A Barnard psychologist has evidence that a chemical, not a nerve connection, controls the body's response to cycles of light and dark.
Rae Silver, the Helene and Mark Kaplan Professor of Natural and Physical Sciences at Barnard and professor of psychology at Columbia, discussed her work at a news briefing Feb. 11 at the American Association for the Advancement of Science's Annual Meeting and Science Innovation Exposition in Baltimore.
Silver does not yet know what that chemical is, but hopes for a molecule small enough to cross the blood-brain barrier. That presumably would allow humans to take a pill to reset their body clocks for shift work or travelling across time zones. Industrial accidents like those at Chernobyl, Bhopal and Three Mile Island are more common late at night when humans tend to be less alert, say chronobiologists, scientists who study the body's cycles, called circadian rhythms.
Until recently, it was thought that all communication in the brain took place among connected nerve cells, or neurons, which transmit electrochemical messages to their neighbors along arms known as axons. Silver has marshalled evidence to show that a part of the brain can emit a chemical signal to other parts of the brain without the help of connections made by neurons.
Scientific research on circadian rhythms has greatly expanded in recent years, and researchers now have a clear idea how the body responds to cycles of day and night. Light is registered by cells in the retina, and that signal is transmitted by optic nerves to a tiny group of cells located just behind the eyes known as the suprachiasmatic nucleus, or SCN, also sometimes called the circadian pacemaker. A pea-sized gland also in the brain, the pineal gland, receives information on light cycles from the SCN and at appropriate times pours a sleep-inducing hormone called melatonin into the bloodstream. Precisely timed exposure to light--to stop or delay the production of melatonin--is already being used to reset the body's clock.
What had been missing from this picture is how the tiny suprachiasmatic nucleus communicated with the rest of the brain, including the pineal gland. In 1987, Silver began a series of experiments in which she transplanted the suprachiasmatic nucleus--the circadian pacemaker--in laboratory rodents, which have circadian rhythms similar to those found in humans. Animals with no circadian pacemaker slept and woke for a few minutes at a time without a discernable pattern, but regained their activity rhythms once they received a new pacemaker, confirming its importance as an internal clock.
In more recent experiments, Silver and her collaborator have shown that transplanted clocks restore activity rhythms and that the precise site in the brain in which the clock is placed is not important. In another experiment, she showed that if all the neural connections to the circadian pacemaker are cut, the clock continues to work and to control activity rhythms.
Columbia University Record -- February 23, 1996 -- Vol. 21, No. 17