Original: http://sciencenow.sciencemag.org/cgi/content/full/2002/524/4

Keeping the Body in One Time Zone

The body's circadian clock finally has received some hands. Scientists discovered a molecule in the brain's master clock that signals to the rest of the body that it's daytime. Injected into the brain, the molecule disrupts the natural daily rhythms of mice for several days. The findings may pave the way for new drugs to treat sleep disorders and jetlag. Like intertwining cogwheels in a mechanical watch, a pool of periodically expressed genes keeps time in a tiny region of the brain called the suprachiasmatic nucleus. Light sensors in the retina normally keep the clock set to the daily cycle of the sun, but even in absolute darkness these genes define a rough 24-hour day-night cycle. Although scientists have learned a great deal about how light sets the clock and have identified many of its components, they haven't understood how the clock in the brain keeps the rest of the body in synch.

What Sets the Biological Clock?

Investigators (nearly) identify melanopsin as a photopigment
(http://www.the-scientist.com/yr2002/jun/research_020610.html)

Copyright Š 2002 by the American Association for the Advancement of Science.