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PubMed1990

Discriminative properties of morphine that modulate associations between tastes and lithium chloride.

Wistar rats learned to withhold consumption of a target solution when morphine preceded presentation of the target solution and lithium chloride (LiCl) and to consume the same target solution when saline preceded the presentation of the solution. After this serial feature discrimination training, morphine did not block the formation of a Pavlovian association between saccharin and LiCl but did suppress consumption of familiar tap water. After Pavlovian conditioning, morphine blocked the formation of an association between saccharin and LiCl but did not suppress consumption of a familiar tap water solution. The roles of morphine and saline can be interchanged. It appears that the morphine discriminative stimulus is calling up a representation of neither the conditioned stimulus nor the unconditional stimulus alone, but rather a modified representation of some aspect of their association.

Animals↗
PubMed1990

The role of response-contingent incentives in lithium chloride-mediated suppression of an operant response.

Three experiments investigated what role a novel incentive plays in the development of operant response suppression mediated by lithium chloride. In all experiments animals were trained to press two levers under concurrent schedules of reinforcement. In Experiment 1 responding on one lever delivered a familiar incentive (food pellets), whereas responding on an alternative lever delivered a novel incentive (sucrose solution) prior to lithium chloride injections. If lithium was administered immediately after the instrumental session, the action associated with the novel, but not with the familiar, incentive was suppressed. By comparison, in a control group for which responding on both levers led to the familiar incentive, both actions were suppressed. Experiment 2 examined whether the novelty, rather than the sensory properties, of the incentive is crucial for observing performance suppression. It was found that animals familiarized with the "target" incentive were insensitive to aversion conditioning by lithium, in that there was no difference in response rates between the action that delivered the familiar incentive from that which earned the "target". In contrast, if animals were unfamiliar with the "target" incentive at the time of aversion conditioning, they suppressed responding on the lever that was associated with the novel incentive but did not suppress responding on the lever associated with the familiar incentive. Experiment 3 investigated the mechanism underlying instrumental performance suppression. After the completion of concurrent lever press training, novel sucrose was introduced in conjunction with the pellets for responding on one lever; responding on the other lever continued to deliver only familiar pellets. Lithium injections were then administered either immediately following the sessions or several hours after the sessions. It was found that the rate of responding on the lever associated with the contingent delivery of sucrose was suppressed below that of the pellet-alone action. By comparison, if lithium injections were administered several hours following the session, an elevation in responding on the sucrose-plus-pellet lever was observed. The outcomes of all three experiments demonstrate not only that the novelty of an incentive is important in obtaining performance suppression, but also that a novel incentive can punish instrumental responding if it has been associated with toxicosis.

Animals↗
PubMed1990

Overshadowing of a context aversion by a novel incentive in operant conditioning.

Two experiments examined the processes underlying the suppression of instrumental behaviours by lithium in rats, as reported by Meachum (1988 and this issue). Experiment 1 examined whether presenting a novel sucrose solution prior to lithium chloride administration would overshadow aversion learning to either the stimuli of the operant chamber or to familiar food pellets. After lever pressing had been established, and in the absence of responding, animals received free deliveries of a novel sucrose solution, familiar food pellets, or both, or they were exposed to only the cues of the operant chamber, prior to lithium injections. Lever pressing for food pellets was then assessed. It was found that the animals receiving the novel sucrose, either alone or with the familiar food pellets, pressed more for pellets than either the group receiving only food pellets or the group exposed to only the context. In addition, there was no appreciable difference in the response rates between the context-only group and the group that received the familiar food pellets. These outcomes were interpreted in terms of the novel sucrose overshadowing aversion learning to the context. Experiment 2 investigated whether in fact aversive contextual conditioning could be obtained using the present parameters. This was accomplished by directly manipulating the contexts. In this experiment animals were trained to lever press in two distinctive contexts. Subsequently, one context was paired with the novel sucrose, and the second was experienced in the absence of reinforcement prior to toxicosis. During a subsequent non-reinforced test it was found that responding in the context paired with the novel sucrose was considerably higher than responding in the context that was experienced alone. These findings stand in contrast to the taste-mediated contextual potentiation observed when a consumatory response is used to assess aversive contextual conditioning.

Animals↗
PubMed1990

A change of context can enhance performance of an aversive but not of an appetitive conditioned response.

In four experiments rats received pairings of one auditory CS and mild shock in one context and of a second auditory CS and shock in a second context. When tested with one of these CSs in the context in which it had never been experienced, they consistently showed enhanced levels of suppression. In one of these experiments, suppression was measured over 15-sec intervals throughout a 90-sec long CS. A change of context resulted in an increased level of suppression at all points throughout the CS, a finding which does not encourage the belief that it was due to an increase in unconditioned suppression at the onset of the CS. Another experiment provided equally little support for an alternative account in terms of increased arousal. The results therefore suggest that a change of context can increase the level of conditioned suppression elicited by a CS paired with mild shock. Two final experiments employing the same CSs and contexts, however, found no evidence that a change of context had any effect at all on the performance of an appetitively conditioned response.

Animals↗
PubMed1987

Capsaicin and its effects on olfaction and trigeminal chemoreception.

Capsaicin injections severely reduced or eliminated nasal trigeminal responses to 3 odorants (Experiment 1). However, capsaicin treated animals exhibited no deficits in locating buried food, in odor avoidance learning, or in operant odor detection and discrimination (Experiments 2 and 3). In addition, capsaicin desensitization did not affect responsiveness to salty or sour, but may have raised rejection thresholds for bitter (Experiment 4). Finally, while desensitized animals rejected menthol solution, they consumed relatively more than controls, suggesting that capsaicin may have menthol sensitivity. The present results suggest that substance P-containing fibers mediate trigeminal responsiveness to odorants and irritants but that the loss of this responsiveness does not appreciably affect smell or taste, per se.

Animals↗
PubMed1989

Transfer of negative occasion setting and conditioned inhibition across conditioned and unconditioned stimuli.

The transfer of negative occasion setting and conditioned inhibition across conditioned stimuli (CSs) and unconditioned stimuli (USs) was examined in four experiments that used Pavlovian appetitive feature negative discrimination training procedures with rats. After training with simultaneous compounds (A+, XA-), X inhibited conditioned responding (CRs) elicited by other CSs and CRs supported by other appetitive USs that had not been involved in discrimination training. After training with serial compounds (A+, X----A-), X's power to set the occasion for nonresponding transferred across CSs and USs only if those events had also been involved in serial feature negative discrimination training. The results supported the suggestion that the acquisition of negative occasion setting involves the representation of individual events in a higher order memory system, separate from that involved in simple association, and that negative occasion setters act only on events that are represented in that system.

Animals↗
PubMed1986

Conditioned aversions and their memories in 5-day-old rats during suckling.

Association learning during suckling was investigated. Five-day-old rats equipped with tongue cannulae placed either 2 mm rostral or 4-6 mm caudal to the intermolar eminence received sweet or salty solutions while suckling. This ingestion was followed by lithium chloride toxicosis. Pups with anterior cannulae took in considerably less fluid than control pups when tested 5 or 16 days later. A series of control groups demonstrated that this acquired aversion was associative in nature. Pups with posterior cannulae did not form the association. The failure of 5-day-old rats with posterior cannulae to form associations while suckling is not due to the prevention of conditioning by the act of suckling per se. Rather, the failure rests in the fluid's not reaching anterior taste receptors when injected into the posterior oropharynx, where the nipple normally empties its contents. These findings are discussed in terms of the transfer of information obtained during suckling prior to weaning, to feeding and drinking during and after weaning.

Animals↗
PubMed1987

Activation of the opioid and nonopioid analgesic systems: evidence for a memory hypothesis and against the coulometric hypothesis.

It has been suggested that the magnitude and form of hypoalgesia elicited by an aversive event can be predicted from its coulometric product (Intensity X Duration). According to this hypothesis, small products elicit opioid hypoalgesia, and large products elicit nonopioid hypoalgesia. This suggests that increasing the duration of an aversive event should heighten the nonopioid hypoalgesia. Contrary to this prediction, in Experiment 1 I found that increasing the duration of a mild shock attenuated the nonopioid hypoalgesia. In Experiment 2 I tested another implication of the coulometric hypothesis, namely, that mild shocks that have the same coulometric product should elicit equivalent hypoalgesia. The results did not support this prediction. We discuss how these findings are consistent with an alternative theory, the "working memory hypothesis." According to this theory, the representation of an aversive event in working memory elicits hypoalgesia. In Experiment 3 a novel prediction of this theory was tested, namely, that displacing the representation of intense shock from working memory, by following the intense shock with a weak shock "distractor", should attenuate hypoalgesia. The results support this prediction. I conclude by discussing the relation of this work to other findings in the analgesia literature.

Animals↗
PubMedDate not supplied

Neurobehavioral and biochemical response to manganese and selenium exposure in rats.

Aiming to extend previous findings, male Wistar rats were treated per os for 13 weeks with manganese chloride in two doses: 300 mg/kg body weight (group I) and 20 mg/kg b.w. (II), the former was associated (III) with a microdose (1 ppm) of natrium selenite. The findings show an impairment of active avoidance learning in group III, a decrease of swimming performance and histological lesions in several brain areas (both especially in group III), changes of the aggressive behavior and decreases in the brain tissue of superoxide dismutase activity (I & II) and of lipid peroxidation (in all groups).

Animals↗
PubMed1988

Context-US learning in Aplysia californica.

Two experiments explored learning about the relation between an unconditioned stimulus (US) and the context in which that US was delivered in Aplysia californica. Subjects were exposed to 2 different contexts. They received a series of moderate electric shock USs in one context but not in the other. Experiment 1 revealed that the context-shock pairings were sufficient to establish an association between that context and the shock. That association was demonstrated by the ability of the reinforced context to enhance a defensive reflex and to reduce learning about a conditioned stimulus (CS) that was subsequently paired with the shock US. Experiment 2 provided evidence that the context-US association could be extinguished by simple nonreinforced exposure to the reinforced context. These results show that context conditioning is not unique to vertebrate learning. We argue that this learning is difficult to accommodate within current contiguity-based neuronal models of learning.

Animals↗
PubMed1987

Effects of vasopressin on the brain lipid metabolism during learning and retention of conditioned avoidance behaviour.

Intracerebral vasopressin pretreatment impairs acquisition and consolidation, but delays extinction of conditioned avoidance behaviour. The latter effect of the peptide is associated with a pronounced suppression of the incorporation of labelled precursor in total lipids of the hippocampus. Results suggest that memory-improving effects of vasopressin are probably related to alterations of the brain lipid metabolism.

Animals↗
PubMed1987

Associative effects of US preexposure: modulation of conditioned responding by an excitatory training context.

In two experiments we examined factors that contribute to retarded emergence of conditioned responding to a conditioned stimulus (CS) trained in a context in which unsignaled unconditioned stimuli (USs) had previously been administered. In both experiments water-deprived rats were used in a conditioned lick suppression task to measure the conditioned response elicitation potential of the CS and the training context. From Experiment 1 we determined that nonreinforced exposure to the excitatory context after US preexposure and prior to CS-US pairings in that context eliminated the conditioned response deficit observed on a subsequent test of the CS. The recovery from the US preexposure deficit was nearly as great in animals that received nonreinforced exposure to the excitatory training context after the CS-US pairings but prior to the ultimate test of the CS. From Experiment 2 we determined that the recovery induced by contextual deflation after CS training was specific to deflation of the context in which the CS was trained as opposed to another excitatory context. In total, these experiments suggest that context-US associations partially mask the expression of a learned CS-US association. These results are discussed in terms of recent models of conditioned response generation.

Animals↗
PubMedDate not supplied

Comparison of behavioral teratogenic effects of ethanol and n-propanol administered by inhalation to rats.

Despite extensive testing of ethanol, there has been little research on the reproductive effects of other alcohols. We investigated the behavioral teratogenicity of inhalation exposures to ethanol and n-propanol. Groups of 18 male (approximately 450 g) and 15 pregnant female Sprague-Dawley rats were exposed 7 hours/day for six weeks or throughout gestation, respectively, to 16 000, 10 000, or 0 ppm ethanol or to 7 000, 35 000, or 0 ppm n-propanol. Pregnant females exposed to 7 000 ppm n-propanol, but not to ethanol, showed reduced weight gain, and female offspring also had reduced weight gain through three weeks of age; there was also slight teratogenicity observed at this concentration. Exposed males were mated with unexposed females; fertility was reduced in males exposed to 7 000 ppm n-propanol (two viable litters from 17 matings), but there were no differences from controls in maternal weight gain, feed intake, or water consumption in any other groups. In both maternally- and paternally-exposed groups, litters were culled to four pups of each sex and fostered to untreated females. One female and one male pup per litter were administered tests of neuromotor coordination (ascent on wire mesh screen, rotorod), activity levels (open field, running wheel), or learning ability (avoidance, operant conditioning), but no significant differences from controls were found with either alcohol, despite the reduction in maternal and female offspring body weight and minimal teratogenicity with 7 000 ppm n-propanol. Calculations for predicting blood ethanol levels with inhalation exposure are also presented.

Animals↗
PubMed1985

Uptake, distribution and behavioral effects of inhalation exposure to manganese (MnO2) in the adult mouse.

Adult male mice were exposed either to sublethal levels of MnO2 dust or filtered air (control group) 7 hours/day, 5 days/week for 16 to 32 weeks. Following a 16 week initial exposure period, randomly selected samples (8 animals) from both the control and Mn-exposed groups were observed for behavioral performance (ambulations and rearings in the open-field, "hole-in-board" explorations, rotarod) and learning (passive avoidance) and tissue Mn levels were determined via atomic absorption spectrometry. Exposure continued for the remaining animals and the sampling procedure was repeated biweekly for an additional 8 time points. At week 32, Mn exposure was terminated. However, biweekly testing of the remaining animals continued for an additional 3 time points. Mn-exposed animals had significantly higher blood, liver, kidney, lung, cerebrum, cerebellum plus brainstem, and testis Mn levels than control animals. With the exception of the liver, these levels declined with increasing exposure time. No histopathologic effects attributable to Mn-exposure were observed. However, significant overall effects on growth and behavior were obtained. Specifically, Mn-exposed subjects weighed more, executed more rearings in the open-field, and tended to exhibit longer latencies to enter the open-field. When the post-exposure data were analyzed separately, no significant effects were obtained. While no general relationship was obtained between tissue Mn levels and behavior, selected behavioral measures did correlate with tissue Mn levels. Animals exposed via feeding to comparable Mn levels across the same length of exposure employed in the inhalation study did not demonstrate any significant behavioral alterations.

Air Pollutants↗
PubMed1985

Time, space and value.

The ability of animals to associate stimuli depends on whether the stimuli are processed by the cognitive system or the affective system. Historically, a distinction was made between "thinking" and "feeling" by the empirical philosophers of the Renaissance. Recent evidence indicates that cognition and affect can be fruitfully applied to animal research. When animals are required to search an external environment for hidden food baits, they display an objective mastery of time and space as if they have acquired a "cognitive map" of the test area. Tests of an animal's ability to span the time between two external events yield intervals which can best be measured in seconds or fractions thereof. When animals consume a food, the affective value of that food is adjusted according to its utility in the internal milieu. If the food is nutritious, visceral feedback raises the preference value of the food. If nausea ensues, the taste becomes disgusting. Tests of an animal's ability to span the time between eating and nausea yield intervals which can best be described in hours or fractions thereof. Cognitive and affective processes are qualitatively distinct and subserved by different neural systems, yet they are both essential for associative learning. We offer a theoretical scheme designed to weld the two components into a single unitary sequence.

Affect↗