Navigation Links
The smell of danger
Date:6/28/2011

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 Sciences 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."


'/>"/>

Contact: David Cameron
david_cameron@hms.harvard.edu
617-432-0441
Harvard Medical School
Source:Eurekalert

Related biology news :

1. Clubbers can smell a good nightspot
2. Smell and taste experts at international conference -- April 13-17, 2011
3. Researchers unlock new secret to how smells are detected
4. The brain knows what the nose smells, but how? Stanford researchers trace the answer
5. Study shows pregnant mothers diet impacts infants sense of smell
6. Mice that smell light could help us better understand olfaction
7. New findings on taste and smell
8. Could smell play a role in the origin of new bird species?
9. Smelling the scenery in stereo
10. Monell Center joins with CAS to host Beijing meeting on taste and smell research
11. How the 100th protein structure solved at Diamond impacts our understanding of how insects smell
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:12/12/2016)... , Dec. 12, 2016  Researchers at Trinity ... for graphene by combining the material with Silly ... sensitive pressure detector able to sense pulse, blood ... small spider.  The research team,s ... be read here:  http://science.sciencemag.org/content/354/6317/1257 ...
(Date:12/7/2016)... 7, 2016 According to a new market research report ... (Facial Expression, Voice Recognition), Service, Application Area, End User, And Region - Global ... from USD 6.72 Billion in 2016 to USD 36.07 Billion by 2021, at ... Continue Reading ... MarketsandMarkets Logo ...
(Date:12/7/2016)... 2016   Veridium , a leader in ... new CEO James Stickland . Stickland, a ... experience, has served in senior executive roles for ... in expanding a pipeline of venture capital and ... recently served as managing director of U.K.-based fintech ...
Breaking Biology News(10 mins):
(Date:1/19/2017)... ... 2017 , ... The American Medical Informatics Association (AMIA) today ... Policy. Specifically, the nation’s leading informatics experts, said data sharing plans should be ... recommended that NIH earmark funding for researchers to produce and execute data sharing ...
(Date:1/19/2017)... , ... January 19, 2017 , ... ... with services spanning the full spectrum of drug and device development, and ... to pharma/device companies and clinicians, today announced Verified Clinical Trials (VCT) ...
(Date:1/19/2017)... , Jan. 18, 2017 Acupath Laboratories, ... announces the formation of an Executive Committee that will ... beyond. John Cucci , a 15-year ... from Director of Business Development to Chief Sales ... Mr. Cucci served in senior sales leadership roles at ...
(Date:1/18/2017)... 18, 2017 According to a new market research report ... Infectious Disease), & End User (Molecular Diagnostic Laboratories, Academic and Research Institutions) - ... USD 739.9 Million by 2021 from USD 557.1 Million in 2016, growing at ... ... MarketsandMarkets Logo ...
Breaking Biology Technology: