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 Water forms 'spine of hydration' around DNA, group finds
26.05.2017 | Cornell University

nachricht How herpesviruses win the footrace against the immune system
26.05.2017 | Helmholtz-Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>