Researchers Detect Receptor For Day/Night Cycles

Rods and cones in the outer retina are the eyes' main photoreceptors, explains Nicholas Mrosovsky, professor emeritus in zoology at U of T. When these rods and cones degenerate, mammals and animals become blind. Despite this, however, some animals can synchronize their biological clocks to the day/night cycle, a problem that has perplexed scientists for the past decade.

"We believed there must be some other specialized receptor for detecting night and day. We now have evidence that this long sought-after photoreceptor is a layer of cells, located in the inner retina, that contain melanopsin, a pigment chemically related to other opsins [a type of protein] found in the rods and cones of the outer retina."

In their study, the researchers deleted melanopsin from the inner retinal cells of transgenic mice. Mrosovsky found that melanopsin-free mice could not synchronize their biological rhythms to day/night cycles or react normally to light stimuli. This research may be applicable to humans who are blind but who have the melanopsin receptor. They may still be able to synchronize their biological rhythms, he says.

Recently published online in Nature, this research was supported by the U.S. National Eye Institute, the U.K. Biotechnology and Biological Sciences Research Council, the Wellcome Trust and the Canadian Institutes of Health Research.