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)     

Activation and odor conditioning of suckling behavior in 3-day-old albino rats.

Investigated circumstances under which a novel odor could elicit nipple attachment behavior in 3-day-old Sprague-Dawley rats. In Exp I, Ss suckled washed nipples scented with citral (a lemon odor) only if they either had received tactile stimulation (by stroking with a soft brush) or had been administered amphetamine in the presence of citral prior to the suckling test. Ss stimulated in citral's absence or only exposed to citral without stimulation failed to suckle such nipples. In Exp II, Ss stimulated in a benzaldehyde (an almond odor) ambience suckled washed nipples scented with benzaldehyde but not those with citral scent. The opposite held for those stimulated in a citral-rich environment. The stimulus conditions that supported this conditioning were investigated in Exp III. Simultaneously increasing citral concentration and raising ambient temperature markedly attenuated the phenomenon. Exp IV demonstrated that not all classes of stimulation produced conditioning. Caffeine, in a wide range of doses, did not allow citral to elicit suckling on washed nipples. Findings are discussed within a framework of higher-order conditioning and may provide a mechanism by which naturally occurring stimuli come to elicit the species- and age-typical behavior of suckling. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned stimulus intensity and acquired alimentary aversions in the rat.

Studied 188 male Long-Evans hooded rats. Three groups were made ill following the ingestion of 1 of 3 intensities of salt taste and then were tested several times for aversions to each of the 3 intensities after this single training trial, yielding a 3 by 3 factorial design. ANOVA from this design revealed a significant positive effect on degree of aversion of both training intensity and testing intensity, and a significant interaction between these 2 intensity variables. The interaction was further analyzed into a component implying a multiplicative relationship between training intensity and testing intensity in determining strength of aversion, and into a component interpreted as indicating a decrement of the aversion when tested with intensities other than the training intensity. Results suggest a lawfulness of stimulus–response relationships comparable to those found in studies employing more typical conditioned responses. Previous conditioning studies, however, have demonstrated only the effect of conditioned stimulus intensity on "performance" (testing intensity effect), not on "learning" (training intensity effect). (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversions and drugs of abuse: A reinterpretation.

A new hypothesis (and supporting data) provides a solution to the 25-yr-old paradox whereby positively reinforcing drugs of abuse also support a conditioned taste aversion (CTA). The results show that unlike LiCl-induced CTAs, morphine- and cocaine-induced suppression of conditioned stimulus (CS) intake depends on the rewarding properties of the gustatory CS. This finding argues against the long-standing CTA interpretation in favor of a new reward comparison account. That is, rats decrease intake of a gustatory CS following taste–drug pairings because the value of the CS is outweighed by that of a highly reinforcing psychoactive drug. Suppression of CS intake, then, is a consequence of the well-documented positive reinforcing, rather than the hypothetical aversive, properties of drugs of abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned taste aversions are not readily disrupted by external excitation.

Thirsty male rats were given saccharin water followed by delayed illness. During the delay, some of the rats were exposed to events designed to stimulate their external systems (i.e., the system that processes external events such as auditory and tactile stimulation). Access to females, mild footshocks, and pain from hypertonic saline injections did not interfere with either the acquisition or extinction of a taste aversion. In fact, when administered intraperitoneally, the hypertonic saline slightly increased the strength of the aversion. Exposure to heat, which changed both skin temperature and core temperature, slightly attenuated the formation of the aversion. Overall, these results emphasize the independence of the internal system (i.e., the system that deals with internal events such as taste, illness, and core temperature) and the external system. Furthermore, the associating of events related to the internal system is not readily interfered with by events related to the external system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned vocalization in rats.

Examined 2 crucial variables which might explain inconsistent results of attempts to condition vocalization in the rat: mobility of the S during conditioning and variability of the intertrial interval (ITI). 12 male Long-Evans rats were tested in 4 conditions of mobility-immobility, and fixed and variable ITI. Results support the importance of immobilizing the S, but not of varying the ITI during conditioning. It is suggested that vocal behavior in the rat may be conditioned only when no competing species-specific defense reaction (e.g., freezing) is available to the S. (31 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)     

Dietary thiamin supply during gestation effects thiamin status of lactating rats and their suckling offspring

A paired-comparison study of manual and automated (PAPNET) screenings of cervico-vaginal smears (Pap tests) was conducted to determine whether primary PAPNET screening was a reliable alternative to manual screening. A series of 5,037 consecutive Pap tests was first screened by the manual method. Next they were scanned by the PAPNET system, the DAT tapes were reviewed, and using a nonspecific triage protocol, abnormal tests were identified for limited, manual rescreening. False-negative rates (FNR) for each method were calculated and analyzed for due cause. By manual and PAPNET screening, respectively, there were 436 (8.6%) and 250 (4.9%) abnormal results. Manual screening missed 18 abnormals (5 SIL) and PAPNET 202 (7 SIL). The primary, manual screenings relating to the PAPNET false-negative tests were reviewed and revised to normal in 30. Based on the changes in the other 172 tests, cellular features ostensibly missed by the PAPNET system were listed to form part of a specific triage protocol, and were used to scrutinize the companion 172 DAT tapes: 150 tapes were abnormal. The manual FNR for an abnormal (SIL) result was 4% and (8.8%), respectively. Equivalent FNR pre- and postreviews for the PAPNET system were 44.6% (10.6%) and 5.2% (1.3%), respectively. This study discovered that the evaluation of some cell features in monitor-based, video images was the most important factor limiting the application of the PAPNET system as a primary screener. When governed by a specific triage protocol incorporating these features, primary PAPNET screening has the potential to equal the laboratory threshold of manual screening and be a better detector of SIL.     

Reversal of conditioned aversions in normal and micrencephalic rats.

When administered to pregnant rats, the drug methylazoxymethanol acetate (MAMA) causes a dose-dependent reduction in the mass of the cerebral cortex of the offspring. In the present experiment, it was found that MAMA-produced micrencephalic female hooded Long-Evans rats developed conditioned flavor aversions as easily as 10 normal controls. Both normal and micrencephalic Ss reversed a relative preference between 2 flavors easily and repeatedly. Results are discussed in relation to various contemporary theories of conditioned aversions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned and unconditioned fear inhibition in rats.

Conducted 3 experiments with a total of 74 male Fisher344 rats in which tone stimuli suppressed avoidance responding despite the fact that they had never been administered to the Ss previously. These same stimuli attenuated the conditioned emotional response suppression of operant responding for water reinforcement. The stimuli thus appear to have unconditioned fear inhibitory properties. These unconditioned effects were compared with conditioned ones. It is suggested that results of some conditioning procedures (e.g., extinction below zero) may depend upon the unconditioned properties of the stimuli used as conditioned stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned flavor aversions to familiar tap water in rats: An adjustment with implications for aversion therapy treatment of alcoholism and obesity.

Notes that conditioned flavor aversions, readily established in rats by pairing a novel palatable flavor with radiation-induced or drug-induced illness, are highly efficient adjustments with implications for the treatment of alcoholism and obesity. Recent experiments show that such aversion acquisition is diminished by preconditioning familiarity with the conditioned stimulus (CS) flavor. However, these studies involved single pairings of the target flavor with postingestional illness. In the present experiment with Sprague-Dawley-derived male rats, multiple conditioning trials and discrimination training were combined to produce a marked aversion to a highly familiar and relatively bland substance, plain tap water. This conditioned water aversion demonstrates the transient nature of the CS familiarity effect, thus weakening any contention that preconditioning exposure to target flavors will necessarily render aversion therapy for alcoholism or obesity ineffective. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Self-stimulation in 7- and 10-day-old rats.

It has been shown that the infant rat exhibits learned behaviors characteristic of the adult. With a modified self-stimulation paradigm, the present study explored whether 7- and 10-day-old Long-Evans rat pups could learn a discriminated operant to obtain direct electrical stimulation in neural sites that support self-stimulation in adults. By nudging 1 of 2 response manipulanda, at 2 ages (7 and 10 days) and temperatures (22 and 35°C), Ss self-stimulated with electrodes implanted in a variety of forebrain sites, including the prefrontal cortex, bed nucleus of the stria terminalis, medial nucleus of the amygdala, and the medial forebrain bundle. The only temperature-sensitive site might be the nucleus accumbens, which was positive only at the higher temperature in 10-day-olds. Results indicate that several forebrain sites demonstrate rewarding properties of stimulation in the preweanling rat pup. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned aversions to copulatory behaviors in male rats.

Used LiCl for an aversive effect on copulatory behavior in adult experienced and inexperienced male hooded rats (Exp I) and in inexperienced adult male Holtzman rats (Exp II). When males received an injection of LiCl immediately after an encounter with an estrous female, the vigor of subsequent copulatory responding was initially unaffected. After 5–20 such pairings, however, males displayed an aversion to copulatory behaviors; they ceased to copulate entirely. These aversions persisted when Ss were tested in a novel environment and extinguished after 4 nonreinforced trials. This multiple-trial adaptation of the conditioned taste aversion paradigm provides a new approach to the aversive control of sexual behavior. (15 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)     

Conditioned opioid release in ten-day-old rats.

Ten-day-old rats, for whom an orange scent predicted morphine injections at 5 days of age, exhibited a marked preference for orange that was fully naltrexone reversible. Moreover, such rats, when smelling orange during a heat-escape task, exhibited a higher pain threshold than control rats. Together, these findings suggest that the orange odor in conditioned rats caused a release of endogenous opioids that both sustained choice behavior and modulated pain systems. (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)     

Conditioned insulin secretion and meal feeding in rats.

Previous researchers have reported that rats placed upon a feeding regimen such that they receive only 2 hrs of food/day (meal-fed rats) develop hyperinsulinemia at the time of the day associated with feeding, even in the absence of food. Controls fed ad lib show no such response. In the 3 experiments reported here, the 74 meal-fed Charles River rats had elevated insulin levels at only the specific time of the day associated with feeding, and the increment of insulin at that time could be eliminated with atropine. The 58 free-feeding controls, on the other hand, always had higher insulin levels than the meal-fed rats, did not have an elevation of insulin at the time of the day that the meal-fed rats normally ate, and had insulin values that were unaffected by atropine. Further experimentation showed that hyperinsulinemia could become associated with arbitrary stimuli always associated with eating for meal-fed rats. It is concluded that the hyperinsulinemia of meal-fed rats associated with their feeding time is a learned response. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Conditioned physiological changes associated with learned aversions to tastes paired with thiamine deficiency in the rat.

Describes an experiment with 72 male Sprague-Dawley rats. Thiamine deficiency and recovery from deficiency were paired with distinctively flavored drinking solutions in a procedure previously shown to produce learned aversions and/or preferences for tastes. Data suggest that tastes paired with deficiency elicited the symptoms of deficiency, while tastes paired with recovery elicited responses seen in recovery. Findings are discussed within the framework of a classical conditioning model of learned aversions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned odor potentiation of startle in rats.

An odor previously paired with shock was shown to be an effective stimulus for potentiating the startle response in rats; (Experiments 1 and 2). This effect required more than 1 odor-shock pairing (Experiment 3), was relatively long lasting (Experiment 4), and was specific to the odor previously paired with shock (Experiment 5). The implications of these findings for the startle probe procedure and for neural models of learning and memory based on results obtained with that procedure are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)