Sleepless aged rats show biological cloc...( gle cells. The hub of circadian...)

The hub of circadian rhythm in rats and humans and other mammals is found in the suprachiasmatic nucleus (SCN), a part of the hypothalamus that can be found on the bottom of the brain just above the roof of your mouth where your optic nerves cross. There are roughly 10,000 cells in this nucleus. The timekeeping mechanism in these cells depends on daily cycles in gene activity. The first of these genes identified in mammals was called CLOCK, for "circadian locomotor output cycles kaput."

The first thing that Herzog and his collaborators have established in studying this region is that SCN neurons can act as autonomous pacemakers, keeping time without input from other cells. While the SCN is required for circadian rhythmicity, there are other circadian oscillators in the body and in different parts of the brain. However, without the SCN, other circadian rhythms disappear. Herzog and his colleagues study rat SCN cells in vitro outside the body and hope to gain knowledge of how these cells normally work and what happens in cases of jet lag, shift work, blindness, fever, aging and other conditions that appear to alter our daily schedules.

"We think that there is a master clock in the SCN, and many slave clocks in the brain and body," Herzog said. "The slave clocks may receive daily synchronizing signals from the master, but when they get out of phase, it takes several days to catch up. That very well may be happening with jet lag. Its not the SCN that gets out of whack in a different environment for instance, after flying to Paris but other structures inside and outside of the brain."

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Contact: Tony Fitzpatrick
tony_fitzpatrick@aismail.wustl.edu
314-935-5272
Washington University in St. Louis
13-Aug-2001