Pineal gland speaks to the brain.

Pineal gland speaks to brain

The mammalian pineal gland, which sets the daily rhythm of hormone release that underlies many seasonal patterns of growth and behavior, keeps time in response to nerve signals received from the brain. Scientists have believed that the nerve signals go just one way--no nerve signals travel from the pineal gland back to the brain. But in the Feb. 14 SCIENCE, researchers at the National Institutes of Health (NIH) in Bethesda, Md., and at the Justus-Liebig University of Giessen in West Germany report evidence of connections from the pineal to the brain. The finding "dramatically cha ges our concept of the mammalian pineal gland," says David Klein of NIH.

To search to pineal-to-brain connections, the scientists took advantage of recently discovered similarities between the pineal gland and the retina of the eye (SN: 11/9/85, p. 298). From vision researchers, they borrowed a fluorescently labeled antibody that binds to a protein called S-antigen, found in both the eye and the pineal but not in other parts of the brain. In experiments on hamsters, the antibody revealed thin nerve connections running from pineal cells to the regions called the posterior commissure and the habenula. These regions in turn send signals to brain areas that influence mood and sleep.

Whether these pineal-to-brain connections exist in other mammals has not yet been established. But Klein suggests that such connections in the human brain might help explain the improvement that bright light provides for some patients who become depressed as the days shorten in winter (SN: 3/9/85, p. 152). In some reptiles the pineal gland acts as a light sensor, has direct neural connections with the brain and is though to help control daily rhythms of sleep wakefulness.