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<a rel = "lightbox" href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2018/scientistsin.gif" title = "When surrounded by DEET, C. elegans do not turn to their favorite perfumes. Credit: Rockefeller University ">
When surrounded by DEET, C. elegans do not turn to their favorite perfumes. Credit: Rockefeller University
DEET, considered the most effective insect repellent available, may not be an insect repellent at all.
It's not that DEET does not keep the creatures away, that's right. However, Leslie B. Vosshall, Professor Robin Chemers Neustein of Rockefeller, has shown that DEET does not work by repelling insects, but by confusing them, playing with the neurons that help animals feel their environment. In addition, the effects of DEET are not limited to insects: spiders, ticks and many other parasites also act strangely in the presence of the chemical.
In this sense, DEET may be less of an insect repellent and more of an invertebrate. The term is not quite far from the language, but new research from Vosshall's lab supports this name change of the chemical.
In a recent article published in Nature, Vosshall and former Emily Dennis Scholar show that, like insects, the nematode C. elegans succumbs to confusion when DEET is there. The team also describes the genetic and cellular mechanisms that underlie this response, highlighting how a single chemical might disrupt very different species senses.
Everything in the DEET-garlic
First developed in the 1940s, DEET is found in most of the bug sprays used today. Research has shown that in flies and mosquitoes, the chemical interacts with insect-specific odor receptors. This research, however, can not explain how DEET exerts its effect on non-insect species.
Seeking an explanation, Dennis and Vosshall teamed up with Cori Bargmann, Professor Torsten N. Wiesel of Rockefeller, to determine if and how the DEET was changing the behavior of the spiders. C. elegans, a relatively simple animal with an elaborate sense of smell. When the researchers presented the tiny worms with DEET samples alone, the animals did not try to avoid the chemical, indicating that DEET does not just repel all the organisms that cross its path.
Single or Individual C. elegans the worm stops (left) when it detects the DEET. Later, the worm begins to crawl (right). This image covers several images of a worm movie. Credit: Emily Dennis and Leslie Vosshall
The scientists then mixed small amounts of DEET into the agar, the gelled substance C. elegans crawl into petri dishes. The presence of DEET has limited the movement of worms towards isoamyl alcohol, a chemical that usually attracts them; he also reduced their avoidance of 2-nonanone, a compound that they usually avoid. Yet worms reacted normally to other chemicals. These results suggest that DEET may interfere with reactions to both "good" and "bad" odors, but that it does not completely stop the olfaction.
The researchers also found that the sensitivity of DEET to worms depends on a gene called str-217which is expressed in neurons called ADL cells. When the researchers artificially activated these neurons, the worms stopped – a behavior also observed in C. elegans navigate in DEET infused agar. Together, these results indicate that the chemical works, in part, by activating the pausing neurons.
"In a way, the activation of ADL places the worms in a state of mind where they are more introspective, they stop more, they do not pay so much attention to smells, "says Vosshall. "But if you remove the right gene or neuron, that spell is broken."
Indeed, researchers have shown that worms lacked either str-217 or ADL neurons are less affected by DEET. They conclude that str-217 codes probably for a DEET receptor, and that ADL cells play an important role in mediating the response to the chemical.
<a href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2018/1-deetscramble.jpg" title = "A DEET-sensitive neuron that expresses the gene str-217 (green) plays a role in the confusing response of worms to the insect repellent. Credit: E. Dennis et al./nature 2018 ">
A DEET-sensitive neuron that expresses the gene str-217 (green) plays a role in the confusing response of worms to the insect repellent. Credit: E. Dennis et al./nature 2018
A special chemical
Vosshall's laboratory has previously demonstrated that DEET repels mosquitoes by interacting with odor receptors to confuse the animals' sense of smell. This latest study shows that DEET causes similar confusion in C. elegansbut through totally different mechanisms.
"We went into this study thinking that we might find some conserved DEET receptors common to all species," says Dennis. "But we found that in C. elegans, a completely unique gene is required for the response to DEET. "
Although the study did not result in the discovery of a magic receptor, it nonetheless provides insights into the effectiveness of the chemical on a wide variety of species.
"The common theme for all these organizations is that DEET does something to affect the perception of smells – it's like sabotage of the sensory system," says Vosshall.
Dennis adds, "Something about DEET is really special, and I think we're just beginning to discover all the ways it can affect different neurons, receptors, and species."
Explore more:
The chemical insecticide spray works by masking human odors
More information:
Emily J. Dennis et al, a natural variant and an artificial mutation in GPCR favor DEET resistance in C. elegans, Nature (2018). DOI: 10.1038 / s41586-018-0546-8
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