Time of day-dependent latent inhibition of conditioned taste aversions in rats

We have determined that the temporal context of drinking can modulate latent inhibition of learned saline aversions in Wistar rats by changing the time of day of drinking of the preexposure and conditioning phases. Latent inhibition was absent in the group preexposed and conditioned to saline at different times of the day, but not in the group that was preexposed and conditioned at the same time of day. The results confirm a previous report that the time of day can modulate taste aversion learning independently of other environmental cues. It is proposed that the features and duration of the habituation training to the temporal contexts used may be critical for time-dependent latent inhibition to appear.     

Ethanol-mediated taste aversions and state-dependency in preweanling (16-day-old) rats

Requirements for conditioning of an ethanol-mediated taste aversion in 16-day-old rat pups were examined. Experiment 1 demonstrated that preweanling rats are capable of acquiring, in two trials, an aversion to a 15% sucrose solution when followed by intragastric intubation of a 1.2 g/kg dose of 17% v/v ethanol, but not when followed by a 0.4 g/kg dose. Comparison was with control animals given sucrose followed by an equivalent volume isocaloric Half and Half. When the 0.4 g/kg dose of ethanol preceded sucrose presentation by 30 min (Experiment 2), the aversion was learned, suggesting that the effective delay between the sucrose and the critical consequences of the ethanol had been too long with the former procedure. Expression of the sucrose aversion required, however, the reinstatement of the context of intoxication--state-dependent retention. Finally, the results of Experiment 3B indicated that, in addition to the association between the sucrose and the aversive consequences of alcohol intoxication, the orosensory cues resulting from alcohol's direct elimination, via such processes as respiration and salivation, became associated with the appetitive properties of the sucrose. This was evidenced by a conditioned increase in preference for ethanol odor. Possible age-related differences in the ability to associate stimuli with alcohol's unconditioned consequences, and in state dependency are discussed.     

The acquisition of taste aversions in humans

A written questionnaire or an interview was given to 517 undergraduates concerning their acquisition of illness-induced (taste) aversions to foods and drinks. The subjects reported 415 aversions, with 65% of the subjects reporting at least one aversion. The aversions were more likely to be reported as having been formed through forward rather than simultaneous or backward conditioning, and long-delay learning was frequent. The aversions usually formed to the taste of the foods, rather than the appearance or other aspects of the foods. Extinction appeared more effective in decreasing the aversions than did forgetting. The illness responsible for the aversion's forming was usually attributed to the subsequently aversive food, but for 21% of the reported aversions subjects were sure that something else had caused their illness. Aversions were more likely to have formed to relatively less familiar and less preferred foods. Aversions were also more likely to form between the ages of 13 and 20. Generalization of the aversions to similar foods occurred in 29% of the cases. Approximately one fourth of the aversions were to alcoholic beverages. Finally, instances of aversions forming without food or drink consumption and instances of observational learning were reported. The data were quite similar to laboratory taste aversion data collected using other species and can help in optimizing taste aversion treatments of eating and drinking disorders. Taste aversions among humans are frequent and strong.     

Taste familiarity and apomorphine-induced taste aversions in humans

Human volunteers learned taste aversions to a relatively novel cranberry flavor paired with apomorphine-induced illness. These aversions were significantly reduced by pretreatment familiarization to the flavor unless an unpalatable interfering flavor was introduced just prior to the administration of apomorphine. The outcomes have implications for taste-aversion learning in humans and for the control of flavor preferences in patients undergoing illness-inducing chemotherapy.     

Anorexia and conditioned taste aversions in the rat

The present study examined whether or not certain anorexic agents produced flavor aversions. Rats showed comparable anorexia when injected with lithium chloride, ammonium sulfate, arginine·HCl, and d-glucose. Only lithium chloride produced a flavor aversion to either a novel liquid or food. Only arginine was found to interfere with the formation or recall of an association. The effects of the other chemicals were discussed in terms of the relationship between anorexia and induced sickness.     

Failure of sodium- and calcium-deficient rats to acquire conditioned taste aversions to the object of their specific hunger.

Attempts were made to condition taste aversions to the objects of two mineral-specific hungers. Both the innate preference of adrenalectomized rats for sodium and the learned preference of parathyroidectomized rats for calcium were studied. None of the sodium-deficient rats poisoned after drinking sodium chloride (NaCl) reached a taste-avoidance criterion, even after nine pairings of salt ingestion with aversive lithium chloride injections. Six of 11 calcium-deficient rats did not meet the salt-avoidance criterion after 10 pairings. Nondeficient control subjects learned to avoid these salt solutions completely after an average of only three such pairings. Besides unmasking a surprising degree of similarity between the learned and innate specific hungers studied, the results clearly demonstrate a powerful influence of physiological need on aversion conditioning.     

Conditioned taste aversions: From poisons to pain to drugs of abuse

Learning what to eat and what not to eat is fundamental to our well-being, quality of life, and survival. In particular, the acquisition of conditioned taste aversions (CTAs) protects all animals (including humans) against ingesting foods that contain poisons or toxins. Counterintuitively, CTAs can also develop in situations in which we know with absolute certainty that the food did not cause the subsequent aversive systemic effect. Recent nonhuman animal research, analyzing palatability shifts, has indicated that a wider range of stimuli than has been traditionally acknowledged can induce CTAs. This article integrates these new findings with a reappraisal of some known characteristics of CTA and presents a novel conceptual analysis that is broader and more comprehensive than previous accounts of CTA learning.     

Role of illness in producing learned taste aversions in rats: a comparison of several rodenticides.

Several toxic agents were compared in order to test the effect of various types of illness in producing learned taste aversions. After a 10-min sucrose drinking trial, groups of rats were injected intraperitoneally with lithium chloride or with a strong, near lethal dose of a rodenticide. Strong sucrose aversions were acquired by groups injected with lithium chloride, copper sulfate, sodium fluoroacetate, or red squill, and very weak or no aversions were learned by groups injected with thallium, warfarin cyanide, or strychnine. The results were discussed in terms of onset of symptoms, duration of symptoms, and kinds of physiological effects necessary to produce aversions. It was concluded that the effects of different drugs may be mediated by different physiological systems learned taste aversions.     

Learned taste aversions in rats as a function of delay,speed, and duration of rotation

Rats fed a saccharin solution and then rotated on a turntable showed an aversion to the saccharin solution on later testing. In the first experiment, the rats learned to avoid saccharin with delays of as much as 9 hr between drinking the saccharin and the start of rotation. The second experiment showed that the critical determinant of aversiveness of rotation was number of rotations. The rats avoided saccharin as much after rotation at high speeds for short durations as after rotation at low speeds for long durations.     

A comparison of two methods of measuring conditioned taste aversions

Two methods of measuring conditioned taste aversions were compared. Following adaptation to a daily 10-min water drinking schedule, rats were made ill with an injection of cyclophosphamide after presentation of a novel-tasting fluid. Three days after this treatment, Ss were tested by (1) measuring the amount of the novel fluid consumed on the continuing 10-min access schedule or (2) measuring their preference between plain water and the novel fluid. When the drinking behavior of the conditioned animals was compared with that of appropriate controls, the preference method proved to be the more sensitive.     

Loss of latent inhibition in conditioned taste aversion following exposure to a novel flavour before test

Killcross, Kiernan, Dwyer, andWestbrook (1998b) observed that latent inhibition(LI) of contextual fear was attenuated if animals received post-conditioning exposure to a novel context similar to the pre-exposure context. Six experiments used a conditioned taste aversion (CTA) procedure to examine this effect. Experiments 1A-1C demonstrated that LI of CTA was attenuated by a similar post-conditioning manipulation, establishing the generality of previous findings. Experiment 2A manipulated the taste elements to which animals were exposed after conditioning, revealing that exposure to a common element X, present at pre-exposure and conditioning, was not responsible for loss of LI. Experiment 2B manipulated test solution and showed that loss of LI depended on the presence of the full pre-exposed cue AX at test. These two results are contrary to predictions derived from the Dickinson-Burke (Dickinson & Burke, 1996) theory of retrospective revaluation or comparator theory (Miller & Matzel, 1988), and they support recent findings suggesting that retrospective effects may occur by several mechanisms. Experiment 3 showed that a novel element B had to be present during post-conditioning exposure for an attenuation of LI to be observed. Implications for the loss of LI following aretention interval between conditioning and test and retrieval-failure theories of LI are discussed.     

The acquisition of taste aversions in humans with eating and drinking disorders

A written questionnaire or interview concerned with acquisition of illness-induced (taste) aversions to foods and drinks was given to three groups of people with eating and drinking disorders. These groups consisted of 101 male and 1 female hospitalized alcoholics, 8 male and 8 female college-student heavy consumers of alcohol and 18 females with anorexia nervosa and/or bulimia. In most respects taste-aversion acquisition in these three groups was similar to taste-aversion acquisition in a general college-student population previously studied by Logue, Ophir and Strauss (1981), and to taste-aversion acquisition in other species. In all three groups the aversions were more likely to be reported as having been formed through forward rather than simultaneous or backward conditioning, and long-delay learning was frequent. The aversions usually formed to the tastes rather than to the appearance or other aspects of the foods and drinks. Extinction appeared more effective in decreasing the aversions than did forgetting. While the illness responsible for the aversions forming was usually attributed to the subsequently aversive food or drink, in at least one third of the cases subjects reported that something else might have caused their illness. Aversions were more likely to have formed to relatively less familiar and less preferred foods and drinks. However, the hospitalized alcoholics reported fewer aversions, less generalization of aversions, and stronger nausea as the cause of the aversions than did Logue et al.'s (1981) subjects. About 15% of these subjects reported taste aversions to alcoholic beverages. The college-student heavy consumers of alcohol reported no generalization of their taste aversions, but in other respects were similar to Logue et al.'s subjects. Thirty-one percent of these subjects reported taste aversions to alcoholic beverages. The anorexic and bulimic subjects were also similar to Logue et al.'s subjects with the exception that they, like the hospitalized alcoholics, reported stronger nausea as the cause of the aversions. These data may help to understand and treat people with eating and drinking disorders     

Effects of prior exposure on conditioned taste aversion in the rat: androgen- and estrogen-dependent events

The effects of preexposure and gonadal hormone manipulation on the extinction of a conditioned taste aversion were investigated. In Experiment 1, male rats were given one prior exposure to sucrose at some selected time (Days 4, 2, or 1) before a second exposure (Day 0) to sucrose and an LiCl injection. Controls received no prior exposure to sucrose but experienced only the sucrose + LiCl condition (Day 0). under the single exposure condition (Day 0) castrated animals extinguished the aversion faster than either testosterone-treated castrated rats or sham-operated rats. Sham-operated and castrated rats that had received preexposure treatment (Days 4, 2, or 1) were not distinguishable on a within-groups comparison of behavior but differed from their respective controls by exhibiting faster rates of extinction. However, in the testosterone-treated group only the Day 4 preexposure group exhibited a faster extinction rate. In Experiment 2, estradiol, dihydrotestosterone, and testosterone were studied by using only a Day 1 preexposure condition. The testosterone-treated group maintained the aversion for the longest period of time, followed by dihydrotestosterone-treated, sham, castrated, and estradiol-treated groups. It appears that estradiol augments the castration effect whereas dihydrotestosterone attenuates the effect. In Experiment 3, estradiol was administered alone or in combination with two different doses of dihydrotestosterone, and a Day 1 preexposure condition was used. The findings indicate that the outcome of behavior is dependent on the ratio of estradiol to dihydrotestosterone, with variations in this ratio resulting in fast (estrogen effect) to slow (androgen effect) rates of extinction.