lithium-chloride and maltodextrin

Food-deprived rats learned to avoid a flavor negatively correlated with access to a rich nutrient, 20% maltodextrin (20M) solution. This avoidance in two-bottle choice tests was produced by training consisting of either an unpaired condition where sessions of unflavored 20M were intermixed with sessions of 2 or 3% maltodextrin (2M or 3M) flavored with salt (Experiment 1) or almond (Experiments 3 and 4) or a differential conditioning procedure where one flavor was mixed with 20M and another with 2M (Experiment 2). Avoidance was counter-conditioned by mixing the target flavor with 20M (Experiment 1), generalized to a neutral context (Experiment 3), and displayed strong resistance to extinction (Experiment 4). The results demonstrated that food avoidance learning can occur in the absence of an aversive unconditioned stimulus and indicated that unpaired control groups and differential conditioning procedures may be misleading in flavor preference learning research when further control conditions are absent.

Topics: Analysis of Variance; Animals; Avoidance Learning; Choice Behavior; Conditioning, Classical; Conditioning, Operant; Female; Flavoring Agents; Food; Food Deprivation; Food Preferences; Generalization, Psychological; Inhibition, Psychological; Lithium Chloride; Male; Polysaccharides; Rats; Rats, Sprague-Dawley; Rats, Wistar; Time Factors

The intestinal taste aversion paradigm has previously demonstrated that animals could orally discriminate between carbohydrate and fat subsequent to pairing a gastrointestinal (GI) infusion of 1 nutrient with lithium chloride (LiCl), whereas they could not discriminate between 2 nonnutritive flavors (A. L. Tracy, R. J. Phillips, M. M. Chi, T. L. Powley, & T. L. Davidson, 2004). The present experiments assessed the relative salience of nutritive and nonnutritive stimuli when presented either intestinally or orally. Two compound stimuli, each comprising 1 nutrient and 1 nonnutritive flavor, were presented in training and were paired with LiCl or saline. Subsequent oral intake of the nutrients alone, the flavors alone, or the compounds was measured. Results showed that rats discriminated both nutrients and flavors independently after GI or oral training, whereas the compounds were discriminated only after oral training, indicating substantive differences in the processing of these stimuli. This suggests that nutrient activation of the GI tract may potentiate learning about nonnutritive flavors analogously to taste-potentiated odor conditioning. The ability to learn about the oral properties of stimuli in the GI tract suggests a new account of delayed taste aversion learning as well as learning about the positive nutritive consequences of food consumption.

Topics: Analysis of Variance; Animals; Avoidance Learning; Behavior, Animal; Conditioning, Psychological; Eating; Flavoring Agents; Food; Intestines; Intubation, Gastrointestinal; Lithium Chloride; Male; Polysaccharides; Rats; Rats, Sprague-Dawley; Taste

To develop and use a behavioral paradigm for assessments of what nutrient properties are detected by intestinal chemoreceptors, we combined features of the "electronic esophagus" preparation (Elizalde G and Sclafani A. Physiol Behav 47: 63-77, 1990) and the conditioned taste aversion protocol (Garcia J and Koelling RA. Psychon Sci 4: 123-124, 1966). In four experiments, separate groups of food-deprived rats with gastric (experiments 1-4) or duodenal (experiment 4) catheters were infused with either carbohydrates (maltodextrin) or fats (corn oil) into their stomachs or small intestines, either while they consumed nonnutritive flavored solutions (experiments 1 and 2) or in the absence of any intake (experiments 3 and 4). For some animals, one of the macronutrient infusions was paired with lithium chloride injections shown to support conventional conditioned aversions. After training, in various oral preference test trials, animals were given opportunities to taste and consume the nonnutritive solutions that had served as oropharyngeal conditioned stimuli as well as the nutrients that had been infused intragastrically, with or without poisoning, but never sampled by mouth. As previously established, preferences for the nonnutritive flavors were enhanced by association with intragastric infusions of macronutrients, with carbohydrates producing the greater preference. On first exposure to the two macronutrients for oral consumption, animals reduced their intake of the nutrient that had been previously poisoned when it was infused into the gastrointestinal tract. These results, along with additional controls, suggest that nutrient tastes detected in the intestines can be recognized centrally based on oropharyngeal gustatory stimulation.

Topics: Animals; Avoidance Learning; Body Weight; Chemoreceptor Cells; Conditioning, Operant; Corn Oil; Dietary Carbohydrates; Dietary Fats; Duodenum; Esophagogastric Junction; Intestines; Intubation, Gastrointestinal; Lithium Chloride; Male; Polysaccharides; Rats; Rats, Sprague-Dawley; Taste

Food-restricted rats with ibotenic acid lesions of the lateral hypothalamus (LHx) learned to prefer a flavour paired with concurrent intragastric (i.g.) infusions of maltodextrin, although their preference was weaker than that displayed by sham controls. Unlike controls, the LHx rats failed to acquire a flavour preference when the i.g. maltodextrin infusion was delayed by 15 min. The same rats learned to avoid flavours paired with i.g. lactose or lithium chloride over short delays (15-30 min), but were impaired, relative to controls, at a long conditioned-unconditioned stimuli delay (2 h). These data indicate that the LH is critical for the formation of flavour-postingestive consequence learning over a delay, particularly with nutrient reinforcement. Lateral hypothalamus lesions might specifically impair the processing of nutrient-generated unconditioned stimuli and, more generally, could interfere with the maintenance of flavour memories.

Topics: Animals; Avoidance Learning; Conditioning, Psychological; Eating; Flavoring Agents; Hypothalamic Area, Lateral; Ibotenic Acid; Lactose; Lithium Chloride; Male; Memory; Neurotoxins; Polysaccharides; Rats; Rats, Sprague-Dawley; Reinforcement, Psychology; Taste; Toxins, Biological