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

Investigated the ability of animals to form taste aversions following neural manipulations. In Exp 1, 10 rats received intraoral infusions of sucrose every 5 min starting immediately after the injection of LiCl. 12 controls were injected with NaCl. Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected Ss decreased their ingestive taste reactivity over time; aversive behavior increased. Controls maintained high levels of ingestive responding and demonstrated virtually no aversive behavior following sodium injection. Ss were tested several days later for a conditioned taste aversion (CTA). Rats previously injected with lithium demonstrated significantly more aversive behavior than controls. Exp 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, difference in the ingestive behavior was observed. In Exp 2, naive rats were injected with NaCl or LiCl but did not receive their 1st sucrose infusion for 20 min. Ss also received infusions at 25 and 30 min postinjection. There were no differences in the task reactivity behavior displayed. Rats dramatically changed their oromotor responses to sucrose during the period following LiCl administration, provided the infusions started immediately after injection, a change attributable to associative processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste agnosia following gustatory neocortex ablation: Dissociation from odor and generality across taste qualities.

In Exp I, 18 male Long-Evans hooded rats trained to avoid drinking in the presence of a compound odor (benzyl acetate) and taste (sucrose) CS lost the taste habit but retained the odor habit following gustatory neocortex (GN) ablation. Conversely, olfactory bulb ablation resulted in loss of the odor habit but retention of the taste habit. In Exp II, with 60 Ss, Ss lacking GN did not retain preoperatively instated learned aversions to a suprathreshold quinine hydrochloride (bitter) taste solution that had been employed as a CS. However, Ss with GN lesions that were virtually identical to those of the bitter-trained group retained a preoperatively learned aversion to a hydrochloric acid (sour) CS. Exp III, with 60 Ss, demonstrated that reliable agnosia for an acid CS could be produced by lesions that extended more deeply into perirhinal areas near the claustrum at the level of the GN. It is concluded that the agnosia following GN ablation is relatively specific to gustation and that agnosia for preoperatively acquired tasted aversion habits occurs for all 4 basic gustatory stimuli following anterolateral cortex ablations centered on the GN. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste reactivity analysis of 6-hydroxydopamine-induced aphagia: Implications for arousal and anhedonia hypotheses of dopamine function.

Deficits in feeding and drinking that result from 6-hydroxydopamine (6-OHDA) lesions of the mesostriatal dopamine system are often explained using either sensorimotor arousal or anhedonia hypotheses. Sensorimotor arousal hypotheses posit that dopamine systems facilitate the capacity of sensory stimuli to activate any motor output. The anhedonia hypothesis suggests that dopamine systems amplify the hedonic impact of positive reinforcers. Natural palatability-dependent ingestive and aversive actions, which are emitted by rats to tastes, provide a sensitive test that can discriminate between these hypotheses: A reduction of sensorimotor arousal should diminish the ability of tastes to elicit any actions; anhedonia should shift the balance between positive and aversive actions. To directly compare these hypotheses, taste reactivity was examined in rats made aphagic by intranigral 6-OHDA injections. Results did not support either of these predictions: Taste reactivity was essentially unchanged. The persistence of normal taste reactivity argues against both an anhedonia and a global sensorimotor arousal interpretation and provides further evidence that the capacity for hedonics can be neurologically dissociated from motivated appetitive behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of differential associative responses to novel and familiar taste stimuli in rats lacking gustatory neocortex.

24 Long-Evans hooded rats lacking gustatory neocortex and 24 normal rats were familiarized to either hydrochloric acid or quinine hydrochloride solutions during free-drinking trials. Ss were subsequently trained to avoid either the familiar or the novel taste stimulus, using a balanced design, by pairing the to-be-associated taste with ip injections of apomorphine hydrochloride. Balanced, nonpaired presentations of the other taste solution and water were also presented. Normal Ss learned to avoid the novel taste more efficiently than the familiar taste. Ss with gustatory neocortex lesions did not differentiate novel from familiar tastes. They learned aversions to both in a manner highly similar to the aversion learning of familiar tastes by the normal group. Therefore, results demonstrate that Ss lacking gustatory neocortex displayed an associative deficiency only when they were trained on novel stimuli. This suggests that gustatory neocortex lesions disrupt the conditionability of taste stimuli by reducing or eliminating responses to taste novelty. This interpretation is supported by the absence of a "neophobic" response in the lesioned rats to the first presentation of a taste stimulus. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failure of sodium- and calcium-deficient rats to acquire conditioned taste aversions to the object of their specific hunger.

Attempted to condition taste aversions to the objects of 2 mineral-specific hungers in 2 experiments with a total of 116 male Sprague-Dawley rats. Both the innate preference of adrenalectomized Ss for sodium and the learned preference of parathyroidectomized Ss for calcium were studied. None of the sodium-deficient Ss poisoned after drinking NaCl reached a taste-avoidance criterion, even after 9 pairings of salt ingestion with aversive lithium chloride injections. 6 of 11 calcium-deficient Ss did not meet the salt-avoidance criterion after 10 pairings. Nondeficient control Ss learned to avoid these salt solutions completely after an average of only 3 such pairings. Besides unmasking a surprising degree of similarity between the learned and innate specific hungers studied, results clearly demonstrate a powerful influence of physiological need on aversion conditioning. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual consequences of electrical stimulation in the gustatory system.

To investigate the role of temporal coding in the neural processing of taste, trains of electrical pulse of varying frequency were delivered to the nucleus of the solitary tract (NTS) in awake rats. The temporal patterns of these trains mimicked the temporal patterns of electrophysiological responses of single neurons to natural tastes. In Exp 1, water-deprived rats were first trained to lick water in an experimental chamber. On training days, licking water produced a sucroselike electrical pulse train in the NTS. At the end of these sessions, experimental animals were made ill by an injection of LiCl and subsequently learned to avoid licking when LiCl was paired with NTS stimulation. In Exp 2, rats refused to lick water when licking produced a quininelike pattern of NTS stimulation but licked enthusiastically when licking produced a pattern of NTS stimulation similar to the natural response to sucrose. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thalamocortical relations in taste aversion learning: II. Involvement of the medial ventrobasal thalamic complex in taste aversion learning.

Examined the involvement of the gustatory thalamic nuclei in fundamental taste reactivity, gastrointestinal reactivity, and conditioned taste aversion (CTA) learning. In Exp I, using 72 male Long-Evans rats, bilateral electrolytic lesions were produced in the medial ventrobasal thalamic complex (VBm), including the thalamic gustatory nuclei, in 1 group of Ss. For a 2nd group, at the conclusion of conditioning, lesions were produced in the anterior insular gustatory neocortex (AIGN). Results indicate that destruction of VBm thalamus attenuated taste reactivity to sucrose, citric acid, and quinine hydrochloride. Elimination of VBm thalamus markedly attenuated CTA learning. Results of neocortical lesion manipulations showed that the AIGN contributed to initial CTA learning in Ss lacking a mediodorsal-periventricular thalamus. Whether Ss lacking VBm thalamus used olfactory cues associated with drinking solutions to acquire CTAs was evaluated in Exp II, using 72 male Long-Evans rats. Results demonstrate that Ss lacking VBm thalamus and the olfactory bulbs could not acquire aversions to ingested LiCl following 8 conditioning trials. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sodium depletion enhances salt palatability in rats.

Stereotyped fixed action patterns (FAPs) elicited in rats by oral infusions of taste solutions 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. The present 2 experiments, with 5 male Sprague-Dawley rats, demonstrated that when the physiological state of the S was altered by sodium depletion, the pattern of FAPs elicited by oral infusions of 0.5 M NaCl shifted 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 1st time the Ss were made sodium deplete. A similar shift did not 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 was 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. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

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

Control of fluid palatability by exteroceptive Pavlovian signals.

Two experiments, with 15 male albino rats, investigated whether discrete auditory conditioned stimulus/stimuli (CS) that signal the availability or onset of taste unconditioned stimulus/stimuli (UCS) (sucrose, quinine) can control orofacial responses in the absence of those UCSs. In Exp I, one auditory stimulus (CS+) was paired with the delivery of a sucrose solution to the magazine floor, and another auditory stimulus (CS–) was never followed by sucrose. Following conditioning, oral infusions of water that were preceded by the CS+ were found to elicit more ingestive (sucrose-typical) orofacial responses than did water alone or water preceded by the CS–. In Exp II, the conditioned ingestive reactions to a signal for sucrose observed in Exp I again occurred, and conditioned aversive (quinine-typical) orofacial responses occurred in response to water infusions preceded by a former signal for quinine. Data suggest that perceived palatability may be influenced by Pavlovian associations involving exteroceptive CSs and illustrate the importance of supporting stimuli in modulating the effects of Pavlovian associations on behavior. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Chronic morphine treatment exaggerates the suppressive effects of sucrose and cocaine, but not lithium chloride, on saccharin intake in Sprague-Dawley rats.

Three experiments examined the effect of chronic morphine treatment on cocaine-, sucrose-, and lithium chloride (LiCl)-induced suppression of saccharin intake in Sprague-Dawley rats. All rats were either water- or food-deprived and then implanted subcutaneously with 1 morphine (75 mg) or vehicle pellet for 5 days. They were then given brief access to 0.15% saccharin and soon thereafter injected with either cocaine (10 mg/kg sc) LiCl (0.009 M, 1.33 ml/100 g body weight ip), or saline, or in Exp 2, given a 2nd access period to either a preferred 1.0 M sucrose solution ot the same 0.15% saccharin solution. There was 1 taste–drug or taste–taste paring per day for a number of days. The results showed that a history of chronic morphine treatment exaggerated the suppressive effects of a rewarding sucrose solution and cocaine but not those of the aversive agent, LiCl. These data provide further support for the reward compairison hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

ACTH and ACTH4–20 modification of neophobia and taste aversion responses in the rat.

A series of 6 experiments assessed the effects of ACTH and the ACTH analog ACTH4–20 on drinking in conditioned taste aversion and neophobic situations using a total of 168 male Sprague-Dawley rats as Ss. Both substances delayed the extinction of a conditioned taste aversion established by a single pairing of lithium chloride with milk (Exp I). However, in this situation, the ACTH parent peptide was more potent behaviorally. ACTH supressed milk consumption in Ss with no toxicosis experience (Exp II). This effect was apparently not due to the conditioning of a taste aversion (Exp III) with ACTH serving as a weak aversive UCS. Exogenous ACTH (Exp IV) or ACTH4–20 (Exp V) did not enhance neophobia; however, repeated injections of ACTH suppressed drinking. This ACTH suppression was related to the familiarity/novelty of the substance being consumed. The neophobic response to milk was not accompanied by pituitary-adrenal activation (Exp VI). Both neophobic and conditioned taste aversion situations appear to be useful for assessing peptide effects on consummatory behavior. (36 ref) (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)     

Ibotenate lesions of the hippocampus enhance latent inhibition in conditioned taste aversion and increase resistance to extinction in conditioned taste preference.

In 2 experiments, the effects of axon-sparing lesions of the hippocampus on performance in aversive and appetitive taste conditioning tasks were investigated. In Exp 1, hippocampally lesioned rats showed no impairment of conditioned taste aversion learning relative to controls, but they did display an increased sensitivity to latent inhibition (LI). In Exp 2, the same hippocampectomized rats acquired a conditioned taste preference but failed to show any evidence of extinction. The influence of the neurotoxic lesion on LI is in the opposite direction to the effect typically found following hippocampal damage induced by traditional methods. Accordingly, the data present challenges for most current theories of hippocampal function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraoral intake and taste reactivity responses elicited by sucrose and sodium chloride in chronic decerebrate rats.

Oral stimulating effects of sucrose and NaCl were assessed in chronic decerebrate and pair-fed intact control rats by measuring oral motor taste-reactivity responses (TRRs) and intraoral intake (II) volume. TRRs were videotaped during the 1st minute of the intraoral taste infusion. The infusion continued until the taste solution was rejected from the mouth, and the intake volume was computed accordingly. The number of ingestive TRRs and the volume of II consumed by pair-fed control and decerebrate rats increased with increasing sucrose concentration. Sucrose intake increased as concentration increased, then plateaued for both groups. For controls, intraoral NaCl elicited an inverted U-shaped function for both TRRs and intake. TRRs of chronic decerebrate rats varied with NaCl concentration. In contrast with controls, intake of NaCl did not differ from that of water for decerebrate rats. Data indicate that caudal brain-stem mechanisms are sufficient to control sucrose intake but not adequate for the concentration dependent intake of NaCl. Data indicate it is possible for taste-elicited oral motor responses to be dissociated from intake. Roles of taste and postingestive factors in sucrose and NaCl intake are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

THC-induced place and taste aversions in Lewis and Sprague-Dawley rats.

The hedonic properties of delta-9-tetrahydrocannabinol (THC) were assessed in place and taste conditioning paradigms in both Lewis and Sprague-Dawley rat strains. THC produced place avoidance, taste avoidance, and aversive taste reactivity responses in both strains. The Lewis strain displayed more aversive taste reactions and a stronger taste avoidance when conditioned with lower doses of THC than did the Sprague-Dawley strain of rats. THC is an anomalous drug of abuse that appears to be aversive to rats when assessed by these measures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parabrachial nucleus lesions and conditioned taste aversion: Evidence supporting an associative deficit.

Three experiments examined the conditioned taste aversion (CTA) deficit that occurs following electrolytic lesions of the parabrachial nucleus (PBN). In Exp 1, lesioned rats failed to avoid either a gustatory or an olfactory stimulus that had been paired with lithium chloride-induced toxicosis. In Exp 2, however, all rats learned a conditioned flavor preference. Finally, in Exp 3, all controls and 7 of the 12 lesioned rats learned a conditioned place aversion. Together, these results demonstrate that the disruption of CTA in lesioned rats cannot be ascribed to an inability to process either gustatory or visceral afferent information per se. Rather, the data suggest that PBN-lesioned rats are unable to form a specific association between gustatory and visceral cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

CER suppression, passive-avoidance learning, and stress-induced suppression of drinking in the Syracuse high- and low-avoidance strains of rats (Rattus norvegicus).

The Syracuse strains of Long-Evans rats were selectively bred for good (SHA) or poor (SLA) avoidance learning in a two-way shuttle box, which resulted in a phenotypic difference that is correlated with behavior patterns indicative of emotional reactivity, SLA animals showing evidence of greater emotional reactivity than SHA animals. The first three experiments examined conditioned suppression of bar pressing and compared paired and unpaired conditioned- and unconditioned-stimulus presentations to evaluate the influence of conditioning versus primary aversive stimulation on baseline responding. SLA animals acquired conditioned suppression faster than SHA animals and also showed greater suppression of baseline responding than SHA animals. In Experiment 4, SLA animals learned a passive-avoidance task faster than SHA animals. In Experiment 5, SLA animals showed greater stress-induced suppression of drinking a weak quinine solution than SHA animals. These data are consistent with the hypothesis that SLA animals are more emotionally reactive than SHA animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)