When something smells foul, vinegar flies can't perceive pleasant odors

Brooks Hays
Bad smells block vinegar flies from perceiving good smells, a protective mechanism that keeps flies away from danger. Photo by Benjamin Fabian
Bad smells block vinegar flies from perceiving good smells, a protective mechanism that keeps flies away from danger. Photo by Benjamin Fabian

March 15 (UPI) -- Vinegar flies can't process pleasant odors when something smells bad. When faced with conflicting odors, the repellent odor supersedes, according to a new study.

Previous studies showed the brain of the vinegar fly features separate neural circuits for good and bad smells. The studies also showed multiple pleasant odors can be perceived simultaneously by vinegar flies. When scientists layered good smells, the flies altered their behavior.


For the latest study, published this week in the journal Nature Communications, researchers exposed vinegar flies to conflicting smells.

Functional imaging technologies allowed the scientists to observe the brains of vinegar flies as they were exposed to both good odors and smells that repel. The experiments showed the repellent odor blocks the reception of the attractive odor.

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"This inhibition correlates with a reduced attraction to the odor source," Silke Sachse, researcher at the Max Planck Institute for Chemical Ecology, said in a news release.

Analysis of the brain images revealed cross-connections between the two circuits used to process good and bad smells.

"Our data demonstrate a specific, inhibitory cross-talk in the olfactory center of the fly's brain," researcher Ahmed Mohamed said. "Using further genetic tools we were able to show that glomeruli, spherical functional units in the olfactory center, that respond to attractive odors, are linked via specific inhibitory neurons to the repellent-specific glomeruli."

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Through experiments, scientists determined that not all foul odors have an influence on the circuitry responsible for receiving pleasant smells. One odor molecule, geosmin, responsible for the smell of toxic bacteria or mold, fails to inhibit pleasant odor receptors.

"It is conceivable that this geosmin glomerulus has no strong interactions with other glomeruli and cannot influence them accordingly," said researcher Markus Knaden.

Researchers estimate similar cross-connections are found among the neural circuitry in mammals, including humans. The inhibitory mechanism could have evolved to help protect flies, mammals and humans from spoiled foods.

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In future experiments, scientists will attempt to measure the effect of different physiological states, like the state of hunger, on the unique olfactory mechanism.

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