Magazine article Science News

Eyes Possess Their Own Biological Clocks

Magazine article Science News

Eyes Possess Their Own Biological Clocks

Article excerpt

In the eye, many daily cycles, such as the regeneration of light receptors and increased sensitivity to light, appear timed to the cadence of a unique drummer. Now, two biologists have shown that the retinas of hamsters carry their own circadian timepieces to maintain these rhythms on a roughly 24-hour cycle.

The eye timepieces are distinct from the hub of tissue in the brain's hypothalamus that serves as an orchestral conductor, pacing the symphony of interwoven daily rhythms, from sleep-wake cycles and pain sensitivity to hormone production. Until about 20 years ago, the brain's suprachiasmatic nucleus (SCN) was accepted as the one and only body clock. Then, biologists found they could throw the eyes' rhythms out of sync with other circadian cycles. Since that time, several researchers have confirmed that eye rhythms persist-and can be reset-even after the SCN, or the eyes' ability to communicate with it, is destroyed.

From such findings, Michael Terman of Columbia University and his colleagues published a hypothesis in 1991 arguing that the eye must possess its own clock, independent of the SCN. However, Terman now notes, because the studies at that time used whole animals, 'there was always a nagging suspicion in the field that these results were artifactual'-that they reflected some indirect influence by other systems in the body.

Gianluca Tosini and Michael Menaker of the University of Virginia in Charlottesville have now erased such doubts by finding resettable circadian rhythms in retinas removed from hamsters and maintained in culture in the lab for several days. …

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