Catnip is more than just a natural high
If you are a cat person, you’ll know the fun that can be had with a bit of catnip – Nepeta cataria. – It sends most cats into a sort of temporary, drugged state. On getting a whiff of the stuff, their eyes glaze over and they start scratching, chewing, biting, licking, and rubbing their faces in it. Then after about five or 10 minutes of this, they’ll get up and wander off, completely disinterested. In Japan and China, a plant called silver vine (Actinidia polygama) has the same effect. This year, a team of researchers from Japan and the United Kingdom have published a couple of studies showing why cats go wild for silver vine.
It turns out that as well as getting a natural and non-addictive high from it, they are also covering themselves in mosquito repellent.
The researchers started by making extracts from silver vine leaves to isolate the compounds present. They then placed bits of filter paper containing each compound on the floor and let the cats at them. The compound that got the cats most excited was nepetalactol, a member of a family of compounds called iridoids. Dogs and mice are completely uninterested in nepetalactol but a leopard, two jaguars, and two lynxes from the local zoo also went wild for the stuff.
Nepetalactol activates a cat’s opioid system, releasing a burst of endorphins, which in humans are natural pain relievers and feel-good chemicals. Nepetalactol had no effect if the cats were first given an injection of naxolone, a medicine used to block or reverse the effects of opioid drugs like morphine and heroin.
In looking at the insect repelling properties of nepetalactol the researchers focused on the Asian tiger mosquito, Aedes albopictus, which can carry disease-causing microbes like the virus responsible for dengue fever. When exposed to the tiger mosquitoes, they found that if a cat had been rubbing in nepetalactol or silver vine leaves, fewer mosquitoes landed on its head.
The researchers were also curious as to why cats bite and chew at silver vine leaves. It turns out that damaged leaves released nepetalactol as part of an iridoid cocktail that was more potent than nepetalactol on its own. Just the smell of this cocktail was enough for cats to start trying to chew and bite at it.
When watching my cat enjoy catnip, I’ve often wondered why she only rubs her head in it. Now it makes sense. There’s no point wasting any of that natural mozzie repellent when her ears and nose are the most likely places a mosquito will try to feed, given how furry she is everywhere else.