Biomedical subjects

J M Moerschbaecher

Publications and source records attributed to J M Moerschbaecher.

60 records · Page 4Linked to original sources

PubMed1978

Effects of d-amphetamine and cocaine on repeated acquisition with timeout from avoidance.

The acute effects of d-amphetamine and cocaine on a repeated acquisition baseline with timeout from avoidance were investigated in two rats. Each session the animals acquired one of two different three-member response sequences. Each sequence member was associated with a different response lever. The first two correct responses of each sequence postponed shock for a fixed period of time. The third correct response initiated a signalled timeout (30 sec) from avoidance. Incorrect responses did not postpone shock. The baseline performance was characterized by a decrease in errors within each session, similar to patterns of repeated acquisition maintained by food. In comparison to control sessions, both d-amphetamine and cocaine increased errors and altered the pattern of within-session acquisition. d-Amphetamine increased the rate of sequence completion and the rate of shock delivery in both animals. Cocaine increased the rate of sequence completion in one animal and increased the rate of shock delivery for the other.

Animals↗

PubMed1978

Operant methodology in the study of learning.

A series of experiments is described in which operant methodology is used to study the effects of drugs on "learning." Emphasis is placed on the technique of repeated acquisition as a behavioral baseline for studying this type of transition state. In this technique, each subject is required to learn a new discrimination each session. Multiple-schedule procedures are also described in which acquisition is compared to a "performance" task, where the discrimination is the same each session. The learning baseline is more sensitive to the disruptive effects of a variety of drugs (e.g., cocaine, d-amphetamine, haloperidol) than is the performance baseline. This general finding obtains across procedural variations and species (pigeons and monkeys). The potential usefulness of these procedures for studying both acute and chronic behavioral toxicity is discussed.

Animals↗

PubMed1978

Repeated acquisition of conditional discriminations.

A new technique was developed to study the repeated acquisition of conditional discriminations. Using a discrete trial procedure, pigeons were required to learn during each session a different two-member chain of conditional discriminations. Key color and geometric forms were used as stimuli. After the pigeons had reached a steady state of relearning (40 to 60 sessions), the technique was used to investigate variables that have previously been shown to affect the repeated acquisition of response sequences. Various (0 to 90 seconds) durations of timeout for errors were investigated in Experiment I. The stimulus change associated with a timeout, rather than its duration, was found to be the critical variable in acquisition of the discrimination. Extended training on a single chain was found to reduce total errors across sessions in Experiment II. Extended training (three sessions) did not, however, change the pattern of within-session error reduction. In some cases, extended training facilitated acquisition of a partially reversed discrimination. In Experiment III, color rather than chain position was found to control behavior, for three of the four birds, as the second stimulus dimension in the conditional situation. The results of these experiments replicate and extend previous findings concerning some of the variables that affect the repeated acquisition of response sequences.

Journal Article↗

PubMed1978

Variability of response location on fixed-ratio and fixed-interval schedules of reinforcement.

Variability of response location was studied in monkeys performing in a six-lever chamber. Fixed-ratio schedules, ranging from FR 1 to FR 300, generated a high degree of stereotypy of response location. In contrast, fixed-interval schedules of comparable reinforcement frequencies (0.06 to 4 minutes) generated much greater variability. These results failed to confirm any simple relationship between response variability and intermittence of reinforcement. Rather, variability seems to be determined by the particular characteristics of the reinforcement schedule.

Journal Article↗

PubMed1976

Sequential reacquisition as a function of timeout from avoidance.

Rats learned to reacquire four similar three-member response sequences. Each sequence member was associated with a different response lever, and the correct sequence of levers (i.e., 3-1-2, 2-1-3, 1-3-2, and 2-3-1) changed each session. The first two correct responses of each sequence postponed shock for a fixed period of time. The third correct response initiated a signalled timeout from avoidance. Incorrect responses did not affect the shock interval or reset the sequence. The effects of manipulating timeout duration on the sequential reacquisition baseline were investigated. All subjects displayed biphasic reacquisition performances similar to those controlled by food. The phases were characterized by an initial increase in accuracy, which reached a stable level during the latter portion of each session. Timeout duration affected rate of sequence completion and shock density, but not percentage of errors. Rate of sequence completion was fastest with intermediate timeouts (15 to 60 sec), and slowest with extreme durations (1 or 120 sec). Shock densities peaked with extreme durations and were at minimum with intermediate timeout values. The percentage of errors was the same across timeout durations. These data extend the generality of sequential reacquisition as a procedure for studying learning, and demonstrate timeout from avoidance to be a controlling variable.

Journal Article↗

PubMedDate not supplied

Chronic brief restraint decreases in vivo binding of benzodiazepine receptor ligand to mouse brain.

This study examines the effects of chronic brief restraint on in vivo benzodiazepine (BZD) receptor binding in mouse brain. Three groups of mice were used. Mice in group 1 were neither restrained nor injected (ACUTE control). Mice in group 2 were restrained for 5-6 s by grabbing the back skin and holding the subject upside-down at a 45 degrees angle as if to be injected (CHRONIC SHAM control) for 7 d. Mice in group 3 (CHRONIC SALINE) received daily single intraperitoneal (ip) injections of saline (5 mL/kg) for 7 d. On d 8 BZD receptors were labeled in vivo by administration of 3 microCi [3H]flumazenil (ip). The levels of ligand bound in vivo to cerebral cortex (CX), cerebellum (CB), brain stem (BS), striatum (ST), hippocampus (HP), and hypothalamus (HY) were determined. Results indicated that the level of binding was significantly (p < 0.01) lower by 30-50% (depending on the brain region) in saline-injected or sham control groups compared to acute control animals. Furthermore, the values for sham control were similar to the saline-treated group. Our data suggest that exposure to chronic mild restraint produces a decrease in in vivo binding of [3H]flumazenil in mouse brain and supports the hypothesis that chronic mild stress produces a decrease in BZD receptor binding sites.

Animals↗