UC Researchers Find New Link Between the Eye and the Clock in the Brain

Results of a study done by a team of researchers working in the laboratories of Michael Lehman, PhD, professor, Department of Cell Biology, Neurobiology, and Anatomy at the UC College of Medicine, will appear in the February issue of Nature Neuroscience.  In Nature Neuroscience, the UC researchers report on how the eye influences a group of cells in the brain that control the body’s daily rhythms and act as the “master clock.”

Scientists have long known that the “master clock” in the brain, that regulates circadian (daily) rhythms in sleep, wakefulness and other functions, is synchronized by light information conveyed through the eyes.  Now UC researchers have discovered a new role for the eye in regulating circadian rhythms.  The molecular rhythm of a subset of brain cells in the central “clock” is dependent on the presence of the eye. Interestingly, this influence of the eye is also seen in animals housed in constant darkness, making the circadian clock independent of the effects of light.

The brain’s “clock,” called the suprachiasmatic nucleus (SCN), is made up of pacemaker cells responsible for a wide variety of rhythms in behavior and physiology.  One reason why the SCN is considered to be a “master clock” is that, up to now, all rhythms exhibited by SCN cells have appeared to be independent of other parts of the brain and body. Besides the SCN, the only tissue shown to contain an independent circadian clock is the eye, but the function of that clock has remained a mystery.  Lehman and his colleagues were studying molecular rhythms of  a specific protein in the SCN, when they were surprised to discover that this rhythm was absent in animals lacking input from the eye.  Additionally, the rhythm was missing in a distinct group of cells that also receives direct input from the eye and is located in the core of the SCN. The “clock” in the eye may help cells in the SCN anticipate what time of day it is, in order to be prepared for the onset of light. Lehman’s group is currently following up these experiments to see if other rhythms expressed by the SCN are also dependent on the eye.

Dr. Lehman said, “It is interesting that the SCN, long considered to be the “master clock” in the body contains an area that behaves as a “slave” under the control of eye tissues.”  The discovery may help explain some of the problems that blind people have with sleep and circadian rhythms, when their blindness is due to loss of the eyes or optic nerve damage.

Han Lee, first author of this published paper, is a student in the UC Neuroscience Graduate Program, and is also a student in UC’s Physician Scientist Training Program.  Jenny Nelms, PhD, and Mary Nguyen, co-authors on the paper, are also past and current students, respectively, in the UC Neuroscience Graduate Program. Rae Silver, PhD, a long-time collaborator of the Lehman lab, is also co-author on this work. Dr. Silver is the Mark and Helen Kaplan Professor of Psychology at Columbia University in New York City.