Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The Smell of Danger

29.06.2011
Rodent olfaction and the chemistry of instinct

The mechanics of instinctive behavior are mysterious. Even something as simple as the question of how a mouse can use its powerful sense of smell to detect and evade predators, including species it has never met before, has been almost totally unknown at the molecular level until now.

David Ferrero and Stephen Liberles, neuroscientists at Harvard Medical School, have discovered a single compound found in high concentrations in the urine of carnivores that triggers an instinctual avoidance response in mice and rats. This is the first time that scientists have identified a chemical tag that would let rodents sense carnivores in general from a safe distance. The authors write that understanding the molecular basis of predator odor recognition by rodents will provide crucial tools to study the neural circuitry associated with innate behavior.

Their findings were published online in the Proceedings of the National Academy of Science on June 20, 2011.

The search began in 2006, when Stephen Liberles, now Assistant Professor of Cell Biology at Harvard Medical School, was working as a post-doc in the lab of Linda Buck. Buck was part of the team that won the Nobel Prize for identifying the receptors that allow olfactory neurons to detect odors. While in her lab, Liberles identified a new type of olfactory receptor, the trace amine-associated receptors (TAARs).

Mice have about 1200 kinds of odor receptors, and 14 kinds of TAARs. In comparison, humans —who rely more on vision than smell— have about 350 odor receptors and five TAARs.

Liberles’s initial findings indicated that several of the TAARs detect chemicals found in mouse urine, including a chemical with enriched production by males. He wondered, could TAARs (which appear to have originally evolved from neurotransmitter receptors that mediate behavior and emotion) play a role in the social behavior of rodents? What other kinds of naturally occurring odors might they be able to detect?

In Liberles’s lab at Harvard Medical School, graduate student David Ferrero began a search for other natural compounds that were detected by the TAARs. Working with commercially available predator and prey urine (used by gardeners to keep pests out of their crops and by hunters to mask their own scent or as lures for prey), Ferrero discovered that one of the 14 TAARs, TAAR4, detected the odor of several carnivores.

It seemed they had found a kairomone, a chemical that works like a pheromone, except that it communicates between members of different species instead of members of the same species. Prior to this discovery, the only known rodent-carnivore kairomones were a volatile compound produced by foxes, but not in that of other predators, and two non-volatile compounds produced by cats and rats (which prey on mice). Volatile compounds aerosolize and can be smelled at great distances; non-volatile compounds need to be sniffed more directly, something that would not be helpful in avoiding a predator directly but rather their terrain.

“One of the things that’s really new here is that this is a generalized predator kairomone that’s volatile,” said Ferrero.

For rodents, it’s the smell of danger.

Ferrero identified the compound that activates TAAR4 as 2-phenylethylamine, a product of protein metabolism. He then obtained specimens from 38 species of mammals and found elevated levels of 2-phenylethylamineby 18 of 19 species of carnivores, but not by non-carnivores (including rabbits, deer, primates, and a giraffe).

“It’s been known so long that predator odors are great rodent deterrents, but we’ve discovered one molecule that’s a key part of this ecological relationship,” Ferrero said.

In a series of behavior tests, rats and mice showed a clear, innate avoidance to the smell of 2-phenylethylamine. The behavioral studies were repeated using a carnivore samples that had been depleted of 2-phenylethylamine. Rats failed to show full avoidance of the depleted carnivore urine, indicating that 2-phenylethylamine is a key trigger for predator avoidance.

Lacking the gene for TAAR4, humans can’t experience anything like what rodents do when they smell 2-phenylethylamine. To us, it has a mildly inoffensive odor. But trimethylamine, a related organic compound that activates TAAR5, a receptor found in humans, is deeply repugnant to people.

What happens between the receptors and the parts of the brain that trigger that avoidance behavior remains a mystery, one with direct medical relevance.

According to Liberles, “In humans, the parts of the brain that deal with likes and dislikes go awry in many diseases, like drug addiction, and predator odor responses have been used to model stress and anxiety disorders. Going from chemicals to receptors to neural circuits to behaviors is a Holy Grail of neuroscience.”

“The neural circuits are like a black box, but here we have identified a chemical stimulant and a candidate receptor that trigger one behavior,” Ferrero said. “We feel this is an important first step to understanding the neural circuitry of innate behavior.”

This research was funded by the National Institute On Deafness And Other Communication Disorders.

Written by Jake Miller

David Cameron | EurekAlert!
Further information:
http://www.hms.harvard.edu

More articles from Life Sciences:

nachricht New catalyst controls activation of a carbon-hydrogen bond
21.11.2017 | Emory Health Sciences

nachricht The main switch
21.11.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Nanoparticles help with malaria diagnosis – new rapid test in development

The WHO reports an estimated 429,000 malaria deaths each year. The disease mostly affects tropical and subtropical regions and in particular the African continent. The Fraunhofer Institute for Silicate Research ISC teamed up with the Fraunhofer Institute for Molecular Biology and Applied Ecology IME and the Institute of Tropical Medicine at the University of Tübingen for a new test method to detect malaria parasites in blood. The idea of the research project “NanoFRET” is to develop a highly sensitive and reliable rapid diagnostic test so that patient treatment can begin as early as possible.

Malaria is caused by parasites transmitted by mosquito bite. The most dangerous form of malaria is malaria tropica. Left untreated, it is fatal in most cases....

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

Previous evidence of water on mars now identified as grainflows

21.11.2017 | Physics and Astronomy

NASA's James Webb Space Telescope completes final cryogenic testing

21.11.2017 | Physics and Astronomy

New catalyst controls activation of a carbon-hydrogen bond

21.11.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>