What has opioid addiction got to do with cats?

Screenshot 2021-02-04 at 15.06.19Cat lovers will know the effect of catnip on their beloved pets only too well. Catnip (Nepeta cataria) is a member of the mint family and along with a similar plant called silver vine (Actinidia polygamy) it elicits a feline euphoria followed by a period of placid tranquillity, lasting perhaps 15-30 minutes. The effects were first reported by the Japanese botanist E Kaihara in 1709 but we haven’t really learned that much more about the reason for catnip intoxication since that time – that is until recently.

What we thought we knew was that the euphoria-causing constituent of catnip was nepetalactone a member of the iridoid family of plant chemicals. The scientific consensus was that the odour of nepetalactone was like certain cat pheromones, but this was largely supposition. More recently however, scientists identified a related but more potent chemical in catnip called nepetalactol. Plants biosynthesise nepetalactone, nepetalactol, and indeed all iridoids, from a plant chemical called geraniol that gives geraniums their smell. I’ve blogged on this class of compounds before describing how the substances that give aromatic plants their fragrance travel down a biochemical pathway ending up as rubber and even cannabinoids. Such is the versatility of plant biochemistry.

Plants don’t spend their precious metabolic resources merely to pleasure cats and the iridoids act as repellents to certain insects such as aphids. Catnip doesn’t just affect domestic cats, but experimenters have demonstrated its euphoric properties on lions, jaguars, leopards and the lynx. Scientists believe these animals exploit the insect repelling properties of the iridoids, which coincidently then also make the animals high! Until recently the pharmacology of iridoids was largely unknown but a recent paper has shed some surprising light on the subject.

It turns out opioids taken by humans and iridoids in cats both bind onto receptors in the brain which are triggered by endorphins. The body produces endorphins in response to stress and pain and when bound to their brain receptors they elicit the release of dopamine – sometimes (rather inaccurately) called the pleasure chemical*. Opioids and endorphins bind to the same brain receptors but opioid compounds cause a much greater dopamine release. It’s this trigger of dopamine by opioids that is the prime reason for addiction. While opioids trigger dopamine in humans, so iridoids do the same in cats. The pharmacology has in fact now been demonstrated by blocking feline opioid receptors which results in the cat losing interest in catnip.

There is still much we don’t know about how catnip works. It seems it has no effect on other species such as dogs and mice. Presumably therefore, there’s something special about feline opioid receptors?  Not all cats are susceptible to the narcotic effects of catnip and so there may well be a genetic component involved. If humans can become addictive to opioids, can cats become addicted to catnip? The jury is out on that one partly because addiction in animals is more difficult to study than it is in humans. The best advice is to use catnip sparingly. But if you do give catnip to your cat, your pet might end up seeing you as the local drug dealer – be warned!

* – opioid pharmacology is a little more involved than this – if you want to know more here’s a great short video.

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