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PubMedDate not supplied

Involvement of the parafascicular nucleus of the thalamus and the cholinoreactive system of the neostriatum in controlling a food-procuring reflex in rats at different stages of learning.

A model of a Skinner box food-procuring reflex in rats was used to study the relationship between the strength applied to a pedal and disruption of the parafascicular nucleus of the thalamus and microinjections of the cholinolytic scopolamine and the cholinomimetic carbachol into the neostriatum at different stages of learning. In untrained rats at the stage of learning to press strongly on the pedal without the conditioned signal being switched on (i.e., every strong press was rewarded) showed (a) a decrease in the rate of learning to press strongly and an increase in the number of weak pedal presses after bilateral lesioning of the parafascicular nucleus of the thalamus; (b) that rats with bilateral lesions of this nucleus responded to microinjections of scopolamine into the neostriatum with increases in the number of strong presses, with no change in the number of weak pedal presses, while microinjections of carbachol decreased the number of strong and increased the number of weak presses as compared with the pre-microinjection baseline. In trained rats at the stage of recovery the reflex (i.e., strong pedal presses were reinforced only during exposure to the conditioned signal), lesioning of the parafascicular nucleus of the thalamus had the effect that the time required for recovery of the reflex became dependent on the level of pre-operative training; scopolamine microinjections into the neostriatum of rats achieving high levels of correct performances of the reflex only after surgery led to sharp degradation in performance of the reflex on the day of microinjections; microinjection of carbachol into the neostriatum of rats with low post-operative levels of performance of the reflex had no effect on this measure.

Animals↗
PubMedDate not supplied

The effects of vasopressin on memory processes in Java monkeys.

The roles of vasopressin (arginine-vasopressin) in controlling conditioned operant food-procuring reflexes and various types of memory were studied in monkeys. Types of memory were: conditioned reflex, image (Hunter-Kerr test), short-term, and long-term. The effects of vasopressin were assessed in terms of objective measures of higher nervous activity: movement and autonomous functions. These studies showed that administration of vasopressin to monkeys had different effects on simple operant food-procuring responses and memory processes. Vasopressin had greater effects on memory processes and the restoration of memory after functional derangements of higher nervous activity. The question of the formation of the two types of effect of vasopressin on higher nervous activity is discussed in relation to the evolution of mammals.

Animals↗
PubMedDate not supplied

The effects of uncontrollable, unpredictable aversive and appetitive events: similar effects warrant similar, but not identical, explanations?

Exposure to uncontrollable, unpredictable appetitive events produces a variety of cognitive debilitations and vegetative changes, as does exposure to uncontrollable, unpredictable aversive events. Similarities include impaired escape from aversive events, impaired discrimination, finicky consumption, analgesia, and body weight loss. However, in stark contrast, uncontrollable aversive stress causes reduced motor activity where as similar appetitive treatment does not; aversively induced debilitation is causally related to energy regulation, whereas the appetitively induced effects are not. Parallel mechanisms are suggested to explain these effects in terms of a revised anxiety account of the aversive effects, and a frustration account of the appetitive effects. Finally, factors likely to limit important research to resolve the many remaining issues are identified: negative presentation of animal research, political decision making, and ignorance and fear in committees which review the ethics of research.

Animals↗
PubMedDate not supplied

Discrete and contextual cue alterations eliminate the instrumental appetitive-to-aversive transfer impairment in phenytoin-treated rats.

We have shown previously that the antiepileptic phenytoin impairs transfer in an instrumental learning task (Banks et al., 1999). The present study examined the effects of contextual alterations on appetitive-to-aversive transfer performance of rats treated with either phenytoin or tang. Adult rats were tested in tone-signaled appetitive and aversive instrumental tasks, where the animal bar-pressed to obtain a food reward (sugar pellet) or to avoid shock. Rats were trained on the appetitive task for 31 days. Beginning on the twenty-first day, rats were gavaged with either phenytoin or tang twice daily. Animals were then transferred to aversive training, with the phenytoin or tang treatment continuing throughout the 25 testing days. For some animals, contextual changes were introduced as they shifted from appetitive to aversive training, while for other animals these changes were not made. Phenytoin-treated rats that were presented with changes in context as they transferred from the appetitive to the aversive task learned the avoidance response to levels substantially higher than drug-treated rats not presented with the contextual changes. These results indicate that phenytoin impairs avoidance learning following transfer from the appetitive task, and that this impairment can be eliminated by introducing changes in context at the point of transfer. In the tang-treated control subjects, on the other hand, there was no improvement in transfer learning performance associated with the changes in contextual cues. This pattern of results suggests that contextual encoding processes in rats being trained in an instrumental appetitive-to-aversive paradigm are dramatically affected by phenytoin.

Acoustic Stimulation↗
PubMedDate not supplied

The nootropic properties of ginseng saponin Rb1 are linked to effects on anxiety.

Previous studies have shown that crude ginseng extracts enhance performance on shock-motivated tasks. Whether such performance enhancements are due to memory-enhancing (nootropic) properties of ginseng, or to other non-specific effects such as an influence on anxiety has not been determined. In the present study, we evaluated both the nootropic and anxiolytic effects of the ginseng saponin Rb1. In the first experiment, 80 five-day-old male chicks received intraperitoneal injections of 0, 0.25, 2.5 or 5.0 mg/kg Rb1. Performance on a visual discrimination task was evaluated 15 minutes, 24 and 72 hours later. Acquisition of a visual discrimination task was unaffected by drug treatment, but the number of errors was significantly reduced in the 0.25 mg/kg group during retention trials completed 24 and 72 hours after injection. Animals receiving higher dosages showed trends towards enhancement initially, but demonstrated impaired performance when tested 72 hours later. Rb1 had no effect on response rates or body weight. In the second experiment, 64 five-day-old male chicks received similar injections of Rb1 (0, 0.25, 2.5 or 5.0 mg/kg) and separation distress was evaluated 15 minutes, 24 and 72 hours later. Rb1 produced a change in separation distress that depended on the dose and environmental condition under which distress was recorded. These data suggest that Rb1 can improve memory for a visual discrimination task and that the nootropic effect may be related to changes in anxiety.

Animals↗
PubMedDate not supplied

Heart rate changes accompanying jaw movement Pavlovian conditioning in rabbits: concomitant blood pressure adjustments and effects of peripheral autonomic blockade.

Two experiments were conducted to ascertain the cardiovascular accompaniments of differential Pavlovian jaw movement (JM) conditioning. The first examined the blood pressure (BP) changes that accompany the tachycardiac conditioned responses (CRs) associated with JM conditioning. The BP response in all instances consisted of a depressor response that was greater to the reinforced CS+ than CS-, although the magnitude of the CR was quite small. The second experiment determined the effects of peripheral autonomic antagonists on the cardiac accelerations associated with JM conditioning. It was found that the peripheral vagal antagonist methyl scopolamine completely abolished responses to both CS+ and CS-, whereas atenolol, a beta adrenergic antagonist, augmented the response, compared to saline control injections. The JM responses were also affected by the autonomic blockades, with minimal responding occurring in the scopolamine group but slightly more JM CRs in the atenolol group, compared to saline control animals. These results suggest that the major cardiovascular response to an appetitive stimulus, which evokes JM conditioning, consists of cardiac accelerations with the BP depressor responses playing a minimal, if any, role. Moreover, these conditioned cardiac increases appear to be due solely to the release of vagal inhibition.

Animals↗
PubMedDate not supplied

Differential mastication kinematics of the rabbit in response to food and water: implications for conditioned movement.

Analysis of naturalistic chewing patterns may provide insight into mapping the neural substrates of jaw movement control systems, including their adaptive modification during the classically conditioned jaw movement (CJM) paradigm. Here, New Zealand White rabbits were administered food and water stimuli orally to evaluate the influence of stimulus consistency on masticatory pattern. Chewing patterns were recorded via video camera and movements were analyzed by computerized image analysis. The mandibular kinematics, specifically the extent of dorsal/ventral, medial/lateral, and rostral/caudal movement, were significantly larger in food-evoked than water-evoked chewing. Water-evoked chewing frequency, however, was significantly higher than that of food-evoked movements. In light of known cortical mastication modulatory centers, our findings implicate different neural substrates for the responses to food and water stimuli in the rabbit. A detailed delineation of jaw movement patterns and circuitry is essential to characterize the neural substrates of CJM.

Animals↗
PubMedDate not supplied

The effects of estradiol on avoidance learning in ovariectomized adult rats.

The present study examined the effects of ovariectomy and subsequent estradiol replacement on learning in young adult rats using a set of instrumental avoidance paradigms differing in the nature and extent of prior experience in the learning context. Thus, one group of animals was placed directly into avoidance learning (AV). A second group was trained on an appetitive task first, and then transferred into the aversive context (AP-AV). The third group was exposed to the training context without any specific appetitive response requirement, and then required to learn an active avoidance response (Context-AV). We found that estradiol (OVX+E) impaired avoidance acquisition in all cases relative ovariectomized controls (OVX). In contrast, while avoidance learning is improved following appetitive training or context exposure in both OVX+E and OVX animals, the OVX+E animals profit to a greater extent from the appetitive or context experience than do the OVX controls. We suggest that this difference may be due to enhanced attentional processes or improved hippocampal processing of contextual factors. Thus, estradiol negatively influences simple associative avoidance learning in ovariectomized rats, but appears to promote positive transfer.

Animals↗
PubMedDate not supplied

Are there two classes of classically-conditioned responses?

It is proposed that two response classes interact during classical conditioning: (1) a specific effect which directs responding towards or away from the CS, depending upon whether a positive or negative outcome is signaled, and (2) a general, emotional effect which interferes with responding. The interaction between these two response classes can account for the varied results obtained under CER and autoshaping procedures, and must be considered in any analysis which attempts to account for the complex nature of the conditioned response.

Animals↗
PubMedDate not supplied

Personality and conditioning: factors of classical CR acquisition and extinction and their relationship to personality types.

A number of psychophysiological, cognitive and personality measures, and classical appetitive and aversive SR acquisition and extinction rates were taken from a sample of 25 male undergraduate volunteers. Principal Components Analysis of the data revealed general acquisition and extinction factors which were indexed by the psychophysiological variables. Regression analyses showed additionally that Eysenck's E-I dimension predicts both acquisition and extinction rates, and that imagery may be an important mediational variable in CR acquisition.

Adolescent↗