Bioactive iridoids in catnip and silver vine cheer cats up and repel mosquitos

By Joyce Yixuan Wang

Ever wondering why your beloved cat is obsessed with catnip and silver vine? It’s widely known that cats rub their heads and faces on the plants and roll all over the ground, as if the plants had put a spell on them. The neurophysiology of the well-known phenomenon, however, remains unknown until recently Professor Masao Miyazaki’s team revealed that this behaviour is caused by the bioactive iridoid compounds in catnip and silver vine.

Which chemical and how was it discovered?

Domesticated and undomesticated felines including 25 laboratory cats, 30 feral cats and some big cats were presented with filter paper soaked with silver vine extracts and the responses to nepetalactol-containing fraction was most evident. Then, 12 cats among the extract-responsive cats were selected and comparison of their response toward known bioactive iridoids showed that nepetalactol was the most potent chemical in silver vine leaves. On the contrary, non-felines like dogs and lab mice were not at all interested in the compound.

So, how exactly does it intoxicate my cat?

The physical response of cats to catnip are deemed as extreme pleasure, prompting the researchers to hypothesise that olfactory reception of nepetalactol triggers the μ-opioid system governing rewarding and euphoric effects in humans. They examined plasma levels of β-endorphin (a peptide hormone and an endogenous opiate) five minutes before and after five cats were exposed to nepetalactol and found an increase only after the exposure. To test if the μ-opioid system directly regulates the response to nepetalactol, cats were drugged to inhibit their μ-opioid receptors, and the previous rubbing and rolling disappeared, further supporting the hypothesis.

Such a consistent behaviour… Can the response to the plants actually does cats any good?

It may be surprising that the answer is yes. The researchers found out that considerably more Aedes albopictus mosquitos avoided cats showing the typical catnip-response and having their head covered in the chemical. This evidenced that the characteristic response of cats to the plants helps to transfer the mosquito-repelling compound onto their fur. Face rubbing with catnip and silver vine can protect the cats’ exposed facial regions e.g. mouth and nose from being bitten by mosquitos. According to Professor Miyazaki, the rubbing behaviour may also be “against viruses and parasitic insects.” The response is a good sample of animal exploitation of plant metabolites for insect pest protection. Interestingly, the catnip behaviour is autosomal dominant in domestic cats.

Will my cat be addicted to the chemical?

There’s no need to worry about this as the response is nonaddictive. This is probably due to the endogenous nature of the opiate β-endorphin, distinct from the exogenous ones like morphine. So, feel free to plant potted catnip and silver vine or buy catnip-laced toys for your lovely furball.

Reference

Uenoyama, R. et al. (2021) ‘The characteristic response of domestic cats to plant iridoids allows them to gain chemical defense against mosquitoes’, Science Advances, 7(4), p. eabd9135. doi: 10.1126/sciadv.abd9135.

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