Cells in eyes help set internal clocks

SYDNEY - We run our lives largely by the clock that remind us when it’s time for meals, after-school pick-up and other activities. We also have internal “clocks” and a study has found that a type of cell in the eyes are responsible for “setting” it in low light conditions.

The internal clocks help set our circadian rhythms, regulating everything from our sleep-wake cycles to our appetites and hormone levels.

Light coming into our brains via our eyes set those clocks, though no one is sure exactly how this happens.

A Johns Hopkins biologist - working in collaboration with scientists at the University of Southern California and Cornell University - has unlocked part of that mystery recently, according to a Johns Hopkins statement.

Their study found that rod cells - one of three kinds of exquisitely photosensitive cells found in the retina of the eye - are the only ones responsible for “setting” those clocks in low light conditions.

What’s more, the study found that rods - which take their name from their cylindrical shape - also contribute (along with cones and other retinal cells) to setting internal clocks in bright light conditions, reports the journal Nature Neuroscience.

These findings are surprising for several reasons, according to study leader Samer Hattar, a biologist.

“One is that it had previously been thought that circadian rhythms could only be set at relatively bright light intensities, and that didn’t turn out to be the case,” he explained.

“And two, we knew going in that rods ‘bleach’, or become ineffective, when exposed to very bright light, so it was thought that rods couldn’t be involved in setting our clocks at all in intense light. But they are,” he added.