The effect of swimming experience on acquisition and retention of swimming-based taste aversion learning in rats

Swimming endows rats with an aversion to a taste solution consumed before swimming. The present study explored whether the experience of swimming before or after the taste-swimming trials interferes with swimming-based taste aversion learning. Experiment 1 demonstrated that a single preexposure to 20 min of swimming was as effective as four or eight preexposures in causing the interference effect. Experiment 2 found that a single 5-min preexposure was enough to cause the interference effect. Experiment 3 showed that preexposure to swimming interfered with but did not completely thwart the acquisition of swimming-based taste aversion learning. Experiment 4 failed to demonstrate a reliable retroactive interference effect by swimming postexposures. With a modified procedure, however, Experiment 5 successfully demonstrated a reliable effect by four postexposures. The associative and habituation accounts of these results are discussed.     

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.     

Facilitation of Sodium Aversion Learning in Sodium-Deprived Rats

Two experiments with rats explored the effects of sodium deprivation induced by furosemide injections upon acquisition of taste aversion to sodium chloride (NaCl). In Experiment 1, rats under either sodium deprivation or a balanced nutrition condition were given access to a limited amount of NaCl solution prior to poisoning. When all rats were tested under sodium repletion, the previously sodium-deprived rats consumed less NaCl than did the nondeprived rats. This finding was replicated in Experiment 2A in which ingestion of a compound solution of NaCl and hydrochloric acid (HCl) was followed by poisoning. Consumption of HCl, however, showed the opposite pattern: the sodium-deprived rats drank more HCl than did the nondeprived rats, a result that was replicated in Experiment 2B. These results suggest that sodium deprivation strengthens the salience of NaCl, thereby facilitating acquisition of aversion to this taste and strongly overshadowing that to a simultaneously presented taste.     

Conditioned ethanol aversion in rats induced by voluntary wheel running,forced swimming,and electric shock: An implication for aversion therapy of alcoholism

This study was planned to demonstrate rats’ acquisition of aversion to ethanol solution consumed before voluntary running, forced swimming, or electric shock delivery. Wistar rats under water deprivation were allotted to four groups of eight rats each, and all rats were allowed to drink 5% ethanol solution for 15 min. Immediately after the ethanol drinking, rats of Group Run were put into the individual running wheels for 15 min, those of Group Swim were put into the individual swimming pools for 15 min, those of Group Shock received electric shocks for 15 min (15 0.45-mA shocks of 0.7s with the intershock interval of 1 min) in the individual small chambers, and those of Group Control were directly returned back to the home cages. This procedure was repeated for six days, followed by a two-day choice test of ethanol aversion where a bottle containing 5% ethanol solution and a bottle of tap water were simultaneously presented for 15 min. In the test, Groups Run, Swim, and Shock drank ethanol solution significantly less than tap water, while Group Control drank both fluids equally. The effects of running, swimming, and shock were equivalent. The successful demonstration of acquired ethanol aversion induced by exercise (running and swimming) or shock in rats suggests an avenue for clinical application of exercise and shock treatments for human alcoholics, though there are many issues to be resolved before the practical use.     

Conditioned Ethanol Aversion in Rats Induced by Voluntary Wheel Running, Forced Swimming, and Electric Shock: An Implication for Aversion Therapy of Alcoholism

This study was planned to demonstrate rats' acquisition of aversion to ethanol solution consumed before voluntary running, forced swimming, or electric shock delivery. Wistar rats under water deprivation were allotted to four groups of eight rats each, and all rats were allowed to drink 5% ethanol solution for 15 min. Immediately after the ethanol drinking, rats of Group Run were put into the individual running wheels for 15 min, those of Group Swim were put into the individual swimming pools for 15 min, those of Group Shock received electric shocks for 15 min (15 0.45-mA shocks of 0.7s with the intershock interval of 1 min) in the individual small chambers, and those of Group Control were directly returned back to the home cages. This procedure was repeated for six days, followed by a two-day choice test of ethanol aversion where a bottle containing 5% ethanol solution and a bottle of tap water were simultaneously presented for 15 min. In the test, Groups Run, Swim, and Shock drank ethanol solution significantly less than tapwater, while Group Control drank both fluids equally. The effects of running, swimming, and shock were equivalent. The successful demonstration of acquired ethanol aversion induced by exercise (running and swimming) or shock in rats suggests an avenue for clinical application of exercise and shock treatments for human alcoholics, though there are many issues to be resolved before the practical use.     

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.

     

Within-compound associations of taste and temperature

In two experiments, rats were given exposures to two solutions of different tastes (sucrose or sodium chloride) at two different temperatures (warm or cold). In Experiment 1, the rats were then given either one of the tastes at room temperature followed by LiCl injections, or distilled water at one of the temperatures followed by LiCl injections. Rats poisoned after drinking a taste were then given a choice between distilled water at the two temperatures, while those poisoned after drinking distilled water at a temperature were given a choice between the two flavors at room temperature. Rats drank less of the solution that contained the stimulus previously paired with the poisoned cue, demonstrating within-compound associations of tastes and temperatures. Experiment 2 found that tastes were better conditioned in a taste aversion procedure when the taste-temperature compound was the same during conditioning as during preexposure. This result is interpreted as evidence against a view of within-compound learning that treats the compound as a unitary stimulus.     

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.     

Further Evidence for Swimming-Based Pica in Rats

Aberrant pica behavior (i.e., kaolin clay ingestion) has been regarded as a behavioral marker of nausea in rats that cannot vomit because of anatomical and/or neural reasons. The previous study reported that a single swimming session of 40 min generated pica behavior, implying that swimming induces nausea in rats. However, the rats tested in that report were not experimentally naive. The present study successfully replicated swimming-based pica with experimentally naive rats (Experiment 1). It also showed that pica was observed with pool confinement of 20 min but not with that of 10 min (Experiments 2A and 2B) and that roaming in shallow water did not generate pica (Experiment 3). These results taken together suggest that swimming for at least 20 min induces nausea in rats, implying that rats’ taste aversion learning based on swimming is mediated by gastrointestinal discomfort.     

Taste aversion after ingestion of lithium chloride: An associative analysis

In five experiments with rats we examined the aversion established by consumption of a solution of lithium chloride (LiCl). Experiment 1 showed that consumption of LiCl established an aversion to saline (NaCl). Experiment 2 showed that the size of the aversion was reduced in rats given pre-exposure to saline (a latent inhibition effect). Experiment 3 showed that experience of a sucrose-saline compound prior to consumption of LiCl generated an aversion to sucrose (a sensory preconditioning effect). Experiments 4 and 5 examined the effects produced by consumption of a sucrose-LiCl compound and demonstrated reciprocal overshadowing between the two tastes. These results confirm that consumption of LiCl establishes an aversion to the taste of this substance. Their implications for the use of orally consumed LiCl as a technique for the control of predatory behaviour are discussed.     

以兔抗鼠淋巴细胞血清为非条件刺激的条件性免疫抑制

采用一种生物类免疫抑制剂-兔抗鼠淋巴血清（rabbit anti-rat lymphocyte serum,ALS）为非条件刺激（UCS）,糖精水为条件刺激（CS）,以双瓶给水法置于鼠笼前端饮用偏好侧。在一次性CS-UCS结合训练后,单独再次给予CS,使卵清蛋白（OVA）免疫过的大鼠表现出脾淋巴细胞对有丝分裂原PWM的增殖反应降低,血抗OVA抗体的总量及脾内抗OVA抗体生成细胞的减少,但动物未表现出条件性味觉厌恶的行为反应。这些结果表明条件性免疫抑制与味觉厌恶行为条件反射没有必然联系,并非是厌恶行为反应或情绪应激的伴随产物。UCS也并非必需具有感觉的毒副作用,条件性免疫抑制是脑高级神经活动调节免疫功能的结果。     

Intragastric copper sulfate produces a more reliable conditioned taste aversion in vagotomized rats than in intact rats

Although copper sulfate is an emetic stimulus, preliminary experiments failed to obtain a taste aversion in intact rats following intragastric administration as had been previously reported in the literature. Several experiments were therefore run to further investigate the capacity of intragastric copper sulfate to function as an unconditioned stimulus for taste aversion learning and the role of the vagus in mediating that learning. The results of the first series of experiments showed that intragastric administration of copper sulfate (5 mg/kg X 5H2O) was more effective in reliably producing a taste aversion in vagotomized rats than in sham-operated control rats. The second experiment examined the effects of area postrema lesions on the acquisition of a taste aversion produced by intragastrically administered copper sulfate in vagotomized rats. The results indicated that the taste aversion observed following treatment with intragastric copper sulfate in vagotomized rats could be prevented by lesions of the area postrema. The present results indicate that intragastric administration of copper sulfate is a more reliable unconditioned stimulus for taste aversion learning in vagotomized rats than in intact rats. It is not certain what factors might account for the discrepant results between the present experiments and previously published research.     

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 aversion induced by motion is prevented by selective vagotomy in the rat

The role of the vagus nerve in motion-induced conditioned taste aversion (CTA) was studied in hooded rats. Animals with complete, selective gastric vagotomy failed to form conditioned taste aversion after multiple conditioning sessions in which the conditioned stimulus (a cider vinegar solution) was drunk immediately before a 30-min exposure to vertical axis rotation at 150 degrees/s. Results are discussed with reference to the use of CTA as a measure of motion-induced "sickness" or gastrointestinal disturbance, and, because motion-induced CTA requires that both the vagus nerve and the vestibular apparatus be intact, in light of the possible convergence of vagal and vestibular functions.     

Cholinergic dependence of taste memory formation: evidence of two distinct processes

Learning the aversive or positive consequences associated with novel taste solutions has a strong significance for an animal's survival. A lack of recognition of a taste's consequences could prevent ingestion of potential edibles or encounter death. We used conditioned taste aversion (CTA) and attenuation of neophobia (AN) to study aversive and safe taste memory formation. To determine if muscarinic receptors in the insular cortex participate differentially in both tasks, we infused the muscarinic antagonists scopolamine at distinct times before or after the presentation of a strong concentration of saccharin, followed by either an i.p. injection of a malaise-inducing agent or no injection. Our results showed that blockade of muscarinic receptors before taste presentation disrupts both learning tasks. However, the same treatment after the taste prevents AN but not CTA. These results clearly demonstrate that cortical cholinergic activity participates in the acquisition of both safe and aversive memory formation, and that cortical muscarinic receptors seem to be necessary for safe but not for aversive taste memory consolidation. These results suggest that the taste memory trace is processed in the insular cortex simultaneously by at least two independent mechanisms, and that their interaction would determine the degree of aversion or preference learned to a novel taste.     

Instrumental Outcome Devaluation Is Attenuated by the Anti-emetic Ondansetron

In three experiments we assessed the effect of an anti-emetic, the selective S-HT antagonist ondansetron, on (1) the conditioning of a taste aversion using lithium chloride (LiCl); (2) the expression of that aversion; and (3) instrumental outcome-devaluation effects. In Experiment 1 it was found that ondansetron reduced the aversion induced by LiCl when administered prior to the LiCl injection and also attenuated the expression of that aversion when administered prior to test sessions. In Experiments 2 and 3, thirsty rats were trained, in a single session, to lever press and chain pull for sucrose and saline solutions concurrently before being injected with LiCl. They were then re-exposed to both solutions, one after injection of vehicle and the other after injection of ondansetron. In a choice extinction test on the levers and chains, animals performed more of the action whose training outcome was re-exposed under ondansetron than the other action, whether the test was conducted after an injection of vehicle or after one of ondansetron.     

Taste preconditioning augments odor-aversion learning

On the basis of previous work that has shown a taste can potentiate odor-aversion conditioning in AX+ conditioning, 6 experiments used rats to examine the effects of pairing a preconditioned taste (A) with a novel odor cue (X) in an A+/AX+ aversion conditioning design. Experiments 1A and 1B demonstrated that a preconditioned taste produced a robust odor aversion that was significantly stronger than a potentiated odor aversion. The results of Experiment 2 showed that the robust odor aversion produced by A+/AX+ conditioning was not the result of the potentiated odor aversion summating with generalization from the taste aversion. The augmented odor aversion was produced only when the taste and odor stimuli were presented simultaneously (Experiment 3) and the preconditioned taste aversion was intact at compound conditioning (Experiment 4). Pairing a novel odor with a preconditioned taste was not sufficient to condition an aversion to odor (Experiment 5), although other results implicated a role for an association between odor and taste in the odor augmentation effect (Experiment 6). The present results have implications for current models of taste + odor interactions in flavor-aversion conditioning.     

Conditioned taste aversion is enhanced when the unconditioned stimulus is presented in a different context

Using a conditioned taste aversion procedure with rats as the subjects, two experiments examined the effect of presenting a conditioned stimulus (CS saccharin solution) in one context followed by an unconditioned stimulus (US LiCl) in a different context. Experiment 1 showed that animals which received the above-mentioned procedure (Group D) showed a more marked conditioned aversion to the CS than animals which were given both the CS and the US in the same context (Group S). Experiment 2 found that in both Group D and Group S, aversion to the CS increased when the subjects were exposed to the conditioned context after the conditioning. These findings supported the argument that the strength of the CS-US association acquired during conditioning is compared with that of the context-US to determine the magnitude of aversion revealed to the CS.     

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

The time course of memory decay for infant rats may shed light on the processes responsible for infantile amnesia. A taste aversion conditioning procedure appropriate for both neonatal and adult rats was employed in four experiments to investigate the ontogeny of extended retention. In Experiment 1, 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 rats conditioned when 20 or 60 days old demonstrated significant taste aversions. Experiments 2 and 3 established that rats 14-15 days old and older were able to retain significant taste aversions following a 25-day retention interval. Younger rats did, however, acquire and retain the aversion for several days and showed a gradual retention loss over progressively longer retention intervals (Experiment 4). These 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.     

Gastrointestinal reactivity in rats lacking anterior insular neocortex

Behavioral and physiological studies have shown that the insular neocortex participates in a wide variety of special visceral processes, in particular, the higher-order integration of taste stimuli and the regulation of autonomic activity. The present experiment examined the involvement of the anterior insular (gustatory) neocortex (AIGN) in gastrointestinal reactivity and taste learning in rats by the use of a modified taste aversion training procedure. Normal rats and rats lacking AIGN demonstrated similar "illness thresholds" to the early onset symptoms of ingested LiCl. Conversely, animals lacking AIGN showed significant impairments in taste aversion learning ability. From a consideration of several research findings it is concluded that animals lacking AIGN can normally perceive tastes and illness, but these animals experience reliable impairments in taste aversion learning ability.