Catnip protects cats from mosquitoes

Does your cat rub against and wriggle around when it sees catnip or silver vine? It’s not the only one. Intrigued, scientists sought to understand the biological significance of this behavior and the underlying neurophysiological mechanisms. The results suggest, in particular, that the main bioactive compound in these plants affects cats’ opioid system in order to protect them from mosquito bites.   Catnip (Nepeta cataria) and silver vine (Actinidia polygama) hold a special place in cats’ hearts. They rub their heads against them and roll on the ground with undeniable pleasure, almost as if they were intoxicated. Although this behavior has been known for over three hundred years, scientists still know very little about its biological significance and the neurophysiological mechanisms it triggers. To better understand this attraction, a team of researchers from Japan and the United Kingdom tested the reactions of 25 laboratory cats, 30 wild cats, and several captive big cats—including a leopard, two jaguars, and two Eurasian lynx—when exposed to the main bioactive compound in catnip, nepetalactol. While laboratory dogs and mice showed no interest in the molecule, this was not the case for the felines. In addition to this expected behavior, their plasma β-endorphin levels increased in response to the active iridoid compounds present in the plants. However, when the felines’ opioid receptors were blocked with a pharmacological antagonist (naloxone), this increase disappeared, as did the cats’ specific behavior. This suggests that neurons in the feline olfactory system, which detect the iridoids emitted by the leaves of the silver vine, stimulate the release of β-endorphins, which in turn activate the animals’ μ-opioid receptors. This activation is responsible for the unusual behaviors that cats exhibit in the presence of the plant. But why do they rub against the plant and become “high” upon contact with it? Researchers attribute this to the mosquito-repellent properties of the iridoids found in catnip and silver vine. In fact, after rubbing against the plant, cats attract far fewer mosquitoes—sometimes up to 50% fewer. The insects therefore avoid animals that like to rub against catnip. Cats are thought to have developed olfactory receptors specific to the iridoids found in catnip, as well as a sense of euphoria upon contact with the plant, which encourages the transfer of these bioactive compounds—which have mosquito-repellent properties. According to the researchers, this protection could potentially extend to other insects, and even to certain viruses or parasites. In particular, they are considering using this chemical defense to protect humans against harmful insects. Nepetalactone is reportedly up to ten times more effective at repelling mosquitoes than N,N-diethyl-3-methylbenzamide (DEET), the repellent used in most insecticides currently on the market.