Jefferson Neuroscientists Uncover Novel Receptor In The Human Eye To Control Body's Biological Clock

They have discovered what appears to be a fifth human "photoreceptor," and which is the main one to regulate the biological - and non-visual - effects of light on the body.

They have identified a novel photopigment in the human eye responsible for reacting to light and controlling the production of melatonin, which plays an important role in the body's circadian rhythms.

They also discovered that wavelengths of light in the blue region of the visible spectrum are the most effective in controlling melatonin production.

"This discovery will have an immediate impact on the therapeutic use of light for treating winter depression and circadian disorders," says George Brainard, Ph.D., professor of neurology at Jefferson Medical College of Thomas Jefferson University in Philadelphia, who led the work. "Some makers of light therapy equipment are developing prototypes with enhanced blue light stimuli.

"In the long range, we think this will shape all artificial lighting, whether it's used for therapeutic purposes, or for normal illumination of workplaces, hospitals or homes - this is where the impact will be," he says. "Broad changes in general architectural lighting may take years, but the groundwork has been laid."

Dr. Brainard and his co-workers at Jefferson and at the Uniformed Services University of Health Sciences in Bethesda, Md., report their work August 15 in the Journal of Neuroscience.

"We have strong evidence for a novel, fifth photoreceptor and it appears to be independent of the classic photoreceptor for vision," he says. "It influences the biological effects of light. It regulates circadian rhythms and hormones in the body. We've also shown the fingerprint of wavelength sensitivity for the regulation of the hormone melatonin," he says.

Four cells in the human retina capture light and form the visual system. One type, rod cells, regulates night vision. The other three types, called cone cells, control color vision.

It's known that exposure to light at night can disrupt the body's production of melatonin, which is produced by the pineal gland in the brain and p