Expansionary Institute

Harvard Researchers Discover Clear Link Between Light and the Internal Body Clock (with PHOTO)(Biogenesis),

Harvard Researchers Discover Clear Link Between Light and the Internal Body Clock (see PHOTO-)
December 26, 2001 8:10 CDT

Researchers at Harvard Medical School have just gotten a lot closer to being able to unwind and re-set the body's circadian clock. They recently got a glimpse of just how that clock works and what makes it tick.

It turns out that there is a tiny cluster of nerve cells behind the eyes and sends out signals that control natural daily rhythms. It's located in the brain's suprachiasmatic nucleus, or SCN. This tremendous new discovery of the tiny cluster may well have a very big influence in helping scientists figure out how the whole process works and enable them to help people with certain sleep disturbances.

In the past few years much progress has been made in identifying the genes and proteins that make circadian clock cells tick on a 24-hour basis. What had them stumped was deciding just how the machinery of these cells actually controls daily rhythms such as body temperature and sleep/wake cycles. They suspected that in order to make things work, the cells must be switching molecular patterns on and off, but couldn't quite point to exactly how-until now.

The first factor in controlling those things has now been identified, by studying another mammal-the hamster--and tracking their circadian movement patterns. (Humans also have circadian body movement patterns, but they are highly influenced by a variety of other external factors. Hamsters lead much more boring lives and were much more compliant candidates for the study.) The factor, named TGF-alpha works through a middleman called the EGF receptor.

Both proteins appear to be highly expressed in exactly the spots that had been predicted-TGF-alpha in the SCN and the EGF receptor in the nearby hypothalamus. To their delight, not only did these two centers seem to be the place for controlling daily physical activity patterns, but they found that they also seemed crucial in determining the alternating pattern of wakefulness and sleep as well.

This EGF receptor middleman appears to receive information in the form of TGF-alpha from a couple of sources. In addition to the clock, it is also influenced by the outside world-specifically light that is transmitted through the retina. This opens up an exciting new possibility, that the signal from the retina and the SCN might involve the same ligand, or at least a ligand for the same receptor.
In further support of the study, it was found that a mutant strain of hamsters that were deficient in EGF receptors did not show normal circadian movement patters. That fits in perfectly with the finding of the study. Researchers now plan to take things one-step further and see if other circadian behaviors are as elegant in design and function, using these same techniques.

Nerves behind eyes may control body's circadian rhythms

Sun Dec 30