Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Eye’s light-detection system revealed

15.01.2003


A research team led by Johns Hopkins scientists has discovered that a special, tiny group of cells at the back of the eye help tell the brain how much light there is, causing the pupil to get bigger or smaller. The findings, which appeared in the Jan. 10 issue of Science, largely complete the picture of how light levels are detected in the eye.



"This tiny group of cells, together with rods and cones, are the bulk of the eye’s mechanisms for detecting levels of light and passing that information to the brain," says King-Wai Yau, Ph.D., professor of neuroscience and a Howard Hughes Medical Institute investigator at the Johns Hopkins School of Medicine.

The team previously had shown that this set of retinal cells, all of which contain a protein called melanopsin, are naturally sensitive to light. They also showed that the cells connect to the brain in such a way that they are poised to control how the pupil reacts to light and how animals adapt to day and night.


The new work proves that these melanopsin-containing cells, a subset of so-called retinal ganglion cells, are in fact a working part of the body’s light-detection system and complement the light-detecting role of rods and cones, which also convey information about the color, shape and movement of objects.

"Rods and cones provide high sensitivity to light, allowing the pupil to constrict, but melanopsin-containing cells seem to be crucial for completing the pupil’s response in bright light," says Samer Hattar, Ph.D., a postdoctoral fellow in neuroscience at Johns Hopkins. "Without melanopsin, the pupil fails to constrict fully, even in very bright light."

First authors Hattar and Robert Lucas, Ph.D., of the Imperial College, London, measured how small the pupil of each of two kinds of "knockout" mice became when exposed to known amounts of light. One set of mice were missing the gene for the melanopsin protein, the others lacked rods and cones. In mice without melanopsin, only rods and cones send light to the brain, and in mice without rods and cones, only retinal ganglion cells do so.

In normal mice, the pupil becomes the size of a pinhole when exposed to very bright light. The pupils of "rod-less/cone-less" mice got just as small, but in mice without melanopsin, the smallest attainable size was three times larger than in other mice, the researchers found.

Importantly, they also proved that, even without melanopsin, retinal ganglion cells still develop and connect to the brain in the same way, underscoring that the decreased pupil response is due to melanopsin’s absence.

"In the olfactory system, knocking out certain proteins changes the way the system is wired to the brain, and that easily could have been the case here," says Yau. "Melanopsin is clearly involved in light detection in these retinal ganglion cells, but it is not crucial for their development or connectivity."

At this point the scientists can’t rule out a third contributor in the eye’s light detection system, but report that combining the responses of the two sets of knockout mice matches the pupil response of normal mice very well. "Any other factor in detecting light is of minor importance, at least for the pupil reflex," says Yau.


###
The U.S. researchers were funded by the National Eye Institute and the Howard Hughes Medical Institute. The researchers in England were funded by the U.K. Biotechnology and Biological Sciences Research Council and Hammersmith Hospital Special Trustees. Authors on the paper are Hattar and Yau of Johns Hopkins; Lucas and Russell Foster of the Imperial College, London; and Motoharu Takao and David Berson of Brown University.

Johns Hopkins Medical Institutions’ news releases are available on an EMBARGOED basis on EurekAlert at www.eurekalert.org and from the Office of Communications and Public Affairs’ direct e-mail news release service. To enroll, call 410-955-4288 or send e-mail to bsimpkins@jhmi.edu.

Joanna Downer | EurekAlert!
Further information:
http://www.hopkinsmedicine.org/
http://www.sciencemag.org

More articles from Life Sciences:

nachricht Newly designed molecule binds nitrogen
23.02.2018 | Julius-Maximilians-Universität Würzburg

nachricht Atomic Design by Water
23.02.2018 | Max-Planck-Institut für Eisenforschung GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>