When exposed to catnip or silver vine, cats engage in some fairly predictable behaviours, such as licking and chewing the leaves, rubbing their heads and faces against the plants, and rolling on the ground. Cats get a real kick out of these plants, but surprising new research points to a more practical purpose than just wanting to get high.
Nepetalactol — the most potent active ingredient in catnip (Nepeta cataria) and silver vine (Actinidia polygama) — provides cats with a chemical defence against mosquitoes, according to new research published in Science Advances. The discovery could explain why felines, whether domesticated cats or hulking jungle predators, display similar behaviours after being exposed to these plants.
The new research, led by Masao Miyazaki from Iwate University in Japan, offers fresh insights into nepetalactol and how it affects feline behaviour and their opioid receptors. That nepetalactol deters mosquitoes is a stunning revelation, and it could result in an entirely new class of insect repellent, according to the researchers. Nepetalactol had previously been associated with mosquito repellent activity, but “our data is the first to show it,” explained Miyazaki in an email.
What’s more, the new paper is the “first to show that nepetalactol is a potent bioactive compound to cats.” Indeed, it’s no secret that the chemical has some kind of neurological effect on cats, but catnip, a plant from the mint family, and silver vine, a kind of kiwifruit, contain a plethora of other bioactive compounds, such as isoiridomyrmecin, iridomyrmecin, isodihydronepetalactone, and dihydronepetalactone. Miyazaki and his colleagues, including researchers from Nagoya University in Japan and the University of Liverpool in the U.K., focused on nepetalactol because of its suspected potency.
After coming into contact with catnip and silver vine, cats engage in some stereotypical behaviours, such as rubbing their heads and faces against the plants, rolling on the ground, and giving the impression of euphoria. This lasts for around five to 15 minutes and is followed by the crash phase, in which the cats lounge for around an hour or more. The effect these plants have on cats has been known for centuries, but scientists don’t fully understand the purpose of all this, such as a biological or evolutionary reason for it — assuming it’s not just some quirky coincidence having to do with the feline brain.
To learn more, the team studied a bunch of different felines, including 25 lab cats, 30 feral cats, and several captive big cats, including leopards, jaguars, and lynx. They documented the cats’ reactions to filter paper laced with nepetalactol. All the cats exhibited the classic behavioural response. Dogs and mice exposed to the chemical exhibited no response.
The scientists also studied the cats’ reactions to some of the other bioactive agents found in silver vine and found nepetalactol to be the most potent.
“This study has found that…nepetalactol is the major bioactive compound in the leaves of silver vine that induces characteristic rubbing and rolling in cats,” write the authors in their study. “Further, nepetalactol had similar bioactivity in Amur leopard, jaguar, and Eurasian lynx. As most of the [feline] species so far tested have shown positive responses toward catnip (13 of 21 species tested from a total of 41 living species in this family), it is likely that this characteristic response to nepetalactol will also be common across many [felines].”
The group also measured the cats’ endorphin levels both before and after exposure, finding that the feline reaction to nepetalactol is regulated by their opioid system; elevated levels of endorphins were only observed after exposure to nepetalactol. What’s more, when the scientists suppressed their opioid receptors with special drugs, the cats no longer displayed their characteristic behaviours when exposed to the chemical.
As for silver vine’s role as a possible mosquito repellant, the researchers found that cats with fur covered in nepetalactol attracted significantly fewer mosquitoes, specifically the species A. albopictus, than the untreated control group — in some cases by as much as half.
“These results show that nepetalactol, transferred to face and head fur by rubbing against silver vine leaves, functions as a repellent against A. albopictus in cats,” the authors write. “This is convincing evidence that the characteristic rubbing and rolling response functions to transfer plant chemicals that provide mosquito repellency to cats.”
This, the authors argue, could explain why the behaviour evolved. The cats get high on these plants, roll around in the leaves, and unwittingly become protected against mosquitoes in the process. This theory makes a lot of sense, but scientists now need to explain why this behaviour isn’t seen in other animals, and if the repellant action actually happens in nature, not just in a laboratory setting. We also need to find out if nepetalactol works to repel A. aegypti, the mosquito responsible for spreading yellow fever, dengue, and Zika.
Miyazaki said there might be a very good reason why felines have evolved this special relationship with catnip and silver vine. Many felines “rely on stealth to stalk and ambush their prey,” requiring them to remain quiet and still, he said. A repellant that “reduces their susceptibility to both the irritation of biting mosquitoes and the diseases that these insect vectors carry is likely to provide a strong selective advantage.” This explains why this characteristic has been retained by many cat species, but it “does not explain why the behaviour has evolved only in felines,” said Miyazaki.
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One possible explanation is that an ancestor to modern cats evolved special olfactory receptors, which may have been a “crucial pre-adaptation” that provided the opportunity for this behaviour to evolve, speculated Miyazaki.
Looking ahead, the team wants to identify the olfactory receptors linked to nepetalactol, as well as the genes responsible for the behaviour. Miyazaki said team members tested nepetalactol on their arms, and it appeared to keep the mosquitoes away. But this “is for patent data only,” he said.
Ah yes, the almighty dollar. But this is a case in which good science might lead to a good and welcomed commercial product. Indeed, the researchers may have stumbled upon a new type of mosquito repellant, but time will tell if it actually works better than conventional repellants and if it makes economic and practical sense to synthesise this compound in large batches.