Comparison of nutritive and non -nutritive stimuli in the intestinal taste aversion and classical conditioned taste aversion paradigms

Andrea L Tracy, Purdue University


Previous results obtained using the intestinal taste aversion (ITA) paradigm demonstrated that animals could learn to orally discriminate between a carbohydrate (maltodextrin) and fat (corn oil) based on previous pairing of a gastric or duodenal infusion of one nutrient with LiCl-induced illness (Tracy, et al., 2004). Using this same paradigm, it was also shown that two non-nutritive flavors (lemon-lime and orange) were not discriminable based on GI sensory cues. The present experiments were designed to directly compare the relative salience of these two types of stimuli when presented directly to the gut and when presented orally. This was done using two compound stimuli, each comprised of one nutrient (maltodextrin or corn oil) and one non-nutritive flavor (grape or cherry), presented either via GI infusion (Experiment 1) or orally (Experiment 2). One compound was paired with LiCl and the other with saline. In both experiments, oral test sessions compared intake of the two nutrients alone, the two flavors alone, or the two compounds. Results showed that animals were capable of oral discrimination of both nutrients and flavors alone after training via either the GI or oral route, while discrimination of the compound was apparent only after oral training, indicating both qualitative and quantitive differences between oral and GI processing of these stimuli. This replicates previous findings that sensory stimuli produced in the GI tract can be recognized as oral stimuli and supports previous results indicating that this is not due to direct stimulation of oral receptors during training. Additionally, these results indicate that nutrient activation in the GI tract may potentiate learning about non-nutritive flavors in a way analogous to taste-potentiated odor conditioning, suggesting another functional similarity between oral and GI "taste" systems. Finally, the ability to learn about the oral properties of stimuli in the GI tract suggests that there may be greater temporal contiguity between "taste" stimuli and the post-ingestive properties of foods, potentially providing a new account of long-delay taste aversion learning, as well as learning about the positive nutritive and caloric consequences of food consumption.




Davidson, Purdue University.

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