UNIVERSITY OF UTAH MEDIA RELEASE
Embargoed by the journal Nature for release at noon MST Weds. March 21, 2001
Contacts: Neil Vickers, biologist -- office (801) 585-1930, home (801) 466-7976Lee Siegel, science writer -- office (801) 581-8993, cell (801) 244-5399, [email protected]Coralie Alder, public relations director -- (801) 581-5180, cell (801) 556-8405
AROUSED MOTHS FLY IN WIND TUNNELSTO HELP BIOLOGISTS STUDY THE SENSE OF SMELL
March 21, 2001 -- Biologists placed male moths in small wind tunnels and let them smell the odor of female moths' sexual attractant in a study that revealed clues about how odors are converted into nerve impulses in the brain.
The study was good for science, but frustrating for the moths, which were wired to electrodes that measured what their antennas and brains were sensing.
"You've got the males all gung-ho to fly upwind in the wind tunnel," said Neil J. Vickers, an assistant professor of biology at the University of Utah. "They don't know that at the end of the line is not a female, but either a piece of rubber or a paper disk with pheromone [chemical sex attractant] on it. When they get there, they are pretty disappointed."
Vickers' study found that nerve cells in the olfactory (smell) center of the male moth brain fired in a way that was directly related to variations in the concentration of sex attractant in the plume of odor sprayed into the small wind tunnels. He said that contradicts earlier research suggesting that the nerve cells fire in a wave-like pattern or "oscillation" that is not related to changes in the concentration of odor in space and time.
The study will be published in the March 22 issue of the journal Nature. Vickers, an entomologist, conducted the research with neurobiologists Thomas Christensen and John Hildebrand of the University of Arizona, Tucson, and entomologist Thomas C. Baker of Iowa State University, Ames.
Such studies of how insects smell odors "are directly relevant to humans and other mammals because the neuroanatomical nuts and bolts of the [olfactory] systems are directly comparable," Vickers said.
Vickers said that when an odor is released into the air, it is not a homogenous cloud of smelly molecules, but a plume that varies in space and time as the molecules waft on breezes. He conducted the new study to learn how such variations in an odor plume affect how the brain processes what is smelled.
The researchers performed three experiments in the new study, which involved the insect equivalent of a nose, namely, antennas which have hundreds of tiny hairs containing cells that sense odors.
First, the researchers took a detached male moth antenna and wired electrodes to either end. Fine silver wires attached the electrodes to an amplifier. The antenna was placed at one end of a wind tunnel that was constructed with a plastic tube about a yard long and 16 inches diameter. A plume of female sex attractant was blown in through the other end. When the odor struck the antenna, the olfactory sensors in the antenna responded, and that electrical activity was picked up by the electrodes, amplified and measured by what is called an "electroantennogram."
"It's like measuring brain waves," Vickers said.
That experiment showed "the odor plume fluctuates rapidly, so there are brief and rapid fluctuations in odor intensity as measured by the antennogram," he said. "We're showing the odor is not continual. It's fluctuating with rapid ons and offs" both in the air and as sensed by the antenna.
In the second experiment, a detached antenna, also wired to electrodes, was attached to the back of a live moth using a tiny piece of Velcro. Vickers calls it a "cyclops antenna" because it was attached between and perpendicular to the moth's own pair of antennas. The method let Vickers and colleagues measure what pattern of odors the moth contacted as he flew upwind in the wind tunnel.
The experiment showed that the intensity of odor sensed by the moths depends to some extent on their flight path through an odor plume.
The third experiment was the key part of the study. In this case, one of a live moth's two antennas was wired to an electrode, while a tiny microelectrode was inserted into the olfactory lobe, part of the moth's brain at the base of that antenna.
The moth was restrained in a tiny glass tube and placed in the larger tube that served as a wind tunnel. As a plume of female sex attractant was blown into the wind tunnel, the scientists recorded electrical activity both from the olfactory cells in the moth's antenna and the olfactory nerve cells in the brain.
The results showed that the dynamics of the odor -- namely, changes in the odor's intensity over space and time -- correlated closely with electrical firings of neurons or nerve cells in the moth's brain, Vickers said.
"In other words, odor-responsive moth brain cells follow the pattern and fluctuations of odor puffs that waft by the antenna," he explained.
That conflicts with other research suggesting that when an animal encounters an odor, the pattern of nerve-cell firings creates a code in the form of a wave or "oscillation" of brain activity. That code tells the brain whether it is sensing orange, apple, moth sex attractant or something else, according to the theory.
Vickers' findings indicate that the fluctuations do not form a code, but instead simply represent fluctuations in the intensity of the odor plume.
Why is this important?
"It matters in terms of how the brain is actually recognizing different smells," Vickers said. "We are saying you have to pay attention to the pattern of odor that these animals are sensing."
The moth species used in the study was Heliothis virescens, the tobacco budworm, which is a major agricultural pest that damages tobacco, fruit, soy, cotton, corn and other crops, Vickers said.
This news release and a downloadable close-up photo of a moth with a third or "cyclops" antenna attached to its back may be found after noon MST Monday March 19 athttp://www.utah.edu/unews/032101_mothsmell.html
University of Utah Marketing & Communications201 S Presidents Circle, Room 308Salt Lake City, Utah 84112-9017(801) 581-6773 fax: 585-3350
RSS