Morphine enhancement of sucrose palatability: analysis by the taste reactivity test

The ability of morphine to modify sucrose palatability was assessed by the taste reactivity test. In Experiment 1, rats were injected with morphine (0.0, 0.5, 2.0, and 10.0 mg/kg, subcutaneously), 30 min before receiving a 10-min intraoral infusion of 2% or 20% sucrose solution. A dose of 2.0 mg/kg morphine enhanced ingestive reactions elicited by both concentrations of sucrose solution. In Experiment 2, the interval between morphine pretreatment and the taste reactivity test was manipulated. Rats given 2.0 mg/kg morphine 30 or 120 min before testing displayed enhanced ingestive reactions elicited by 20% sucrose solution during the first 5 min of a 10-min test. The results support the hypothesis that morphine enhances the hedonic assessment of sucrose solution.     

Amphetamine and morphine produce a conditioned taste and place preference in the house musk shrew (Suncus murinus).

Rats have been shown to avoid consuming a flavor, but prefer a location, previously paired with amphetamine or morphine. A series of 4 experiments evaluated the hedonic properties of amphetamine and morphine in the house musk shrew (Suncus murinus), an insectivore that (unlike rats) is capable of vomiting when exposed to toxins. Unlike rats, amphetamine (20 mg/kg) and morphine (20 mg/kg) produced both a conditioned sucrose (0.3 M) and saccharin (0.1%) preference in shrews (administered intraperitoneally), when measured by both a 1-and a 2-bottle test. At the same dose, both drugs also produced a place preference in shrews. These results suggest that the potential of rewarding drugs to produce taste avoidance may vary on the basis of the ability of the species to vomit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resumption of morphine self-administration by ex-addict rats: An attempt to modify tendencies to relapse.

Studied relapse tendencies in 69 morphine-dependent male hooded rats which had learned to drink bitter solutions of the drug in preference to water. Prolonged enforced abstinence (110 days) did not prevent Ss from resuming self-administration of morphine. Since the bitter taste of morphine may have become a secondary reinforcer, an attempt was made to extinguish responding for this source of reward. Abstinence was shortened to 12 days, during which Ss were given solutions of quinine to drink. On subsequent relapse tests these Ss consistently took less morphine than controls. Ss injected with methadone during the 1st 8 days of abstinence initially consumed slightly more morphine on relapse tests than did controls, but this difference was not maintained. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context conditional flavor preferences in the rat based on fructose and maltodextrin reinforcers.

In three experiments, rats were exposed to a flavor preference procedure in which flavor A was paired with the reinforcer and flavor B presented alone in Context 1, while in Context 2 flavor A was presented alone and flavor B with the reinforcer. With fructose as the reinforcer both two- and one-bottle training procedures produced a context-dependent preference (Experiments 1 and 2). With maltodextrin as the reinforcer two-bottle training produced a context-dependent preference (Experiment 1). Following one-bottle training with maltodextrin reinforcement rats demonstrated a context-dependent preference when the conditioned stimulus (CS)- was presented with a dilute solution of the reinforcer during training (Experiment 3B) but not when the CS- was presented alone (Experiments 2 and 3A). The pattern of results with maltodextrin reinforcement suggests that there was competition between the cue flavors and the taste of the maltodextrin as predictors of the postingestive consequences of the maltodextrin reinforcer. The fact that rats were able to display context-dependent flavor preferences is consistent with the idea that learned flavor preferences rely on the sort of cue-consequence associations that underpin other forms of conditioning which produce accurate performance on biconditional tasks. The differences between fructose- and maltodextrin-based preferences are discussed in terms of configural and elemental learning processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

In 2 experiments, access to a .15% saccharin solution was followed on alternating days by access to a 32% sucrose solution and the same saccharin solution. In Exp 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. Exp 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morphine- and naltrexone-induced modification of palatability: Analysis by the taste reactivity test.

Used the taste reactivity (TR) test, a direct measure of the hedonic properties of a tastant, to assess in Sprague-Dawley rats the ability of morphine (an opiate agonist) and naltrexone (an opiate antagonist) to modify the palatability of a bitter quinine solution and a sweet sucrose solution. Morphine reduced the aversive hedonic properties of both novel and familiar quinine solution (0.05% and 0.1%) but did not modify the palatability of 20% sucrose solution. Naltrexone reduced the positive hedonic properties of sucrose solution (2% and 20%) but did not modify the palatability of 0.05% quinine solution. The pattern of results suggests that the modification of feeding produced by opiate agonists and antagonists may be mediated by a hedonic shift in the palatability of the tastant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual Learning Enhances Retrospective Revaluation of Conditioned Flavor Preferences in Rats.

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The modulating effect of the thyrotropin-releasing hormone on genetically induced mechanisms of morphine sensitivity

The influence of thyrotropin-releasing hormone (TRH) on morphine-induced analgesic and reinforced responses was studied in two inbred strains of rats, Fischer-344 (F344) and Wistar Albino Glaxo/GSto (WAG). Conditioned place preference, voluntary consumption of morphine solution and analgesic action of morphine in tail immersion test were studied. There were interstrain differences in pain sensitivity, i.e., F344 rats had longer latency of tail immersion and deeper analgesic effect of morphine (5 mg/kg, ip) than WAG rats. TRH (1 mg/kg, ip) produced a stronger analgesic effect in WAG rats, while F344 rats demonstrated only slight increase in pain threshold. Administration of TRH in combination with morphine significantly stronger potentiated the effect of the latter in WAG than in F344 rats. F344 rats preferred morphine in the two-bottle choice test and consumed relatively larger amount of morphine solution in the drinking paradigm than WAG rats. Morphine in the dose of 5 mg/kg (ip) induced place preference in both rat strains. Intraventricular administration of TRH (1 mcg) produced a slight effect of place preference only in F344 rats. Preceded by morphine, such injection reduced the effect of place preference. It is suggested that WAG and F344 rats have different sensitivity of brain structures to TRH. This is probably determined by genetic differences in dissociation of analgesic and reinforcing effects of morphine.     

Taste of sugars: Brief exposure single-stimulus behavioral method.

Used a brief exposure, single-stimulus test procedure to assess taste of sugars in 86 male Fischer rats. Ss were trained to sample the test solution immediately upon presentation. Intake was measured periodically for 10 min using fructose, glucose, or sucrose as a stimulus and water as a control. The stimulus-response functions and kinetics were different for the 3 sugars. Relative "sweetness" was predicted from the data to be sucrose > fructose > glucose. This prediction was confirmed by additional brief-exposure tests as well as by a 3-choice 24-hr test. Control experiments using a 2-choice 24-hr preference test showed that glucose was ingested preferentially. The brief exposure single-stimulus method appears to give a clearer indication of taste effectiveness than does the classical 2-choice 24-hr preference test. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste avoidance, but not aversion, learning in rats lacking gustatory cortex.

Control rats rapidly learned to avoid drinking either a sucrose solution (Exp 1) or an NaCl solution (Exp 2) when the taste was paired with illness. These rats also produced aversive reactivity to each of these solutions in a taste reactivity test. Rats that lacked gustatory cortex (GC) learned to avoid drinking sucrose and NaCl, albeit at a slower rate than control rats. GC rats failed to display aversive reactivity to these tastes. The GC rats did show normal aversive reactivity to a strong quinine HCl solution during additional tests. It is suggested that the avoidance developed by GC rats did not entail a palatability shift of the conditional stimulus as it did in control rats. This altered learning strategy may account for the consistent learning deficits found in GC rats trained to avoid tastes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parabrachial nucleus lesions block taste and attenuate flavor preference and aversion conditioning in rats.

Rats with ibotenic acid lesions of the parabrachial nucleus (PBN) failed to learn a taste aversion induced by lithium chloride (LiCl) toxicosis. The same rats also did not learn to prefer a taste that was paired with intragastric (IG) carbohydrate infusions during 22 hr/day trials. The PBN-lesioned rats did learn to prefer a flavor (odor?+?taste) paired with the IG carbohydrate infusions over a different flavor paired with IG water. The PBN-lesioned rats also learned to avoid a flavor paired with IG LiCl infusions during 22 hr/day trials. The flavor preference and aversion, however, were less pronounced than those displayed by control rats. These data indicate that the PBN is essential for forming orosensory-viscerosensory associations when taste is the primary cue but is less critical when more complex flavor cues are available. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Taste reactivity responses elicited by cocaine-, phencyclidine-, and methamphetamine-paired sucrose solutions": Correction to Parker.

Reports an error in "Taste reactivity responses elicited by cocaine-, phencyclidine-, and methamphetamine-paired sucrose solutions" by Linda A. Parker (Behavioral Neuroscience, 1993[Feb], Vol 107[1], 118-129). Table 1, on page 119, contains two errors. In the first section, the dose/route for the agent nicotine should read as follows: 1.2-2.0 mg/kg sc. In the second section, the dose/route for the agent morphine should read as follows: 2-80 mg/kg ip. Also, on page 121, paragraph 3, line 14, the parenthetical information after 40 mg/kg cocaine should read (40C; 2 × 20 mg/kg/3 cc). (The following abstract of the original article appeared in record 1993-24959-001.) The nature of flavor–drug associations produced by a range of doses of the reinforcing agents cocaine (5, 10, 15, 20, or 40 mg/kg, sc), phencyclidine (0.5, 2, 10, or 20 mg/kg, sc), and methamphetamine (2, 5, or 10 mg/kg, ip) were assessed by the taste reactivity (TR) test and the conditioned taste avoidance (CTA) test. Even at the highest doses tested, none of the agents produced aversive TR responding. At doses that produced equivalent-strength CTA, lithium did establish aversive TR responding. Results provide evidence that drugs that serve as reinforcers in other paradigms produce conditioned flavor avoidance that is not motivated by a conditioned dislike for the flavor. (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)     

Flavor preferences conditioned by intragastric nutrient infusions in rats fed chow or a cafeteria diet

Numerous studies demonstrate that chow-fed rats learn to prefer flavors that are associated with the postingestive effects of nutrients. The rats> limited dietary experience (i.e. only lab chow) may have facilitated preference learning because of the novelty of the training stimuli. This possibility was investigated by comparing nutrient conditioning in rats fed chow or a varied "cafeteria" diet. Rats in Experiment 1 were trained during alternate sessions (30 min/day) to drink two different flavors paired with concurrent intragastric infusions of 16% Polycose or water. Both diet groups displayed similarly strong preferences (89%) for and increased acceptance of the Polycose-paired flavor. A more demanding learning task was used in Experiment 2: new flavors were paired with delayed (15 min) infusions of Polycose or water. The chow and cafeteria groups both showed reduced, but comparable (78%, 77%) preferences for the Polycose-paired flavor. In Experiment 3, new flavors were paired with concurrent infusions of 7.1% corn oil or water. Again, the cafeteria and chow groups developed similar preferences for the nutrient-paired flavor (85%, 78%). Also, both groups preferred the Polycose-paired flavor of Experiment 1 to the oil-paired flavor of Experiment 3 (76%, 78%). These results indicate that dietary variety does not interfere with nutrient-conditioned flavor preference learning in rats.     

Nutritive expectancies mediate cholecystokinin's suppression-of-intake effect.

In previous studies of cholecystokinin's (CCK's) effect on consumption, physical features (e.g., taste, texture, and odor) of test meals were confounded with the nutritive expectancies elicited by those features. To separately assess the role of these two factors in supporting CCK's suppression-of-intake effect, we varied the caloric expectancies elicited by a flavored test solution, while holding constant its actual caloric density, as well as all other unconditioned stimulus features. On alternate days for a 12-day period, hungry rats drank grape or orange Kool-Aid (noncaloric) mixed with a caloric 5% ethanol solution; on the other days, they drank the alternate flavor mixed with plain water. In a subsequent choice test between the flavored solutions without ethanol, the ethanol-associated flavor (Ef) was preferred over the water-associated flavor (Wf). Two days later, the rats were injected with either cholecystokinin octapeptide (CCK-8; ip, 2 μg/kg) or isotonic saline, and then given access to their Ef or their Wf for 1 hr. Consumption of the Ef was supressed by CCK-8; intake of the Wf was unaffected. These results suggest that CCK-8's effectiveness in suppressing intake of a test meal may be treated not to the unconditioned stimulus features of that meal but to the nutritive expectations elicited by those features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sucrose-water preference reversal in the water-deprived rat.

Exposed 4 water-deprived male albino Carworth rats to each of 3 preference conditions. When given a 15-min preference test between a 7.4% sucrose solution and water, Ss ingested 81-91% of their total fluid intake from the sucrose bottle. When given a choice between 1 lick of water and 1 lick of the sucrose solution, Ss consistently preferred water. To determine if this water preference was related to dehydration, Ss were allowed to drink water immediately before the 1-lick preference test. In general, water preference was inversely proportional to amount of pretest drinking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hunger enhances the expression of calorie- but not taste-mediated conditioned flavor preferences.

Compared ethanol-mediated flavor preferences to preferences mediated by saccharin, which is sweet but noncaloric, and sucrose, which is both sweet and caloric in 4 experiments, using 74 Long-Evans rats. Ss learned to associate grape or orange flavor conditioned stimulus/stimuli (CS) with (1) ethanol or saccharin solution or (2) either the other unconditioned stimulus/stimuli (UCS) or plain tap water. They were then given 2-bottle choice tests between the flavor CSs apart from the UCSs. Flavors associated with 5% ethanol were preferred over saccharin-paired and water-paired flavors by sated Ss, and food deprivation during the choice test enhanced this preference. Flavors associated with 8% sucrose were preferred over water-paired flavors, and this preference was also enhanced by food deprivation. Flavors associated with 0.028% or 0.25% saccharin were preferred over flavors paired with water. In all cases, calorie-mediated preferences, at their highest levels, were stronger than taste-mediated preferences. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavor preexposure and "learned safety."

Conducted 3 experiments with a total of 131 male Wistar rats. Results indicate that (a) a single preexposure to a distinctive flavor resulted in both a retardation of aversion learning (if the flavor was later paired with toxicosis) and a preference for this flavor (if the flavor was not paired with toxicosis); (b) preexposure-induced preferences were retained over a 24-day period and were not attributable to thirst reduction consequent upon ingestion; and (c) Ss evidenced a preference for a preexposed solution by subsequently ingesting relatively great amounts of this solution when it was the only fluid available (as well as by choosing it over an alternative, simultaneously available solution). Results are discussed in terms of a "learned safety" interpretation of the deleterious effects of flavor preexposure on flavor-aversion learning. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

LSD produces place preference and flavor avoidance but does not produce flavor aversion in rats.

The hedonic properties of lysergic acid diethylamide (LSD) were assessed using the place conditioning, taste reactivity, and taste avoidance tests. LSD produced a conditioned place preference, but only at the highest dose tested (0.2 mg/kg). A single preexposure to the conditioning chamber (latent inhibition) prevented the establishment of a place preference. When paired with sucrose, doses of 0.05 to 0.2 mg/kg of LSD produced taste avoidance, but no dose of LSD produced an aversion to the taste as assessed by the taste reactivity test. These results suggest that LSD, like other rewarding drugs, produces taste avoidance by a mechanism other than that produced by emetic drugs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)