Biomedical subjects

J Feldon

Publications and source records attributed to J Feldon.

At least 163 records · Page 9Linked to original sources

PubMed1987

The abolition of the partial reinforcement extinction effect (PREE) by amphetamine: disruption of control by nonreinforcement.

Two groups of rats were trained to run in a straight alley. The continuously reinforced (CRF) group received a food reward on every trial. The partially reinforced (PRF) group was rewarded on a quasi-random 50% schedule. d-Amphetamine 1 mg/kg was administered to PRF animals in acquisition in a 2 X 2 design, i.e., drug-no drug on reinforced trials and drug-no drug on nonreinforced trials. In four CRF groups, the drug was administered in the same sequence as in the PRF groups. Following acquisition, all animals were given 4 days of CRF retraining and tested in extinction. No drug was given in retraining and extinction. The PREE, i.e., increased resistance exhibited by PRF animals as compared to CRF animals, was obtained in groups which received placebo on all acquisition trials or amphetamine on rewarded trials and placebo on nonrewarded trials. The PREE was abolished when amphetamine was administered throughout the acquisition trials or on nonrewarded trials, irrespective of drug treatment on rewarded trials.

Animals↗

PubMed1986

The effects of prenatal chlordiazepoxide administration on avoidance behavior and benzodiazepine receptor density in adult albino rats.

Adult male and female offspring of rats injected daily with 10 mg/kg chlordiazepoxide during their pregnancy exhibited a facilitated acquisition of a two-way active avoidance response. Benzodiazepine receptor assays carried out on cortex and cerebral samples taken from experimental and control female rats showed a significant decrease in the density of benzodiazepine receptors, without changes in receptor affinity.

Animals↗

PubMed1986

The effects of clonidine on the partial reinforcement extinction effect (PREE).

Clonidine has been reported to exert anti-anxiety effects in animals and man similar to those of benzodiazepines. The present experiment examined the effects of clonidine administration on the partial reinforcement extinction effect (PREE) which is known to be sensitive to benzodiazepine action. Two groups of rats were trained to run in a straight alley. The continuously reinforced (CRF) group received food reward on every trial. The partially reinforced (PRF) group was rewarded on a quasi-random 50% schedule. All animals were then tested in extinction. Clonidine 50 micrograms/kg was administered in a 2 X 2 design, i.e., drug-no drug in acquisition and drug-no drug in extinction. The PREE, i.e., increased resistance to extinction exhibited by PRF animals as compared to CRF animals, was obtained in animals that received saline in acquisition, independently of drug treatment in extinction, as well as in animals that received clonidine in both acquisition and extinction, but not in animals that received clonidine in acquisition alone. The administration of clonidine in extinction alone increased resistance to extinction in both the CRF and PRF animals. The increase in resistance to extinction, typically obtained with benzodiazepine treatment, indicates that clonidine exerts anxiolytic effects, supporting the involvement of the noradrenergic system in anxiety. However, clonidine did not fully reproduce the effects of benzodiazepines on the PREE, suggesting that the two classes of drugs may act via different noradrenergic mechanisms.

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PubMed1986

Reversal and nonreversal shifts under amphetamine.

Rats were trained in a Y maze on a two-choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Half of the animals were then switched to reversal, where the reinforcement contingencies of the original training were reversed, and the other half were switched to nonreversal, in which they learned a simultaneous right-left discrimination. Nonreversal was acquired faster than reversal in saline injected animals. The administration of 1 mg/kg d-amphetamine did not affect the acquisition of the initial brightness discrimination and of nonreversal. In contrast, the drug facilitated dramatically reversal learning. The results indicate that amphetamine enhances the attention to, or the associability of, the discriminative stimuli, leading to rapid learning to these stimuli under changed contingencies of reinforcement.

Animals↗

PubMed1986

The effects of intrahippocampal ibotenate on resistance to extinction after continuous or partial reinforcement.

Intracerebral injections of ibotenate were used to produce, in rats, extensive cell loss in the hippocampus and dentate gyrus (complete hippocampal, CH), in the CH plus subiculum (SUB + CH), or in the subiculum plus entorhinal cortex (SUB + EC). These rats and sham-operated controls were trained to run in a straight alley for food reward delivered on a continuous (CR) or partial (PR) reinforcement schedule. In controls PR training gave rise to the well-known partial reinforcement extinction effect (PREE), i.e., greater resistance to extinction than that observed in CR-trained animals. Previous work had shown that large aspiration lesions of the hippocampal formation eliminate the PREE by increasing resistance to extinction in CR-trained animals and decreasing resistance to extinction in PR-trained animals. In the present experiments the PREE survived CH lesions, which increased resistance to extinction in both CR and PR training conditions; these effects were observed in the start and run (but not goal) sections of the alley. In contrast, subicular cell loss (in both SUB + CH and SUB + EC groups) abolished the PREE (but in the goal section only) by increasing resistance to extinction in the CR condition and decreasing resistance to extinction in the PR condition. In addition, some of the effects of PR training on start and run speeds during acquisition were altered by the CH and SUB + CH lesions. These results confirm previous data showing that the hippocampal formation plays a role in mediating the behavioural effects of PR training, but require modification of the model previously proposed to account for these data.

Animals↗

PubMed1986

Amphetamine does not affect the partial punishment effect (PPE).

The effects of amphetamine on the partial punishment effect (PPE) at one trial per day, were examined. Two groups of animals were trained to run in a straight alley. The continuously reinforced (CRF) group received food reward on every trial. The partially punished (PP) group received food reward on every trial but in addition, received footshocks of a gradually increasing intensity in the goal box on a random 50% of the trials. In the test stage, all animals received both food and footshock on each trial. dl-Amphetamine 1.5 mg/kg was administered in a 2 X 2 design, i.e. drug-no drug in training and drug-no drug in test. The partially punished animals exhibited increased persitence in running to the goal box during test, and this "partial punishment effect" was unaffected by amphetamine.

Amphetamine↗

PubMed1986

Effects of prenatal stress on vulnerability to stress in prepubertal and adult rats.

This study investigated the hypotheses that unpredictable prenatal stress has effects on the offspring, similar to those induced by perinatal administration of glucocorticoids and increases the vulnerability to stressful situations at adulthood. Rats were exposed to random noise and light stress throughout pregnancy. Offspring were tested for the development of spontaneous alternation behavior (SA) and at adulthood, their response to novel or aversive situations, open field, extinction and punishment following acquisition of an appetitive response and two-way active avoidance, were assessed. In prenatally stressed rats, the development of SA was significantly delayed. On repeated exposure to an open field they were less active; control rats had elevated plasma corticosterone (CCS) on days 2 and 4 of open field exposure, while prenatally stressed rats had significantly raised plasma CCS after each exposure (days 1-8). Furthermore, punishment-induced suppression of an appetitive response was enhanced. Acquisition of active avoidance was faciliated in female but reduced in male prenatally stressed offspring. It is suggested that random prenatal noise and light stress may cause impairment of development of hippocampal function which lasts into adulthood. This impairment is manifested as an increase in vulnerability and a decrease in habituation to stressful stimuli.

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PubMed1986

Simultaneous brightness discrimination and reversal: the effects of amphetamine administration in the two stages.

Rats were trained in a Y-maze on a two-choice simultaneous brightness discrimination with light as S+ and dark as S- (Stage 1), and were then switched to reversal, where the reinforcement contingencies of the original training were reversed (Stage 2). d-Amphetamine, 1 mg/kg, was administered in a 2 X 2 design, i.e., drug-no drug in Stage 1 and drug-no drug in Stage 2. The administration of the drug in Stage 1 improved the acquisition of the initial brightness discrimination and facilitated reversal learning independently of the drug administered in Stage 2. In addition, the administration of the drug in Stage 2 only improved performance towards the end of reversal training. The results indicate that amphetamine enhances the attention to, or the associability of, the discriminative stimuli, leading to a rapid learning to these stimuli under changed contingencies of reinforcement.

Animals↗

PubMed1986

Amphetamine potentiation of anti-conflict action of chlordiazepoxide.

A modified Geller-Seifter paradigm was employed to test in male albino rats the effects of subthreshold doses of amphetamine and chlordiazepoxide (CDP), administered separately or in combination, on shock induced suppression of food-reinforced lever-pressing. MK-801, a newly synthesized sympathomimetic with anxiolytic and anticonvulsant properties, was also tested. dl-Amphetamine in doses of 0.1, 0.2, 0.3, and 1.0 mg/kg had no anxiolytic nor anxiogenic effects, but at 1.0 mg/kg it increased non-conflict responding. CDP in doses of 0.1, 0.2, and 0.4 mg/kg had no significant effect on conflict and non-conflict responding. CDP in the dose of 0.8 mg/kg tended to increase conflict responding. Coadministration of amphetamine (0.2 mg/kg) and CDP (0.4 mg/kg) had a significant anti-conflict effect. MK-801 at 50 micrograms/kg and 100 micrograms/kg caused a significant increase in non-conflict responding. MK-801 at 50 micrograms/kg exerted also a significant anti-conflict effect. The disinhibitory effects of amphetamine coadministered with CDP were discussed in terms of a possible enhanced noradrenergic or dopaminergic activity and their interaction with GABA neurotransmission at GABA-benzodiazepine coupled sites.

Amphetamine↗

PubMed1986

Amphetamine and the overtraining reversal effect.

Rats were trained in a Y-maze on a two choice simultaneous brightness discrimination with light as S+ and dark as S- (position irrelevant). Animals in the Mastery group were trained until they reached criterion and were then switched to reversal, where the reinforcement contingencies of the original training were reversed. Animals in the Overtraining group received a further 110 trials before being switched to reversal. The administration of 1 mg/kg d-amphetamine facilitated dramatically reversal learning in Mastery group. Overtraining improved reversal in saline injected animals and slowed down reversal in amphetamine-treated animals. The drug also facilitated the acquisition of the initial brightness discrimination.

Amphetamine↗

PubMed1985

Prenatal chlordiazepoxide effects on metrazol seizures and benzodiazepine receptors density in adult albino rats.

Adult offsprings of rats treated with daily injection of chlordiazepoxide (10 mg/kg, i.p.) during pregnancy showed a significant decrease in benzodiazepine receptors in the cortex and the cerebellum without apparent changes in receptor affinity. A reduced susceptibility to metrazol-induced epileptogenesis paralleled this change. These findings are discussed in relation to the differential vulnerability of various types of benzodiazepine receptors.

Animals↗

PubMed1985

The effects of early handling on latent inhibition in male and female rats.

Latent inhibition (LI) is a behavioral paradigm in which repeated exposure to stimuli not followed by meaningful consequences renders these stimuli ineffective for subsequent learning. The development of LI is considered to reflect learning not to attend to, ignore, or tune out irrelevant stimuli. The present study investigated the differences in the development of LI between handled and nonhandled males and females. Infantile handled (Days 1-22) and nonhandled, male and female Wistar rats were tested in maturity in the LI paradigm. The LI procedure consisted of two stages: pre-exposure, where animals received 60 presentations of the to-be-conditioned stimulus (tone) and test, where the animals acquired a two-way active avoidance response with the tone serving as the warning signal. Handled animals reached higher percentage of avoidance responses as compared with nonhandled animals. Latent inhibition was obtained in both the handled and the nonhandled females, but only the handled males showed the LI effect. Nonhandled males failed to develop LI. The results indicate that the effects of handling are evident in learning tasks that do not involve motivational-emotional variables, i.e., learning to ignore irrelevant stimuli; handling differentially affects males and females, with a much greater impact on males and the nonhandling procedure has significant deleterious consequences on adult behavior.

Animals↗

PubMed1985

Resistance to extinction after schedules of partial delay or partial reinforcement in rats with hippocampal lesions.

Two experimental procedures were employed to establish the reason why hippocampal lesions apparently block the development of tolerance for aversive events in partial reinforcement experiments, but do not do so in partial punishment experiments. Rats were trained to run in a straight alley following hippocampal lesions (HC), cortical control lesions (CC) or sham operations (SO), and resistance to extinction was assessed following differing acquisition conditions. In Experiment 1 a 4-8 min inter-trial interval (ITI) was used. Either every acquisition trial was rewarded immediately (Continuous Reinforcement, CR), or only a randomly selected half of the trials were immediately rewarded, the reward being delayed for thirty seconds on the other trials (Partial Delay, PD). This delay procedure produced increased resistance to extinction in rats in all lesion groups. In Experiment 2 the ITI was reduced to a few seconds, and rats were trained either on a CR schedule, or on a schedule in which only half the trials were rewarded (Partial Reinforcement, PR). This form of partial reinforcement procedure also produced increased resistance to extinction in rats in all lesion groups. It thus appears that hippocampal lesions only prevent the development of resistance to aversive events when the interval between aversive and subsequent appetitive events exceeds some minimum value.

Animals↗

PubMed1985

Fornix-fimbria section and the partial reinforcement extinction effect.

Rats were trained to run in an alley for food reward given on every trial (continuous reinforcement, CR) or on a random 50% of trials (partial reinforcement, PR) and were then extinguished. Sham-operated controls showed the normal partial reinforcement extinction effect (PREE), in that PR-trained animals were significantly more resistant to extinction than CR-trained animals. The PREE was significantly reduced by lesions of the fornix-fimbria. The reduction was largely a consequence of a reduction in resistance to extinction in PR-trained rats with fimbria-fornix lesions. These results are discussed in the light of other experiments that have studied disconnections in the septo-hippocampal system.

Animals↗

PubMed1985

The abolition of the partial reinforcement extinction effect (PREE) by amphetamine.

The effects of amphetamine administration on the partial reinforcement extinction effect (PREE) at one trial a day, were examined. Two groups of rats were trained to run in a straight alley. The continuously reinforced (CRF) group received food reward on every trial. The partially reinforced (PRF) group was rewarded on a quasirandom 50% schedule. All animals were then tested in extinction. dl-Amphetamine 1.5 mg/kg was administered in a 2 X 2 design, i.e., drug-no drug in acquisition and drug-no drug in extinction. The PREE, i.e., increased resistance to extinction exhibited by PRF animals as compared to CRF animals, was obtained in animals that received saline in acquisition, independently of drug treatment in extinction. In contrast, amphetamine administered in acquisition abolished the PREE irrespective of drug treatment in extinction. In addition, amphetamine administered in extinction alone increased resistance to extinction in PRF animals.

Amphetamine↗

PubMed1985

The effects of delaying reward on choice preference in rats with hippocampal or selective septal lesions.

Two experiments are reported in which rats were trained to choose one of two goal arms in a Y-maze, for water reward. In one arm, the rats always received water (the continuously reinforced-CRF-arm). In the other arm the rats only sometimes received water (the partially reinforced-PRF-arm). During the critical test phase in both experiments, we delayed the reward in the CRF arm only by 10 s. Experiment 1 tested intact rats given saline injections, or injections of chlordiazepoxide hydrochloride (Librium, 5 mg/kg), and rats with hippocampal or cortical control lesions. When reward was immediate in both arms all rats preferred the CRF arm. Once reward was delayed, the rats with hippocampal lesions switched their preference to the PRF arm, while the rats in the other treatment groups did not. Experiment 2 tested rats with medial septal lesions, lateral septal lesions or control operations in the same way. The rats with medial septal lesions, and to a lesser extent those with lateral septal lesions, switched their preference to the PRF arm when compared to the sham-operated controls. We conclude that damage to the hippocampus or its afferent pathway from the septum increases rats' sensitivity to temporal discontiguities between the outcome of a response and its emission.

Animals↗

PubMed1984

Abolition of the expression but not the acquisition of latent inhibition by chronic amphetamine in rats.

The animal amphetamine model of schizophrenia has been based primarily on stereotyped behavior. The present study sought to demonstrate an amphetamine-induced deficit in attentional processes. To this end, the effects of acute and chronic (14 days) 1.5 mg/kg dl-amphetamine administration on the ability of rats to ignore irrelevant stimuli were examined using the paradigm of latent inhibition (LI) in a conditioned emotional response (CER) procedure. The procedure consisted of three stages: pre-exposure, in which the to-be-conditioned stimulus, tone, was presented without being followed by reinforcement; acquisition, in which the pre-exposed tone was paired with shock; and test, in which LI was indexed by animals' suppression of licking during tone presentation. Experiment 1 showed that chronic but not acute treatment abolished LI. Experiment 2 showed that animals receiving chronic amphetamine pretreatment but pre-exposed and conditioned without the drug, exhibited normal LI. In Experiment 3, animals which received chronic amphetamine pretreatment and were pre-exposed under the drug but conditioned without it, also showed normal LI. The implications of these results for the animal amphetamine model of schizophrenia are discussed.

Amphetamine↗

PubMed1984

Long term effects of chronic chlordiazepoxide (CDP) administration.

Three experiments were carried out to test the long-term behavioral effects of 12 days administration of CDP (5 mg/kg/day) in rats. In the first two experiments, 4 weeks after the end of drug administration (CDP or placebo), and after 2 weeks of training to run a straight alley for food reward, animals were tested in extinction, i.e., following omission of reward (Expt. 1) or with punishment, i.e., 0.3 mA electric shock in addition to the food reward (Expt. 2). Drug-treated animals showed significantly increased resistance to extinction and to punishment compared with controls. In the third experiment, 10 weeks after drug administration, animals were exposed to 60 s of intense noise to induce audiogenic seizures. The convulsant metrazol was injected 5 min prior to successive sessions (10 min apart) with doses starting at 10 mg/kg an increased by 10 mg/kg each session up to 40 mg/kg. Drug-treated animals were significantly less susceptible to seizures than their placebo controls. These results suggest that chronic benzodiazepine treatment causes long-term neurochemical changes which are responsible for the observed behavioral effects.

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