Cat owners flood the internet with videos of their kitties euphoricallyrolling and flipping out over catnip-filled bags and toys. But exactly howcatnip—and a substitute, known as silver vine—produces this feline high haslong been a mystery. Now, a study suggests the key intoxicating chemicals inthe plants activate cats’ opioid systems much like heroin and morphine do inpeople. Moreover, the study concludes that rubbing the plants protects thefelines against mosquito bites.

“This study essentially has revealed a new potential mosquito repellent” byexamining the “pharmaceutical knowledge” of cats, says Emory Universitybiologist Jacobus de Roode, who did not participate in the study.

Catnip ( Nepeta cataria ) and silver vine ( Actinidia polygama ) bothcontain chemical compounds called iridoids that protect the plants againstaphids and are known to be the key to the euphoria produced in cats. Todetermine the physiological effect of these compounds, Iwate Universitybiologist Masao Miyazaki spent 5 years running different experiments using theplants and their chemicals.

First, his team extracted chemicals present in both catnip and silver vineleaves and identified the most potent component that produces the feline high:a minty silver vine chemical called nepetalactol that had not been shown toaffect cats until this study. (The substance is similar to nepetalactone, thekey iridoid in catnip.) Then, they put 10 leaves’ worth of nepetalactol intopaper pouches and presented them, together with pouches containing only asaline substance, to 25 domestic cats to gauge their response. Most of theanimals only showed interest in the pouches with nepetalactol.

To make sure this was the object of the felines’ attraction, they repeated theexperiment with 30 feral cats—and one leopard, two lynxes, and two jaguarsliving in Japan’s Tennoji and Oji zoos. Big or small, the felines surrenderedto the substance, rubbing their heads and bodies in the patches for an averageof 10 minutes (see video, above). In contrast, dogs and mice that were testedshowed no interest in the compound.

Next, the researchers measured beta-endorphins—one of the hormones thatnaturally relieves pain and induces pleasure by activating the body’s opioidsystem—in the bloodstreams of five cats 5 minutes before and after exposure.The researchers found that levels of this “happiness hormone” becamesignificantly elevated after exposure to nepetalactol compared with controls.Five cats that had their opioid systems blocked did not rub on thenepetalactol-infused pouches.

But the researchers wanted to know whether there was a reason for the cats togo wild, beyond pure pleasure. That is when one of the scientists heard aboutthe insect-repelling properties of nepetalactone, which about 2 decades agowas shown to be as good as the famed mosquito-stopper DEET. The researchershypothesized that when felines in the wild rub on catnip or silver vine,they’re essentially applying an insect repellant.

They first showed cats can transfer the chemical to their skin, and thenconducted a live mosquito challenge—similar to when people’s arms are used toevaluate insect repellants. They put the nepetalactol-treated heads of sedatedcats into chambers full of mosquitoes and counted how many landed on them—itwas about half the number that landed on feline heads treated with a neutralsubstance, they report today in Science Advances.

Most scientists and pet owners assumed the only reason that cats roll aroundin catnip was for the euphoric experience, Miyazaki says . “Our findingssuggest instead that rolling is rather a functional behavior.”

The researchers speculate that cat ancestors might have rubbed their bodiesagainst the plants by chance, enjoyed the feeling, and kept doing it. It isnot clear, though, whether it was the euphoric response—or the insect-repelling properties of the plant—that kept them rolling. “Anyone who has eversat in the field to observe animals ambushing prey knows just how difficult itis for them to keep still when there are many biting mosquitoes around,”Miyazaki says . “It does not seem unreasonable, therefore, to argue thatthere is a strong selection pressure” to keep away annoying bugs.

The team, which has already patented an insect repellent based onnepetalactol, plans next to identify the cat genes involved in the catnipresponse and examine the substance’s action against other insect pests. DeRoode, who is impressed by how thorough the experiments were, says the workprovides a “really interesting” example of how insects can shape animalbehavior. “It is amazing how much we can learn from animals.”

Source: Sciencemag.org

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