Featured Research

from universities, journals, and other organizations

Scientists Find Just How Discriminating A Worm Can Be: Unique System Of Overlapping Odor Sensors Discovered

Date:
April 10, 2001
Source:
University Of California, San Francisco
Summary:
With only 32 of its 302 nerves dedicated to detecting the odors that drift through its world, the lowly roundworm seems hard pressed to smell food, let alone discriminate friend from foe. But researchers have discovered a unique system of overlapping sensors that enables the creature to tell smells apart.

With only 32 of its 302 nerves dedicated to detecting the odors that drift through its world, the lowly roundworm seems hard pressed to smell food, let alone discriminate friend from foe. But researchers have discovered a unique system of overlapping sensors that enables the creature to tell smells apart.

The system seems well designed for the nerve-challenged worm. In mice and humans, each of millions of odor sensing nerves has only one type of odor detecting receptor, allowing the brain to distinguish between odors by tracking which nerve did the sensing. But in a compromise between the need to detect many odors and the scarcity of available nerves, the roundworm's odor sensing neurons are studded with receptors for different odors. It has been a biological puzzle how a nerve that senses many odors can distinguish between them.

Scientists at the University of California, San Francisco uncovered a clever combination strategy in the worm's odor sensing nerves. Paired nerves, they found, have receptors tuned to some of the same odors, yet each member of the pair also supports receptors tuned to unique odors not detected by the partner.

With this partially overlapping detection system, the nerve pairs can sense more odors than would be possible if they had identical receptors or even if each were tuned to completely different smells, the scientists found. More importantly, the combinatorial approach allows the nerve pairs to discriminate between different odors, a lifesaving trait if the worm has to find one source of food in a bewildering array of aromas.

"The worm can solve amazingly complex sensory problems with few olfactory nerves," said senior investigator of the study, Cornelia I. Bargmann, PhD, an investigator in the Howard Hughes Medical Institute and professor and vice chair of anatomy at UCSF.

"Each nerve cell has a private window into the world of smells and a shared window with its partner. Any one nerve cell can get confused, but by comparing the private and shared information, the animal sorts out and distinguishes all possible combinations of odors."

The combinatorial approach may be unique to this simple creature, Bargmann suggests, or it may be a clue to how higher organisms including humans solve the same problem: how a sensory system or another part of the brain can process a nearly limitless number of environmental cues with a finite number of nerves.

"We want to understand the relationship between genes, cells and behavior in the brain," she said, "but our own brains are complex beyond belief. In this fairly simple animal, we can decode the 'thinking strategy' used by every cell in the brain."

The research is published in the April 5 issue of Nature. Lead author is Paul D. Wes, PhD, a post-doctoral scientist in Bargmann's laboratory. (In a parallel paper in the same issue, a research group in Oregon found similar results in the worm's taste center, a system that is organized much like the taste system in humans.)

The worm in question is C. elegans, or more elegantly, Caenorhabditis elegans, a millimeter-long soil dweller widely studied by geneticists and developmental biologists because it displays many developmental processes and instinctive behaviors common to higher organisms. The worm is tiny and transparent, with a very small brain that can be studied in detail.

The key odors of interest in the UCSF study were benzaldehyde, which gives off a scent somewhat like almond, and butanone which has an oily smell. Both are thought to be produced by bacteria, the worm's food, but both can also be pervasive smells without useful information. Under those circumstances a sensible worm ought to ignore them, Bargmann said.

The scientists assayed a worm's ability to distinguish between the two odors by exposing it to a high concentration of butanone and then testing its ability to be attracted to benzaldehyde in this odor environment.

They examined the odor sensing abilities of a pair of olfactory neurons, known as AWC, which has been the focus of the Bargmann lab for ten years. Her research group has determined that this nerve pair not only senses at least five attractive odors, but can also distinguish between the odors.

The lab recently discovered that the two neurons, which had been thought to be identical left-right members of a pair, actually differ in one subtle, but critical respect. During the development of the nerves, an odor receptor known as STR-2 becomes active on one of the nerves but not on the other. Whether the receptor is expressed on the left or the right nerve is apparently random, they found.

Bargmann and Wes used standard techniques to search among mutant worms for those that were unable to detect the difference between benzaldehyde and butanone and then showed that these genetic mutants, known as ky542, possess an active STR-2 receptor on both members of the AWC neuron pair, unlike normal worms.

They further showed that they could induce this odor discrimination deficit in normal worms by killing one of the paired AWC cells with a laser beam. Either the mutant worms or the operated worms could sense both odors perfectly well, but with a change in one of the AWC neurons, discrimination was lost. The difference between detection and discrimination is the first step in higher processing in the senses, Bargmann said, and the experiment showed where that step occurs.

Only one of the paired AWC nerves, the one that expresses STR-2, responds to butanone, the scientists found, while both this neuron and its STR-2-silent partner can detect benzaldehyde. The nerve with the silenced STR-2 is required for discrimination between butanone and benzaldehyde, because it can smell benzaldehyde without sensing the confusing butanone odor. In turn, that silenced nerve senses a third odor, a buttery smell, that its partner can't detect. So, each nerve cell can recognize smells that are either buttery or oily but not both, and they both recognize almond-like smells. By comparing the private and shared information, the animal can detect more odors than if each of the paired nerves sensed entirely different smells.

The research is funded by the Howard Hughes Medical Institute and the National Institutes of Health.


Story Source:

The above story is based on materials provided by University Of California, San Francisco. Note: Materials may be edited for content and length.


Cite This Page:

University Of California, San Francisco. "Scientists Find Just How Discriminating A Worm Can Be: Unique System Of Overlapping Odor Sensors Discovered." ScienceDaily. ScienceDaily, 10 April 2001. <www.sciencedaily.com/releases/2001/04/010405081652.htm>.
University Of California, San Francisco. (2001, April 10). Scientists Find Just How Discriminating A Worm Can Be: Unique System Of Overlapping Odor Sensors Discovered. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2001/04/010405081652.htm
University Of California, San Francisco. "Scientists Find Just How Discriminating A Worm Can Be: Unique System Of Overlapping Odor Sensors Discovered." ScienceDaily. www.sciencedaily.com/releases/2001/04/010405081652.htm (accessed October 21, 2014).

Share This



More Plants & Animals News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

'Cadaver Dog' Sniffs out Human Remains

'Cadaver Dog' Sniffs out Human Remains

AP (Oct. 21, 2014) Where's a body buried? Buster's nose can often tell you. He's a cadaver dog, specially trained to find human remains and increasingly being used by law enforcement and accepted in courts. These dogs are helping solve even decades-old mysteries. (Oct. 21) Video provided by AP
Powered by NewsLook.com
White Lion Cubs Born in Belgrade Zoo

White Lion Cubs Born in Belgrade Zoo

AFP (Oct. 20, 2014) Two white lion cubs, an extremely rare subspecies of the African lion, were recently born at Belgrade Zoo. They are being bottle fed by zoo keepers after they were rejected by their mother after birth. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
Traditional Farming Methods Gaining Ground in Mali

Traditional Farming Methods Gaining Ground in Mali

AFP (Oct. 20, 2014) He is leading a one man agricultural revolution in Mali - Oumar Diatabe uses traditional farming methods to get the most out of his land and is teaching others across the country how to do the same. Duration: 01:44 Video provided by AFP
Powered by NewsLook.com
Goliath Spider Will Give You Nightmares

Goliath Spider Will Give You Nightmares

Buzz60 (Oct. 20, 2014) An entomologist stumbled upon a South American Goliath Birdeater. With a name like that, you know it's a terrifying creepy crawler. Sean Dowling (@SeanDowlingTV) has the details. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins