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Light sensors controlling body clock are discovered

The eye contains not just rods and cones but a light detector that could unlock mood and sleep treatments.

June 14, 2008|Wendy Hansen | Times Staff Writer

Scientists have discovered the function of a third type of light sensor in the eye -- not vision, but control of the body's internal clock -- opening a new pathway for potential treatments of light-related mood and sleep disorders.

The sensors, found in 2% of retinal cells, are dedicated to detecting the presence and intensity of light through the use of a light-sensitive molecule called melanopsin, researchers reported this week in the journal PLoS ONE.

They found that mice without the sensor were unable to reset their internal biological clocks. The nocturnal animals woke up half an hour earlier every evening, never properly adjusting to a 24-hour day, researchers reported.

Scientists have been searching for light-level sensors since the 1920s, when it was noted that some blind patients' pupils dilated in response to bright light, suggesting the existence of a sensor separate from the rod and cone cells responsible for vision.

Project leader Satchin Panda of the Regulatory Biology Laboratory at the Salk Institute for Biological Studies in La Jolla said that searches of the recently sequenced mouse and human genomes revealed that both contained an extra light sensor gene.

The researchers pinpointed the sensor to a small number of retinal cells. They genetically engineered mice with sensor cells sensitive to a particular toxin. When the mice were exposed to the toxin, only the cells containing melanopsin died.

The animals could still see normally and retained depth perception: In tests, they avoided stepping off a simulated cliff. But their ability to discern and respond to light intensity was destroyed.

The results confirm separate experiments reported in the journal Nature this year.

Dysfunctional light responses have been implicated in illnesses such as depression and difficulty sleeping. "So now that we have found these cells regulate all this stuff, we can develop new therapies to address this," Panda said.

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wendy.hansen@latimes.com

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