Featured Research

from universities, journals, and other organizations

Tick tock: Rods help set internal clocks, biologist says

Date:
September 18, 2010
Source:
Johns Hopkins University
Summary:
Rod cells -- one of three kinds of exquisitely photosensitive cells found in the retina of the eye -- are surprisingly found to be the only ones responsible for setting our internal "clocks" in low light.

We run our modern lives largely by the clock, from the alarms that startle us out of our slumbers and herald each new workday to the watches and clocks that remind us when it's time for meals, after-school pick-up and the like.

Related Articles


In addition to those ubiquitous timekeepers, though, we have internal "clocks" that are part of our biological machinery and which 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.

But a Johns Hopkins biologist -- working in collaboration with scientists at the University of Southern California and Cornell University -- unlocked part of that mystery recently. 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. The study appeared in a recent issue of Nature Neuroscience.

These findings are surprising for several reasons, according to study leader Samer Hattar of the Department of Biology at the Krieger School of Arts and Sciences.

"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."

In the study, Hattar's team used a group of mice which were genetically modified to have only rod photoreceptors, meaning their cones and intrinsically photosensitive retinal ganglion cells -- both of them light-sensitive cells in the animals' retinas -- were not functional. The team then exposed the rodents to varying intensities of light, measuring the animals' responding level of activity by how often they ran on hamster wheels.

The study results are important because they indicate that prolonged exposure to dim or low light at night (such as that in homes and office buildings) can influence mammals' biological clocks and "throw off" their sleep-wake cycles. Hattar suggested that one way people can mitigate this effect is to make sure to get some exposure to bright day light every day. (The exposure to brighter, natural daylight will firmly reset the clocks to a proper asleep-at-night-awake-in-the-day cycle.)

In addition, the study has possible implications for older people being cared for in nursing homes and hospitals, he said.

"Older adults often lose their rod cells to age, which means that their caretakers would be well advised to regularly and deliberately expose them to bright natural daylight in order to make sure that their natural, biological rhythms remain in sync so their sleep-wake cycles remain accurately set," Hattar said. "Otherwise, they could have sleep disturbances, such as intermittent waking or difficulty falling asleep, not to mention the impact on their appetite and other bodily functions."

Hattar's study was funded by the National Institute of General Medical Sciences.


Story Source:

The above story is based on materials provided by Johns Hopkins University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Cara M Altimus, Ali D Gόler, Nazia M Alam, A Cyrus Arman, Glen T Prusky, Alapakkam P Sampath, Samer Hattar. Rod photoreceptors drive circadian photoentrainment across a wide range of light intensities. Nature Neuroscience, 2010; 13 (9): 1107 DOI: 10.1038/nn.2617

Cite This Page:

Johns Hopkins University. "Tick tock: Rods help set internal clocks, biologist says." ScienceDaily. ScienceDaily, 18 September 2010. <www.sciencedaily.com/releases/2010/09/100917161154.htm>.
Johns Hopkins University. (2010, September 18). Tick tock: Rods help set internal clocks, biologist says. ScienceDaily. Retrieved November 28, 2014 from www.sciencedaily.com/releases/2010/09/100917161154.htm
Johns Hopkins University. "Tick tock: Rods help set internal clocks, biologist says." ScienceDaily. www.sciencedaily.com/releases/2010/09/100917161154.htm (accessed November 28, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Friday, November 28, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Ebola Leaves Orphans Alone in Sierra Leone

Ebola Leaves Orphans Alone in Sierra Leone

AFP (Nov. 27, 2014) — The Ebola epidemic sweeping Sierra Leone is having a profound effect on the country's children, many of whom have been left without any family members to support them. Duration: 01:02 Video provided by AFP
Powered by NewsLook.com
Experimental Ebola Vaccine Shows Promise In Human Trial

Experimental Ebola Vaccine Shows Promise In Human Trial

Newsy (Nov. 27, 2014) — A recent test of a prototype Ebola vaccine generated an immune response to the disease in subjects. Video provided by Newsy
Powered by NewsLook.com
Pet Dogs to Be Used in Anti-Ageing Trial

Pet Dogs to Be Used in Anti-Ageing Trial

Reuters - Innovations Video Online (Nov. 26, 2014) — Researchers in the United States are preparing to discover whether a drug commonly used in human organ transplants can extend the lifespan and health quality of pet dogs. Video provided by Reuters
Powered by NewsLook.com
Today's Prostheses Are More Capable Than Ever

Today's Prostheses Are More Capable Than Ever

Newsy (Nov. 26, 2014) — Advances in prosthetics are making replacement body parts stronger and more lifelike than they’ve ever been. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins