Many compounds have been assessed for their efficacy in generating CTA for vertebrate control. Most fail because they are either ineffective or unstable when
Ž administered orally, e.g., apomorphine Pharmaceutical Society of Great Britain, 1979;
. Ž
Conover, 1989 ; are unsafe at the effective dose, e.g., carbachol Nicolaus and Nellis, .
Ž .
1987; Gill et al., in prep. and emetine Conover, 1989 ; or because they are too Ž
. detectable at levels required to generate an aversion, e.g., lithium chloride Burns, 1980 .
Safe and effective alternatives are needed. Two compounds, cinnamamide and thiabendazole, warrant further study. Cinna-
mamide is a synthetic derivative of cinnamic acid, a naturally occurring plant secondary compound. It is repellent to both birds and mammals, acting through its taste and smell
Ž and through a post-ingestional effect at higher doses e.g., Watkins et al., 1995; Gurney
. et al., 1996; Gill et al., 1997 . When its taste and odour were masked, a single oral dose
of 160 mgrkg induced a CTA to sweet water in captive house mice Mus musculus which, under two-choice testing against plain water, lasted throughout a 64-day trial
Ž .
Ž .
Watkins et al., 1998 . This dose is 10 of the oral LD for mice 1600 mgrkg and no
50
long lasting ill effects were noted. Thiabendazole is approved for use as a systemic fungicide and an anthelmintic for mammals. Timber wolves fed a single dose of 55–80
mgrkg thiabendazole avoided some meat-based foods, especially when they had not Ž
. been food-deprived Zeigler et al., 1983 . New Guinea wild dogs and dingoes fed two
Ž doses of 40–80 mgrkg in lamb meat refused to eat untreated lamb meat Gustavson et
. al., 1983 , and black bears reduced their damage to beehives after consuming beeswax
Ž .
and ‘slum gum’ bait containing 160 mgrkg Polson, 1983 . The doses of thiabendazole Ž
used in these experiments are - 6 of its lowest documented oral LD in rats 3100
50
. mgrkg .
We compared the ability of cinnamamide, thiabendazole, and 17a ethinyl oestradiol to induce a CTA to a novel food in the laboratory rat. Novel foods were used because
they more readily induce CTAs than do familiar foods that previously have produced no Ž
. ill effects Revusky and Bedarf, 1967; Wittlin and Brookshire, 1968 .
2. Materials and methods
2.1. Test compounds Ž
. The test compounds were dissolved cinnamamide and ethinyl oestradiol or sus-
Ž .
Ž .
Ž .
pended thiabendazole in polyethylene glycol 400 mol wt. and distilled water 1:1 , and administered by a single oral intubation at a volume of 2 mlrkg rat weight. 17a
Ethinyl oestradiol was administered at 4 mgrkg, a dose shown to induce a robust CTA Ž
. in rats Nicolaus et al., 1989a . Cinnamamide was administered at 160 mgrkg, as used
Ž .
with mice by Watkins et al. 1998 , and thiabendazole at 100 mgrkg, a dose midway Ž
between effective doses for bears and canids Gustavson et al., 1983; Polson, 1983; .
Zeigler et al., 1983 . Owing to an inconclusive result obtained with thiabendazole at 100 mgrkg, and considering its wide safety margin, this compound was also tested at 200
Ž .
mgrkg 6.5 of its oral LD in the rat . Compounds were tested one at a time. All
50
Ž .
chemicals were obtained from Sigma Aldrich Poole, UK .
2.2. Animals Ž
. Adult Wistar rats Tuck and Son, Battlesbridge, UK of both sexes were individually
housed in wire mesh cages with mesh floors containing paper wool bedding and an Ž
individually labelled food bowl. They were fed ground SDS rat diet Special Diet .
Services, Witham, UK ad libitum, and were neither visually nor aurally isolated. The Ž
. room was maintained at 21 28C with a 12 h lightrdark cycle 0600r1800 h . Water
was available ad libitum at all times from a drinking bottle on the front of the cage. For each compound and dose, rats were randomly assigned to one of the three
Ž . groups: ‘Treated’ T group which received a single intubation of the test chemical;
Ž .
‘Treatment Control’ TC group which received a single intubation of the PEG and Ž .
water carrier; and ‘Control’ C group which were fed and handled in the same way as the other two groups but were not intubated. Equal numbers of each sex were allocated
to each treatment. All rats were tested in the same room and the positioning of rats receiving different treatments was random within the cage racks, thus minimising any
effects that social interactions between rats may have on the rats’ responses to their treatments. Rats were weighed before treatment and a dose and intubation volume
calculated for each individual. Normal food consumption of each individual was determined by daily measurement of ground SDS for G 7 days before treatment. T and
Ž TC rats were used to test only one compound or dose; C rats were re-used once in order
. to minimise the total number of animals used in these experiments for a different
compound or dose, but never with the same novel food. 2.3. NoÕel foods
The following foods were used to ensure novelty of food to all rats in each trial: Ž
. ground cinnamon and crushed digestive biscuit 1:40 was used with 17a ethinyl
Ž .
oestradiol and thiabendazole 100 mgrkg; and icing sugar and porage oats 1:15 and Ž
. almond essence
1 drop: 20 g oats and sugar was used with cinnamamide and
thiabendazole 200 mgrkg. 2.4. Treatment
Ž .
Rats deprived of food for 16 h overnight were presented with 20 g of a novel food Ž
in their own bowl wiped out with a damp cloth to remove SDS dust and placed in .
its normal position in the cage for 30 min. The time taken for each rat to investigate the bowl was recorded and consumption was measured after 30 min. Bowls were then
washed and dried. Any rat which ate - 1 g novel food was excluded from the trial. Rats which ate 1 g were treated according to their group allocation 30 min after the novel
food had been removed. After treatment, each rat was returned to its home cage. Individuals in groups T and TC were observed closely for at least 1 h after treatment,
with regular monitoring over the following 6 h; any obvious ill-effects were recorded. Two hours after treatment, each rat’s food bowl was returned containing a measured
amount of SDS diet. The time taken to investigate the bowl was measured.
Consumption of SDS diet was measured daily to identify any effects of treatment on consumption of normal diet, and to determine when the rats had recovered from
treatment.
2.5. Post-treatment testing Post-treatment testing began when all rats had recovered from any ill-effects of
treatment and had resumed their normal consumption of SDS; G 7 days were allowed for this. Rats from all groups were food deprived overnight for 16 h and then presented
with 20 g of the same ‘novel’ food they received prior to treatment for 30 min. As on treatment day, this food was provided in each rat’s own bowl that had been wiped out
with a damp cloth. The time taken for each rat to investigate the bowl and the rat’s activity during the 30-min presentation were recorded. Consumption was measured on
removal of the bowl. Bowls were then emptied, washed and dried, and returned to the rats 1 half h later containing a measured amount of SDS. The time taken to investigate
the bowl was recorded. Post-treatment testing of all groups was repeated every 7 days
Ž .
for up to 5 weeks post-treatment tests 1–5 or until consumption of novel food did not differ significantly between groups.
In order to allow time to carry out procedures and observations for each treatment, Ž
. the timing of all procedures pre-treatment, treatment, and post-treatment was staggered
by 30 min for each treatment group: for example, C group rats had their SDS taken away at 1630 h the previous day and received their novel food between 0830 and 0900
h; TC group rats’ SDS was removed at 1700 h and they received novel food between 0900 and 0930 h; and T group rats’ SDS was removed at 1730 h and novel food was
presented between 0930 and 1000 h.
Minitab for Windows was used for all data analyses. The study was carried out under Ž
. a UK Home Office license, in accordance with the Animals Scientific Procedures Act,
1986.
3. Results
