BACKGROUND
the living environment of domestic cats  largely determines their quality of life.
cats kept indoors exclusively can become bored and stressed more easily than cats that can roam around freely outside, especially in the absence of good  company.
lack of environmental features such as vertical space, hiding places, scratching posts, and opportunity to play and chase are known to contribute to variable combinations of behavioral problems  and physical disease such as lower urinary tract disease, upper respiratory disease, inappetence, and obesity  <cit> .
these problems compromise feline health and well-being, and also contribute to cats being relinquished or returned to shelters  <cit> .
although effective improvements to the living environments of cats are well known and often used to increase their quality of life, olfactory stimulation is often overlooked as a means of enrichment, despite recognition of the importance of environmental smells for cats by the american association of feline practitioners and the international society of feline medicine  <cit> .
cats have highly developed olfactory systems and are capable of detecting volatile stimuli  as well as pheromones.
furthermore, some plants are known to produce semiochemicals that attract and stimulate cats.
this serendipitous effect is the result of the plant releasing allomones into the air to repel herbivorous insects that  cause damage to the plant, or to attract predators and parasitoids for these insects.
the chemical profiles of these phytodistress signals may differ between plants, the attacking herbivore, and whether or not the plant is being attacked  <cit> .
one of these plants is catnip, which produces allomones that happen to have an apparently euphoric effect on cats, including the big cats  <cit> .
this effect is quite rare in animals, and could be used to improve the quality of cats’ lives  <cit> .
the effect of catnip is caused exclusively by its smell rather than its taste  <cit> .
typically, cats respond to catnip by sniffing, licking and biting it, shaking their head, rubbing their head, chin or cheeks against it, and rolling over, sometimes accompanied by drooling and kicking the material with their hind feet .
this behavioral response is not sexual,  <cit>  and catnip is generally believed to be neither addicting nor harmful  <cit> .
unfortunately, approximately one out of every three domestic cats does not respond to catnip .
furthermore, whereas lions, jaguars, leopards and snow leopards appear to be sensitive to catnip, most tigers do not respond to it  <cit> .
other plants can have similar positive effects on cats .
in  <dig>  a letter was published in science about cats appreciating silver vine as a new “cat delicacy” after it was imported from china by the arboretum of harvard university  <cit> .
this plant, also known as matatabi in east asia, is commonly used as a cat stimulant in japan.
similar anecdotes of plants attracting and exciting cats exist for, among others, tatarian honeysuckle, valerian root, and the fresh roots of indian nettle   <cit> .
unfortunately, to the knowledge of the authors, none of these effects have been documented.
to evaluate whether veterinarians and veterinary technicians were familiar with catnip alternatives, we asked  <dig> veterinarians and  <dig> veterinary technicians in the usa and australia if they were aware of silver vine or tatarian honeysuckle.
twelve were feline-only veterinarians and six out of six were feline-only veterinary technicians.
thirty-six of the  <dig> veterinarians  and all six veterinary technicians  answered this question negatively, suggesting that most veterinarians and veterinary technicians  are unaware of silver vine or tatarian honeysuckle and their effects on cats.
nepetalactone has been identified as the compound causing the catnip effect  <cit> .
interestingly, not one, but half a dozen other active components similar in structure to nepetalactone  have been identified in silver vine , one of which also was detected in valerian root  <cit>  and two, recently, in indian nettle  <cit> .
to the knowledge of the authors, nothing is known about the active compound present in tatarian honeysuckle.
data on the percentage of cats responding to silver vine are scarce and of poor quality  <cit>  and, to the knowledge of the authors, non-existent for tatarian honeysuckle and valerian root.fig.
<dig> compounds identified in catnip and silver vine known or believed to have a stimulating effect on cats
the purpose of this study was to compare the responsiveness of domestic cats to catnip and to these catnip alternatives.
in addition, we investigated if the pattern of responsiveness to these plants could be explained by the presence or absence of certain chemical compounds.
methods
study population
one hundred randomly selected cats of six months or older living in a cat sanctuary , riverside, ca, usa) , in an adoption guarantee  shelter , riverside, ca, usa) , in homes  , and in an american association of feline practitioners-certified cat friendly practice with gold status   were included in this study.
the r8mcf housed cats in five rooms, with on average 20– <dig> cats per room , whereas the msrpac housed cats in individual cages .
about 55% of the surface space at the r8cmf was outdoors, and the cats could freely move between indoors and outdoors.
cats at the msrpac were allowed outside of their cages into a  <dig> square meters open room to interact with each other daily for eight hours.
all cats at both facilities had continuous access to hiding places, cat beds, shelves and cat trees, scratching boards, litter boxes and water.
the cats at the r8cmf had continuous access to dry food and received wet food at least once daily, whereas the cats at the msrpac received dry food twice daily.
at the r8cmf window fans were used to help cool the rooms, whereas at the msrpac a constant temperature of  <dig> °c was maintained.
cats in isolation areas or with signs of upper respiratory disease were excluded.
data were missing for some cats because they were adopted while the study was in progress.
only cats for which we had data for all four stimuli  were included in the response pattern analyses.
cat age, sex, and breed were recorded when available.
ages were available for  <dig> cats, although for seven senior cats it could only be reliably determined they were at least 10 years of age.
to test whether responsiveness to the plant materials differed between younger, generally more playful, cats and older cats, the group of  <dig> cats was divided into a younger  and older  group using the median age of these  <dig> cats as a cutoff between the groups.
the average age for the younger group was 1 year and 11 months  and at least 9 years and 2 months  for the older group.
cats also were classified  into three different behavioral categories:  scared or shy ,  intermediate , and  affectionate or friendly  to study the influence of social behavior on the response to the plant materials.
plant materials
dried, cut and sifted organic catnip  leaves and flowers were obtained from frontier  and smarty kat .
dried, cut and sifted organic valerian  root was purchased from organic bio herbs  and frontier .
tatarian honeysuckle  wood and sawdust were purchased from the cat house inc. .
powder from dried silver vine  fruit galls was purchased from smack  and gendai pharmaceutical .
dried normal silver vine fruit and silver vine fruit galls were kindly provided by hangzhou botanical technology .
we were unable to obtain any indian nettle material for this study.
to prevent possible degradation of active compounds, all plant materials were ordered just prior to the start of the experiments.
during the study period  all plant materials were stored tightly sealed in their original bag, at room temperature and in the dark.
exposure
cats were exposed to  <dig>  to  <dig>  g silver vine powder  inside a thin, porous sock , or  <dig>  to  <dig>  g silver vine powder spread out on approximately  <dig> square cm of a piece of  <dig>  square m of frieze carpet .
this type of carpet was used because it allowed more direct exposure to the materials than did the socks, while still minimizing the ability of the cats to ingest the plant material.
equal volumes of catnip , valerian root  and tatarian honeysuckle sawdust  were offered inside a sock.
this amount of plant material filled the sock about half full, and allowed tying a knot to close off the sock.
tatarian honeysuckle also was offered as an approximately 10 cm long piece of wood .
catnip  and valerian root  also were offered on carpet.
we chose these amounts and volumes of catnip, tatarian honeysuckle and valerian root to ensure that the cats would be exposed to an amount of active compounds that would allow for a positive response.
we did not use a similar volume of silver vine powder because this would greatly exceed the manufacturer’s recommendation.
furthermore, the high price and limited supply of commercially available silver vine powder outside of east asia would prevent the use of such large quantities in everyday life .
results from preliminary experiments demonstrated that  <dig> g of silver vine powder was enough to elicit a positive response in each of the cats tested .
socks or carpet were placed on the floor of the cat’s environment, within one meter of the cat’s head, in its line of sight or in the center of the room, respectively.
when a cat seemed unaware of the presence of the plant material, the sock was repositioned within sight of the cat, once.
plant materials were never forced onto any of the cats, nor were they repositioned when a cat walked away from it.
cats responding positively to the plant materials on the carpet also responded positively to the plant materials in the sock , suggesting that the fabric did not significantly interfere with the exposure of the active compound to the cats.
all plant materials were stored inside separate, sealed plastic bags to prevent cross-contamination.
identical carpet without plant materials and an identical, empty sock were used as negative controls.fig.
<dig> photographs of several of the plant materials used in this study.
a tatarian honeysuckle wood .
b a dried silver vine fruit gall, also referred to as deformed fruit .
c a dried normal silver vine fruit
the majority of the cats were exposed to all four plant materials on three different days , at different times of the day , for up to one hour.
the minimum number of exposures for each cat was two, on different days, and the minimum exposure duration for each cat was ten minutes per exposure.
all cats were exposed to the plant materials presented in a sock and the majority of them also were exposed to a piece of tatarian honeysuckle wood, and once to the plant materials on the carpet.
each plant material was offered at separate times, in random order, with a washout period of at least five minutes in between to avoid recording false positive responses resulting from a carry-over effect.
the length of this washout period was based on results from preliminary experiments .
new plant material was only offered to a cat when it would not or no longer show any of the behavior associated with the catnip response  when offered a negative control sock.
when a positive, complete response  was recorded, the stimulus was removed from the cat.
this was done to prevent possible response saturation  from negatively affecting responses to the plant materials tested subsequently.
in addition, plant materials to which the cat responded positively were offered last during subsequent exposures on other days.
observing a positive response after a negative one demonstrated that environmental , mental  and physical  conditions did not prevent the cat from responding positively.
this too was done to prevent scoring false negative responses.
all cats were exposed to the plant materials in their normal living environment, and only after a period of at least ten minutes during which the cats could acclimate to the presence of the investigator.
each cat was given the opportunity to experience the plant materials without interference or intimidation from other cats and in the absence of other possible distractions, which sometimes required retesting cats at other moments.
a schematic overview of a typical exposure experiment is presented as fig  <dig> fig.
<dig> schematic overview of a typical exposure experiment for the domestic cats.
this experiment was done for each cat.
the different shapes  represent the various plant materials the cats were exposed to.
a negative control  was always offered together with each plant material.
the wash-out period is represented by a tilde.
the responses are an example; these are not results.
on the first exposure day circle and triangle were removed from the cat as soon as a positive response was scored.
this was done to prevent the cat from not responding to diamond because of loss of interest, fatigue or saturation to active compounds that also may be present in the plant materials the cat had already been exposed to during the experiment on this day.
square and diamond were offered first  on the second day the cat was tested, because no positive response was observed on the previous testing day.
this was done for the same reasons as previously mentioned.
diamond was removed when the cat was scored positive for this sample.
triangle and circle were offered to the cat last , to try to confirm the results obtained on the first test day, and also to establish that the cat’s environment  and its physical and mental state were not preventing the cat from responding positively.
this method was repeated on day 3: the sample to which the cat did not respond positively  was offered first, followed by samples to which the cat had already responded positively.
in this example the cat would have been scored negative for square and positive for circle, triangle and diamond.
pos., positive; neg., negative
scoring
ninety-eight of the  <dig> cats were scored live by the same researcher , who knew which plant materials were being offered to the cats at each exposure.
two cats living in a private home were scored  based on video recordings.
cats showing the characteristic catnip response  and rolling on their back, sometimes accompanied by drooling and raking ) to a plant material were scored as positive for that plant material.
each positive response was scored as either intense/complete  or mild/partial .
cats’ responses were scored as negative when none of at least two exposures resulted in a positive response to the plant material.
negative responses of cats present in the same room but not exposed were not recorded.table  <dig> ethogram of domestic cat and bobcat behavior  <cit>  observed during a positive response to catnip, silver vine, tatarian honeysuckle or valerian root
raking a
a this behavior is also referred to as hind leg kicking or bunny kicking
exposure to various parts of silver vine
to study the response of cats to various parts of the silver vine plant in more detail, nine randomly selected domestic cats  at the mrspac were exposed on multiple days to the following six plant materials, all contained within socks:  <dig> g dried silver vine fruit galls,  <dig> g dried normal silver vine fruit,  <dig>  g powder of dried normal silver vine fruit, sun-dried and fresh leaves  from a three year old silver vine plant not bearing fruit galls  and  <dig> g woodchips made from commercially available silver vine wood sticks  .
to generate the powder, two gram of dried normal silver vine fruit was ground using a mixer mill  <dig>  at 25 cycles per second for three minutes.
in all experiments, contact time between the cat’s face and the sock was recorded.
the plant material was removed after five minutes of indifference, or after the cat stopped actively engaging with the sock for one minute.table  <dig> overview of the experiments in which cats were exposed to different parts of the silver vine plant
a the sock with the woodchips was offered first; the sock with the fruit galls was added after the cat lost interest in the sock with the woodchips.
during all other exposures socks containing the silver vine plant material were offered simultaneously to the cats
other felidae: tigers and bobcats
nine tigers   and five bobcats   living at big cat rescue, a sanctuary for exotic cats, in tampa, fl, usa were included in this study.
twenty gram of catnip  or  <dig>  g of silver vine powder  was offered to the tigers inside a folded paper bag  with small holes made in it  or uncontained  by a big cat rescue staff member  who was certified to hand out enrichment to cats of all sizes.
tigers were first offered catnip, followed by silver vine five minutes later.
if a tiger responded positively to the catnip, silver vine was offered at least 5 min after the tiger had lost interest in the catnip.
in the absence of a positive response to catnip, silver vine was offered to the tigers without first removing the catnip, which, in some cases, resulted in exposing them to the silver vine within a couple of meters of the catnip.
all bobcats received catnip  or silver vine powder  in crumpled up paper bags  with no holes made in them.
the plant materials were placed within  <dig>  meter of the cat’s face, without disturbing them, so that all animals were aware of the presence of the materials.
minimum possible exposure to each plant material was five minutes for each cat.
the cats were not tested between 11: <dig> and 16: <dig>  because of their low level of activity during these hours.
chemical analysis
dried catnip , dried normal silver vine fruit, dried silver vine fruit galls, dried valerian root and tatarian honeysuckle wood, taken from the batches used for the responsiveness studies, were analyzed using gas chromatography coupled with mass spectrometry to determine concentrations of five known or claimed cat-stimulating compounds isolated from catnip and silver vine: cis-trans nepetalactone  <cit>  , trans-cis nepetalactone  <cit>  , actinidine  <cit>  , iridomyrmecin   and isodihydronepetalactone  <cit>  .
for extractions,  <dig>  g of each plant material was extracted with 3 ml of dichloromethane while stirred at room temperature for 7 days.
the solutions were filtered through a short silica gel column and concentrated by evaporating the solvent at room temperature to  <dig>  ml.
one hundred μl tridecyl acetate  was added to each sample as internal standard to allow for quantification of the compounds and comparison between samples.
extracts were analyzed by gas chromatography coupled with a mass selective detector .
the gc-ms system was equipped with an hp-5 ms fused silica capillary column ).
conditions were as follows: inlet pressure:  <dig> kpa, he-flow:  <dig>  ml/min, injector: 250 °c, transfer line 300 °c, electron energy 70 ev.
the gc oven temperature was kept at 50 °c for 5 min, followed by raising the temperature with 5 °c/min to 320 °c.
identification of compounds was performed by comparison of their mass spectra and retention indices ) to those of reference compounds  and commercial mass spectral libraries  .
the amount of compound is expressed per gram of dried plant material.
the lower limit of detection under these conditions was  <dig>  μg per gram.
statistical analysis
statistical analysis was performed using graphpad prism version  <dig>  .
a p-value <  <dig>  was considered statistically significant.
overlaps between responses to the various plant materials were calculated and plotted as a venn diagram in r  using a custom script from dr. thomas girke .
RESULTS
to investigate the responsiveness of domestic cats to catnip and catnip alternatives, we exposed cats to catnip, silver vine, tatarian honeysuckle and valerian root in their normal living environment .
none of the cats studied responded positively to the control sock or carpet.
in agreement with the results from our preliminary experiment  we did not observe positive responses to the control sock after removing the plant materials from the cat, suggesting no or a minimal carry-over effect.
no differences in response to the plant materials offered inside a sock or on carpet were observed, therefore these results were not recorded separately.
seventy-nine of the  <dig> domestic cats responded positively to silver vine .
significantly more cats responded to silver vine   or catnip   than to tatarian honeysuckle  or valerian root  .
although no statistically significant difference was observed between the percentage of cats responding to silver vine or catnip , the response to silver vine was more intense than to catnip .fig.
<dig> the number of cats that responded to silver vine, catnip, tatarian honeysuckle and valerian root.
the response of the total study population to each plant material is shown in a different color.
significantly more cats responded positively to silver vine and catnip than to tatarian honeysuckle and valerian root.
responses to silver vine were more intense than to catnip
our study population consisted of  <dig> neutered male cats,  <dig> neutered female cats and  <dig> neutered cats of unknown sex.
no differences were observed between the number of male and female cats responding to the four plant materials .
in addition, the average number of stimuli that the cats responded to was similar for males  and females , and no difference in response intensity was observed between male and female cats .
we found no evidence that younger age was associated with increased responsiveness.
there was no difference in the number of cats responding positively to the various plant materials between the younger  and older  groups of cats  and cats in the younger group did not respond to more plant materials than did cats in the older group  and  <dig>   out of  <dig>  respectively).
however, more partial/mild responses and less complete/intense responses to catnip were observed in the older group as compared to the younger group .
no differences in response intensity were observed for the other three plant materials between the younger and older group .
we did not find an association between responsiveness and behavioral category.
scared or shy cats responded as often and as intensely to the various plant materials as did affectionate or friendly cats .
cats categorized as either scared/shy , intermediate , or affectionate/friendly  responded positively to the same number of plant materials .
because most  of the cats studied were  domestic short-haired breeds, we did not study associations between breed and responsiveness to the materials tested.
also, because of the small number of cats with the same fur color and pattern, as well as the difficulties in determining these characteristics , we did not test for differences in responsiveness between the various fur colors and patterns.
overlap in responses to the various plant materials
to investigate which of the plant materials elicited responses in cats not responding to catnip, we analyzed the overlap in responses to the four different plant materials.
ninety-four of the  <dig> cats  responded to at least one of the four stimuli, whereas six cats  did not respond to any of the materials.
twenty-three of the  <dig> cats  that were exposed to all four different plant materials responded to all of them .
of the  <dig> cats not responding to catnip,  <dig>  responded to silver vine,  <dig>  to tatarian honeysuckle, and  <dig>  to valerian root .
these results suggest that silver vine is the best alternative to catnip, also because there were only three cats out of the  <dig>  that did respond to tatarian honeysuckle or valerian root, but not to silver vine or catnip.
twenty of the  <dig> cats  that were offered all four different plant materials responded to just one stimulus, the majority of which  responded exclusively to silver vine, suggesting that silver vine contains chemical compounds that are either absent or present in lower concentrations in catnip, tatarian honeysuckle and valerian root.fig.
<dig> response patterns and alternatives to catnip.
a venn diagram  showing the overlap in responses to catnip, silver vine, tatarian honeysuckle and valerian root.
ninety-five of the  <dig> cats tested were exposed to all four plant materials, of which  <dig> are included in this plot.
the remaining six cats did not respond to any of the plant materials and are therefore not shown in this diagram.
b of the  <dig> cats that did not respond to catnip,  <dig>  responded positively to silver vine,  <dig>  to tatarian honeysuckle and  <dig>  to valerian root
responses to various parts of the silver vine plant
the silver vine powder used in this study was made from dried silver vine fruit galls  , caused by the gall midge pseudasphondylia matatabi  <cit> .
matatabi fruit gall midges leave the fruit when the larvae have matured.
it is speculated that cats respond more strongly to dried silver vine fruit galls than to dried normal, oval shaped fruit with a smooth surface .
we tested this hypothesis by offering nine cats a sock filled with dried normal fruit and a sock filled with dried fruit galls, simultaneously , and measured the time spent with each sock.
we found that the cats spent significantly more time with the fruit galls  than with the normal fruit   .
eight of the nine cats responded positively to the silver vine fruit galls.
although some time was spent with the sock containing the dried normal fruit, none of the nine cats responded positively to it.fig.
<dig> time each cat  spent with a sock filled with dried normal silver vine  fruit or dried silver vine fruit galls.
the socks were offered simultaneously.
horizontal lines represent the medians.
note that the ordinate is a logarithmic scale, with the minor ticks denoting  <dig>   <dig> and 500 s
we subsequently investigated if cats responded to silver vine woodchips made from the wood of a plant not bearing fruit galls , dried and fresh leaves from a plant without fruit galls, or powder made from dried normal fruit.
eight of the same nine cats  were exposed to socks containing these materials .
none of the eight cats showed any interest in the powder made from dried normal fruit, or in the dried and fresh leaves.
although seven out of eight cats also did not respond to the silver vine wood, one cat did respond positively to this material, on four different testing occasions.
however, during each of the two exposures for which we counted facial contact time, the response to the galled fruit lasted longer than to the woodchips , even though the galled fruit was offered after the cat had lost interest in the sock filled with silver vine woodchips.
qualitative response
the way in which cats responded to the various plant materials  was similar to the catnip response that has been described in detail before , indicating that this characteristic response is not restricted to catnip.
although we did not attempt to document the behavioral response in detail, we did observe a response to the plant materials that, to the best of our knowledge, has not been described before.
in several of the responding domestic cats we observed undulation of the skin overlying the dorsal lumbosacral region of the back shortly after exposure to the plant materials.
the wave-like motions only lasted a few seconds and were possibly associated with contractions of the cutaneous trunci muscles, a broad sheath of skeletal muscle that lies directly underneath the skin  <cit> .
other felidae: tigers and bobcats
unlike the other big cats, tigers are known not to, or at best only mildly, respond to catnip  <cit> .
tigers typically seem to be less interested in any form of olfactory enrichment  compared to other wild cats .
since we observed that many domestic cats that did not respond to catnip did respond to silver vine, we were interested to learn how tigers would respond to silver vine.
to the knowledge of the authors, silver vine has not been tested on tigers before.
catnip and silver vine powder were offered to nine tigers.
one tiger responded mildly positive  to catnip, but the other eight tigers were indifferent to the presence of this plant material.
four of the nine tigers also were indifferent to the silver vine powder, whereas the other five responded disapprovingly to it: after sniffing the plant material the animals backed off and walked away from it.
this disapproving response to silver vine was distinct from their negative response to catnip.
for this reason we decided to not offer the plant materials to the tigers multiple times.
in contrast to the response of the tigers, another non-domesticated member of the felidae, bobcats, did respond positively to silver vine  as well as to catnip .
this positive response was characterized by holding the paper bag containing the plant material close to their head using their forelegs  while chin and cheek rubbing it, rolling over on their back from one side to the other, and drooling.
this response lasted several minutes, sometimes longer than 15 min.
to the knowledge of the authors, this is the first time silver vine has been tested on bobcats.fig.
<dig> an eight year old female bobcat holding a paper bag with silver vine powder between her forelegs while she is rolling around and giving it chin and cheek rubs
chemical analysis
concentrations of cis-trans nepetalactone, trans-cis nepetalactone, actinidine, iridomyrmecin and isodihydronepetalactone in the four plant materials were determined using gas chromatography coupled with mass spectrometry.
reference compounds and reference spectra for isoiridomyrmecin , dihydronepetalactone  and neonepetalactone  were not  available and these compounds could therefore not be identified.
the highest concentration of cis-trans nepetalactone was found in catnip, whereas minimal quantities were detected in the other plant materials .
only a relatively small amount  of trans-cis nepetalactone was found in catnip.
actinidine concentrations were highest in silver vine fruit galls, valerian root and tatarian honeysuckle and marginal in catnip.
the concentration of iridomyrmecin and isodihydronepetalactone was highest in silver vine fruit galls, while valerian root contained some iridomyrmecin and catnip some isodihydronepetalactone.
in addition, relatively high concentrations of three different isodihydronepetalactone isomers  were identified in silver vine fruit galls.table  <dig> allomone concentrations in the plant materials used in this study
a cn catnip, sv silver vine fruit galls, ths tatarian honeysuckle, vr valerian root
b concentrations are expressed as μg per gram dried plant material
we also analyzed these compounds in dried normal silver vine fruit.
when comparing dried silver vine fruit galls to normal silver vine fruit, we observed higher concentrations of actinidine, iridomyrmecin and isodihydronepetalactone, as well as three isodihydronepetalactone isomers and other compounds similar in structure  in the dried fruit galls .
mass spectra and retention indices of the three isodihydronepetalactone isomers are shown in additional file  <dig>  concentrations of all these compounds were nearly undetectable  in the dried normal silver vine fruit.fig.
<dig> total ion chromatograms comparing the extracts of dried normal silver vine fruit  to the extracts of dried silver vine fruit galls .
the normal fruit only contained marginal levels of actinidine  and isodihydronepetalactone  compared to the fruit galls.
relatively large amounts of actinidine , isodihydronepetalactone , iridomyrmecin  and its isomers  were present in the fruit galls.
note the higher concentrations of other lactones  in the fruit galls.
only a small quantity of cis-trans nepetalactone was detected in the fruit galls.
<dig>  cis-trans nepetalactone;  <dig>  actinidine;  <dig>  iridomyrmecin;  <dig>  isodihydronepetalactone; * different isodihydronepetalactone isomers; is, internal standard
discussion
olfactory stimulation by catnip is a well-known method to provide enrichment for a cat’s living environment.
although it has been long known that not all cats respond to catnip, only limited data are available about plants that may be used as an alternative.
this study was designed to compare the responsiveness of cats to catnip, silver vine, tatarian honeysuckle and valerian root.
the sample size  and the comparison of responses to four different plant materials make this study the most comprehensive on this subject thus far.
in addition, this is the first study to document responses of domestic cats to silver vine fruit galls, tatarian honeysuckle and valerian root, and those of tigers and bobcats to catnip and silver vine.
nearly all domestic cats responded to at least one of the plant materials tested, with the largest numbers of cats responding to silver vine  and catnip .
our results indicate that cats predominantly responded to the powder of silver vine fruit galls, and much less frequently to the wood of the silver vine plant.
in contrast, katahira and iwai  <cit>  found that  <dig> out of  <dig> cats  responded positively to a dried silver vine branch.
this discrepancy may be explained by the methodology of their study.
experiments were performed on laboratory cats housed in small cages  that were offered a dried branch of silver vine.
approaching and trying to bite the branch within three minutes was considered a positive response, and no negative controls were used in their study.
the percentage of non-responders to catnip in our study is in line with findings from previous studies: 35%  <cit> , 28%  <cit>  and 18%  <cit> .
pooling the data from these studies gives a total of  <dig> non-responders out of  <dig> cats , which is very similar to the  <dig> out of  <dig> cats  that did not respond to catnip in our study .
also in line with our observations, a similar percentage of cats with mild or partial responses to catnip was reported by palen and goddard  <cit>  .fig.
<dig> the absolute number and percentage of cats that responded positively to catnip in three previous studies  .
the pooled results from these three studies are similar to our findings
our observation that tigers did not respond to catnip agrees with results of previous studies.
todd found that  <dig> of the  <dig> tigers  tested did not respond at all, six  only sniffed, licked and shook their head, and two tigers  showed a partial response including chin and cheek rubs  <cit> .
none of the tigers rolled over.
hill et al.
found that three out of four tigers did not respond to catnip, whereas one showed a mild or partial response  <cit> .
results from these studies also indicated that all other members of the genus panthera  tested, did respond positively to catnip.
todd and hill et al.
also tested catnip on bobcats  <cit>  and their findings were contradictory, possibly because only two bobcats were tested in each study.
although data specific for cats are not available, all four plant species used in this study are generally considered safe and not toxic or addictive for cats and humans.
cats have been exposed to silver vine and catnip, in a variety of different forms, for many years.
we could only find one anecdote related to the potential addictive properties of silver vine  <cit> .
in the 1970s, the smell of an unspecified form and concentration of silver vine was reportedly preferred by large cats  kept in cages in a zoo in japan over food and sexual intercourse.
however, their response to the silver vine was one of excitement and joy; no data were presented supporting any negative health effects.
the scientific value of their claim that silver vine is addictive recently has been disputed by others  <cit> , and there is currently no scientific data supporting any addiction potential, nor are there any other negative anecdotes known to the authors, despite the widespread use of silver vine in japan.
a recent literature review on the use of silver vine concluded that its enrichment potential has been largely overlooked, and the authors encouraged further investigation of feline behavioral responses to silver vine  <cit> .
the cat house inc. has sold thousands of pieces of tatarian honeysuckle since  <dig>  and has never received a report of adverse reactions .
none of the four plants used in this study are listed as poisonous or toxic by the animal poison control center  or the american society for the prevention of cruelty to animals .
all plant materials used in this study are commercially available, and are sold as  toys or enrichment products specifically for cats.
finally, inquiry to the pet poison helpline   taught us that valerian root is generally considered safe, and that no toxicity has been reported from exposure to silver vine or tatarian honeysuckle wood.
the berries of tatarian honeysuckle  may cause mild gastrointestinal irritation because of the presence of terpenoids.
the results of our chemical analysis suggest there are significant differences in the concentrations of compounds known or claimed to have a stimulating effect on cats between the various plant materials tested.
however, interpretation of table  <dig> is somewhat hampered by lack of knowledge of the limit of detection for these compounds for cats, and if there is a dose-response relationship.
our findings suggest that cis-trans nepetalactone is the dominant and possibly the only compound in catnip to which cats respond.
the higher concentrations of actinidine in silver vine, tatarian honeysuckle and valerian root may explain, in part, the responsiveness of cats that did not respond positively to catnip to these plant materials.
in addition, cats that only responded to silver vine may specifically detect iridomyrmecin and isodihydronepetalactone in silver vine fruit galls .
indeed, 25%  of the cats that responded to silver vine did not respond to tatarian honeysuckle or valerian root, despite similar concentrations of actinidine in these plant materials.
in normal silver vine fruit, we detected actinidine at very low concentrations  compared to the fruit galls , tatarian honeysuckle, and valerian root.
sakan et al.
also detected actinidine in leaves of the silver vine plant  <cit> , but did not report the concentration they detected.
like normal silver vine fruit, leaves did not elicit a response in any of the cats we tested, so it is likely that the concentration of actinidine in silver vine leaves is also very low.
while actinidine has previously been identified in silver vine and valerian root , this is, to the knowledge of the authors, the first study demonstrating that tatarian honeysuckle contains actinidine, and that the amount is comparable to concentrations found in silver vine fruit galls and valerian root .
the low levels of cis-trans and trans-cis nepetalactone, iridomyrmecin and isodihydronepetalactone in tatarian honeysuckle suggest that actinidine may be the only compound in the wood that cats respond to.
indeed, we found large overlaps between the plant materials that contained high concentrations of actinidine: 93%  and 88%  of the cats that responded positively to valerian root or tatarian honeysuckle also responded to silver vine .
however, because of technical limitations, we were unable to identify all of the known or claimed active compounds, which leaves room for the possibility that other compounds are involved as well.
this possibility is further supported by the observation that despite similar concentrations of all the measured compounds in tatarian honeysuckle and valerian root, only  <dig> of the  <dig> cats  that responded positively to tatarian honeysuckle or valerian root responded positively to both these plant materials.
the popularity of silver vine fruit galls among cats may be explained by the relatively high concentrations of several compounds: actinidine, iridomyrmecin, isodihydronepetalactone and its isomers, although it is unknown if the latter have a stimulating effect on cats.
the observation that fewer cats responded positively to silver vine wood than to silver vine fruit galls suggests that lower concentrations of these compounds are present in the wood and that the concentration of these chemicals in the plant material as well as the detection threshold of the cat contribute to the outcome of the cat’s response.
evidence that certain compounds have an apparently euphoric effect on cats is scarce.
in the early 1940s, mcelvain and colleagues performed a bioassay using seven adult lions to demonstrate that nepetalactone is the active compound in catnip, but they did not discriminate between the cis-trans and trans-cis form of nepetalactone  <cit> .
results from subsequent studies that investigated which of the two nepetalactone isomers causes the catnip response suggest both isomers do, but the design of these studies and the reporting thereof were of poor quality  <cit> .
while sakan and colleagues claimed that certain compounds in silver vine have cat-attracting or stimulating properties, evidence was not presented .
the limited information available about bioassays performed by sakan and colleagues was written in japanese  <cit> .
they stated: “we mainly used cats and a compound was considered active when one or more of the following were observed: express interest in the sample, lick the sample, salivate, exhibit the flehmen response, rub their neck against something, rub their back against the ground and move around, become entranced, or fall asleep.
actinidine and matatabilactone  showed strong activity in lions, tigers and panthers, and actinidine even showed some activity in dogs.” other than this, no data were provided to support their claims.
well-controlled studies in which cats are exposed to isolated, pure compounds and scored according to relevant and well-defined behavioral characteristics are required to conclusively establish which compounds cause the apparently euphoric response of cats to the various plant materials.
the precise mechanism by which allomone production in silver vine and other plants is stimulated and regulated is unclear.
it is known that some gall-inducing insects promote growth of plant tissue to help provide them with food and shelter  <cit> .
it seems that in response to the invasion of the fruit by the larvae, silver vine plants produce and secrete volatile compounds trying to repel the matatabi fruit gall midge.
alternatively, these compounds could function by attracting midge predators or parasitoids.
because nepetalactone has been found to be an insect repellant  <cit>  and all the cat-stimulating compounds are similar in structure , the former may be more plausible.
although few in number, we did see some cats respond positively to silver vine wood, whereas no cats responded to silver vine leaves or normal silver vine fruit.
we did not perform chemical analysis of silver vine wood tissue.
actinidine, iridomyrmecin, isoiridomyrmecin, dihydronepetalactone, isodihydronepetalactone and neonepetalactone were first identified in silver vine leaves and silver vine fruit galls  <cit> .
it was not specified if these leaves were from silver vine plants with or without fruit galls.
in addition, it is unknown if the plant’s response to the local attack by the matatabi fruit gall midge larvae is local or systemic, and thus if allomone concentrations can increase in leaves and wood of the plant.
it would be interesting to learn whether cats respond differently to silver vine wood from plants bearing galled fruit as compared to wood from vines without fruit galls.
each of the four plant materials tested in this study can be a valuable addition to a cat’s environment, whether indoor or outdoor, but some come with a few disadvantages.
many cats respond to catnip, which is inexpensive and easy to obtain or grow.
silver vine, although perhaps even more popular among cats than catnip, is more expensive and difficult to obtain; it is predominantly available online and comes from east asia.
producing silver vine fruit galls in areas outside of the natural habitat of silver vine is practically impossible because it would require the presence of pseudasphondylia matatabi.
the life span of the adult fly is one to two days.
females of p. matatabi lay their eggs in the flower buds of silver vine in may.
the larvae spend the summer in the fruit galls, but silver vine is not flowering when the flies emerge from the fruit galls in autumn.
because of their short life span, the gall midge needs to use a different host plant during the winter season to survive  <cit> .
to this day, this host has not been identified .
although inexpensive and easy to obtain, valerian root comes with a strong smell that is not appreciated by everybody.
tatarian honeysuckle wood may be the most difficult plant material to obtain, but the wood comes in many different sizes, and will last a lifetime.
the various plant materials tested may be used to increase playtime of cats, which is especially valuable for less active, obese or under-stimulated cats.
they also can be given to cats for distraction when left home alone for a long time.
in animal shelters, these plant materials could be used by staff or volunteers to help socialize cats or to increase the chance of rehoming more timid adult cats.
indeed, playfulness of a cat was identified as one of the most important selection criteria used by potential adopters when choosing a cat  <cit> .
we have observed several fearful, withdrawn cats, brought into the sanctuary days or weeks before we tested them, that were attracted by the plant materials and responded seemingly euphorically after encountering them.
these cats would normally hide when staff or volunteers were present.
this suggests that trap-neuter-return programs also may benefit from using these plant materials.
indeed, a previous study already suggested that catnip may be effective for luring feral cats  <cit> .
the plant materials also might be used for training purposes, where exposure to these stimuli may be used as a reward instead of food, which is most often used.
recent studies, including a systematic review, have demonstrated the lack of evidence that synthetic feline pheromones  can relieve stress in cats  <cit> .
it would be worthwhile to investigate if the plant materials studied here can be used to alleviate distress in cats, for example during medical procedures, transportation or boarding.
before these plant materials can be used for anything other than enrichment, it is critical that multiple well-controlled, independent studies with sufficient sample size have demonstrated their effectiveness.
CONCLUSIONS
olfactory enrichment using silver vine, tatarian honeysuckle or valerian root may, similar to catnip, be an effective means to improve the quality of life for cats.
nearly all cats responded positively to at least one of these plants.
for cats that do not respond to catnip, these other plants are good alternatives.
because veterinarians and their support staff are the primary educators of cat owners, it is of great importance that they become aware of the existence of these plant materials and the potential response of cats to them.
future studies will be needed to evaluate if these plant materials can be used to improve the quality of life for confined cats, reduce distress, for training, socializing or in trap-neuter-return programs.
additional files
additional file 1: wash-out period.tif.
schematic representation  of the results from our preliminary experiment to establish the wash-out period.
four cats where offered a sock with  <dig> g silver vine  powder  and an empty control sock.
the sock with sv was removed when an intense  response was observed and was replaced with the negative control sock.
the positive response ceased immediately or near immediately  after the plant material was removed from the cat.
the sock with sv was reintroduced to confirm that this loss of the positive response was not because of fatigue, distraction or loss of interest.
indeed, on most occasions a positive response was observed again instantly after exposure to the reintroduced sv sock.
these results suggest that the risk of a carry-over effect  from one plant material to another is minimal when at least 5 min transpire between the exposures.
additional file 2: raw data.xlsx.
microsoft excel  <dig> file containing raw data  for the domestic cats as well as for the tigers and bobcats.
additional file 3: isodihydronepetalactone isomers mass spectra.tif.
mass spectra and retention indices of three isodihydronepetalactone isomers that were detected in silver vine fruit galls, but not in normal silver vine fruit.
ri, retention index.

 the living environment of domestic cats largely determines their quality of life. cats kept indoors exclusively can become bored and stressed more easily than cats that can roam around freely outside, especially in the absence of good company. lack of environmental features such as vertical space, hiding places, scratching posts, and opportunity to play and chase are known to contribute to variable combinations of behavioral problems and physical disease such as lower urinary tract disease, upper respiratory disease, inappetence, and obesity. these problems compromise feline health and well-being, and also contribute to cats being relinquished or returned to shelters. although effective improvements to the living environments of cats are well known and often used to increase their quality of life, olfactory stimulation is often overlooked as a means of enrichment, despite recognition of the importance of environmental smells for cats by the american association of feline practitioners and the international society of feline medicine. cats have highly developed olfactory systems and are capable of detecting volatile stimuli as well as pheromones. furthermore, some plants are known to produce semiochemicals that attract and stimulate cats. this serendipitous effect is the result of the plant releasing allomones into the air to repel herbivorous insects that cause damage to the plant, or to attract predators and parasitoids for these insects. the chemical profiles of these phytodistress signals may differ between plants, the attacking herbivore, and whether or not the plant is being attacked. one of these plants is catnip, which produces allomones that happen to have an apparently euphoric effect on cats, including the big cats. this effect is quite rare in animals, and could be used to improve the quality of cats’ lives. the effect of catnip is caused exclusively by its smell rather than its taste. typically, cats respond to catnip by sniffing, licking and biting it, shaking their head, rubbing their head, chin or cheeks against it, and rolling over, sometimes accompanied by drooling and kicking the material with their hind feet. this behavioral response is not sexual, and catnip is generally believed to be neither addicting nor harmful. unfortunately, approximately one out of every three domestic cats does not respond to catnip. furthermore, whereas lions, jaguars, leopards and snow leopards appear to be sensitive to catnip, most tigers do not respond to it. other plants can have similar positive effects on cats. in a letter was published in science about cats appreciating silver vine as a new “cat delicacy” after it was imported from china by the arboretum of harvard university. this plant, also known as matatabi in east asia, is commonly used as a cat stimulant in japan. similar anecdotes of plants attracting and exciting cats exist for, among others, tatarian honeysuckle, valerian root, and the fresh roots of indian nettle. unfortunately, to the knowledge of the authors, none of these effects have been documented. to evaluate whether veterinarians and veterinary technicians were familiar with catnip alternatives, we asked veterinarians and veterinary technicians in the usa and australia if they were aware of silver vine or tatarian honeysuckle. twelve were feline-only veterinarians and six out of six were feline-only veterinary technicians. thirty-six of the veterinarians and all six veterinary technicians answered this question negatively, suggesting that most veterinarians and veterinary technicians are unaware of silver vine or tatarian honeysuckle and their effects on cats. nepetalactone has been identified as the compound causing the catnip effect. interestingly, not one, but half a dozen other active components similar in structure to nepetalactone have been identified in silver vine, one of which also was detected in valerian root and two, recently, in indian nettle. to the knowledge of the authors, nothing is known about the active compound present in tatarian honeysuckle. data on the percentage of cats responding to silver vine are scarce and of poor quality and, to the knowledge of the authors, non-existent for tatarian honeysuckle and valerian root.fig. compounds identified in catnip and silver vine known or believed to have a stimulating effect on cats the purpose of this study was to compare the responsiveness of domestic cats to catnip and to these catnip alternatives. in addition, we investigated if the pattern of responsiveness to these plants could be explained by the presence or absence of certain chemical compounds. methods study population one hundred randomly selected cats of six months or older living in a cat sanctuary, riverside, ca, usa), in an adoption guarantee shelter, riverside, ca, usa), in homes, and in an american association of feline practitioners-certified cat friendly practice with gold status were included in this study. the r8mcf housed cats in five rooms, with on average 20– cats per room, whereas the msrpac housed cats in individual cages. about 55% of the surface space at the r8cmf was outdoors, and the cats could freely move between indoors and outdoors. cats at the msrpac were allowed outside of their cages into a square meters open room to interact with each other daily for eight hours. all cats at both facilities had continuous access to hiding places, cat beds, shelves and cat trees, scratching boards, litter boxes and water. the cats at the r8cmf had continuous access to dry food and received wet food at least once daily, whereas the cats at the msrpac received dry food twice daily. at the r8cmf window fans were used to help cool the rooms, whereas at the msrpac a constant temperature of °c was maintained. cats in isolation areas or with signs of upper respiratory disease were excluded. data were missing for some cats because they were adopted while the study was in progress. only cats for which we had data for all four stimuli were included in the response pattern analyses. cat age, sex, and breed were recorded when available. ages were available for cats, although for seven senior cats it could only be reliably determined they were at least 10 years of age. to test whether responsiveness to the plant materials differed between younger, generally more playful, cats and older cats, the group of cats was divided into a younger and older group using the median age of these cats as a cutoff between the groups. the average age for the younger group was 1 year and 11 months and at least 9 years and 2 months for the older group. cats also were classified into three different behavioral categories: scared or shy, intermediate, and affectionate or friendly to study the influence of social behavior on the response to the plant materials. plant materials dried, cut and sifted organic catnip leaves and flowers were obtained from frontier and smarty kat. dried, cut and sifted organic valerian root was purchased from organic bio herbs and frontier. tatarian honeysuckle wood and sawdust were purchased from the cat house inc.. powder from dried silver vine fruit galls was purchased from smack and gendai pharmaceutical. dried normal silver vine fruit and silver vine fruit galls were kindly provided by hangzhou botanical technology. we were unable to obtain any indian nettle material for this study. to prevent possible degradation of active compounds, all plant materials were ordered just prior to the start of the experiments. during the study period all plant materials were stored tightly sealed in their original bag, at room temperature and in the dark. exposure cats were exposed to to g silver vine powder inside a thin, porous sock, or to g silver vine powder spread out on approximately square cm of a piece of square m of frieze carpet. this type of carpet was used because it allowed more direct exposure to the materials than did the socks, while still minimizing the ability of the cats to ingest the plant material. equal volumes of catnip, valerian root and tatarian honeysuckle sawdust were offered inside a sock. this amount of plant material filled the sock about half full, and allowed tying a knot to close off the sock. tatarian honeysuckle also was offered as an approximately 10 cm long piece of wood. catnip and valerian root also were offered on carpet. we chose these amounts and volumes of catnip, tatarian honeysuckle and valerian root to ensure that the cats would be exposed to an amount of active compounds that would allow for a positive response. we did not use a similar volume of silver vine powder because this would greatly exceed the manufacturer’s recommendation. furthermore, the high price and limited supply of commercially available silver vine powder outside of east asia would prevent the use of such large quantities in everyday life. results from preliminary experiments demonstrated that g of silver vine powder was enough to elicit a positive response in each of the cats tested. socks or carpet were placed on the floor of the cat’s environment, within one meter of the cat’s head, in its line of sight or in the center of the room, respectively. when a cat seemed unaware of the presence of the plant material, the sock was repositioned within sight of the cat, once. plant materials were never forced onto any of the cats, nor were they repositioned when a cat walked away from it. cats responding positively to the plant materials on the carpet also responded positively to the plant materials in the sock, suggesting that the fabric did not significantly interfere with the exposure of the active compound to the cats. all plant materials were stored inside separate, sealed plastic bags to prevent cross-contamination. identical carpet without plant materials and an identical, empty sock were used as negative controls.fig. photographs of several of the plant materials used in this study. a tatarian honeysuckle wood. b a dried silver vine fruit gall, also referred to as deformed fruit. c a dried normal silver vine fruit the majority of the cats were exposed to all four plant materials on three different days, at different times of the day, for up to one hour. the minimum number of exposures for each cat was two, on different days, and the minimum exposure duration for each cat was ten minutes per exposure. all cats were exposed to the plant materials presented in a sock and the majority of them also were exposed to a piece of tatarian honeysuckle wood, and once to the plant materials on the carpet. each plant material was offered at separate times, in random order, with a washout period of at least five minutes in between to avoid recording false positive responses resulting from a carry-over effect. the length of this washout period was based on results from preliminary experiments. new plant material was only offered to a cat when it would not or no longer show any of the behavior associated with the catnip response when offered a negative control sock. when a positive, complete response was recorded, the stimulus was removed from the cat. this was done to prevent possible response saturation from negatively affecting responses to the plant materials tested subsequently. in addition, plant materials to which the cat responded positively were offered last during subsequent exposures on other days. observing a positive response after a negative one demonstrated that environmental, mental and physical conditions did not prevent the cat from responding positively. this too was done to prevent scoring false negative responses. all cats were exposed to the plant materials in their normal living environment, and only after a period of at least ten minutes during which the cats could acclimate to the presence of the investigator. each cat was given the opportunity to experience the plant materials without interference or intimidation from other cats and in the absence of other possible distractions, which sometimes required retesting cats at other moments. a schematic overview of a typical exposure experiment is presented as fig  fig. schematic overview of a typical exposure experiment for the domestic cats. this experiment was done for each cat. the different shapes represent the various plant materials the cats were exposed to. a negative control was always offered together with each plant material. the wash-out period is represented by a tilde. the responses are an example; these are not results. on the first exposure day circle and triangle were removed from the cat as soon as a positive response was scored. this was done to prevent the cat from not responding to diamond because of loss of interest, fatigue or saturation to active compounds that also may be present in the plant materials the cat had already been exposed to during the experiment on this day. square and diamond were offered first on the second day the cat was tested, because no positive response was observed on the previous testing day. this was done for the same reasons as previously mentioned. diamond was removed when the cat was scored positive for this sample. triangle and circle were offered to the cat last, to try to confirm the results obtained on the first test day, and also to establish that the cat’s environment and its physical and mental state were not preventing the cat from responding positively. this method was repeated on day 3: the sample to which the cat did not respond positively was offered first, followed by samples to which the cat had already responded positively. in this example the cat would have been scored negative for square and positive for circle, triangle and diamond. pos., positive; neg., negative scoring ninety-eight of the cats were scored live by the same researcher, who knew which plant materials were being offered to the cats at each exposure. two cats living in a private home were scored based on video recordings. cats showing the characteristic catnip response and rolling on their back, sometimes accompanied by drooling and raking ) to a plant material were scored as positive for that plant material. each positive response was scored as either intense/complete or mild/partial. cats’ responses were scored as negative when none of at least two exposures resulted in a positive response to the plant material. negative responses of cats present in the same room but not exposed were not recorded.table ethogram of domestic cat and bobcat behavior observed during a positive response to catnip, silver vine, tatarian honeysuckle or valerian root raking a a this behavior is also referred to as hind leg kicking or bunny kicking exposure to various parts of silver vine to study the response of cats to various parts of the silver vine plant in more detail, nine randomly selected domestic cats at the mrspac were exposed on multiple days to the following six plant materials, all contained within socks: g dried silver vine fruit galls, g dried normal silver vine fruit, g powder of dried normal silver vine fruit, sun-dried and fresh leaves from a three year old silver vine plant not bearing fruit galls and g woodchips made from commercially available silver vine wood sticks. to generate the powder, two gram of dried normal silver vine fruit was ground using a mixer mill at 25 cycles per second for three minutes. in all experiments, contact time between the cat’s face and the sock was recorded. the plant material was removed after five minutes of indifference, or after the cat stopped actively engaging with the sock for one minute.table overview of the experiments in which cats were exposed to different parts of the silver vine plant a the sock with the woodchips was offered first; the sock with the fruit galls was added after the cat lost interest in the sock with the woodchips. during all other exposures socks containing the silver vine plant material were offered simultaneously to the cats other felidae: tigers and bobcats nine tigers and five bobcats living at big cat rescue, a sanctuary for exotic cats, in tampa, fl, usa were included in this study. twenty gram of catnip or g of silver vine powder was offered to the tigers inside a folded paper bag with small holes made in it or uncontained by a big cat rescue staff member who was certified to hand out enrichment to cats of all sizes. tigers were first offered catnip, followed by silver vine five minutes later. if a tiger responded positively to the catnip, silver vine was offered at least 5 min after the tiger had lost interest in the catnip. in the absence of a positive response to catnip, silver vine was offered to the tigers without first removing the catnip, which, in some cases, resulted in exposing them to the silver vine within a couple of meters of the catnip. all bobcats received catnip or silver vine powder in crumpled up paper bags with no holes made in them. the plant materials were placed within meter of the cat’s face, without disturbing them, so that all animals were aware of the presence of the materials. minimum possible exposure to each plant material was five minutes for each cat. the cats were not tested between 11: and 16: because of their low level of activity during these hours. chemical analysis dried catnip, dried normal silver vine fruit, dried silver vine fruit galls, dried valerian root and tatarian honeysuckle wood, taken from the batches used for the responsiveness studies, were analyzed using gas chromatography coupled with mass spectrometry to determine concentrations of five known or claimed cat-stimulating compounds isolated from catnip and silver vine: cis-trans nepetalactone, trans-cis nepetalactone, actinidine, iridomyrmecin and isodihydronepetalactone. for extractions, g of each plant material was extracted with 3 ml of dichloromethane while stirred at room temperature for 7 days. the solutions were filtered through a short silica gel column and concentrated by evaporating the solvent at room temperature to  ml. one hundred μl tridecyl acetate was added to each sample as internal standard to allow for quantification of the compounds and comparison between samples. extracts were analyzed by gas chromatography coupled with a mass selective detector. the gc-ms system was equipped with an hp-5 ms fused silica capillary column ). conditions were as follows: inlet pressure: kpa, he-flow:  ml/min, injector: 250 °c, transfer line 300 °c, electron energy 70 ev. the gc oven temperature was kept at 50 °c for 5 min, followed by raising the temperature with 5 °c/min to 320 °c. identification of compounds was performed by comparison of their mass spectra and retention indices ) to those of reference compounds and commercial mass spectral libraries. the amount of compound is expressed per gram of dried plant material. the lower limit of detection under these conditions was  μg per gram. statistical analysis statistical analysis was performed using graphpad prism version. a p-value <  was considered statistically significant. overlaps between responses to the various plant materials were calculated and plotted as a venn diagram in r using a custom script from dr. thomas girke.  to investigate the responsiveness of domestic cats to catnip and catnip alternatives, we exposed cats to catnip, silver vine, tatarian honeysuckle and valerian root in their normal living environment. none of the cats studied responded positively to the control sock or carpet. in agreement with the results from our preliminary experiment we did not observe positive responses to the control sock after removing the plant materials from the cat, suggesting no or a minimal carry-over effect. no differences in response to the plant materials offered inside a sock or on carpet were observed, therefore these results were not recorded separately. seventy-nine of the domestic cats responded positively to silver vine. significantly more cats responded to silver vine or catnip than to tatarian honeysuckle or valerian root. although no statistically significant difference was observed between the percentage of cats responding to silver vine or catnip, the response to silver vine was more intense than to catnip.fig. the number of cats that responded to silver vine, catnip, tatarian honeysuckle and valerian root. the response of the total study population to each plant material is shown in a different color. significantly more cats responded positively to silver vine and catnip than to tatarian honeysuckle and valerian root. responses to silver vine were more intense than to catnip our study population consisted of neutered male cats, neutered female cats and neutered cats of unknown sex. no differences were observed between the number of male and female cats responding to the four plant materials. in addition, the average number of stimuli that the cats responded to was similar for males and females, and no difference in response intensity was observed between male and female cats. we found no evidence that younger age was associated with increased responsiveness. there was no difference in the number of cats responding positively to the various plant materials between the younger and older groups of cats and cats in the younger group did not respond to more plant materials than did cats in the older group and out of respectively). however, more partial/mild responses and less complete/intense responses to catnip were observed in the older group as compared to the younger group. no differences in response intensity were observed for the other three plant materials between the younger and older group. we did not find an association between responsiveness and behavioral category. scared or shy cats responded as often and as intensely to the various plant materials as did affectionate or friendly cats. cats categorized as either scared/shy, intermediate, or affectionate/friendly responded positively to the same number of plant materials. because most of the cats studied were domestic short-haired breeds, we did not study associations between breed and responsiveness to the materials tested. also, because of the small number of cats with the same fur color and pattern, as well as the difficulties in determining these characteristics, we did not test for differences in responsiveness between the various fur colors and patterns. overlap in responses to the various plant materials to investigate which of the plant materials elicited responses in cats not responding to catnip, we analyzed the overlap in responses to the four different plant materials. ninety-four of the cats responded to at least one of the four stimuli, whereas six cats did not respond to any of the materials. twenty-three of the cats that were exposed to all four different plant materials responded to all of them. of the cats not responding to catnip, responded to silver vine, to tatarian honeysuckle, and to valerian root. these results suggest that silver vine is the best alternative to catnip, also because there were only three cats out of the that did respond to tatarian honeysuckle or valerian root, but not to silver vine or catnip. twenty of the cats  that were offered all four different plant materials responded to just one stimulus, the majority of which responded exclusively to silver vine, suggesting that silver vine contains chemical compounds that are either absent or present in lower concentrations in catnip, tatarian honeysuckle and valerian root.fig. response patterns and alternatives to catnip. a venn diagram showing the overlap in responses to catnip, silver vine, tatarian honeysuckle and valerian root. ninety-five of the cats tested were exposed to all four plant materials, of which are included in this plot. the remaining six cats did not respond to any of the plant materials and are therefore not shown in this diagram. b of the cats that did not respond to catnip, responded positively to silver vine, to tatarian honeysuckle and to valerian root responses to various parts of the silver vine plant the silver vine powder used in this study was made from dried silver vine fruit galls, caused by the gall midge pseudasphondylia matatabi. matatabi fruit gall midges leave the fruit when the larvae have matured. it is speculated that cats respond more strongly to dried silver vine fruit galls than to dried normal, oval shaped fruit with a smooth surface. we tested this hypothesis by offering nine cats a sock filled with dried normal fruit and a sock filled with dried fruit galls, simultaneously, and measured the time spent with each sock. we found that the cats spent significantly more time with the fruit galls than with the normal fruit. eight of the nine cats responded positively to the silver vine fruit galls. although some time was spent with the sock containing the dried normal fruit, none of the nine cats responded positively to it.fig. time each cat spent with a sock filled with dried normal silver vine fruit or dried silver vine fruit galls. the socks were offered simultaneously. horizontal lines represent the medians. note that the ordinate is a logarithmic scale, with the minor ticks denoting and 500 s we subsequently investigated if cats responded to silver vine woodchips made from the wood of a plant not bearing fruit galls, dried and fresh leaves from a plant without fruit galls, or powder made from dried normal fruit. eight of the same nine cats were exposed to socks containing these materials. none of the eight cats showed any interest in the powder made from dried normal fruit, or in the dried and fresh leaves. although seven out of eight cats also did not respond to the silver vine wood, one cat did respond positively to this material, on four different testing occasions. however, during each of the two exposures for which we counted facial contact time, the response to the galled fruit lasted longer than to the woodchips, even though the galled fruit was offered after the cat had lost interest in the sock filled with silver vine woodchips. qualitative response the way in which cats responded to the various plant materials was similar to the catnip response that has been described in detail before, indicating that this characteristic response is not restricted to catnip. although we did not attempt to document the behavioral response in detail, we did observe a response to the plant materials that, to the best of our knowledge, has not been described before. in several of the responding domestic cats we observed undulation of the skin overlying the dorsal lumbosacral region of the back shortly after exposure to the plant materials. the wave-like motions only lasted a few seconds and were possibly associated with contractions of the cutaneous trunci muscles, a broad sheath of skeletal muscle that lies directly underneath the skin. other felidae: tigers and bobcats unlike the other big cats, tigers are known not to, or at best only mildly, respond to catnip. tigers typically seem to be less interested in any form of olfactory enrichment compared to other wild cats. since we observed that many domestic cats that did not respond to catnip did respond to silver vine, we were interested to learn how tigers would respond to silver vine. to the knowledge of the authors, silver vine has not been tested on tigers before. catnip and silver vine powder were offered to nine tigers. one tiger responded mildly positive to catnip, but the other eight tigers were indifferent to the presence of this plant material. four of the nine tigers also were indifferent to the silver vine powder, whereas the other five responded disapprovingly to it: after sniffing the plant material the animals backed off and walked away from it. this disapproving response to silver vine was distinct from their negative response to catnip. for this reason we decided to not offer the plant materials to the tigers multiple times. in contrast to the response of the tigers, another non-domesticated member of the felidae, bobcats, did respond positively to silver vine as well as to catnip. this positive response was characterized by holding the paper bag containing the plant material close to their head using their forelegs while chin and cheek rubbing it, rolling over on their back from one side to the other, and drooling. this response lasted several minutes, sometimes longer than 15 min. to the knowledge of the authors, this is the first time silver vine has been tested on bobcats.fig. an eight year old female bobcat holding a paper bag with silver vine powder between her forelegs while she is rolling around and giving it chin and cheek rubs chemical analysis concentrations of cis-trans nepetalactone, trans-cis nepetalactone, actinidine, iridomyrmecin and isodihydronepetalactone in the four plant materials were determined using gas chromatography coupled with mass spectrometry. reference compounds and reference spectra for isoiridomyrmecin, dihydronepetalactone and neonepetalactone were not available and these compounds could therefore not be identified. the highest concentration of cis-trans nepetalactone was found in catnip, whereas minimal quantities were detected in the other plant materials. only a relatively small amount of trans-cis nepetalactone was found in catnip. actinidine concentrations were highest in silver vine fruit galls, valerian root and tatarian honeysuckle and marginal in catnip. the concentration of iridomyrmecin and isodihydronepetalactone was highest in silver vine fruit galls, while valerian root contained some iridomyrmecin and catnip some isodihydronepetalactone. in addition, relatively high concentrations of three different isodihydronepetalactone isomers were identified in silver vine fruit galls.table allomone concentrations in the plant materials used in this study a cn catnip, sv silver vine fruit galls, ths tatarian honeysuckle, vr valerian root b concentrations are expressed as μg per gram dried plant material we also analyzed these compounds in dried normal silver vine fruit. when comparing dried silver vine fruit galls to normal silver vine fruit, we observed higher concentrations of actinidine, iridomyrmecin and isodihydronepetalactone, as well as three isodihydronepetalactone isomers and other compounds similar in structure in the dried fruit galls. mass spectra and retention indices of the three isodihydronepetalactone isomers are shown in additional file concentrations of all these compounds were nearly undetectable in the dried normal silver vine fruit.fig. total ion chromatograms comparing the extracts of dried normal silver vine fruit to the extracts of dried silver vine fruit galls. the normal fruit only contained marginal levels of actinidine and isodihydronepetalactone compared to the fruit galls. relatively large amounts of actinidine, isodihydronepetalactone, iridomyrmecin and its isomers were present in the fruit galls. note the higher concentrations of other lactones in the fruit galls. only a small quantity of cis-trans nepetalactone was detected in the fruit galls. cis-trans nepetalactone; actinidine; iridomyrmecin; isodihydronepetalactone; * different isodihydronepetalactone isomers; is, internal standard discussion olfactory stimulation by catnip is a well-known method to provide enrichment for a cat’s living environment. although it has been long known that not all cats respond to catnip, only limited data are available about plants that may be used as an alternative. this study was designed to compare the responsiveness of cats to catnip, silver vine, tatarian honeysuckle and valerian root. the sample size and the comparison of responses to four different plant materials make this study the most comprehensive on this subject thus far. in addition, this is the first study to document responses of domestic cats to silver vine fruit galls, tatarian honeysuckle and valerian root, and those of tigers and bobcats to catnip and silver vine. nearly all domestic cats responded to at least one of the plant materials tested, with the largest numbers of cats responding to silver vine and catnip. our results indicate that cats predominantly responded to the powder of silver vine fruit galls, and much less frequently to the wood of the silver vine plant. in contrast, katahira and iwai found that out of cats responded positively to a dried silver vine branch. this discrepancy may be explained by the methodology of their study. experiments were performed on laboratory cats housed in small cages that were offered a dried branch of silver vine. approaching and trying to bite the branch within three minutes was considered a positive response, and no negative controls were used in their study. the percentage of non-responders to catnip in our study is in line with findings from previous studies: 35%, 28% and 18%. pooling the data from these studies gives a total of non-responders out of cats, which is very similar to the out of cats that did not respond to catnip in our study. also in line with our observations, a similar percentage of cats with mild or partial responses to catnip was reported by palen and goddard.fig. the absolute number and percentage of cats that responded positively to catnip in three previous studies. the pooled results from these three studies are similar to our findings our observation that tigers did not respond to catnip agrees with results of previous studies. todd found that of the tigers tested did not respond at all, six only sniffed, licked and shook their head, and two tigers showed a partial response including chin and cheek rubs. none of the tigers rolled over. hill et al. found that three out of four tigers did not respond to catnip, whereas one showed a mild or partial response. results from these studies also indicated that all other members of the genus panthera tested, did respond positively to catnip. todd and hill et al. also tested catnip on bobcats and their findings were contradictory, possibly because only two bobcats were tested in each study. although data specific for cats are not available, all four plant species used in this study are generally considered safe and not toxic or addictive for cats and humans. cats have been exposed to silver vine and catnip, in a variety of different forms, for many years. we could only find one anecdote related to the potential addictive properties of silver vine. in the 1970s, the smell of an unspecified form and concentration of silver vine was reportedly preferred by large cats kept in cages in a zoo in japan over food and sexual intercourse. however, their response to the silver vine was one of excitement and joy; no data were presented supporting any negative health effects. the scientific value of their claim that silver vine is addictive recently has been disputed by others, and there is currently no scientific data supporting any addiction potential, nor are there any other negative anecdotes known to the authors, despite the widespread use of silver vine in japan. a recent literature review on the use of silver vine concluded that its enrichment potential has been largely overlooked, and the authors encouraged further investigation of feline behavioral responses to silver vine. the cat house inc. has sold thousands of pieces of tatarian honeysuckle since and has never received a report of adverse reactions. none of the four plants used in this study are listed as poisonous or toxic by the animal poison control center  or the american society for the prevention of cruelty to animals. all plant materials used in this study are commercially available, and are sold as toys or enrichment products specifically for cats. finally, inquiry to the pet poison helpline taught us that valerian root is generally considered safe, and that no toxicity has been reported from exposure to silver vine or tatarian honeysuckle wood. the berries of tatarian honeysuckle may cause mild gastrointestinal irritation because of the presence of terpenoids. the results of our chemical analysis suggest there are significant differences in the concentrations of compounds known or claimed to have a stimulating effect on cats between the various plant materials tested. however, interpretation of table  is somewhat hampered by lack of knowledge of the limit of detection for these compounds for cats, and if there is a dose-response relationship. our findings suggest that cis-trans nepetalactone is the dominant and possibly the only compound in catnip to which cats respond. the higher concentrations of actinidine in silver vine, tatarian honeysuckle and valerian root may explain, in part, the responsiveness of cats that did not respond positively to catnip to these plant materials. in addition, cats that only responded to silver vine may specifically detect iridomyrmecin and isodihydronepetalactone in silver vine fruit galls. indeed, 25% of the cats that responded to silver vine did not respond to tatarian honeysuckle or valerian root, despite similar concentrations of actinidine in these plant materials. in normal silver vine fruit, we detected actinidine at very low concentrations compared to the fruit galls, tatarian honeysuckle, and valerian root. sakan et al. also detected actinidine in leaves of the silver vine plant, but did not report the concentration they detected. like normal silver vine fruit, leaves did not elicit a response in any of the cats we tested, so it is likely that the concentration of actinidine in silver vine leaves is also very low. while actinidine has previously been identified in silver vine and valerian root, this is, to the knowledge of the authors, the first study demonstrating that tatarian honeysuckle contains actinidine, and that the amount is comparable to concentrations found in silver vine fruit galls and valerian root. the low levels of cis-trans and trans-cis nepetalactone, iridomyrmecin and isodihydronepetalactone in tatarian honeysuckle suggest that actinidine may be the only compound in the wood that cats respond to. indeed, we found large overlaps between the plant materials that contained high concentrations of actinidine: 93% and 88% of the cats that responded positively to valerian root or tatarian honeysuckle also responded to silver vine. however, because of technical limitations, we were unable to identify all of the known or claimed active compounds, which leaves room for the possibility that other compounds are involved as well. this possibility is further supported by the observation that despite similar concentrations of all the measured compounds in tatarian honeysuckle and valerian root, only of the cats that responded positively to tatarian honeysuckle or valerian root responded positively to both these plant materials. the popularity of silver vine fruit galls among cats may be explained by the relatively high concentrations of several compounds: actinidine, iridomyrmecin, isodihydronepetalactone and its isomers, although it is unknown if the latter have a stimulating effect on cats. the observation that fewer cats responded positively to silver vine wood than to silver vine fruit galls suggests that lower concentrations of these compounds are present in the wood and that the concentration of these chemicals in the plant material as well as the detection threshold of the cat contribute to the outcome of the cat’s response. evidence that certain compounds have an apparently euphoric effect on cats is scarce. in the early 1940s, mcelvain and colleagues performed a bioassay using seven adult lions to demonstrate that nepetalactone is the active compound in catnip, but they did not discriminate between the cis-trans and trans-cis form of nepetalactone. results from subsequent studies that investigated which of the two nepetalactone isomers causes the catnip response suggest both isomers do, but the design of these studies and the reporting thereof were of poor quality. while sakan and colleagues claimed that certain compounds in silver vine have cat-attracting or stimulating properties, evidence was not presented. the limited information available about bioassays performed by sakan and colleagues was written in japanese. they stated: “we mainly used cats and a compound was considered active when one or more of the following were observed: express interest in the sample, lick the sample, salivate, exhibit the flehmen response, rub their neck against something, rub their back against the ground and move around, become entranced, or fall asleep. actinidine and matatabilactone showed strong activity in lions, tigers and panthers, and actinidine even showed some activity in dogs.” other than this, no data were provided to support their claims. well-controlled studies in which cats are exposed to isolated, pure compounds and scored according to relevant and well-defined behavioral characteristics are required to conclusively establish which compounds cause the apparently euphoric response of cats to the various plant materials. the precise mechanism by which allomone production in silver vine and other plants is stimulated and regulated is unclear. it is known that some gall-inducing insects promote growth of plant tissue to help provide them with food and shelter. it seems that in response to the invasion of the fruit by the larvae, silver vine plants produce and secrete volatile compounds trying to repel the matatabi fruit gall midge. alternatively, these compounds could function by attracting midge predators or parasitoids. because nepetalactone has been found to be an insect repellant and all the cat-stimulating compounds are similar in structure, the former may be more plausible. although few in number, we did see some cats respond positively to silver vine wood, whereas no cats responded to silver vine leaves or normal silver vine fruit. we did not perform chemical analysis of silver vine wood tissue. actinidine, iridomyrmecin, isoiridomyrmecin, dihydronepetalactone, isodihydronepetalactone and neonepetalactone were first identified in silver vine leaves and silver vine fruit galls. it was not specified if these leaves were from silver vine plants with or without fruit galls. in addition, it is unknown if the plant’s response to the local attack by the matatabi fruit gall midge larvae is local or systemic, and thus if allomone concentrations can increase in leaves and wood of the plant. it would be interesting to learn whether cats respond differently to silver vine wood from plants bearing galled fruit as compared to wood from vines without fruit galls. each of the four plant materials tested in this study can be a valuable addition to a cat’s environment, whether indoor or outdoor, but some come with a few disadvantages. many cats respond to catnip, which is inexpensive and easy to obtain or grow. silver vine, although perhaps even more popular among cats than catnip, is more expensive and difficult to obtain; it is predominantly available online and comes from east asia. producing silver vine fruit galls in areas outside of the natural habitat of silver vine is practically impossible because it would require the presence of pseudasphondylia matatabi. the life span of the adult fly is one to two days. females of p. matatabi lay their eggs in the flower buds of silver vine in may. the larvae spend the summer in the fruit galls, but silver vine is not flowering when the flies emerge from the fruit galls in autumn. because of their short life span, the gall midge needs to use a different host plant during the winter season to survive. to this day, this host has not been identified. although inexpensive and easy to obtain, valerian root comes with a strong smell that is not appreciated by everybody. tatarian honeysuckle wood may be the most difficult plant material to obtain, but the wood comes in many different sizes, and will last a lifetime. the various plant materials tested may be used to increase playtime of cats, which is especially valuable for less active, obese or under-stimulated cats. they also can be given to cats for distraction when left home alone for a long time. in animal shelters, these plant materials could be used by staff or volunteers to help socialize cats or to increase the chance of rehoming more timid adult cats. indeed, playfulness of a cat was identified as one of the most important selection criteria used by potential adopters when choosing a cat. we have observed several fearful, withdrawn cats, brought into the sanctuary days or weeks before we tested them, that were attracted by the plant materials and responded seemingly euphorically after encountering them. these cats would normally hide when staff or volunteers were present. this suggests that trap-neuter-return programs also may benefit from using these plant materials. indeed, a previous study already suggested that catnip may be effective for luring feral cats. the plant materials also might be used for training purposes, where exposure to these stimuli may be used as a reward instead of food, which is most often used. recent studies, including a systematic review, have demonstrated the lack of evidence that synthetic feline pheromones can relieve stress in cats. it would be worthwhile to investigate if the plant materials studied here can be used to alleviate distress in cats, for example during medical procedures, transportation or boarding. before these plant materials can be used for anything other than enrichment, it is critical that multiple well-controlled, independent studies with sufficient sample size have demonstrated their effectiveness.  olfactory enrichment using silver vine, tatarian honeysuckle or valerian root may, similar to catnip, be an effective means to improve the quality of life for cats. nearly all cats responded positively to at least one of these plants. for cats that do not respond to catnip, these other plants are good alternatives. because veterinarians and their support staff are the primary educators of cat owners, it is of great importance that they become aware of the existence of these plant materials and the potential response of cats to them. future studies will be needed to evaluate if these plant materials can be used to improve the quality of life for confined cats, reduce distress, for training, socializing or in trap-neuter-return programs. additional files additional file 1: wash-out period.tif. schematic representation of the results from our preliminary experiment to establish the wash-out period. four cats where offered a sock with g silver vine powder and an empty control sock. the sock with sv was removed when an intense response was observed and was replaced with the negative control sock. the positive response ceased immediately or near immediately after the plant material was removed from the cat. the sock with sv was reintroduced to confirm that this loss of the positive response was not because of fatigue, distraction or loss of interest. indeed, on most occasions a positive response was observed again instantly after exposure to the reintroduced sv sock. these results suggest that the risk of a carry-over effect from one plant material to another is minimal when at least 5 min transpire between the exposures. additional file 2: raw data.xlsx. microsoft excel file containing raw data for the domestic cats as well as for the tigers and bobcats. additional file 3: isodihydronepetalactone isomers mass spectra.tif. mass spectra and retention indices of three isodihydronepetalactone isomers that were detected in silver vine fruit galls, but not in normal silver vine fruit. ri, retention index. 
although cats predominantly responded to fruit galls of the silver vine plant, some also responded positively to its wood. in agreement with previous studies, one out of every three cats did not respond to catnip. the best known example of olfactory enrichment is the use of catnip, a plant that can cause an apparently euphoric reaction in domestic cats and most of the pantherinae. it has long been known that some domestic cats and most tigers do not respond to catnip. we tested catnip, silver vine, tatarian honeysuckle and valerian root on domestic cats and observed their response. nearly all domestic cats responded positively to olfactory enrichment. almost 80% of the domestic cats responded to silver vine and about 50% to tatarian honeysuckle and valerian root. unlike domestic cats, tigers were either not interested in silver vine or responded disapprovingly. silver vine powder from dried fruit galls and catnip were most popular among domestic cats. silver vine and tatarian honeysuckle appear to be good alternatives to catnip for domestic cats that do not respond to catnip. olfactory enrichment for cats may have great potential. each cat was offered all four plant materials and a control, multiple times. the plant materials were analyzed by gas chromatography coupled with mass spectrometry to quantify concentrations of compounds believed to exert stimulating effects on cats. of the cats that did not respond to catnip, almost 75% did respond to silver vine and about one out of three to tatarian honeysuckle. the amount of nepetalactone was highest in catnip and only present at marginal levels in the other plants. catnip and silver vine also were offered to nine tigers. silver vine contained the highest concentrations of all other compounds tested. olfactory stimulation is an often overlooked method of environmental enrichment for cats in captivity.
 olfactory stimulation is an often overlooked method of environmental enrichment for cats in captivity. the best known example of olfactory enrichment is the use of catnip, a plant that can cause an apparently euphoric reaction in domestic cats and most of the pantherinae. it has long been known that some domestic cats and most tigers do not respond to catnip. although many anecdotes exist of other plants with similar effects, data are lacking about the number of cats that respond to these plants, and if cats that do not respond to catnip respond to any of them. furthermore, much is still unknown about which chemicals in these plants cause this response. methods we tested catnip, silver vine, tatarian honeysuckle and valerian root on domestic cats and observed their response. each cat was offered all four plant materials and a control, multiple times. catnip and silver vine also were offered to nine tigers. the plant materials were analyzed by gas chromatography coupled with mass spectrometry to quantify concentrations of compounds believed to exert stimulating effects on cats.  nearly all domestic cats responded positively to olfactory enrichment. in agreement with previous studies, one out of every three cats did not respond to catnip. almost 80% of the domestic cats responded to silver vine and about 50% to tatarian honeysuckle and valerian root. although cats predominantly responded to fruit galls of the silver vine plant, some also responded positively to its wood. of the cats that did not respond to catnip, almost 75% did respond to silver vine and about one out of three to tatarian honeysuckle. unlike domestic cats, tigers were either not interested in silver vine or responded disapprovingly. the amount of nepetalactone was highest in catnip and only present at marginal levels in the other plants. silver vine contained the highest concentrations of all other compounds tested.  olfactory enrichment for cats may have great potential. silver vine powder from dried fruit galls and catnip were most popular among domestic cats. silver vine and tatarian honeysuckle appear to be good alternatives to catnip for domestic cats that do not respond to catnip. electronic supplementary material the online version of this article contains supplementary material, which is available to authorized users. keywords olfactionplantsbehaviortigerspheromonesnepetalactoneactinidineiridomyrmecinisodihydronepetalactoneissue-copyright-statement© the author 2017 