Garden Catmint is in the same genus as
Cat-mint Nepeta cataria better known as
Catnip, which contains
Nepetalactone in greater abundance than in Garden Catmint. The odour of Catnip sends cats wild and into a state of euphoria until the smell senses are dulled by over-exposure.
Cat-mint was once much more common as it spreads (it is not sterile like is Garden Cat-mint). All cat-mints will have some effect on cats, but Catnip Nepeta cataria contains more of the hypnotic (to cats) substance
Nepetalactone. It is not only cats which nepetalactone effects in this way; Leopards, Cougars, Lynxes and Servals are also highly susceptible, but Lions and Tigers are less strongly affected and do not react consistently to the odour. Cats will also eat cat-nip, which also sends them wild with euphoria for between about 5 to 15 minutes, until olefactory fatigue sets in (as it does for humans - we become accustomed to a smell in a few minutes thereafter we are completely unable to smell it - until the next time we are exposed to the odour). But about a third of cats are totally immune to Nepetalactone showing no response at all. Your Authors' cats are like that; completely nonplussed. Cat-mint is not alone in plants which puts cats in an entranced state; Common Valerian (Valeriana officinalis) (both root or leaves), Tatarian Honeysuckle (Lonicera tatarica) and the exotic
Silver Vine (aka Cat Powder) (Actinidia polygama). In the case of the latter, the response of susceptible cats is even stronger than it is with Cat-nip and fewer cats are immune to its effects. Cats who do not respond to cat-nip itself will usually respond to one of these other 3 plants, for they contain differing active substances.
In Common Valerian it is the substance Actinidine, which makes susceptible cats behave in a similar they do to
Nepetalactone is a
sesquiterpene lactone whilst Actinidine is an iridoid alkaloid. The two are similar structurally, except that one has a nitrogen atom in the 6-membered ring and is an iridoid alkaloid, whilst the other is also an iridoid, but one which has an oxygen atom in place of the nitrogen atom. Other differences are also apparent, but it must be the structural similarities which bestow upon both the ability to send cats into a ecstatic trance by smell. Nepetalactone is present in all members of the Catmint genera Nepeta whilst Actinidine is present in Tatarian Honeysuckle (Lonicera tatarica).
There are 5 other sesquiterpene lactones having the iridoid skeleton which are also present in both
Catmint and in
Silver Vine which also affects (some) cats the same way. These compounds are:
Some sources also say that the exotic foreign
Silver Vine (Actinidia polygama) plant also has the same effect on (some) cats.
Cats which are immune to the effects of one of these plants may be entranced by one of the other two instead