Retinal cells thoughts to be the same are not: study

July 25, 2011

The old adage "Looks can be deceiving" certainly rings true when it comes to people. But it is also accurate when describing special light-sensing cells in the eye, according to a Johns Hopkins University biologist.

In a study recently published in Nature, a team led by Samer Hattar of the Department of Biology at the Krieger School of Arts and Sciences and Tudor Badea at the National Eye Institute found that these , which were thought to be identical and responsible for both setting the body's circadian rhythm and the pupil's reaction to light and darkness, are actually two different cells, each responsible for one of those tasks.

"In biology, as in life, you can't always trust what you see," said Hattar. "You have to delve deep to find out what's really going on. This study has shown that two structurally similar neurons are actually quite different and distinct, communicate with different regions of the brain and influence different visual functions."

The findings are significant, Hattar said, because doctors sometimes use pupillary light reflex (the pupil's response to light and darkness) as a way of diagnosing patients who may have , and those clinicians now must recognize that the cells controlling pupillary response and those controlling the sleep-wake cycle are different.

"Although the diagnosis may still be valid most of the time, it is important to remember that disrupted pupillary light response with normal sleep or the opposite is possible, and caution should be exercised if clinicians only use pupillary light reflex for diagnosis purposes for deficits in non-image forming visual functions," explained Shih-Kuo (Alen) Chen, a post-doctoral fellow in the Department of Biology and co-author of the Nature article.

Hattar's research focuses on these special light-sensitive cells and how they regulate the physiology and behavior of mammals.

"In human beings, light has an impact on many of our , including sleep and mood," he explains. "We are interested in the cellular, molecular and behavioral pathways by which light has an impact on us, independent of how and what we literally 'see' with our eyes. This includes setting our internal, biological clock to the day and night and constricting our pupils to control the amount of light coming through to our retinas."

In a previous study, Hattar's team revealed that these cells -- called "intrinsically photosensitive Retinal Ganglion Cells" -- also play a role in image formation. Formerly, it was thought that the ipRGCs' role was limited to sleep-wake cycles and pupillary responses.

More information: www.nature.com/nature/journal/vaop/ncurrent/full/nature10206.html

Related Stories

Recommended for you

Crystal clear images uncover secrets of hormone receptors

July 31, 2015

Many hormones and neurotransmitters work by binding to receptors on a cell's exterior surface. This activates receptors causing them to twist, turn and spark chemical reactions inside cells. NIH scientists used atomic level ...

A cheaper, high-performance prosthetic knee

July 30, 2015

In the last two decades, prosthetic limb technology has grown by leaps and bounds. Today, the most advanced prostheses incorporate microprocessors that work with onboard gyroscopes, accelerometers, and hydraulics to enable ...

Flow means 'go' for proper lymph system development

July 27, 2015

The lymphatic system provides a slow flow of fluid from our organs and tissues into the bloodstream. It returns fluid and proteins that leak from blood vessels, provides passage for immune and inflammatory cells from the ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.