Ingestion of a novel flavor before exposure to pups injected with lithium chloride produces a taste aversion in mother rats (Rattus norvegicus)

Abstract

In a series of experiments, the ability of a mother rat to learn aversions to novel flavors ingested prior to the illness of her pups was investigated. In Experiment 1, mother rats learned to avoid a novel flavored solution ingested prior to the illness of their nursing litters. Experiment 2 was designed to investigate the extent to which any adult rat is capable of such learning: Nonlactating multiparous female rats learned aversions to novel flavors ingested prior to exposure to pups injected with lithium chloride, whereas nonlactating nulliparous female and male rats did not learn these aversions. Several possible reasons for differences in this learning ability are discussed. In Experiments 3 and 4, the nature of the unconditioned stimulus for these aversions was investigated. Visual, auditory, and taste cues associated with the lithium-injected pups did not mediate the aversions (Experiments 3A-C). The evidence suggests that olfactory characteristics of the lithium-injected pups mediate the flavor aversions in the present experiments (Experiment 3D). Finally, these olfactory cues did not appear to be general stress signals but instead were likely specific cues for gastrointestinal discomfort (Experiment 4). The results of the experiments are discussed in terms of classical conditioning and also of their adaptive significance for both mother and offspring.