Why cats go so crazy for catnip

A  cat rolls and rubs its body against leaves from a silver vine plant.

(CNN)Catnip isn't just intensely pleasurable for cats. It's also practical.

When your feline friend rubs, rolls against, chews and licks catnip leaves, it's not just playful high jinks sparked by the plant's intoxicating qualities. The behavior leads to the release of certain compounds that might protect cats from pesky mosquitoes, according to new research out of Japan.
Compounds called iridoids in the leaves of catnip (Nepeta cataria) and the plant silver vine (Actinidia polygama) act as an insect repellent as they are released when the cats rub their bodies against the leaves, the same team found in a study published last year.
    Catnip, sometimes called catmint, and silver vine are both flowering plants with aromatic leaves that grow in many places around the world. Dried catnip and silver vine leaves are also used in cat toys.
      The group's latest research has shown that the way cats lick and chew the leaves causes 10 times the amount of these compounds to be released, with damaged leaves thus making the insect repellent properties more effective.
      With the help of 16 cats, the researchers compared feline responses to intact silver vine leaves and leaves the team crumpled and tore by hand. The cats showed a more prolonged interest in interacting with the damaged leaves than with the intact leaves.
      Then, to test whether the felines were reacting to the iridoids specifically, the cats were given dishes with pure nepetalactone and nepetalactol -- key active compounds in catnip and silver vine, respectively.
        "Cats show the same response to iridoid cocktails and natural plants except for chewing," said Masao Miyazaki, a professor in the department of biological chemistry and food sciences at Iwate University in Japan, said in a news release. "They lick the chemicals on the plastic dish and rub against and roll over on the dish."
        A cat involved in the study rolls on leaves belonging to the silver vine plant.
        It's the smell of the plant that triggers the behavior, according to the research.
        "When iridoid cocktails were applied on the bottom of dishes that were then covered by a punctured plastic cover, cats still exhibited licking and chewing even though they couldn't contact the chemicals directly," Miyazaki said. "This means that licking and chewing is an instinctive behavior elicited by olfactory stimulation of iridoids."
        In the case of silver vine, damaging the leaves triggered the release of other iridoids.
        "Nepetalactol accounts for over 90% of total iridoids in intact leaves, but this drops to about 45% in damaged leaves as other iridoids greatly increase," he said. "The altered iridoid mixture corresponding to damaged leaves promoted a much more prolonged response in cats."
          The work might help identify plant enzymes that could be used as insect repellants for humans, the study said.