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H Bercovitz

Publications and source records attributed to H Bercovitz.

7 recordsLinked to original sources
PubMed1989

The effects of amphetamine on a multitrial partial reinforcement extinction effect (PREE) in a runway.

Three experiments examined the effects of d-amphetamine (1 mg/kg) administration on the partial reinforcement extinction effect (PREE) using a multitrial procedure. 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. Experiments 1 and 2 used 6 trials/day with an intertrial interval (ITI) of 5 min. In Experiment 1 the drug was administered only during acquisition, whereas in Experiment 2 it was administered throughout acquisition and extinction. Experiment 3 used 3 trials/day with a 20 min ITI. The drug was administered throughout acquisition and extinction. In all three experiments, amphetamine-treated animals showed a normal PREE, i.e., increased resistance to extinction in PRF as compared to CRF animals. These results stand in marked contrast to the amphetamine-induced abolition of the PREE with 1 trial/day procedure.

Amphetamine↗
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

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↗
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↗
PubMed1983

The effect of verapamil, a calcium antagonist, on the serum-dependent regulation of uridine uptake by cells in culture.

The stimulation of uridine uptake is one of the early events that occur when quiescent cells are stimulated to grow by adding fresh serum. Serum depletion of cells in their exponential phase of growth results in a decrease of uridine uptake rate, a process which is complete before a significant reduction in DNA synthesis is observed. Elevation of extracellular potassium can stimulate the role of serum as an activator of uridine uptake, and can prevent the inhibition of uptake that results from serum depletion. Verapamil, a known antagonist of calcium movement across biological membranes, inhibits uridine uptake. This inhibition is much stronger in serum- or KCl-activated cells than in serum-depleted or quiescent cells. Verapamil can partially prevent the serum-dependent stimulation of uridine uptake. The effect of Verapamil does not depend on the presence of calcium in the extra-cellular medium. Verapamil may interfere with serum-dependent redistribution of Ca2+ within the cells, and thus uncouple the initial event of binding of serum growth factors to membrane receptors, from the subsequent intracellular response-regulation of uridine uptake rates.

Animals↗
PubMed1981

The role of bestatin, an inhibitor of cell surface proteases, in the interaction of serum with untransformed cells in culture.

Bestatin is an inhibitor of cell surface-associated aminopeptidase B and leucine aminopeptidase. This microbial product simulates the role of serum as an activator of uridine uptake in quiescent BHK cells. The compound significantly stimulates the incorporation of labelled thymidine into the acid-insoluble fraction of serum-starved Nil 8 cells in the presence of low concentration of serum. The possible mechanisms of these interactions are discussed.

Aminopeptidases↗