Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study: Nose doesn’t smell like the eyes see

14.07.2005


Johns Hopkins scientists have uncovered new details of how smelly things create signals in the nose that eventually go to the brain. The findings raise issues about how the process involved has been described for many years in biology textbooks.



The textbooks say that our sense of smell converts odors into brain signals just like our vision converts light into brain signals. But the new work shows that while a key protein pathway is used in both, it behaves quite differently in the nose than it does in the eye. The researchers’ findings are published in the June 24 issue of Science.

"Most of the information about this pathway comes from studies of vision, and people just assumed it worked the same way elsewhere in the body," says King-Wai Yau, Ph.D., professor of neuroscience in Johns Hopkins’ Institute for Basic Biomedical Sciences. "But instead of being a model for other systems in the body, our visual system is probably pretty unique."


At issue is the behavior of a huge family of proteins called G-protein-coupled receptors. When activated by light in the eye or a molecule in other settings, each G-protein-coupled receptor uses a similar switch -- the exchange of a tiny bit called GTP for a related bit called GDP on the aptly named G-protein -- to trigger the cell’s response.

Since about 1980, scientists studying vision have understood that light activates a specific G-protein-coupled receptor (the light-detecting molecule rhodopsin) in cells called rods found at the back of the eye. They also know that, once activated by light, this particular receptor stays activated long enough to trigger the GTP-to-GDP switch on a large number of G-protein molecules, substantially amplifying the incoming signal.

"Because of this amplification, rods are extremely sensitive to light," says Yau. "Each cell is capable of signaling the absorption of a single unit, or photon, of light."

Because G-protein signaling is so well understood in the eye, Yau says that scientists just assumed that it would amplify signals in other systems and cells where it’s important. Indeed, some scientists have claimed that G-protein-coupled receptors involved in detecting odors have similar amplification abilities and that, as a result, a single stinky molecule would produce a signal in odor-detecting cells as large as a single unit of light does in rods.

Trouble is, that conclusion has turned out to be wrong. "We found that most of the time, a single molecule does not trigger a response. And even when it does, the response we measured is about 100 times lower than reported for rods," says Vikas Bhandawat, lead author of the study and a graduate student in neuroscience at Johns Hopkins.

In his experiments, Bhandawat used a system developed by co-author Johannes Reisert, Ph.D., that allows precise measurement and control of the amount of odiferous molecules used to stimulate a single odor-detecting nerve cell from a frog, and precise, long-term measurement of the cell’s response to the odors.

"If you don’t know exactly how much of the odor is being used, or exactly how long the exposure lasts, then you can’t figure out what a single odorant molecule does," says Bhandawat. "Johannes’ system allows us to do just that."

The team’s finding underscores the key difference between the eye’s light-detecting system and the nose’s odor-detecting system: the very nature of light and molecules.

"When light hits a rod and is absorbed, it’s a one-time event -- the light disappears forever," says Yau. "In the nose, an odor molecule that’s inhaled probably stays in the nasal mucus long enough to bind to and trigger a number of receptors, essentially enhancing its own signal."

G-protein-coupled receptors are involved in thousands of biological processes, from creating appropriate organizational cues during development to transmitting signals from hormones and other molecules in fully grown adults, and are present in creatures from the amoeba to plants and animals.

"We think the mode of receptor behavior in odor detection is more the norm for chemical-triggered G-protein pathways, which are by far the most common G-protein signaling pathways, than is what happens in the eye," says Yau. "The sense of smell needs to be sensitive, but amplification isn’t the only way to improve sensitivity."

For example, the cells could have many copies of the receptor, or many cells could express the same receptor. These are most likely the reasons why mice and dogs have a heightened sense of smell compared to people, says Yau.

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

More articles from Studies and Analyses:

nachricht Antarctic Ice Sheet mass loss has increased
14.06.2018 | Technische Universität Dresden

nachricht WAKE-UP provides new treatment option for stroke patients | International study led by UKE
17.05.2018 | Universitätsklinikum Hamburg-Eppendorf

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

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

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>