Odor and taste aversions conditioned in anesthetized rats.

Conditioned flavor aversions (CFA) are acquired by anesthetized rats but effects of various anesthetics on acquisition of aversions for separate odor and taste components are unknown. In Experiment 1, rats drank tomato juice and then were tranquilized with "Innovar-Vet" or "Rompun" before receiving injections of lithium chloride. Neither drug interfered with acquisition of aversions. Innovar-Vet alone produced no aversions; Rompun alone produced mild aversions but did not enhance aversions when combined with lithium. In Experiments 2 and 3, rats received a compound odor/taste cue as they drank and then were anesthetized with pentobarbital before lithium injections. Anesthesia alone produced negligible aversions but facilitated taste-lithium aversions. During odor tests, odor aversions were weaker than taste aversions. These data extend previous work and suggest that CFA does not result from ordinary classical conditioning. A tripartite notation that unites CFA and classical conditioning is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions in tbe rat: I. Innate taste preferences and aversions.

Two experiments examined the innate taste preferences and aversions of rats with electrolytic lesions of the gustatory thalamus (GT). Contrary to previous research, GT lesions had only a minor influence on intake of the 4 basic-tastes as assessed with the 24-hr, 2-bottle preference test in Experiment 1. The same lesioned rats, when tested with the same stimuli in the 15-min, single-bottle procedure in Experiment 2, showed normal consumption patterns except for sucrose intake, which was attenuated. The conflicting findings of previous and present research are considered to result from differences in lesion size. The current data suggest that the GT has a relatively minor functional role in the unconditioned acceptance or rejection of sapid stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute alcohol intoxication disrupts brightness but not olfactory conditioning in preweanling rats.

The present experiments tested the effect of acute alcohol administration on Pavlovian conditioning of 21-day-old rats using conditioned stimuli of two different sensory modalities—olfaction, an early developing sensory capacity functional at birth, and vision, a later developing sensory system not becoming functional until approximately 15 days of age. Conditioning and testing were conducted between 30 and 60 min following gastric intubation with either physiological saline or a mildly intoxicating alcohol dose (1.5 g/kg body weight). Brain alcohol levels were observed to remain at a peak and stable concentration during this period (Experiment 1). Alcohol impaired acquisition or expression of conditioned aversions to a visual cue paired with footshock when presented either as a single-element conditioned stimulus or as part of an odor/visual compound stimulus (Experiment 2), but it had no discernible effect on conditioned aversions to an olfactory stimulus that had similarly been paired with footshock (Experiments 2 and 3). The results suggest that alcohol may impair some aspects of learning but spare others, depending perhaps on the particular sensory modality to be conditioned. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor of Taste Stimuli in Conditioned "Taste" Aversion Learning.

The present research addresses whether rats can express odor aversions to the odor of taste stimuli. In Experiment 1, saccharin or salt were either mixed in distilled water, so the rats could taste and smell them, or presented on disks attached to the tubes' metal spouts so the rats could only smell them. Aversions were established to taste stimuli under both conditions. The results of Experiment 2 indicate that conditioning was to the odor of the tastes when they were presented on disks in Experiment 1, hence both taste and odor aversions were established by means of "taste" stimuli. Taste aversion learning thus may more properly be termed flavor aversion learning, with flavor referring to both taste and odor components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective associations in one-day-old rats: Taste–toxicosis and texture–shock aversion learning.

Three experiments investigated cue-consequence specificity and long-delay learning in 187 1-day-old Sprague-Dawley rats and determined whether selective associations are accompanied by long-delay learning early in life. Ss learned aversions to a novel taste paired with Li-induced distress and to a tactile stimulus paired with brief electric shocks. However, aversions did not develop when taste was paired with shock or when the tactile stimulus was paired with Li treatment. The aversions occurred only when Li treatment immediately followed taste exposure and when shock was concurrent with exposure to the tactile stimulus. Findings indicate that selective associations in aversion learning are mediated by innate mechanisms that govern conditioning in the absence of extensive ontogenetic experience and show that selective associations are not sufficient for the occurrence of long-delay learning. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The conditioned stimulus-unconditioned stimulus-feedback feeding sequence: Reply to Ellins, von Kluge, and Cramer (1990).

Taste-potentiated noise aversions have been demonstrated in rats (S. R. Ellins et al, Ellins and S. von Kluge, and M. D. Holder et al; see PA, Vols 73:3082, 74:24095, and 75:28622, respectively). However, these aversions are apparently less readily established than taste-potentiated odor aversions suggesting that all exteroceptive stimuli are not equally well potentiated by taste (Holder et al). Despite the claims of Ellins, von Kluge, and R. E. Cramer (see record 1990-19032-001), we replicated their findings and see no inconsistency between our findings and theirs. Both sets of results are explained by a common theory of conditioning (J. Garcia, 1989; Garcia & Holder, 1985). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Vagotomy produces learned food aversions in the rat.

Two experiments, each with 28 female Long-Evans rats, examined whether some of the depression in food intake observed in rats with vagotomy could be due to the development of aversions to the foods eaten after surgery. In Exp I, significant aversions developed to the specific novel diet consumed after vagotomy, results indicating that the symptoms associated with vagotomy (hypophagia, weight loss, discomfort) can serve as effective UCSs in the acquisition of learned food aversions. Exp II compared vagotomized Ss consuming familiar laboratory chow with those consuming a novel diet. In contrast to the novel diets, learned aversions to the familiar chow did not develop and hypophagia was less persistent and severe. It is concluded that learned food aversions can contribute to the appetite and weight loss exhibited by vagotomized animals. Consideration of the conditions under which these aversions arise after vagotomy surgery may allow for the design of studies so as to minimize the aversions and thereby separate these nonspecific effects from direct regulatory deficits produced by vagotomy. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative structure of fear memory after basolateral amygdala lesions in rats.

The authors have recently demonstrated that rats with basolateral amygdala (BLA) lesions acquire Pavlovian fear conditioning after overtraining. However, it is not known whether the associative basis of Pavlovian fear memory acquired by rats with BLA lesions is similar to that of intact rats. Associations are typically formed between the conditional (CS) and unconditional (US) stimuli (stimulus-stimulus; S-S), although it is possible for stimuli to enter into association with the responses they produce (stimulus-response; S-R). Indeed, the central nucleus of the amygdala, which is essential for fear conditioning in rats with BLA lesions, may mediate S-R associations in some Pavlovian tasks. The authors therefore used a postconditioning US inflation procedure (i.e., exposure to intense footshock USs) to assess the contribution of S-S associations to fear conditioning after overtraining in rats with BLA lesions. In Experiment 1, intact rats that were overtrained and later inflated displayed elevated freezing levels when tested, indicating that S-S associations contribute to overtrained fear memories. Interestingly, neither neurotoxic BLA lesions nor temporary inactivation of the BLA during overtraining prevented the inflation effect (Experiment 2 and 3, respectively). These results reveal that S-S associations support Pavlovian fear memories after overtraining in both intact rats and rats with BLA lesions, and imply that the central nucleus of the amygdala encodes CS-US associations during fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gustatory thalamus lesions in the rat: II. Aversive and appetitive taste conditioning.

The learning capacities of rats with electrolytic lesions of the gustatory thalamus (GT) were investigated in 3 experiments. In Experiment 1, the presence of a taste cue failed to overshadow odor aversion learning in the lesioned rats, yet these same animals acquired normal taste and odor aversions. Thalamic lesions had no discernible effect on the acquisition of a conditioned flavor preference in Experiment 2. Finally, GT lesions completely reversed the anticipatory contrast effect shown by control subjects in Experiment 3. These results suggest that damage to the GT spares taste detection and recognition and simple associative learning but interferes with learning that involves more complex gustatory information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Maternal separation results in early emergence of adult-like fear and extinction learning in infant rats.

Recent studies in rats have shown that extinction occurring early in life is resistant to relapse and may represent the erasure of fear memories. In the present study we examined the effects of early life stress on extinction in the developing rat, which could have important implications for the treatment of anxiety disorders in those who have experienced early life stress. In the present study, we used maternal-separation on postnatal days (P) 2–14 as an early life stressor. On P17, maternally separated and standard-reared animals were trained to fear a noise associated with a footshock. The fear of this noise was then extinguished (through repeated nonreinforced noise presentations) on P18. Animals were tested for contextually mediated, stress-mediated, and GABA-mediated fear relapse the day after extinction. We found that young animals exposed to maternal-separation were more likely to exhibit context- and stress-mediated relapse after extinction than standard-reared animals (Experiments 1 and 2). Further, unlike standard-reared animals, maternally separated rats exhibited a return of fear when the inhibitory neurotransmitter GABA was blocked at test (Experiment 3). These effects were not the result of maternal separation increasing rats' sensitivity to footshock (Experiment 5) and may in part be related to superior long-term memory for contexts in P17 maternally separated rats (Experiment 4). Taken together, these results suggest that early life adversity may prepare young animals to respond more cautiously toward fear signals in their environment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of lesions of the gustatory neocortex on taste aversion learning in the rat.

In 5 experiments, 110 normal male Long-Evans hooded rats and 125 Ss with lesions of the gustatory neocortex (GN) were compared for their ability to learn aversions to taste cues paired with toxicosis. When the taste presentation was followed immediately by toxicosis, normal Ss and 8 Ss with lesions of the posterior (visual) neocortex learned aversions to sucrose, sodium chloride, quinine hydrochloride, and hydrochloric acid solutions. Ss with GN lesions learned aversions to all solutions except sucrose. In preference tests, all solutions were shown to be discriminable from water by both normal and GN-lesioned Ss. Under conditions in which a 6-hr delay separated taste presentation and toxicosis, normals again learned specific aversions to all 4 solutions, but Ss with GN lesions failed to learn specific aversions to sucrose, sodium chloride, and hydrochloric acid solutions. It was shown that the ability of Ss with GN lesions to learn aversions to sucrose and quinine depended on stimulus concentration. It is proposed that the data can be accounted for by postulating a change in the threshold for taste illness associations following GN lesions. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired relational equivalence: Implications for the nature of associative structures.

In 2 experiments, rats received discrimination training in which separate presentations of A and B signaled a common pair of relationships or associations (X?→?food and Y?→?no food), whereas presentations of C and D signaled a different pair of relationships (X?→?no food and Y?→?food). To assess the nature of the associative structures acquired during this training, rats then received 2 types of revaluation procedure: In Experiment 1, A was paired with shock and C was not. In Experiment 2, the relationships that A and B had previously signaled (X?→?food and Y?→?no food) were paired with shock, whereas those that C and D had signaled (Y?→?food and X?→?no food) were not. After both types of revaluation treatment, rats showed greater generalized conditioned suppression in the presence of B than D. These results indicate that A, B, C, and D come to evoke memories of the relationships or associations that they have signaled. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

A series of experiments investigated the ability of Sprague-Dawley mother rats to learn aversions to novel flavors ingested prior to the illness of their pups. In Exp I, 24 mothers learned to avoid a novel flavored solution ingested prior to the illness of their nursing litters. Exp II was designed to investigate the extent to which any adult rat is capable of such learning: 16 nonlactating multiparous females learned aversions to novel flavors ingested prior to exposure to pups injected with LiCl, whereas 16 nonlactating nulliparous females and 16 males did not learn these aversions. Several possible reasons for differences in this learning ability are discussed. In Exps III and IV, the nature of the UCS for these aversions was investigated. Visual, auditory, and taste cues associated with the lithium-injected pups did not mediate the aversions. Evidence suggests that olfactory characteristics of the lithium-injected pups mediated the flavor aversions in the present experiments. These olfactory cues did not appear to be general stress signals but instead were likely specific cues for gastrointestinal discomfort. Results are discussed in terms of classical conditioning and also of their adaptive significance for both mother and offspring. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The US-Preexposure Effect in Lithium-Induced Flavor-Aversion Conditioning Is a Consequence of Blocking by Injection Cues.

In 2 experiments, rats received flavor-aversion conditioning in which the unconditioned stimulus (US) was an orally consumed solution of lithium chloride (LiCl). The resulting aversion was not attenuated by giving preexposure to injections of LiCl, although such preexposure did attenuate aversions established using injected LiCl as the US (Experiment 1). This outcome suggests that blocking by injection-related cues is responsible for the US-preexposure effect observed in this situation. Experiment 2 confirmed this interpretation by showing that presenting such cues (by giving an injection of saline) at the time that the LiCl was drunk resulted in an attenuation of conditioning in animals preexposed to injections of LiCl. The US-preexposure effect obtained in these experiments can be explained solely in terms of blocking by injection cues, although other mechanisms may contribute to the effect seen in other flavor-aversion paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned aversions to proteins in rats on a dietary self-selection regimen.

101 Long-Evans and 38 Wistar rats in 4 experiments were allowed continuous access to protein and carbohydrate macronutrient sources during a sequence of cyclophosphamide (20 or 40 mg/kg, ip) injections. Significant aversions developed to the protein but not the carbohydrate source in the present experiments, in which the composition of both protein and carbohydrate diets was varied. Results suggest that Ss on a dietary self-selection regimen were more likely to develop conditioned aversions to the protein source than the carbohydrate source (Exps I, II, and III). In Exp IV, the generality of these findings was examined by determining whether aversions would selectively arise to proteins but not carbohydrates when these nutrients were conditioned in a single trial with a meal-feeding paradigm. Results show that proteins were again more salient targets for aversions than carbohydrates. Overall, findings suggest that the tendency to associate proteins with drug-induced illness more readily than carbohydrates is not limited to a self-selection regimen. The possible role of taste factors and/or postingestive effects as the basis for the differential conditioning of proteins and carbohydrates is discussed. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Apparatus Exposure Produces Profound Declines in Conditioned Nictitating-Membrane Responses to Discrete Conditioned Stimuli by the Rabbit (Oryctolagus cuniculus).

The present experiments demonstrated that in the rabbit (Oryctolagus cuniculus) nictitacing-membrane (NM) preparation, exposure to the experimental apparatus produces profound declines in conditioned responding to a discrete conditioned stimulus (CS; Experiments 1, 2A, and 3). Moreover, this decremental effect is at most attenuated in only a minor way when the unconditioned stimulus (US) is presented during exposure to the apparatus (Experiment 2B). Controls for retention loss (Experiments 1 and 3) and for handling and placement in a different context (Experiment 3) did not produce significant declines in responding. These findings challenge theories of extinction that rely primarily on context-US associations but are more consistent with theories that assume context-CS-US associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of lesions of the bed nucleus of the stria terminalis, lateral hypothalamus, or insular cortex on conditioned taste aversion and conditioned odor aversion.

The effects of permanent forebrain lesions on conditioned taste aversions (CTAs) and conditioned odor aversions (COAs) were examined in 3 experiments. In Experiment 1, lesions of the bed nucleus of the stria terminalis had no influence on CTA or COA acquisition. Although lesions of the lateral hypothalamus induced severe hypodipsia in Experiment 2, they did not prevent the acquisition of CTAs or COAs. Finally, in Experiment 3, lesions of the insular cortex retarded CTA acquisition but had no influence on COA acquisition. The implications of these findings are discussed with regard to the forebrain influence on parabrachial nucleus function during CTA acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduced palatability in lithium- and activity-based, but not in amphetamine-based, taste aversion learning.

Conditioned taste aversions (CTA) based on lithium chloride (Experiment 1), amphetamine (Experiment 2), and wheel running (Experiment 3) were examined using the analysis of the microstructure of licking to measure the palatability of the taste serving as the conditioned stimulus (CS). Pairing saccharin with amphetamine reduced saccharin intake without reducing the size of licking clusters, initial lick rate, or the distribution of inter-lick intervals (ILIs) within a cluster. By contrast, pairing saccharin with lithium or wheel-running reduced saccharin intake as well as lick cluster size, initial lick rate, and the distribution of ILIs within a cluster. As lick cluster size, initial lick rate, and ILI distribution can be used as indices of stimulus palatability, the current results indicate that taste aversions based on either lithium or activity reduced the palatability of the CS. This suggests that aversions based on both lithium and wheel running involve conditioned nausea to the CS taste. The absence of similar changes in licking microstructure with amphetamine-based CTA is consistent with other evidence indicating this does not involve nausea. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition and extended retention of a conditioned taste aversion in preweanling rats.

Four experiments employed a taste aversion conditioning procedure appropriate for both neonatal and adult rats to investigate the ontogeny of extended retention. In Exp I, 200 outbred albino rats trained at 1, 10, 20, or 60 days of age were tested for retention of the taste aversion 25 days later. At testing, only those Ss conditioned when 20 or 60 days old demonstrated significant taste aversions. Exps II and III, with 190 Ss, established that Ss 14–25 days old and older were able to retain significant taste aversions following a 25-day retention interval. 80 younger Ss did, however, acquire and retain the aversion for several days and showed a gradual retention loss over progressively longer retention intervals (Exp IV). Findings suggest that preweanling rats demonstrate initial consolidation, storage, and retrieval of conditioned taste aversions. It is only after this initial period that retention deficits become evident. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alcohol aversion generalization in rats: Specific disruption of taste and odor cues with gustatory neocortex or olfactory bulb ablations.

Rats with ablations of the gustatory neocortex (Experiment 1) and rats with olfactory bulb ablations (Experiment 2) were compared with normal rats for aversion generalization to both single taste solutions (sucrose, sodium chloride, quinine hydrochloride, hydrochloric acid) and compound taste solutions (pairs of the four single tastants) following alcohol aversion training. All rats acquired equal and strong alcohol aversions. Control rats showed consistent aversion generalization to both the sucrose plus quinine and the sucrose plus hydrochloric acid solutions; no significant generalization occurred to the single tastants except a weak generalization to sucrose in Experiment 2. Rats with gustatory neocortical ablations failed to show aversion generalization to any of the taste solutions. Rats with olfactory bulbectomies displayed the same aversion generalization functions as control rats but exhibited significantly faster extinction of the alcohol aversion than did the trained control rats. Results from the present experiments suggest that during alcohol aversion learning, rats lacking gustatory neocortex use odor cues (no taste generalization), whereas rats lacking olfactory bulbs utilize taste cues (normal taste generalization). (PsycINFO Database Record (c) 2010 APA, all rights reserved)