Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Molecule helps pupils respond to light

10.01.2003


Researchers are reporting progress in understanding whether a second light-sensing pathway in mammals indeed contributes to the detection of ambient light for controlling body functions.



In an article published in the January 10, 2003, issue of the journal Science, the researchers report that the molecule melanopsin is necessary in order for the pupil to constrict properly in response to light, a function termed the pupillary light reflex.

The latest findings by Howard Hughes Medical Institute investigator King-Wai Yau at Johns Hopkins University and his colleagues from Imperial College in London and Brown University build on studies they published last year in which they traced the neural circuitry for this newly discovered light-sensing pathway that is distinct from the primary visual pathway.


In those studies, Yau and his colleagues showed that the neural circuitry is constructed of a small subset of intrinsically photosensitive retinal ganglion cells (RGCs) that carry visual signals from the eye to the brain. These RGCs project specifically to brain centers involved in circadian-pacemaker activity and the pupillary light reflex, accessory visual functions that do not require image-formation on the retina. Biological, or circadian, clocks operate on a roughly 24-hour cycle that governs sleeping and waking, rest and activity, body temperature, cardiac output, oxygen consumption and endocrine gland secretion. In mammals, the internal circadian clock resides in the brain, and sunlight is the cue that resets this clock daily.

Improved understanding of the circadian system could lead to better treatments for jet lag and depression, and may help optimize drug treatments affected by changes in hormone levels.

Although earlier studies had indicated that melanopsin was part of a light-sensing system, in the latest research Yau and his colleagues sought to demonstrate that the molecule is indeed required for the light-sensing ability of this system and that the system has a true physiological function.

They first developed a knockout mouse in which they completely replaced the melanopsin gene with a tracer gene. In initial studies, they found that although knocking out the melanopsin gene did not affect the genesis and wiring of the specific RGCs responsible for the light-sensing pathway, it did make the RGCs unresponsive to light.

"Determining that in such animals these specific retinal ganglion cells were still present but they became light-insensitive was crucial, because it told us, first, melanopsin is indeed required in order for these cells to be intrinsically light-responsive and, second, that whatever functional defect we found in the animal could be directly attributed to the loss of photosensitivity of these retinal ganglion cells rather than to elusive causes such as mis-wiring in the circuitry," said Yau.

To determine the physiological effect of the melanopsin-deficient cells, the researchers chose to measure how the pupils of the knockout mice constricted in response to a gradually increasing intensity of light, because this reflex is fast, precise and can be readily be quantified.

"In a normal animal, increasing the light intensity would progressively increase the constriction of the pupil, until it is no more than a pinhole," said Yau. "But in the knockout animals, while the pupil begins to constrict normally in dim light, at higher intensities of light the reflex seems to ’hang.’ That is, the pupil never constricts down to the same small size as in the normal mouse."

Since the knockout mice still exhibited some pupillary light reflex, albeit diminished, Yau and his colleagues suspected that the melanopsin-dependent reflex might be complemented by the rods and cones, the photoreceptors for the conventional, image-forming visual pathway. Thus, they tested the pupillary reflex in another strain of mouse that have lost the rods and cones due to degeneration.

"We found in these mice that the threshold of the pupil reflex is elevated tremendously," said Yau. "However, as you increase the light intensity, eventually the pupils start to constrict; and at high intensities, it constricts to the normal level." Thus, the pupillary light reflex involves two complementary mechanisms, one being the rod/cone system, and the other being the melanopsin-associated system.

"There is overlap between the two systems," said Yau. " The rods and cones are responsible for the high sensitivity of the reflex, but they cannot complete the job," said Yau. "On the other hand, while the melanopsin system is not highly sensitive to light, it alone can nonetheless bring the reflex to completion."

Could there be yet a third mechanism that aids in the reflex? Yau said that his group’s analysis of the characteristics of the two mechanisms suggests that a third mechanism would have a negligible effect, if it exists at all. In further studies, they plan to produce a mouse lacking both the rod/cone system and the melanopsin-dependent system, to determine whether the mice would lack the pupillary light reflex completely.

"For us, the most important question was whether this melanopsin pathway is of any physiological importance," said Yau. "Now we have shown that it is, based on the simple pupil reflex. The next step will be to examine closely other, more complex physiological functions, such as circadian photoentrainment."

Jim Keeley | EurekAlert!
Further information:
http://www.hhmi.org/

More articles from Life Sciences:

nachricht On the way to developing a new active ingredient against chronic infections
18.08.2017 | Deutsches Zentrum für Infektionsforschung

nachricht New gene catalog of ocean microbiome reveals surprises
18.08.2017 | University of Hawaii at Manoa

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

New gene catalog of ocean microbiome reveals surprises

18.08.2017 | Life Sciences

Astrophysicists explain the mysterious behavior of cosmic rays

18.08.2017 | Physics and Astronomy

AI implications: Engineer's model lays groundwork for machine-learning device

18.08.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>