Light-sensing cells in retina develop bef...( Investigators at Washington University ...)

Investigators at Washington University School of Medicine in St. Louis have found that cells making up a non-visual system in the eye are in place and functioning long before the rods and cones that process light into vision. The discovery should help scientists learn more about the eye's non-visual functions such as the synchronization of the body's internal, circadian clock, the pupil's responses to light and light-regulated release of hormones.

The researchers report in the Dec. 22 issue of Neuron that in the mouse retina, intrinsically photosensitive retinal ganglion cells (ipRGCs) are active and functioning at birth. That was surprising because the mouse retina doesn't develop fully until a mouse is almost three weeks old, and the first rod cells don't appear until about 10 days after birth.

"We were stunned to find these photoreceptors were firing action potentials on the day of birth," says Russell N. Van Gelder, M.D., Ph.D., associate professor of ophthalmology and visual sciences and of molecular biology and pharmacology. "Mice are very immature when they're born. It takes about three weeks after birth for the retina to fully develop. No one previously had detected light-dependent cell firing in a mouse before 10 days."

Van Gelder says the ganglion cells react to light in two ways, sending messages to parts of the brain that control circadian rhythms, and (on the first day or two of life) also setting off a wave of activity that spreads through the retina, possibly helping visual cells develop.

Van Gelder and colleagues have spent the last few years learning how blind animals (and people) can sense light and use it to set their circadian clocks. The ipRGCs were first identified in 2002 -- by David M. Berson, Ph.D., and colleagues at Brown University -- as the cells that could sense light even in visually blind eyes. But it was very difficult and time consuming to isolate and study the cells, requiring precise injection of a tracing d
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Contact: Jim Dryden
jdryden@wustl.edu
314-286-0110
Washington University School of Medicine
21-Dec-2005

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