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Pine voles (Microtus pinetorum) were given sipper tubes containing saccharin solution, and after drinking, were injected with 0.15 M LiCl. Subsequently, two-sipper tests were given to assure the presence of conditioned flavor avoidance (CFA), and then animals were presented with saccharin in carboxymethyl-cellulose on their own fur (autogrooming), or on the fur of cagemates (allogrooming). CFA was expressed in two-sipper tests, and during allogrooming of material from a cagemate's fur, but not during autogrooming. Failure to express CFA during autogrooming was associated with high circulating levels of corticosterone and cortisol, steroids implicated in behavioral arousal. These results are consistent with previous work showing that rats and mice will ingest flavors while grooming that they would otherwise avoid. We speculate that our findings provide a plausible explanation for the successful use of grooming to increase the ingestion of unpalatable toxicants.

Certain unconditioned stimuli (UCS) in flavor avoidance learning sometimes become ineffective after pairings with relatively stronger UCS. This failure of avoidance learning (avfail) has been demonstrated only with rodents. The present investigations were conducted to determine whether avfail might also occur with avian species, the food selection of which is guided primarily by visual cues. In Experiment 1, starlings were given pairings of methiocarb (a relatively weak UCS) and LiCl (a relatively strong UCS). In Experiment 2, red-winged blackbirds were given pairings of two concentrations of methiocarb (relatively weak and relatively strong UCS, respectively). Pairings were followed by a conditioning trial (UCS gavage in the presence of a color cue) and two-choice tests. Conditioned avoidance was always observed except when methiocarb preceded LiCl and when the low preceded the high methiocarb dose in preconditioning pairings. Experiment 3 demonstrated that UCS habituation could not account for the results of Experiments 1 and 2. The data reflect avfail in the visual modality, and a biological implication of the results is that birds may not learn strong avoidance of aposematic prey containing varied levels of toxicant.

In Experiment 1, rats were conditioned to avoid saccharin in tapwater by pairing it with LiCl in carboxymethylcellulose (CMC) applied to the fur. Conditioned flavor avoidance (CFA) of saccharin was then assessed in drinking and grooming tests. In Experiment 2, rats were given saccharin CMC on their fur and NaCl in water (or vice-versa) as conditioned stimuli in a CFA paradigm. Two-choice tests (saccharin vs. NaCl) followed in drinking and grooming contexts. In Experiment 3, rats were given saccharin CMC on one flank and vehicle (CMC only) on the other. After grooming, animals were injected with LiCl and then given 2-choice tests, first between saccharin and water, then between saccharin-CMC and plain-CMC, and finally, between saccharin and water. Strong CFA was exhibited in drinking tests in all 3 experiments. This was not the case in grooming tests. Rats continued to groom when tastant was applied to only one flank (Experiment 1), and exhibited only weak CFA when a different tastant was applied to each flank (Experiments 2 and 3). We conclude that grooming can be directed to minimize the ingestion of noxious substances, but that such ingestion is not sufficiently reduced to affect the efficacy of grooming as a delivery method for unpalatable substances (e.g., rodenticides, chemosterilants). We speculate that grooming represents a weakness in rodents' defenses against dietary poisoning, and that it might be used to deliver toxicants as part of crop protection schemes that make use of CFA.

In Experiment 1, rats drank strychnine solution followed by an injection of LiCl. Generalization of learned strychnine avoidance to 4 non-toxic flavors was then assessed. Additional conditioning and generalization trials followed until 24 flavors had been presented. In Experiment 2, rats were conditioned to avoid individual flavors, or flavor mixtures concocted on the basis of avoidance generalization observed in Experiment 1. Tests followed for generalization of learned avoidance from the simple flavors to the mixtures, from the mixtures to the simple flavors, and from either to strychnine. In Experiment 3, two concentrations of NaCl were mixed with strychnine or one of the flavors (SOA) used in the previous experiments. These stimuli, as well as SOA alone, strychnine alone, and each of the NaCl concentrations, were presented to rats during conditioning. Generalization followed, as in the previous experiments. In Experiment 1, strychnine avoidance generalized to 'bitter' flavors (ps less than 0.01). In Experiment 2, avoidance of flavor mixtures generalized more strongly to strychnine than did learned avoidance of simple flavors (ps less than 0.01). In Experiment 3, NaCl masked or otherwise suppressed the 'bitter' flavor of strychnine or SOA insofar as no groups conditioned with a 'bitter'-salt mixture generalized avoidance to 'bitter' alone (ps less than 0.01). Rats are therefore capable of recognizing the flavor components of strychnine. Moreover, when these components are mixed in proportion to the degree of generalized avoidance, a mimic (either in terms of flavor characteristics or perceived intensity) of strychnine is obtained. Avoidance learning appears useful in the development of rodenticide baits and pre-bait formulations.

Mice (Mus musculus) allowed to groom a paste containing saccharin from their fur before injection with lithium chloride displayed a saccharin aversion in subsequent drinking preference tests. No attenuation of neophobia was observed in mice grooming saccharin because the animals failed to display a neophobia towards saccharin in drinking tests. Rattus norvegicus displayed neophobia towards saccharin in two- and single-bottle drinking tests but this neophobia was not attenuated by grooming experience with the saccharin paste. Rats apparently learn that if a taste is hazardous in the grooming context it is also likely hazardous in an appetitive context. Learned safety in grooming, however, does not generalize into the appetitive context. The results support the view that neophobia and learned taste aversion depend upon different mechanisms.

Four experiments were conducted to determine how the characteristics of conditioned taste aversion (CTA), as described from studies conducted in the drinking and feeding contexts, applied in the grooming context. In Experiment 1, sodium saccharin was mixed with a "neutral-tasting" jelly and applied to the fur of male Sprague-Dawley rats. Rats injected with LiCl after the applications strongly avoided saccharin solutions in subsequent 1-hr, 2-choice (Saccharin solution vs water) drinking tests, whereas rats injected with NaCl or given plain jelly on the fur showed only an initial neophobic response to the saccharin solution. Thus, the taste of saccharin was perceived while grooming and the CTA formed in the grooming context generalized to drinking. In experiments 2-4, we obtained evidence that: (a) rats discriminated between one intensity of saccharin applied to the fur and another used in the test solution; and (b) rats differentiated between qualities of the two tastants applied to the fur in that saccharin overshadowed NaCl; and (c) taste qualities were more important than toxic properties when two stimuli (Saccharin, LiCl) were used (saccharin overshadowed NaCl in subsequent drinking tests). We speculate that taste, while grooming might play a role in social communication in some vertebrates. Further, CTA and grooming might have uses in rodent control (e.g., in agricultural situations) not previously considered such as in delivering a non-attractive, low-salience toxin so that the taste of the crop overshadows that of the bait, and induces crop aversion.