Volume 83, Number 31
WHAT'S THAT STUFF?
The key chemical responsible for the herb's frisk-inducing effects on felines is nepetalactone
Even the most fickle feline cannot resist the lure of catnip, or Nepeta cataria, which is sold in pet stores as the raw herb or essential oil, often in combination with cat toys.
The results of catnip exposure are often dramatic and humorous. A friend of mine has a cat named Lucy who spends nearly all her time in quiet repose. Lucy seems rather cool to the idea of physical activity, but sprinkle catnip on the rug, and Lucy transforms into a hyped-up ball of fur. After a few preliminary sniffs and rubs at the carpet, she wriggles and rolls around with the agility of an Olympic gymnast performing a floor exercise. Minutes later, Lucy returns to her usual sedate self.
One cannot observe catnip's remarkable and sudden, if transient, effect on cat behavior without suspecting that something chemical is afoot. In fact, the key to catnip-induced friskiness is a compound called nepetalactone, says Carolyn M. McDaniel, a veterinarian at the Feline Health Center at Cornell University.
Nepetalactone is one of several related compounds known to initiate the classic catnip response sequence: sniffing, licking, and chewing, followed by head shaking, body and head rubbing, and then repeated head-over-heels rolling. Similarly active compounds are actinidine, iridomyrmecin, and matatabilactone.
McDaniel says a thorough neurological explanation for catnip-induced calisthenics is lacking, but experts infer that cats receive the necessary stimuli from olfactory and possibly oral receptors for nepetalactone and similar compounds.
Until they are around three months old, cats are indifferent to catnip. And many cats--as many as half, says McDaniel--never develop catnip sensitivity. The sensitivity is inherited: A kitten with only one catnip-sensitive parent has a one-in-two chance of inheriting the catnip sensitivity, and a kitten whose parents both exhibit sensitivity has a three-in-four chance. McDaniel says there is no correlation between catnip sensitivity and sex, color, or breed.
Catnip is a member of the mint family of plants. Its cousins include basil, oregano, and spearmint. All these plants produce essential oils that contain flavorful and aromatic terpenoids such as limonene, menthol, and spearmint.
The leaves, stems, and seedpods of catnip are covered with microscopic bulbs called trichomes, which store the essential oil until they reach maturity and burst. External forces, such as a hungry bug biting into a leaf or a passing animal brushing up against the plant and bruising the leaves, can also release the oil.
That the essential oil is contained inside the fragile bulbs may explain why cats are seen rubbing up against, and even chewing, the leaves. Cats gain nothing by ingesting the leaves because the biological activity of nepetalactone is most likely centered in the olfactory tissues. But chewing the leaves will rupture the tiny packets of oil and release nepetalactone into the air.
Although catnip is best known for its intoxicating influence on cats, humans also make use of its biological properties. Long before Europeans were introduced to Asian teas, the infusion of catnip leaves was a popular beverage, according to "The Book of Tea and Coffee." Like chamomile tea, the catnip brew has a mild calming effect on humans.
Folk medicine suggests many other beneficial uses of catnip. The herb has been described as a remedy for colic, minor aches and pains in the gums and teeth, and indigestion, to name just a few examples.
The catnip species originated in Europe and parts of Asia, but its medicinal uses earned it a place in colonial gardens in North America. Of course, the plant soon escaped to the wild and now can be found widely across Canada and the U.S. For commercial use in teas and cat toys, it is cultivated mainly in the Pacific Northwest and parts of Canada, including Alberta and British Columbia.
In the 1960s, Cornell University naturalist Thomas Eisner reported that catnip oil repels insects (Science 1964, 146, 1318). The paper suggested that nepetalactone defends against plant-eating insects. "The insects take a bite and get a mouthful of something they don't like," explains Christopher J. Peterson, a research entomologist with the U.S. Department of Agriculture Forest Service.
As a graduate student at Iowa State University, Peterson worked with entomology professor Joel R. Coats to study the effectiveness of catnip oil as an insect repellent. They treated one end of a glass tube with concentrated nepetalactone and confined 20 mosquitoes inside the tube. Most of the mosquitoes crowded to the untreated end of the tube. The scientists reported that it took 10 times as much DEET (N,N-diethyl-m-toluamide) to produce the same repellent effect as nepetalactone.
DEET, a synthetic chemical, is by far the most widely used active ingredient in insect repellents, Coats says, and it has had a "very good" safety record over its 50-year history as a consumer product. However, he says there exists a market for nepetalactone and other "natural" repellents because of isolated reports of adverse reactions to DEET and also DEET's tendency to dissolve rubber materials.
A crude extract of nepetalactone is easily obtained by boiling or steam-treating catnip, collecting the steam, and extracting the oily component with hexanes. The compound's volatility could account for the fact that it is effective for only a few hours as an insect repellent.
Because nepetalactone is volatile and will degrade over time, cat owners should store catnip in a freezer to preserve its potency. That way, kitty's next 'nip trip will be as wild and crazy as ever. Party on, cats!
|Chemical & Engineering News
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