Perceptual characteristics of the amiloride-suppressed sodium chloride taste response in the rat

The contribution of amiloride-sensitive membrane components to the perception of NaCl taste was assessed by using a conditioned taste aversion procedure. Eight independent groups of adult rats were conditioned to avoid either 0.1M NaCl, 0.5M NaCl; 0.1M NH4Cl, or 1.0M sucrose while their tongues were exposed either to water or to the sodium transport blocker amiloride hydrochloride. In contrast to rats exposed to water during conditioning, rats exposed to amiloride were unable to acquire a conditioned taste aversion to 0.1M NaCl. Differences in the acquisition of taste aversions between the amiloride- and nonamiloride-treated groups were not apparent when the conditioned stimulus (CS) was 0.5M NaCl, 0.1M NH4Cl, or 1.0M sucrose. Although the magnitude of the 0.5M NaCl aversion was similar between amiloride- and non-amiloride-treated rats, the perceptual characteristics of the CS differed between groups. Analyses of stimulus generalization gradients revealed that amiloride-treated rats generally avoided all monochloride salts after conditioning to 0.5M NaCl but not nonsodium salts or nonsalt stimuli. In contrast, rats not treated with amiloride only generalized the 0.5M NaCl aversion to sodium salts. No differences in generalization gradients occurred between groups when the CS was 0.1M NH4Cl or 1.0M sucrose. These findings suggest that the "salty" taste of NaCl is primarily related to the amiloride-sensitive portion of the functional taste response in rats. Conversely, the portion of the NaCl response insensitive to amiloride appears to have "sour-salty" perceptual characteristics and does not appear to be perceived as being salty.     

Development of taste responses in the rat parabrachial nucleus

Extracellular responses from neurons in the parabrachial nuclei (PBN) were studied in rats 4 days old to adulthood during chemical stimulation of the tongue with monochloride salts, citric and hydrochloric acids, sucrose, sodium saccharin, and quinine hydrochloride. Multiunit taste responses were recorded in rats at 4-7 days of age and single-unit responses were recorded from 121 neurons in four other age groups of 14-20 days, 25-35 days, 50-60 days, and adults. PBN neurons in rats 4-7 days old consistently responded to 0.1 M solutions of NH4Cl and NaCl, to 0.5 M solutions of NH4Cl, NaCl, and KCl, and to 1.0 M sucrose, 0.1 M sodium saccharin, 0.1 M citric acid, and 0.1 N HCl. They often did not respond, however, to 0.1 M KCl and 0.01 M quinine hydrochloride. Single PBN neurons in rats 14 days old and older characteristically responded to all stimuli, which consisted of 0.1 and 0.5 M salts, acids, sucrose, sodium saccharin, and quinine hydrochloride. Thus no developmental differences occurred in the number of stimuli to which neurons responded after rats were 14 days old. With the exception of responses to hydrochloric acid, there were significant increases in response frequencies to all stimuli after 14 days of age. Average response frequencies to NH4Cl and citric acid increased after 20 days of age and those to NaCl, LiCl, KCl, sucrose, sodium saccharin, and quinine hydrochloride increased after 35 days of age. Average response frequencies for hydrochloric acid did not alter after 14 days of age. The proportion of single PBN neurons that responded maximally to specific monochloride salts did not change during development. Most single neurons in all age groups responded equally well to NH4Cl, NaCl, and LiCl. No PBN neuron responded maximally to KCl. Developmental differences in response frequencies of third-order gustatory neurons in the PBN generally reflect developmental response changes in first-order neurons of the chorda tympani nerve and second-order neurons of the solitary nucleus. However, unique developmental changes are evident in the PBN. Thus the ontogenetic changes that occur in PBN responses likely relate to modifications of lower-order peripheral and central nervous system afferents and peripheral receptor sensitivities.     

Development of taste responses in rat nucleus of solitary tract

Extracellular responses from neurons in the nucleus of the solitary tract (NST) were studied in rats aged 5 days to adulthood during chemical stimulation of the tongue with monochloride salts, citric and hydrochloric acids, sucrose, sodium saccharin, and quinine hydrochloride. Multiunit taste responses were recorded in rats at 5-7 days of age and single-unit responses were recorded from 111 neurons in four other age groups of 14-20 days, 25-35 days, 50-60 days, and adult. NST neurons in rats aged 5-7 days consistently responded to relatively high concentrations (0.5 M) of NH4Cl and KCl and to citric and hydrochloric acid. However, they often did not respond to 0.5 M NaCl or to 0.1 M NH4Cl. Single NST neurons in rats aged 14 days and older characteristically responded to all 0.1 and 0.5 M salts and to both acids. At least 75% of neurons also responded to sucrose and sodium saccharin, and 46% responded to all of these stimuli and quinine hydrochloride. After 14 days, no developmental changes occurred in the number of stimuli to which neurons responded. There were substantial developmental alterations in the response magnitudes to some chemical stimuli. Average response frequencies increased after 35 days of age for 0.1 and 0.5 M NaCl, LiCl, KCl, and for sucrose and sodium saccharin. Response frequencies for NH4Cl, citric and hydrochloric acid, and quinine hydrochloride, however, did not change throughout development. The proportion of single NST neurons that responded maximally to specific monochloride salts did not change during development. Most single neurons in all age groups responded equally well to NH4Cl, NaCl, and LiCl. No NST neuron responded maximally to KCl. There were also no developmental differences in response latencies in rats aged 14 days and older. Response frequencies of second-order NST neurons generally reflect changes in responses from the primary afferent, chorda tympani fibers, throughout development; however, the increases in salt response frequencies from NST neurons occur comparatively later in development. Furthermore, at all ages, the taste responses to monochloride salts include higher response frequencies and a general loss in response specificity in NST compared to chorda tympani neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Constructing quality profiles for taste compounds in rats: a novel paradigm

We developed a novel behavioral method, adapted from the work by Morrison (1967), for the assessment of taste quality in rats. Four groups of rats were trained to discriminate a standard stimulus (either NaCl, sucrose, quinine, or citric acid, which are widely thought to represent the four basic human taste qualities of salty, sweet, bitter, and sour, respectively) from the remaining three compounds (each at multiple concentrations). Animals were then tested for generalization to the standard stimuli when test compounds were presented and a quality profile was constructed. Rats generalized novel concentrations of standard stimuli completely to their training concentrations and generalized their responses to mixtures of NaCl and sucrose on the basis of the relative concentrations of the stimulus components. In general, the sugars (at high concentrations), denatonium, tartaric acid, and sodium gluconate generalized to sucrose, quinine, citric acid, and NaCl, respectively. Monosodium glutamate generalized to a mixture of sucrose and NaCl. KCl produced a complex generalization profile with notable quinine and citric acid components. Our procedure supplements the current use of the conditioned taste aversion generalization procedure which has some procedural and interpretive limitations. Although our procedure involves the use of a complex stimulus delivery and response measurement apparatus and requires substantial initial conditioning of animals, once trained, a single cohort of animals can be tested for its response to a substantial number of test stimuli over the course of many months without any ostensible loss of stimulus control.     

The suppressive effects of LiCl, sucrose, and drugs of abuse are modulated by sucrose concentration in food-deprived rats.

Suppression of intake of a gustatory conditioned stimulus (CS) occurs when paired with either an aversive or an appetitive unconditioned stimulus (US). Toxic substances, such as lithium chloride (LiCl), induce conditioned taste aversions while rewarding stimuli, such as high a concentration of sucrose, reduce intake through a comparison process referred to as anticipatory contrast. Drugs of abuse also suppress CS intake, but it is not known whether they do so via their rewarding or aversive properties. Using 0.1, 0.3, or 0.5 M sucrose solutions as the gustatory CS, we compared the suppressive effects of LiCl (5.29 mg/kg), morphine (15 mg/kg), cocaine (10 mg/kg), and a 1.0-M sucrose solution in rats that were food deprived. The doses of the three drugs have been equated in terms of their suppressive effects in water-deprived and free-feeding rats. The results showed that in food-deprived rats the sucrose US failed to suppress intake of any of the sucrose CSs, the drugs of abuse failed to suppress intake of the 0.3 and 0.5-M concentration of sucrose, and LiCl failed to suppress intake of the 0.5-M sucrose solution. When taken together, these findings reveal that the suppressive effects of all USs (aversive, appetitive, and drugs of abuse) can be offset by the use of a caloric CS when evaluated in food-deprived rats.     

Estrogen increases the taste threshold for sucrose in rats

Anecdotal and empirical evidence suggests that females' preferences for sweet foods are affected by hormonal fluctuations across the reproductive cycle. In rats, the preference for sweet foods may involve estrogen-mediated changes in response to the taste of sweets. Our recent work showed that ovariectomized female rats lick less to dilute sucrose solutions when given estrogen than when given the oil vehicle. These findings suggest that estrogen decreases the preference for less concentrated sucrose solutions; however, an alternative explanation is that estrogen interferes with the ability to detect dilute sucrose solutions. To distinguish between these possibilities, we conditioned a taste aversion to 0.2 M sucrose in ovariectomized rats by pairing it with injection of LiCl and then examined the generalization of that taste aversion to 0.075 and 0.025 M sucrose solutions during estrogen or oil treatment. Oil-treated rats generalized the LiCl-induced aversion conditioned to 0.2 M sucrose to both 0.075 and 0.025 M sucrose. Estrogen-treated rats generalized the LiCl-induced taste aversion to 0.075 M sucrose but not to 0.025 M sucrose. Moreover, two weeks later, when estrogen had cleared the system, both groups generalized the aversion to both 0.075 and 0.025 M sucrose. These results show that estrogen affects the ability to discriminate dilute sucrose from water and suggest that estrogen may have short-term effects on the detection threshold for sucrose taste in rats.     

Conditioned food aversion elicited by the temperature of drinking water as a conditioned stimulus in rats

It is known that taste can act as a conditioned stimulus (CS) for conditioned food aversion. In the present study, in order to examine whether or not the temperature of drinking water can be a CS, we conducted behavioral experiments in Wistar rats. The following results were obtained: (1) The rats subjected to aversive conditioning to 5 or 40 degrees C distilled water could learn to avoid these CSs, but they did not avoid any taste stimuli. (2) The rats subjected to aversive conditioning to 5 or 40 degrees C 0.1 M sucrose developed a generalized avoidance to sucrose at any temperature. (3) When rats familiarized to 25 degrees C 5 mM saccharin-Na (Sacc) were subjected to aversive conditioning to 5 or 40 degrees C Sacc, they avoided the respective CS, but they did not generalize it to any other stimuli even if having the same temperature as the CS. (4) The rats which had undergone transection of the taste nerves (chorda tympani and glossopharyngeal nerves) could acquire the conditioned response to the temperature of the CS. These results suggest that rats can be conditioned to temperature aversion and that the taste nerves are not needed in the formation of this conditioning.     

Central gustatory lesions and learned taste aversions: unconditioned stimuli

The efficacy of two different unconditioned stimuli (US) in producing conditioned taste aversion (CTA) was tested in rats after bilateral ibotenic acid (IBO) lesions of the gustatory nucleus of thalamus (TTAx) and the medial and lateral parabrachial nuclei (mPBNx, lPBNx). An initial study determined an equivalent dose for the two USs, LiCl and cyclophosphamide (CY), using non-lesioned rats. Subsequently, using a separate set of lesioned animals and their sham controls (SHAM), injections of CY were paired 3 times with one of two taste stimuli (CSs), 0.1 M NaCl for half the rats in each group, 0.2 M sucrose for the other half. After these conditioning trials, the CS was presented twice more without the US, first in a 1-bottle test, then in a 2-bottle choice with water. The acquisition and test trials had 2 intervening water-only days to assure complete rehydration. Two weeks later, the same rats were tested again for acquisition of a CTA using LiCl as the US and the opposite CS as that used during the CY trials. The SHAM and TTAx groups learned to avoid consuming the taste associated with either CY or LiCl treatment. The two PBNx groups failed to learn an aversion regardless of the US.     

Sweet and sour preferences in young children and adults: role of repeated exposure

We investigated the influence of repeated exposure to orangeades with added sucrose and different concentrations of citric acid, on the taste preferences of 6- to-11-year-old children and young adults. During an intervention study of 8 days, 59 children (9.2+/-0.9 years) and 46 young adults (22+/-2.0 years) received, each day, either an orangeade with a sweet taste, a sour taste, or no orangeade (control). Before (baseline) and after the intervention, preferences for a series of orangeades and yoghurt, which varied in balance of sweet and sour tastes, were measured by means of a rank-ordering procedure. The variation in balance of sweet and sour taste was established by adding different amounts of citric acid (orangeade: 0.009, 0.013, 0.020, 0.029, 0.043, and 0.065 M added citric acid; yoghurt: 0.027, 0.038, 0.056, 0.081, 0.12, and 0.17 M added citric acid) to a stock orangeade and yoghurt with 0.42 M sucrose. The sweet and sour tasting orangeade that were consumed during the intervention were equally preferred at baseline. After an 8-day exposure to the sweet orangeade, children's preferences for this orangeade (0.42 M sucrose) significantly increased (p<0.05). A similar trend was observed for the yoghurt with 0.42 M sucrose (p=0.09). An 8-day exposure to the sour orangeade did not have a significant effect on children's preference for this orangeade. The taste preferences of adults did not change after the intervention. The control group of children and adults did not show any change in preferences for sweet and sour tastes. Future research is needed to investigate whether the changed preferences for sweet taste are stable over time and how these changed taste preferences are related to a change in the consumption of sugar rich foods.     

Stimulus preexposure reduces generalization of conditioned taste aversions between alcohol and non-alcohol flavors in infant rats

Results of 3 experiments showed that infant rats (age 13-17 days) generalize conditioned taste aversions between alcohol and non-alcohol tastes such as a mixture of sucrose and quinine, apple cider vinegar, or coffee. Nonreinforced preexposure to those tastes reduced generalized aversions between them. Generalization between alcohol and sucrose-quinine was reduced not only after preexposure to both tastes, but also when only the nonconditioned taste was preexposed, whereas with alcohol and vinegar, both tastes had to be preexposed to obtain that effect. In no case was generalization reduced when only the to-be-conditioned taste was preexposed. Previous experience with alcohol alone, as well as with similar gustatory stimuli, may enhance subjects' ability to differentiate them during infantile stages in rats.     

Conditioned taste aversions: generalization to taste mixtures

Rats were trained to take their daily water ration within a 30-min session, during which the number of licks per 10-sec presentation of a drinking tube could be recorded. During one of these sessions, one of three stimuli (sucrose, NaCl or HCl) was presented, followed by the administration of cyclophosphamide to produce a conditioned taste aversion. When tested with mixtures of the conditioned stimulus (CS) with the other two stimuli and also with quinine hydrochloride, the animals avoided mixtures containing the CS in proportion to its concentration in the mixture. Although the natural preferences and aversions for these stimuli interacted somewhat with the learned taste aversions, rats responded to the presence of a CS in a mixture and did not generalize to other stimuli not containing the CS. Thus, the generalization of conditioned taste aversions provides a good measure of the behavioral similarities among gustatory stimuli.     

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 + quinine and the sucrose + 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).     

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: a tool for the neural analysis of taste-visceral associations

Several explanations may account for deficits in the ability of animals to form taste aversions following neural manipulations. These encompass impairments in conditioned stimulus (CS) and unconditioned stimulus (US) processing, conditioned response (CR) measurement, and expression, memory, and taste-visceral integration. A behavioral procedure that aids in the distinction between some of these possibilities is presented. In Experiment 1, 10 rats received seven intraoral (IO) infusions of sucrose (30 s, 0.55 ml) spaced every 5 min starting immediately after the injection of 3.0 mEq/kg of lithium chloride (LiCl). Control rats (n = 12) were treated identically except that they were injected with sodium chloride (NaCl). Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected rats systematically decreased their ingestive taste reactivity behavior over time, whereas aversive behavior increased. Control rats maintained high and stable levels of ingestive responding and demonstrated virtually no aversive behavior over the 30-min period following sodium injection. Rats were tested several days later for the presence of a conditioned taste aversion (CTA). Rats previously injected with lithium during sucrose infusions demonstrated significantly more aversive behavior than the control group, which demonstrated none. There were no differences in the level of ingestive behavior displayed by the two groups on the CTA test. Experiment 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, a difference in the ingestive behavior between the two groups was observed. In Experiment 2, naive rats were injected with either NaCl or LiCl but did not receive their first sucrose infusion until 20 min later. These rats also received sucrose infusions at 25 and 30 min postinjection. There were no differences in the taste reactivity behavior displayed by lithium- or sodium-injected rats during any of the sucrose infusions. Collectively, these findings indicate that rats dramatically change their oromotor responses to sucrose during the period following LiCl administration, provided that the infusions start immediately after injection. Furthermore, this time-related behavioral change is predominantly attributable to associative processes. This paradigm can be useful in distinguishing between neural manipulations that affect the establishment of taste-visceral associations from others that affect the animal's ability to retain such associations over the commonly employed 24-hr conditioning-test interval.     

Effects of stimulus preexposure on the generalization of conditioned taste aversions in infant rats

Generalization of a conditioned taste aversion in infant rats and how this is affected by stimulus preexposure was investigated in a series of experiments. In Experiment 1 generalization of a conditioned aversion between two tastes (sweet and salty) was found, and the effect of tastes preexposure was a reduction in generalization (Experiment 2). However, when these tastes were combined with a common taste (acid) that was less (Experiment 3) or more intense (Experiment 3b), the effect of stimulus preexposure was a stronger generalization of the conditioned aversion. In this case, a reduction on generalization was again observed by increasing the number of preexposure trials to the taste compounds (Experiment 4). In all cases the generalization levels were directly related to the effect of stimulus preexposure on the acquisition rate of conditioning. It can be concluded that, with the appropriate parameters, a reduction of generalization of a conditioned taste aversion can be obtained after taste exposure in preweanling rats.     

Taste effectiveness of some D- and L-amino acids in mice

To measure the hedonic effectiveness of some D-amino acids two-bottle preference tests were carried out on ddy mice, and subsequently conditioned taste aversion (CTA) experiments were performed to determine to what degree hedonic responses to D- and L-amino acids are related to sweet taste in mice. Mice showed preferences for D-Trp, D-His, and D-Leu over certain concentration ranges, but were behaviorally neutral to D-Ser and D-Val up to 0.1 M. The preference magnitudes for D-amino acids increased with increasing molecular weight (MW) or the bulk of the side chain. CTA experiments using 0.2 M sucrose as a conditioning stimulus and 4 D- and 6 L-amino acids as test stimuli indicated that generalization of sucrose taste became stronger with increasing MW of D-amino acids and decreasing MW of L-amino acids. There was a highly significant positive correlation between the degree of generalization of sucrose taste and the preference magnitude for D- and L-amino acids. The results indicate that preferences for D- and L-amino acids in mice result from sweet taste produced by these chemicals. Comparison of the results with the human psychophysical data reveal similarity between humans and ddy mice in taste sensitivity to amino acids.     

Age and sex effects on taste of sucrose, NaCl, citric acid and caffeine

A procedure combining forced choice discrimination with intensity scaling served to evaluate taste perception of sucrose, NaCl, citric acid and caffeine in 24 young and 24 geriatric subjects. Each group was divided equally by sex. No overall sex differences occurred for taste discrimination, and suprathreshold taste intensity scaling for sucrose and NaCl did not differ by sex or age. However, young adults generally discriminated lower concentrations of citric acid and caffeine from water blanks than did geriatric subjects. Younger subjects judged suprathreshold concentrations of caffeine significantly more intense, as did young females compared to young males; similarly, young females judged citric acid as stronger than did older males. The present results suggest that age and gender are major factors in sour and bitter perception.     

Age and sex effects on taste of sucrose, NaCl, citric acid and caffeine

A procedure combining forced choice discrimination with intensity scaling served to evaluate taste perception of sucrose, NaCl, citric acid and caffeine in 24 young and 24 geriatric subjects. Each group was divided equally by sex. No overall sex differences occurred for taste discrimination, and suprathreshold taste intensity scaling for sucrose and NaCl did not differ by sex or age. However, young adults generally discriminated lower concentrations of citric acid and caffeine from water blanks than did geriatric subjects. Younger subjects judged suprathreshold concentrations of caffeine significantly more intense, as did young females compared to young males; similarly, young females judged citric acid as stronger than did older males. The present results suggest that age and gender are major factors in sour and bitter perception.     

Latent Inhibition and Conditioning in Rat Strains Which Show Differential Prepulse Inhibition

Latent inhibition (LI) is the retardation of associative conditioning resulting from preexposure of the conditioned stimulus (CS) alone prior to conditioning. Schizophrenic patients show deficient prepulse inhibition (PPI) and, at least acutely, deficient LI as well. We recently found that Brown Norway (BN) rats show a PPI deficit compared to Wistar-Kyoto (WKY) rats. If PPI and LI depend on neural processes with common genetic substrates, then LI should be deficient in BN rats as well. Here, LI of a conditioned taste aversion was examined in BN and WKY rats. One group from each strain was preexposed to a saccharin-flavored solution (CS) the day prior to conditioning. For taste aversion conditioning, these two groups again consumed saccharin and were injected with lithium chloride (unconditioned stimulus) 10 min later. A second group from each strain was not preexposed to the CS and was treated identically during conditioning, while a third group was not conditioned (injected with sodium chloride). To test for taste aversion conditioning, saccharin was offered for 20 min/day for 3 days. Nonconditioned BN and WKY rats consumed equal amounts of saccharin on test days. In both strains, conditioned rats showed a saccharin aversion. However, conditioning was less robust in BN than in WKY rats. WKY rats showed good LI of the conditioned taste aversion in that preexposed WKY rats consumed significantly more saccharin on test days than conditioned, nonpreexposed WKY rats. Preexposed BN rats did not consume significantly more saccharin on test days than conditioned, nonpreexposed BN rats. The previously reported deficiency in PPI in the BN rats was confirmed here 1 week after the taste aversion experiment. These results suggest that BN rats show deficient LI as well as PPI and display poor associative learning, a trait also reported in schizophrenia.     

The effect of oral stimulation on human parotid salivary flow rate and alpha-amylase secretion

Unilateral parotid saliva was collected from ten subjects following oral stimulation with water as baseline, and aqueous solutions of starch (2.5, 5.0, and 10%), sucrose (0.1, 0.2, and 0.4 M) sodium chloride (0.075, 0.15, and 0.30 M), and citric acid (0.005, 0.01, and 0.02 M). Salivary flow rate increased with increasing levels of each taste stimulus. At concentrations of equal taste intensity, citric acid evoked the highest flow rate, followed by sodium chloride and sucrose, while starch, in solution, had a minimal effect. Secretion rate patterns for total protein and alpha-amylase mirrored those of flow rate. The total protein and alpha-amylase concentrations of the saliva, and specific activity of alpha-amylase, were influenced by the type but not the concentration of stimulus, with citric acid stimulation resulting in the lowest concentrations and highest specific activity. Sodium ion (Na+) concentration generally increased with increasing stimulated flow rate, while K+, Ca++, and Mg++ concentrations remained relatively constant. Subjects with lower flow rates had a more concentrated saliva than those with high flow, except for Na+ concentration. Oral stimulation resulted in similar changes in protein and alpha-amylase secretion rates for the two groups.     

Postconditioning recovery from the latent inhibition effect in conditioned taste aversion

Two experiments were conducted examining the effects of flavor (CS) preexposure on the retention of conditioned taste aversion. In Experiment 1, rats received preexposure to sucrose solution followed by a sucrose-illness pairing. The expected “latent inhibition” effect was obtained when testing occurred after a two-day but not an eleven-day training-to-test interval. Experiment 2 extended these results by employing five- and twenty-one-day training-to-test interval parameters and provided evidence that the stronger taste aversion displayed by preexposed subjects following long retention intervals is not attributable to differences in training consumption of sucrose solution. This posttraining increase in conditioned taste aversion (CTA) suggests that preexposure blocks expression of memory.