The effect of three procedures for eliminating a conditioned taste aversion in the rat

Although extinction procedures have been the most common techniques used to eliminate conditioned taste aversions, several studies have employed postconditioning exposure to the US instead. To date, a comparison of the effectiveness of these two techniques has not been possible, because there were differences in the conditioning phases of these studies. In the present study, after an aversion to saccharin had been established, rats were administered 1, 5, or 10 extinction trials, 1, 5, or 10 postconditioning exposures to the US, or a period of no treatment. Then, all rats received seven two-bottle extinction tests. Five or ten extinction trials reduced the aversion to saccharin most effectively. Five or ten postconditioning presentations of the US were also effective. However, this effect was not noticeable until the fourth of seven test trials, suggesting an elimination procedure-test trials interaction. Neither the extinction nor the US postexposure procedure completely eliminated the aversion. In addition: (i) a single postconditioning exposure to either the CS or the US was ineffective in attenuating the aversion; and (ii) when no postconditioning treatment was administered, the strength of the aversion was undiminished for 20 days.     

Exteroceptive context in tasteaversion conditioning and extinction: odour, cage, and bottle stimuli

Five experiments investigated the extent to which the exteroceptive context, present on a saccharin aversion conditioning trial with rats, controlled the resulting aversion on one-bottle extinction tests and subsequent preference tests. The presence or absence of the specific odour which had been present on the conditioning trial was found not to influence saccharin intake on extinction tests, whereas the presence of the particular compartment in which, and the bottle from which, the saccharin had been consumed greatly suppressed saccharin intake as compared to the absence of these elements. Preference tests, performed in the respective conditioning contexts, showed extinction to be specific to the compartment + bottle context: groups that had extinguished their saccharin aversion in a context different from the conditioning context, retained their aversion in the conditioning context. No such specificity was found for the odour context. However, in the absence of the taste stimulus during the extinction phase, the odour that had been present on the conditioning trial did control the amount of water consumed, whereas the compartment+bottle context did not. Moreover, on preference tests, groups that had consumed water during extinction in the presence of the odour context, evidenced a lesser saccharin aversion than groups not exposed to the odour. The results are interpreted as demonstrating that rats learn about taste, odour, cage and bottle stimuli on a taste-aversion conditioning trial, and that taste and bottle stimuli seem to be the most salient.     

Conditioned and latent inhibition in taste-aversion learning: clarifying the role of learned safety.

Experiments 1-3 investigated the applicability of the classical conditioning concept of conditioned inhibition to taste-aversion learning. Rats made ill after drinking saccharin and subsequently administered a "safe" exposure to saline (or casein hydrolysate) evidenced an enhanced preference for the safe fluid (relative to either a third, slightly aversive, solution or to water) when compared to controls in which saccharin was not previously poisoned. Such active condition inhibition was significantly reduced in Experiment 4 when two safe exposures to saline preceded saccharin-illness pairings. These results indicate that conditioned inhibition can be established in a taste-aversion procedure and that a latent inhibition manipulation reduces the ability of a taste to become a signal for safety. Implications of these findings for the learned safety theory of taste-aversion learning and the relevance to bait-shyness of principles established within the classical conditioning paradigm are considered.     

The effect of stimulus preexposure upon the context effect in taste-aversion learning in noradrenaline-depleted rats

The present investigation was designed to study the effect of preexposure to a saccharin plus noisy bottle stimulus compound, or to each element by itself, upon the extinction-dependent "context effects" (due to the presencelabsence of the noisy bottle contextual cue) in taste-aversion learning, following noradrenaline (NA) depletion via a single systemic DSP4 injection. Since contextual manipulations have provided a reliable means of studying selective attentional processes the current theorising on the role of noradrenaline can be effectively accommodated. It was found that, under the No Preexposure and Noisy Bottle Preexposure conditions, the "context effect" during the saccharin preference tests, after reinstatement of the noisy bottles for all groups, was totally absent for the NA-depleted rats; in the Saccharin plus Noisy Bottle Preexposure condition the "context effect" was partially blocked for the NA depleted rats and in the Saccharin Preexposure condition it was at least as strong as in the control condition, These findings may be interpreted as supporting our conclusions, concerning NA-depleted rats derived from several different investigations, i.e. that following NA loss rats fail to attend sufficiently to contextual cues in taste-neophobia and taste-aversion situations. Thus, the attentional deficit may be described as an inability to attend to all aspects of the taste stimulus plus exteroceptive context stimulus compound. Although the selective attentional hypothesis of noradrenaline function requires a good deal of alteration, it remains the most parsimonious account that can be described at present.     

The effects of chronic water deprivation on metabolic rate and long-trace taste-aversion conditioning in rats

The effect of chronic water deprivation on metabolic rate and long-trace taste-aversion conditioning was examined in Wistar-derived rats. Subjects were either maintained on a water deprivation regimen or allowed free access to water for a seven-week period prior to conditioning. At conditioning, rats were presented a saccharin CS followed 0-, 45-, 90-, or 180-min later by an i.p. injection of LiCl. Additionally, pseudo-conditioned groups were presented the CS followed immediately by an injection of physiological saline. Heightened oxygen consumption in deprived subjects suggested that chronic water deprivation increased metabolic rate. While no differences in the amount of saccharin intake were observed at conditioning, percent preference for saccharin scores during a 24-h two-bottle water/saccharin test revealed that non-chronically deprived rats supported conditioning at longer CS-US intervals than did chronically water-deprived rats. Results are interpreted in terms of a time-contraction effect stemming from an alteration of an internal metabolic count-down timer.     

Higher-order conditioning and sensory preconditioning of a taste aversion with an exteroceptive CS1

An exteroceptive stimulus compound (context) was employed as CS₁ in higherorder conditioning (H-OC, Experiments I and II), and sensory preconditioning (SPC, Experiment III) of a saccharin (CS₂) aversion in rats. The results indicated that aversions were established with the H-OC as well as with the SPC procedures. Stimulus generalization and first-order conditioning explanations were ruled out by appropriate controls. A CS₁-extinction period, performed prior to testing, did not affect the H-OC aversion, whereas it reduced the SPC aversion at least partially. These findings imply that interoceptive (taste, nausea) and exteroceptive stimuli (context) are readily associable in rats. Implications of the resemblance between the SPC procedure and long-delay taste-aversion learning are discussed.     

The role of the insular cortex in taste function

In spite of over 30 years of research, the role of the Insular Cortex (IC) in taste memory still remains elusive. To study the role of the IC in taste memory, we used conditioned taste aversion (CTA) for two different concentrations of saccharin; 0.1% which is highly preferred, and 0.5% which is non-preferred. Rats that had been IC lesioned bilaterally with ibotenic acid (15 mg/ml) before CTA showed significant learning impairments for saccharin 0.1% but not for saccharin 0.5%. To test CTA memory retention, rats lesioned a week after CTA training became completely amnesic for saccharin 0.1% yet only mildly impaired for saccharin 0.5%. Interestingly, the resulting preference for either concentration matched that of IC lesioned animals when exposed to either saccharin solution for the first time, but not those of sham animals, implying that IC lesions after CTA for either saccharin solution rendered complete amnesia, irrespective of the original preference. Our data indicate that an intact IC is essential for CTA learning and retention, as well as for an early neophobic response, but not for taste preference itself. Our data supports a model where the IC is involved in general taste rejection.     

Taste reactivity and consumption measures in the assessment of overshadowing: Modulation of aversive,but not ingestive,reactivity

Three dependent measures—a taste reactivity test, a two-bottle preference test, and a one-bottle extinction test—were used to investigate the conditioning effects of pairing a taste/taste compound with LiCl-induced illness in rats. Avoidance of saccharin consumption in the one-bottle test was attenuated if saccharin and denatonium were paired during illness training (overshadowing). Also, saccharin was found to be more palatable if paired with denatonium during training as reflected by aversive (but not ingestive) taste reactivity measures. It is argued that overshadowing was reflected mainly by a modulation of aversive taste reactivity behavior with little influence on ingestive taste reactivity. The results are discussed in terms of current palatability issues, and it is suggested that applying taste reactivity tests to phenomena associated with taste avoidance learning (e.g., overshadowing or potentiation) may further our understanding of the mechanisms that guide such learning.     

Taste/tactile cue discriminations in taste-aversion learning foIIowing depletion of noradrenaIine

Four experiments were performed to investigate the effect of noradrenaline (NA) depletion, following systemic DSP4 treatment, upon a tastehactile discrimination in taste-aversion learning. In Experiments 1 and 2 , noisy bottle (A) + lithium chloride pairings were alternated with saccharin (B) + saline pairings, and vice versa, during Phase I conditioning. The particular order of reinforcement presentation in each case was then reversed, so that a noisy bottle (A) + saline pairing was now altered with a saccharin (B) + lithium chloride pairing, etc., during Phase II (reversal) conditioning. In Experiments 3 and 4 , saccharin in noisy bottle (AB) + lithium chloride pairings alternated with either noisy bottle (A) + saline or saccharin (B) + saline pairings, and vice versa, during Phase I conditioning; the order of reinforcement presentation was then reversed, as above. None of the four experiments performed offered any evidence of impairments of the discrimination task as a result of NA depletion. These results are discussed in the context of associative preparedness and of discrimination learning in operant tasks and recent findings on compound conditioning, following the loss of NA.     

Differential effects of beta-adrenergic receptor blockade in basolateral amygdala or insular cortex on incidental and associative taste learning

The importance of central β-adrenergic system has been essentially investigated in aversive/emotional learning tasks. However, recent data suggest that the β-adrenergic system is also required for incidental taste learning. In the present study we evaluated in rats whether β-adrenergic receptor activity is required for taste habituation, an incidental taste learning, and also for conditioned taste aversion (CTA) learning, an associative learning. To address this issue, a low dose of the β-adrenergic antagonist propranolol was infused before learning in either the basolateral amygdala (BLA) or the insular cortex (IC), two forebrain areas reported to play a key role in taste memory formation. Incidental taste learning was assessed using a single presentation of the sweet taste saccharin 0.1%, which is sufficient to increase saccharin consumption (relative to water baseline) during a second presentation. CTA was assessed by pairing the first saccharin 0.1% presentation with a delayed gastric malaise, thus causing a decrease in saccharin consumption (relative to water baseline) during a second presentation. Propranolol infusion in BLA (1 μg/0.2μl) or IC (2.5 μg/0.5 μl) before the first taste exposure impaired incidental taste learning but did not affect CTA. These results highlight the important role played by the β-adrenergic receptor activation in cortical and amygdaloid structures during taste learning. Moreover, they are the first to suggest that incidental learning is more sensitive to blockade of noradrenergic system than associative learning.     

Does Conspecific Fighting Yield Conditioned Taste Aversion in Rats?

Running in an activity wheel yields conditioned aversion to a taste solution consumed before the running, but its underlying physiological mechanism is unknown. According to the claim that energy expenditure or general stress caused by physical exercise is a critical factor for this taste-aversion learning, not only running but also other stressful exercises should yield conditioned aversion to the paired taste. This prediction was disconfirmed in two experiments, because stressful conspecific fighting did not work as an effective agent to establish taste aversion in rats.

     

Negative anticipatory contrast and preference conditioning: flavor cues support preference conditioning, and environmental cues support contrast.

In 2 experiments, access to a 0.15% saccharin solution was followed on alternating days by access to a 32% sucrose solution and the same saccharin solution. In Experiment 1, rats increased both intake of and preference for a flavored saccharin solution that predicted sucrose, but neither effect was found using a predictive odor cue alone. Experiment 2 replicated the predictive flavor results but showed suppression of saccharin intake when environmental cues predicted sucrose. When both flavor and environment predicted sucrose, saccharin intake did not change, but preference for the predictive flavor increased. Discriminative taste cues appear to facilitate the development of preference conditioning, but environmental cues favor negative anticipatory contrast effects. Also, preference conditioning and contrast may develop concurrently and compete for expression.     

Human Flavor-Aversion Learning: A Comparison of Traditional Aversions and Cognitive Aversions

Traditional flavor aversions form when an organism consumes a flavor prior to an illness-producing unconditioned stimulus (US). Rozin (1986), however, introduced a second type of taste-aversion learning produced by a disgust-eliciting US. In the present work, Rozin's disgust categorization is extended to include other human situations (negative information, forced consumption) in which taste aversions are mediated by cognitive processes. College students completed a self-report questionnaire that addressed their experiences with taste-aversion learning. The results show that cognitive aversions were stronger and longer-lasting than traditional aversions, they formed to foods of animal origin more than to other substances, and they could be produced without nausea. Finally, individuals who reported having a cognitive aversion had significantly more taste aversions than individuals who reported having a traditional aversion. These results provide additional evidence that taste-aversion learning can occur without the direct mediation of an illness-producing US.     

Context-dependent latent inhibition in taste aversion learning

The effects of taste stimulus preexposure, either in the presence or in the absence of a specific contextual cue consisting of a specific noise-producing bottle, upon the conditioning and testing of conditioned taste aversions to the taste (saccharin) plus context (noisy-bottle) compound stimulus were investigated. Four groups of rats were given preexposure trials (latent inhibition) to either: (1) novel saccharin in novel noisy bottles, (2) novel saccharin in familiar silent bottles, (3) familiar water in novel noisy bottles, (4) familiar water in familiar silent bottles, in six trials. During conditioning, saccharin was presented in the noisy bottles followed by lithium chloride for all the groups. At testing, saccharin was presented in the noisy bottles for both one-bottle and two-bottle tests of aversion. It was indicated that the conditioning decrement produced after both saccharin and noisy bottle preexposure was overwhelmingly greater than any produced after preexposure to the elements. These results, discussed in relation to current theories of latent inhibition and perceptual learning, further underline the overwhelming significance of exteroceptive contextual elements in conditioned taste aversions.     

Taste-mediated potentiation of noningestional stimuli in rats

Holtzman rats drank saccharin in a distinctive environmental chamber prior to lithium-induced toxicosis. This treatment was administered four times. These animals subsequently drank less water or familiar saline in the chamber than animals which received water in the environment during conditioning. In addition, these environmental stimuli blocked the formation of a lithium-mediated coffee aversion more if they were conditioned in the presence of saccharin than if they were conditioned in the presence of water. Such differential blocking provided further evidence that the presence of a taste during conditioning facilitated aversion learning to the environmental chamber.     

Superlatent inhibition and spontaneous recovery: differential effects of pre- and postconditioning CS-alone presentations after long delays in different contexts

In two pairs of three-stage conditioned taste aversion experiments, we examined the effects of delay interval (1 or 21 days) between the second and third stages, and of context in which the animals spent the delay (same as or different from the context of the other stages) on latent inhibition (LI) and spontaneous recovery following extinction. In the LI experiments (Experiments 1A and 1B), the first stage comprised nonreinforced presentations to saccharin or to water. In the second stage, rats were conditioned by saccharin paired with LiCl. In the extinction experiments (Experiments 2A and 2B), the order of the stages was reversed. For all experiments, Stage 3, the test stage, consisted of three presentations of saccharin alone. There was a super-LI effect in the saccharin-preexposed group that spent the 21-day delay in the different context (Experiment 1A). When the delay was spent in the same context, there was no difference in the amount of LI between the short- and long-delay groups (Experiment 1B). Conversely, there was a spontaneous recovery effect in the long-delay/same-context group (Experiment 2B), but not in the long-delay/different-context group (Experiment 2A). The pattern of results, incompatible with current explanations of delay-induced changes in memory performance, was interpreted in terms of an interaction between the delay conditions (same or different delay context), which modulate the extinction of previously acquired context-CS-nothing associations (during CS-alone presentations), and primacy effects.     

Effects of Cerebroventricle Administration of Acidic Fibroblast Growth Factor on Conditioned Taste Aversion Learning in Rats

Wistar strain rats were given acidic fibroblast growth factor (aFGF) or denatured aFGF into their cerebroventricle before taste aversion conditioning for saccharin solution. Animals administrated with aFGF showed significantly lower aversion threshold for saccharin at the 1st day and preference ratios for saccharin vs distilled water at the 4th, 6th, and 7th day after the conditioning than those administered with denatured aFGF. These results suggests that aFGF in the cerebrospinal fluid facilitates acquisition of the conditioned taste aversion learning.     

Neuronal representation of conditioned taste in the basolateral amygdala of rats

Animals develop robust learning and long lasting taste aversion memory once they experience a new taste that is followed by visceral discomfort. A large body of literature has supported the hypothesis that basolateral amygdala (BLA) plays a critical role in the acquisition and extinction of such conditioned taste aversions (CTA). Despite the evidence that BLA is crucially engaged during CTA training, it is unclear how BLA neural activity represents the conditioned tastes. Here, we incorporated a modified behavioral paradigm suitable for single unit study, one which utilizes a sequence of pulsed saccharin and water infusion via intraoral cannulae. After conditioning, we investigated BLA unit activity while animals experience the conditioned taste (saccharin). Behavioral tests of taste reactivity confirmed that the utilized training procedure produced reliable acquisition and expression of the aversion throughout test sessions. When neural activity was compared between saccharin and water trials, half of the recorded BLA units (77/149) showed differential activity according to the types of solution. 76% of those cells (29/38) in the conditioned group showed suppressed activity, while only 44% of taste reactive cells (17/39) in controls showed suppressed activity during saccharin trials (relative to water trials). In addition, the overall excitability of BLA units was increased as shown by altered characteristics of burst activity after conditioning. The changes in BLA activity as a consequence of CTA were maintained throughout test sessions, consistent with the behavioral study. The current study suggests that the neuronal activity evoked by a sweet taste is altered as a consequence of CTA learning, and that the overall change might be related to the learning induced negative affect.     

Taste Aversion Learning Based on Swimming and Lithium Chloride Injection in Rats: Implications From Cross-familiarization Tests and Stimulus Selectivity1

In rats, swimming causes avoidance of the taste solution consumed immediately before the swimming. Several lines of research have shown that this taste avoidance reflects Pavlovian conditioned aversion based on correlations between the taste and swimming-induced nausea. The present research compared swimming-based taste aversion learning (TAL) with conventional TAL based on nausea-inducing lithium chloride (LiCl). By exploiting cross-familiarization techniques, Experiments 1A and 1B suggested that different physiological states are induced by swimming and LiCl. This claim was supported by Experiment 2, which reports stimulus selectivity in saccharin and sucrose aversions based on swimming and LiCl.     

Characterization of a dose-response curve for nicotine-induced conditioned taste aversion in rats: relationship to elevation of plasma beta-endorphin concentration

In the first experiment a conditioned taste aversion paradigm was used to characterize a dose-response curve for the aversive properties of nicotine in male Sprague-Dawley rats. Doses of nicotine ranging from 0.01 to 0.46 mg/kg, 2.0 ml of 0.47 M lithium chloride, or saline were injected, ip, 10 min after exposure to a novel saccharin solution. Amount of saccharin consumed in a two-bottle test was assessed 72 h later. Nicotine doses of 0.046 mg/kg and above produced a significant degree of conditioned taste aversion. In a second experiment, four groups of 10 rats each were injected with saline, 0.022 mg/kg nicotine, 0.46 mg/kg nicotine, or 2.0 ml 0.47 of M LiCl. Doses of 0.46 mg/kg nicotine and 0.47 M LiCl elevated plasma beta-endorphin concentrations significantly above saline control values. The 0.022 mg/kg dose, the highest dose that did not produce conditioned taste aversion in Experiment 1, did not significantly increase plasma beta-endorphin concentrations. This finding suggests that doses of nicotine that produce conditioned taste aversion also promote the release of pituitary stress hormones. Taken together these data suggest that some of the pharmacological and behavioral effects attributed to nicotine, including the release of endogenous neuromodulators, may be dose-dependent concomitants of the aversive effects of nicotine in nicotine-naive animals.