'Food Clock' May Override Master Sleep Clock in Times of Duress

By Alan Mozes
HealthDay Reporter
Friday, May 23, 2008; 3:00 AM

Copyright © 2008 ScoutNews, LLC. All rights reserved.

THURSDAY, May 22 (HealthDay News) -- New animal research suggests the body's biological clock, which regulates sleep cycles based on the rise and fall of the sun, can be overridden in extreme situations by an internal "food clock."

The finding is based on work with mice and has not yet been tested among humans. But early indications are that, when faced with starvation, the animals automatically adjust their wake-sleep schedule to adapt to the best time to access food.

"In the wild, where starvation is a common threat, this must have evolved as a way for animals to lock onto a new food source, when necessary, to avoid starvation," said study author Dr. Clifford Saper, chairman of the department of neurology at Beth Israel Deaconess Medical Center and a professor of neurology at Harvard Medical School.

Saper and his team reported the findings in the May 23 issue of Science.

They noted that for animals and humans alike, the body's main clock is centered among a group of cells in the brain's hypothalamus region. Referred to as the "suprachiasmatic nucleus", this circadian clock is triggered by visual cues gleaned from the light-dark cycle. Such signals, in turn, activate cells that regulate sleep-wake cycles.

The authors speculated, however, that this standard "master" system could be overridden in situations of extreme duress -- such as starvation.

To test this theory and locate a possible "food clock," the researchers focused on mice genetically altered to lack a gene integral to the master biological clock.

After implanting the mice with transmitters to record body temperature and movement within plastic cages regulated for light and temperature, Saper and his colleagues then restored full light-clock function only to isolated parts of each mouse's brain throughout a rotating series of food deprivation experiments.

Successive two-week long tests were conducted in the context of both a normal light-dark cycle and then a constantly dark setting.

The result: The researchers uncovered the existence of a "feeding clock."