Shift In Palatability Research Articles

Conditioned Sucrose Aversions Produced by Naloxone-Precipitated Withdrawal From Acutely Administered Morphine

The aversive properties of acute naloxone-precipitated morphine withdrawal were examined in the taste reactivity paradigm. Acute naloxone-precipitated withdrawal paired with sucrose solution established conditioned active rejection of the sucrose solution. Active rejection of sucrose was observed when naloxone was administered both 1 h and 22 h after morphine. When the stimulus properties of morphine were present during the conditioning trial, the conditioned sucrose aversion was only expressed when the rats were tested in the same drug state in which they had learned the aversion. However, when the stimulus properties of morphine were not present during conditioning, the aversion was expressed in the absence of the morphine state. The results suggest that palatability shifts can be conditioned to sucrose paired with acute morphine withdrawal.

Pimozide Does Not Shift Palatability: Separation of Anhedonia from Sensorimotor Suppression by Taste Reactivity

PECIÑA, S., K. C. BERRIDGE AND L. A. PARKER. Pimozide does not shift palatability: separation of anhedonia from sensorimotor suppression by taste reactivity. PHARMACOL BIOCHEM BEHAV 58(3) 801–811, 1997.—Several “taste reactivity” studies of dopamine and reward have concluded that pimozide suppresses the hedonic reaction patterns normally elicited by sucrose but enhances aversive reaction patterns elicited by quinine. However, other taste reactivity studies have failed to find hedonic/aversive shifts in reaction patterns after dopamine antagonists or dopamine lesions. The divergent conclusions have come from two different laboratories. To resolve the controversy regarding dopamine blockade and palatability, the present study joined the two laboratories to investigate the effect of pimozide on taste reactivity patterns elicited by sucrose and quinine. The results replicated many (but not all) of the earlier findings and identified procedural factors responsible for different outcomes. Overall, the results provide evidence for sensorimotor effects of pimozide on taste reactivity but not for a hedonic shift in palatability. Pimozide suppressed both hedonic and aversive reaction patterns in a gradual sensorimotor fashion when the eliciting taste stimulus was repeated or continued for several minutes. The general suppression typically did not alter the initial reaction to a taste but emerged only after an oral infusion of sucrose or quinine continued for several minutes or trials. Aversive reactions were never enhanced. The balance between hedonic and aversive reaction patterns was not shifted by pimozide. We conclude that pimozide produces a sensorimotor impairment of taste reactivity patterns but does not shift taste palatability toward anhedonia or aversion.

Oestradiol-induced taste avoidance is the result of a conditioned palatability shift.

Taste avoidances were conditioned in male rats by pairing ingestion of a novel sucrose (0.3 M solution) taste with injections of 17 beta oestradiol (100 micrograms kg-1, s.c.). Following conditioning and prior to a two-bottle choice test (sucrose vs water), taste reactivity responses to three 30 s intraoral sucrose infusions were quantified. A robust conditioned shift in palatability, consisting of reduced ingestive and increased aversive taste reactivity responses, was obtained in the oestradiol group but not the vehicle control group. This conditioned palatability shift was also reflected in subsequent strong avoidance of the sucrose solution in the two-bottle choice test. The findings that oestradiol can condition taste aversions and shift food preferences support a role for oestrogens in the production of anorexia.

Area postrema mediates the formation of rapid, conditioned palatability shifts in lithium-treated rats.

The rapid acquisition and subsequent retention of lithium-induced conditioned changes in taste reactivity responses to sucrose were examined in rats with the area postrema (AP) either ablated or intact. On 2 conditioning days, a series of brief intraoral sucrose infusions was paired with the effects of LiCl or NaCl injections. Repeated associations of the sucrose taste with the effects of lithium significantly reduced ingestive responses and increased aversive responses only in the AP-intact group. AP-ablated rats treated with LiCl and rats injected with NaCl displayed an ingestive pattern of responses. Only the AP-intact rats, previously injected with LiCl, subsequently displayed evidence of a conditioned taste aversion. We conclude that toxin activation of the AP is required to produce the conditioned shift in taste reactivity responses and subsequent expression of a taste aversion in rats treated with lithium.

Area postrema mediates the formation of rapid, conditioned palatability shifts in lithium-treated rats.

The rapid acquisition and subsequent retention of lithium-induced conditioned changes in taste reactivity responses to sucrose were examined in rats with the area postrema (AP) either ablated or intact. On 2 conditioning days, a series of brief intraoral sucrose infusions was paired with the effects of LiCl or NaCl injections. Repeated associations of the sucrose taste with the effects of lithium significantly reduced ingestive responses and increased aversive responses only in the AP-intact group. AP-ablated rats treated with LiCl and rats injected with NaCl displayed an ingestive pattern of responses. Only the AP-intact rats, previously injected with LiCl, subsequently displayed evidence of a conditioned taste aversion. We conclude that toxin activation of the AP is required to produce the conditioned shift in taste reactivity responses and subsequent expression of a taste aversion in rats treated with lithium.

Taste Reactivity in High Alcohol Drinking and Low Alcohol Drinking Rats

High alcohol drinking (HAD) and low alcohol drinking (LAD) rats were tested, in three exposures, for taste reactivity to five concentrations of alcohol (5%, 10%, 20%, 30%, and 40%, v/v), water, and one concentration each of sucrose and quinine. Of the three reactivity exposures, one was done before a 3-week period of continuous access to water and 10% alcohol, the second test was done immediately after the consumption period, and the final reactivity test was done after 1 month of alcohol abstinence. The results showed that the groups did not differ in reactivity on the initial test. After the consumption tests (when the HAD rats consumed significantly more alcohol than the LAD rats), differences in reactivity were found: HAD rats produced significantly more ingestive responses (which promote consumption) and significantly fewer aversive responses (which facilitate fluid rejection) than LAD rats. These differences were maintained even after 1 month of alcohol abstinence. The present data replicate an earlier experiment with alcohol-preferring (P) rats and alcohol-non-preferring (NP) rats, and indicate that the selective breeding process does not produce differences in the innate perception of the taste of alcohol. However, after experience with drinking alcohol, rats selectively bred for high alcohol consumption exhibit a palatability shift reflected by high ingestive responding and little or no aversive responding. Such a shift would clearly contribute to the maintenance of high levels of alcohol consumption.

Toxin-induced conditioned changes in taste reactivity and the role of the chemosensitive area postrema

Conditioned taste avoidances (CTAs) are an important component of behavioral regulation of ingestion. In the laboratory CTAs can be produced by pairing a novel taste stimulus with the physiological feedback produced by a toxin, such as lithium. Such toxins putatively activate a chemosensitive brainstem structure, the area postrema, which ultimately results in the production of a CTA. The present review describes a series of studies which examined conditioned changes in taste reactivity responses (TRRs) when a novel intraoral sucrose taste was paired with the effects of an intraperitoneal (IP) injection of LiCl, and the role of the area postrema in the formation of conditioned palatability shifts. It was first of all necessary to examine the effects of area postrema ablations on TRRs to a range of intraoral sucrose and quinine stimulus intensities. In the first study area postrema lesioned rats exhibited concentration dependent changes in TRRs to these taste stimuli that were very similar to those exhibited by sham lesioned rats. The second study demonstrated that 30 s intraoral infusions of sucrose (0.3 M), presented at 5 or 10 min intervals following an IP injection of LiCl (3.0 meq), resulted in conditioned changes in TRRs. These were characterized by orderly, gradual reductions in ingestive responses and increases in aversive responses. Finally, when area postrema lesioned rats (Study 3) were subjected to this conditioning procedure (brief sucrose presentations paired with the effects of LiCl) no evidence for conditioned or unconditioned changes in TRRs to sucrose were obtained. Lesioned rats injected with LiCl behaved similarly to sham lesioned rats injected with NaCl. These series of studies provide evidence indicating that the chemosensitive area postrema mediates the formation of conditioned palatability shifts induced by treatment with a toxin such as lithium.

Aversive taste reactivity: Reactivity to quinine predicts aversive reactivity to lithium-paired sucrose solution

The ability of a rat's reactivity to the aversive taste properties of quinine to predict its' reactivity to the aversive taste properties of a lithium-paired sucrose solution were assessed. In phase 1, all rats were intraorally infused with 0.05% quinine solution over a 2-min taste reactivity (TR) test. On the basis of their composite aversive reactions, rats were divided into high reactors (HiQ) and low reactors (LoQ). In phase 2, rats were given three TR conditioning/testing trials in which they received a 2-min intraoral infusion of 0.5 M sucrose solution immediately followed by an IP injection of either 127.2 mg/kg lithium chloride or physiological saline. Among rats conditioned with lithium during phase 2, the phase-1 quinine HiQs displayed more aversive reactions than did the phase-1 quinine LoQs. This suggests that reactivity to the aversive properties of quinine may predict the strength of conditioned palatability shifts to a lithium-paired sucrose solution.

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

We 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 an hedonic shift in the palatability of the tastant.

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

Control rats rapidly learned to avoid drinking either a sucrose solution (Experiment 1) or a NaCl solution (Experiment 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.

Apomorphine-induced flavor-drug associations: A dose-response analysis by the taste reactivity test and the conditioned taste avoidance test

Apomorphine is a positively reinforcing drug at low to moderate doses, but appears to lose its reinforcing properties at higher doses. In Experiment 1, across a range of doses (0.5–15.0 mg/kg, intraperitoneally), apomorphine produced a CTA over 5 conditioning/testing trials which was not dose-dependent by a single bottle test. The rejection taste reactivity responses of chin rubbing and gaping, however, only occured at the highest dose of apomorphine (15 mg/kg). In Experiment 2, a CTA test which was designed to more effectively discriminate among the different drug dose conditions indicated that the doses of 2.5, 7.5 and 15 mg/kg of apormophine produce CTAs of equivalent strength. Our results support the contention that CTAs produced by positively reinforcing drugs are not accompanied by a palatability shift.

Palatability shift of a salt-associated incentive during sodium depletion.

Previous studies of natural palatability-sensitive reactions, elicited from rats by tastes, have indicated that the taste of concentrated NaCl becomes more palatable during states of body sodium depletion. A training procedure based upon "sensory preconditioning" or "irrelevant incentive" designs was used here to establish gustatory conditioned labels (quinine or citric acid) for either NaCl or fructose while rats were in a normal physiological state. Experiment 1 replicated demonstrations by others that gustatory conditioned labels for salt can attract and act as independent incentives during the salt appetite induced by sodium depletion. Experiment 2 used the taste reactivity measure to show that the enhanced palatability of the taste of NaCl transfers to produce enhanced palatability of the taste of the isolated conditioned label for salt in a state-dependent fashion. These results offer further support for the proposition that conditioned incentives not only predict hedonic events to follow, but themselves become attributed with the hedonic properties of their reinforcers.

A comparison of avoidance and rejection responses elicited by conditionally and unconditionally aversive tasting solutions

The patterns of taste avoidance responses and taste reactivity responses elicited by either lithium-paired sucrose solution or 0.05% quinine solution were compared. In Experiment 1, rats showed equivalent avoidance of CS + sucrose which had been paired with LiCl on one occasion as they did of 0.05% quinine solution, even though the quinine was rejected in the taste reactivity test much more vigorously than was the lithium-paired sucrose. In Experiment 2, a similar relationship between the development of the avoidance response and the rejection responses was maintained over four conditioning/testing trials. The occurrence of the avoidance response preceded the occurrence of rejection responses. In fact, after two sucrose-lithium pairings, the rats demonstrated stronger avoidance of the CS + sucrose solution, but demonstrated stronger rejection of the quinine solution. The results suggest that a palatability shift accompanies, but is not the only factor which motivates, a lithium-based conditioned taste avoidance.

Sodium depletion enhances salt palatability in rats.

Sterotyped fixed action patterns (FAPs) are elicited in rats by oral infusions of taste solutions. These taste-elicited FAPs can be classified as either ingestive or aversive. They reflect the palatability of the taste and can be modified by learning and by the physiological state of the animal. These studies demonstrated that when the physiological state of the rat is altered by sodium depletion, the pattern of FAPs elicited by oral infusions of 0.5 M NaCl shifts from a mixture of ingestive and aversive components (while sodium replete) to exclusively ingestive ones (while sodium deplete). This shift in taste reactivity occurred the first time the rats were made sodium deplete. A similar shift was not observed to accompany infusions of 0.01 M HCl, a taste solution that also elicited mixed ingestive and aversive FAPs. This result suggests that the shift in response to NaCl is not due to a general change in ingestive bias or to a general taste deficit. On the basis of the change in FAPs, it is concluded that the palatability of highly concentrated salt solutions increases in sodium-deplete rats. Such a shift in salt palatability may be instrumental in directing the appetitive behavior of the animal.

Quality of acquired responses to tastes by Rattus norvegicus depends on type of associated discomfort.

Rats were trained to avoid a sugar solution through pairing with LiCl toxicosis (upper gastrointestinal tract discomfort), shock (peripheral pain), or high levels of lactose (lower gastrointestinal tract discomfort). Among animals matched for strength of avoidance of the sugar solution, only the LiCl group showed orofacial responses (e.g., gaping) indicative of distaste; the other groups continued to show positive orofacial responses to the sugar solution. These results, in conjunction with recent results on humans, are interpreted to represent a distinction between food rejection based primarily on unpalatability (distaste) and food rejection based primarily on anticipated negative consequences of ingestion (danger). The results also support the hypothesis that upper gastrointestinal distress (most probably nausea) plays a special role in negative palatability shifts (acquired distastes). These results have implications for the understanding of predispositions in learning and suggest important differences in the quality (readout) of different types of associations. Prior research, by relying on intake measures alone, was insensitive to the differences revealed here by monitoring a wider range of responses.

Responses to palatability shifts: Effects of varying the retention level

Nondeprived rats were given a 1-h exposure to a sodium-saccharin solution for 28 consecutive days. A temporary shift to tap water then occurred for all Ss. The brief timeout (tap water) led to a positive contrast effect. Lengthy exposure to tap water (30 days) resulted in the possible forgetting of the comparison solution (sacc) or perhaps the response to that solution.