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but interesting... Thursday May 28, 1998 NEW YORK (Reuters) -- A newly discovered, light-sensitive pigment in the eye has been found to control the internal clock in mammals, including humans. The pigment, called cryptochrome, mediates the circadian rhythm, a biological timer that regulates a variety of body functions. Body temperature, blood pressure, intellectual performance, sleeping and waking all are synchronized to light and dark by the circadian rhythm. Drs. Yasuhide Miyamoto and Aziz Sancar, of the University of North Carolina School of Medicine, Chapel Hill, present their findings in the May 26th issue of the Proceedings of the National Academy of Sciences. Other light-absorbing eye pigments, called opsins, have been identified in the retina and are linked to vitamin A. Opsins allow mammals to see by transferring visual signals through the optic nerve to the brain. Scientists had assumed that the same pigment was responsible both for vision and for circadian synchronization. Cryptochromes, however, are linked to vitamin B-2 and are found in a different part of the retina, Sancar explained in a press release. "Understanding how circadian rhythm works has many practical applications," said Sancar. One is in the treatment of seasonal affective disorder (SAD), a type of depression that some people experience during the winter months, when days grow short. "It may be that people with SAD have a defective gene that doesn't produce the pigment properly or simply suffer from a vitamin B-2 deficiency. Maybe we can treat some patients with vitamin B-2," Sancar said. Industrial accidents are known to occur most often during the midnight shift, because mistakes are more likely when people try to counteract the influence of the circadian rhythm. Cancer researchers also are interested in circadian rhythms, since the effects of cancer-fighting drugs -- both therapeutic effects and harmful side effects -- may depend upon the time of day at which the drugs are administered, Sancar said. SOURCE: Proceedings of the National Academy of Sciences 1998;95:6097-6102. -- Judith Richards, London, Ontario, Canada [log in to unmask]