insensitive to food stimuli.

This study gives more insight into the circuits connecting brain and body during complex behavioral tasks such as feeding patterns. The results from this and other studies in the same field might ultimately help employees who work on changing shifts, such as nurses or fire fighters, to acclimate their bodies to their schedules.