Vagotomy facilitates extinction of conditioned taste aversions in rats.

Results from 3 experiments indicate that severing the subdiaphragmatic vagus in male Sprague-Dawley rats increased the rate of extinction of learned taste aversions. In Exp I, when the illness-inducing agent was the blood-borne toxin apomorphine, vagotomized Ss tended to consume more saccharin than controls during repeated extinction tests. In Exp II, vagotomy disrupted retention and increased extinction of a preoperatively acquired saccharin aversion. Disruptions were found when the taste aversion was induced by copper sulfate, a local gastric irritant, or apomorphine. Exp III demonstrated that vagotomy did not affect retention or extinction of a shock-induced conditioned emotional response to noise. It is concluded that integrity of the vagus is not necessary for acquisition of a learned taste aversion when a blood-borne toxin is used as the illness-inducing agent. However, the vagus apparently mediates an integral portion of the CR following taste–illness acquisition. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aversion learning in 5-day-old rats: Taste–toxicosis and texture–shock associations.

Five-day-old Holtzman rats that received a single pairing of a novel saccharin flavor (NF) with lithium (Li) treatment learned to suppress ingestion of saccharin on subsequent occasions (Exp I). This NF aversion (AV) learning was inversely related to the interval (IN) between the NF experience and drug administration, with significant AVs being learned with INs of 0 and 30 min but not with INs of 60 and 90 min (Exp II). Conditioning was observed when hypertonic Li served as the UCS but not with isotonic Li or hypertonic saline injections (Exp III). AV learning in infant Ss was shown to be a result of the joint action of 2 factors—pure drug effects and the somatic pain and irritation produced by the tonicity of the injected agent. Taste AV learning was specific to the drug-paired NF, and evidence is presented suggesting that 5-day-old rats display a natural hesitancy to consume novel edibles (neophobia) (Exp IV). In Exp V, 5-day-old Ss selectively associated NF stimuli with the gastrointestinal consequences of Li injection but not with cutaneous shock and selectively associated tactile stimuli with shock but not with the gastrointestinal consequences of Li. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Punishment of saccharin drinking by amphetamine in rats and its reversal by chlordiazepoxide.

Demonstrates, in a conditioned taste-aversion paradigm, that doses of dextroamphetamine which are intravenously self-administered by rats may punish saccharin drinking. Ss were male Wistar rats. In Exp I (n = 42), single-trial, dose-related aversion was shown. Aversion was not antagonized by chlorpromazine. Exp II (n = 32) demonstrated dose-related acquisition of taste aversion with repeated administration of very low amphetamine doses. In Exp III (n = 18), drug-induced saccharin aversion was reversed by chlordiazepoxide; this action paralleled the action of chlordiazepoxide in numerous other aversive-conditioning situations. Exp IV (n = 30) ruled out the possibility that depression of saccharin drinking was due to a direct pharmacological action of the drug and not to learned saccharin avoidance. Results indicate that the reinforcing action of amphetamine depends on the response with which its effects are correlated. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ingestional aversion learning in preweanling rats.

In 4 experiments, ingestional aversions were conditioned in 12- and 15-day-old Sprague-Dawley rats by infusing a .5% solution of saccharin into the oral cavity and following this oral infusion by the injection of lithium chloride. At both ages, Ss for which the saccharin exposure was followed by lithium injection within 2–3 min drank less when the saccharin solution was again presented by oral infusion 12 hrs later; such suppressions of intake were not observed in Ss that previously received the saccharin and lithium in an unpaired fashion (Exps I and III). Ingestional aversions were also learned by 12-day-olds when a 30-min interval was introduced between saccharin exposure and lithium toxicosis but not when toxicosis was delayed by 120 min (Exp II). In contrast, 15-day-olds learned aversions with both the 30- and 120-min-delay intervals (Exp III). Despite the absence of long-delay learning in 12-day-olds, ingestional aversions conditioned at 12 days of age were retained for 2 wks (Exp IV). Results provide further evidence of the associative abilities of neonatal rats and illustrate a developmental aspect of long-delay learning. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption of conditioned taste aversion in the rat by stimulation of amygdala: A conditioning effect, not amnesia.

Conducted 2 experiments with a total of 143 male Wistar rats to determine whether the disruption of conditioned taste aversion by amygdaloid brain stimulation (BST) during conditioning could be attributed to the stimulus properties of the BST. In Exp I, Ss receiving BST (a) while drinking saccharin, (b) during the onset of LiCl toxicosis, or (c) in the interval between taste exposure and toxicosis drank significantly more saccharin solution during a 48-hr retest than implanted or unoperated controls receiving similar taste–toxicosis pairings. In contrast, Ss receiving BST during both conditioning and retention trials developed a strong conditioned aversion. Exp II confirmed that BST formed a compound with the taste of the saccharin solution. A small but significant aversion was displayed by groups exposed to BST plus taste during conditioning and to either taste alone or BST alone during the retest. Again, the group presented with BST and taste prior to and following LiCl toxicosis displayed a strong conditioned aversion. Results suggest that disruption of conditioned taste aversion with amygdaloid BST represents a conditioning effect, not amnesia. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional decortication by cortical spreading depression does not prevent forced extinction of conditioned saccharin aversion in rats.

In 2 experiments conditioned taste aversion established in Druckrey hooded rats by association of saccharin drinking with subsequent lithium chloride intoxication decreased saccharin intake to 22% of normal consumption. Force-feeding saccharin to intact and functionally decorticate trained Ss returned saccharin consumption on the next day to 62% (n = 18) and 77% (n = 19), respectively. Overtrained conditioned saccharin aversion was affected by forced extinction in a similar way (saccharin intake increased from 28% to 50% and 63%, respectively). Intact-brain Ss refused to swallow saccharin during forced feeding, while functionally decorticate Ss showed no signs of aversion; extinction was almost equal in both cases. Application of lithium chloride after forced feeding of saccharin in functionally decorticate Ss neither prevented extinction of conditioned taste aversion nor reestablished the aversion habit extinguished earlier with intact brain. It is concluded that acquisition of the conditioned taste aversion requires cortical input to a short-term memory file, whereas decorticate extinction can be induced by subcortical gustatory processing analogous to the mechanism controlling feeding behavior during the preweaning period. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned taste aversions over long delays in rats: The role of learned safety.

Tested the proposal that learned safety accounts for the delay gradient in learned taste aversions in 4 experiments. In Exp I and II, 132 female Sprague-Dawley rats drank a small quantity of a nontoxic solution toward which they had a mild aversion. It was found, in support of the learned safety concept, that the intake in a 2nd test was a function of the delay time between tests. Exp III with 72 Ss demonstrated that no additional curve of learned safety would occur when Ss had previously received extensive experience with the solution. Exp IV with 81 Ss found, however, that learned safety was not a sufficient explanation for the delay gradient in learned taste aversions by showing that the gradient still persisted even when the experimental procedure minimized the effects of learned safety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of intrahippocampal administration of colchicine on incentive contrast and on radial maze performance.

Examined the behavior of rats given intradentate injections of colchicine (COL). In Exp 1, COL-treated, artificial cerebrospinal fluid (CSF)-treated, and untreated Ss did not differ in the intake of 32% and 4% sucrose solutions, nor did they differ in degree of successive negative contrast when the 32% solution was changed to 4% sucrose. In Exp 2, the COL-treated and CSF-treated Ss did not differ in degree of suppression in the intake of a 0.15% saccharin solution when it preceded 32% sucrose in once-daily pairings (anticipatory contrast), nor did they differ in reversal performance when saccharin–sucrose and saccharin–saccharin pairings were reversed. In Exp 3, the COL-treated Ss were substantially impaired in radial-arm maze performance compared with CSF-treated controls. Results suggest that a completely functioning hippocampus is not necessary for the memory of reward quality, the comparison of rewards, the suppression of behavior when reward is decreased, the formation of associations between 2 levels of reward, and the reversal of this association, as long as these processes are reflected in consummatory behavior. Data are interpreted in terms of differences between instrumental behavior and sensory memory and/or consummatory behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversion in lean and obese rats with ventromedial hypothalamic knife cuts.

Assessed the development of a conditioned taste aversion (CTA) in 60 female Sprague-Dawley rats made hyperphagic with parasagittal knife cuts in the ventromedial hypothalamus (VMH). Ss were water deprived and presented with a .1% saccharin solution paired with injections of either LiCl or NaCl. In Exp I, VMH Ss tested at a nonobese weight level did not differ from sham-operated controls in acquisition and extinction of the CTA. In Exp II, moderately obese VMH Ss displayed a stronger CTA than did sham-operated controls as evidenced by slower extinction. A 2nd group of obese VMH Ss given an amount of LiCl equivalent to that given to the controls also displayed retarded extinction of the CTA. Results reflect an obesity-induced suppression in appetitive motivation. (29 ref) (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)     

Chronic lithium chloride infusions: Conditioned suppression of food intake and preference.

Developed a modified learned food aversion paradigm that simulated the prolonged food and illness exposure likely to characterize nutrient deficiencies or tumor growth. In this paradigm, a continuously available food was associated with a slow, continuous infusion of LiCl provided by an osmotic minipump. In Exps I and II, 68 rats were implanted with minipumps with LiCl or with empty pumps and exposed to novel or familiar diets. In Exp III, conducted with 40 Ss, the variable was prior exposure to the same diet. Significant aversions were acquired when the available diet was novel but not when it was familiar. Effects of drug infusions on daily food intake paralleled those on aversion formation. Marked, persistent suppression of food intake was seen in drug-treated Ss consuming a novel diet, but only transient declines were seen in those with a familiar diet. By separating the direct from the conditioned effects on food intake of chronic drug infusions, these studies provided strong evidence that learned food aversions can lead to anorexia. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Within-compound learning with US presentation in taste aversion.

Determined whether the presentation of a LiCl unconditioned stimulus/stimuli (UCS) disrupts within-compound learning in a taste aversion preparation, using 30 male and 32 female rats in 3 experiments. In Exp I, Ss showed stronger associations between 2 solutions presented in a compound when the compound was followed by LiCl. Exp II showed that an immediate LiCl injection produced stronger flavor–flavor association than a delayed injection. Exp III provided a comparison with Ss that did not receive the treatment to enhance consumption of salty solutions. Results indicate that the effects of Exp II depended on the treatment that altered consumption of 1 component. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversions and neophobia in rats with hippocampal lesions.

In Exp I extensive hippocampal lesions retarded, but did not prohibit, the conditioning of a strong taste aversion to physiological saline (the CS) in 16 male Holtzman albino rats when illness (the UCS) was induced by apomorphine injection 15 min following ingestion of the saline. In Exp II hippocampal lesions reduced the aversiveness of novelty in a drinking fluid for 21 thirsty Ss. It is suggested that the mild impairment of taste aversion learning in Ss with hippocampal lesions was not the result of destruction of mnemonic mechanisms that serve to span the long CS-UCS interval but rather that the reduced intensity of the aversion resulted from a lesion-altered neophobic disposition that weakened the saliency of the novel flavor CS. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Four experiments employed a taste aversion conditioning procedure appropriate for both neonatal and adult rats to investigate the ontogeny of extended retention. In Exp I, 200 outbred albino rats trained at 1, 10, 20, or 60 days of age were tested for retention of the taste aversion 25 days later. At testing, only those Ss conditioned when 20 or 60 days old demonstrated significant taste aversions. Exps II and III, with 190 Ss, established that Ss 14–25 days old and older were able to retain significant taste aversions following a 25-day retention interval. 80 younger Ss did, however, acquire and retain the aversion for several days and showed a gradual retention loss over progressively longer retention intervals (Exp IV). Findings suggest that preweanling rats demonstrate initial consolidation, storage, and retrieval of conditioned taste aversions. It is only after this initial period that retention deficits become evident. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A natural food aversion in Norway rats.

During a single 1-hr feeding test, adult male Norway rats were offered intact carcasses of adult male rodents, sacrificed by CO? asphyxiation. In Exp I, 79 Ss fed more readily on conspecifics dead 24–220 hrs than on conspecifics dead 10 min or 6 hrs. In Exp II, 22 Ss fed readily on roof rats (Rattus rattus) whether they had been dead 10 min or 24 hrs. In Exp III, 15 Ss rendered anosmic by zinc sulfate treatment fed more readily on conspecifics dead for 10 min than did 17 controls. In Exp IV, 34 Ss consumed more flesh from house mice coated with roof rat urine than from mice coated with Norway rat urine. It is concluded that Norway rats exhibit a natural aversion to feed on the intact carcasses of freshly sacrificed adult conspecifics in the sense that they are more likely to feed on other species of rodent. The aversion diminishes with the dissipation of the chemoreceptive cue(s) identifying the carcass as a conspecific. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some determinants of a natural food aversion in Norway rats.

Adult male Long-Evans rats were permitted to feed on the carcasses of adult male rodents, freshly sacrificed by CO? asphyxiation. In a 2-choice preference test (Exp I), hungry Ss were offered 1 conspecific and 1 house mouse, the pair of carcasses being either intact or skinned. 18 Ss offered intact carcasses fed on the mouse or on neither carcass, but 18 Ss offered skinned carcasses fed indiscriminately, usually on both carcasses. In Exp II, 10 hungry Ss that earlier had observed a cagemate feeding on intact conspecific carcasses fed more readily on a similar carcass during a single-choice test than did 8 controls. In Exp II, 20 food-deprived Ss (96 hrs) fed more readily and consumed more tissue from an intact conspecific carcass than did 20 nondeprived Ss. It is concluded that the aversion to feeding on the intact carcass of a freshly sacrificed adult conspecific is deprivation dependent and is mediated by chemoreceptive stimuli from the skin and/or fur. The aversion is diminished by social facilitation. (25 ref) (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)     

Effects of prior exposure on conditioned taste aversion in the rat: Androgen- and estrogen-dependent events.

Studied the effects of preexposure and gonadal hormone manipulation on the extinction of a conditioned taste aversion in 198 male Sprague-Dawley rats. In Exp I, Ss were given 1 prior exposure to sucrose at some selected time (Days 4, 2, or 1) before a 2nd exposure (Day 0) to sucrose and a LiCl injection, or they were given only a single exposure (Day 0). Under single exposure, castrated Ss extinguished the aversion faster than either testosterone-treated castrated Ss or sham-operated Ss. In Exp II, estradiol, dihydrotestosterone, and testosterone were studied by using only a Day 1 preexposure condition. The testosterone-treated group maintained the aversion for the longest period, followed by dihydrotestosterone-treated, sham, castrated, and estradiol-treated groups. In Exp III, estradiol was administered alone or in combination with 2 doses of dihydrotestosterone. Findings indicate that the outcome of behavior was dependent on the ratio of estradiol to dihydrotestosterone, with variations in this ratio resulting in fast (estrogen effect) to slow (androgen effect) rates of extinction. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phrasing cues and hierarchical organization in serial pattern learning by rats.

In Exp I, 42 female albino Sprague-Dawley rats received food quantities in a T-maze in a serial pattern. Ss learned under either no cue, temporal cue, place cue, and/or combined temporal-place cue conditions. In Exp II, 45 female albino Sprague-Dawley rats in the T-maze were trained in complex subpatterns with place cues or no cues. Exp I showed that phrasing facilitated pattern learning as long as phrasing cues were available but that Ss learned different things when different kinds of phrasing cues were used. Exp II showed that phrasing a pattern into formally complex rather than formally simple chunks produced poor learning. Overall findings demonstrate the rat's capacity to abstract and use higher-order rules in hierarchical serial patterns, especially when phrasing cues are available to facilitate the process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)