Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Perfect Vision but Blind to Light

12.06.2008
Mammals have two types of light-sensitive detectors in the retina. Known as rod and cone cells, they are both necessary to picture their environment.

However, researchers at the Salk Institute for Biological Studies have found that eliminating a third sensor — cells expressing a photopigment called melanopsin that measures the intensity of incoming light —makes the circadian clock blind to light, yet leaves normal vision intact.

“It is entirely possible that in many older people a loss of this light sensor is not associated with a loss of vision, but instead may lead to difficulty falling asleep at the right time,” says Satchidananda Panda, Ph.D., an assistant professor in the Regulatory Biology Laboratory, who led the study.

Understanding how melanopsin does its job may one day allow scientists to reset the body’s biological clock with a pill to alleviate symptoms associated with jet lag, shifts in work schedules, seasonal changes in day lengths and disorders such as insomnia and depression, the researchers say. Their findings are published in the June 11, 2008 issue of the PLoS ONE.

Visual processing begins when photons entering the eye strike one or more of the 125 million light-sensitive nerve cells in the retina at the back of each eye. Rod cells use rhodopsin to pick up dim light, while cone cells rely on related photopigments to discriminate color. This first and outermost layer of cells converts the information into electrical signals and sends them to an intermediate layer, which in turn relays signals to the optic nerve. Melanopsin is different from the classical rod and cone opsins, which help us see.

“It functions like a light meter in a camera, but does more than set our biological clock,” explains Panda. “The incoming information about light intensity is also used to adjust the aperture or pupil size, regulate melatonin synthesis and physical activity.”

Unlike the millions of rod and cone cells imparting vision, melanopsin is only present in roughly 2,000 cells, which are known as melanopsin-expressing retinal ganglion cells or mRGCs. Embedded in the inner retina, these spidery cells signal directly to the human circadian clock, a cluster of cells less than half the size of a pencil eraser, which sits just above the point where the optic nerves cross.

Through these signals, the clock synchronizes the body’s daily rhythms with the rising and setting of the sun. It tells the body when it’s time to go to sleep, when to be hungry, when to wake up and makes us feel completely out of sync when we cross several time zones.

While it had been known that blind mice without functional rods and cones can still use mRGCs to adjust their biological clock, the aperture of their pupils and light-dependent activity ¬— collectively known as non-image forming visual responses — mice without melanopsin were not completely blind to light.

Since mice developing without melanopsin might compensate during their development for the lack of incoming information about light intensity, resulting in muddled results, postdoctoral researcher and first author Megumi Hatori, Ph.D., developed a system that allowed her to specifically and efficiently shut down all melanopsin-expressing cells while leaving the retina intact.

She genetically engineered mice to render their mRGCs susceptible to diptheria toxin, which she exploited to kill melanopsin-expressing cells at eight weeks of age. “We found that killing the melanopsin-expressing cells makes the mouse circadian clock completely blind to light,” says Hatori, “but these mice can still perform normal image-forming visual tasks perfectly fine.”

The mammalian time keeping system relies on information from melanopsin -- and to a lesser extent from rods and cones -- to collect information about light intensity. The Salk researchers experiments pinpointed mRGCs as the location where all the incoming information about the brightness of ambient light is integrated and forwarded to the circadian clock.

“Since all the information passes through mRGCs, these cells have emerged as a unique cellular target for therapeutic intervention in circadian clock related disorders,” says Panda, who has started screening small molecules for their ability to tweak melanopsin’s light sensing properties and thereby slowing down or enhancing the resetting of our biological clock.

Researchers who also contributed to this work include researchers Hiep Le, Christopher Vollmers, Sheena Racheal Keding and Nobushige Tanaka, Ph.D., in the Panda laboratory, Christian Schmedt, Ph.D., Associate Director of Genetics at the Genomics Institute of the Novartis Research Foundation, San Diego, and assistant professor Timothy Jegla, Ph.D., at The Scripps Research Institute, La Jolla.

The Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.

Gina Kirchweger | newswise
Further information:
http://www.salk.edu

Further reports about: Melanopsin PANDA Retina circadian mRGCs melanopsin-expressing

More articles from Life Sciences:

nachricht Turning carbon dioxide into liquid fuel
06.08.2020 | DOE/Argonne National Laboratory

nachricht Tellurium makes the difference
06.08.2020 | Friedrich-Schiller-Universität Jena

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: ScanCut project completed: laser cutting enables more intricate plug connector designs

Scientists at the Fraunhofer Institute for Laser Technology ILT have come up with a striking new addition to contact stamping technologies in the ERDF research project ScanCut. In collaboration with industry partners from North Rhine-Westphalia, the Aachen-based team of researchers developed a hybrid manufacturing process for the laser cutting of thin-walled metal strips. This new process makes it possible to fabricate even the tiniest details of contact parts in an eco-friendly, high-precision and efficient manner.

Plug connectors are tiny and, at first glance, unremarkable – yet modern vehicles would be unable to function without them. Several thousand plug connectors...

Im Focus: New Strategy Against Osteoporosis

An international research team has found a new approach that may be able to reduce bone loss in osteoporosis and maintain bone health.

Osteoporosis is the most common age-related bone disease which affects hundreds of millions of individuals worldwide. It is estimated that one in three women...

Im Focus: AI & single-cell genomics

New software predicts cell fate

Traditional single-cell sequencing methods help to reveal insights about cellular differences and functions - but they do this with static snapshots only...

Im Focus: TU Graz Researchers synthesize nanoparticles tailored for special applications

“Core-shell” clusters pave the way for new efficient nanomaterials that make catalysts, magnetic and laser sensors or measuring devices for detecting electromagnetic radiation more efficient.

Whether in innovative high-tech materials, more powerful computer chips, pharmaceuticals or in the field of renewable energies, nanoparticles – smallest...

Im Focus: Tailored light inspired by nature

An international research team with Prof. Cornelia Denz from the Institute of Applied Physics at the University of Münster develop for the first time light fields using caustics that do not change during propagation. With the new method, the physicists cleverly exploit light structures that can be seen in rainbows or when light is transmitted through drinking glasses.

Modern applications as high resolution microsopy or micro- or nanoscale material processing require customized laser beams that do not change during...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“Conference on Laser Polishing – LaP 2020”: The final touches for surfaces

23.07.2020 | Event News

Conference radar for cybersecurity

21.07.2020 | Event News

Contact Tracing Apps against COVID-19: German National Academy Leopoldina hosts international virtual panel discussion

07.07.2020 | Event News

 
Latest News

Rare Earth Elements in Norwegian Fjords?

06.08.2020 | Earth Sciences

Anode material for safe batteries with a long cycle life

06.08.2020 | Power and Electrical Engineering

Turning carbon dioxide into liquid fuel

06.08.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>