The reward-effort model: An economic framework for examining the mechanism of neuroleptic action

Nucleus accumbens dopamine depletions alter relative response allocation in a T-maze cost/benefit task

This experiment was conducted to study the role of nucleus accumbens dopamine in the performance of a novel T-maze cost/benefit procedure. Rats were trained on a T-maze task for food reinforcement. Under one of the test conditions, one arm of the maze contained a high reinforcement density (4 x 45 mg Bioserve pellets) and the other arm contained a low reinforcement density (2 x 45 mg pellets). A large vertical barrier (44 cm) was placed in the arm that contained the high density of food reinforcement. In the second test condition, a separate group of rats was trained in the same T-maze, in which there were 4 food pellets in the arm that was obstructed by the barrier, yet there were no food pellets in the unobstructed arm. After training rats received intra-accumbens of injections 6-hydroxydopamine or ascorbate vehicle. Nucleus accumbens dopamine depletions substantially decreased the number of selections of the obstructed arm with the high reinforcement density when the unobstructed arm also contained 2 food pellets. Dopamine-depleted rats in this condition showed increased selection of the no-barrier arm as well as decreased entry into the arm that contained the barrier. These effects persisted throughout the 3 weeks of post-surgical testing. Nevertheless, when the unobstructed arm contained no food pellets, and the only way to obtain food was to climb the barrier, rats with nucleus accumbens dopamine depletions showed only a modest effect on selections of the obstructed arm, which recovered by the second week of testing. Dopamine-depleted rats that were tested with food in the unobstructed arm showed significantly fewer barrier crossings than dopamine-depleted rats that were tested with no food in the unobstructed arm. Thus, the present findings are not consistent with the notion that nucleus accumbens dopamine depletion rendered the animals unable to climb the barrier, or set an absolute ceiling on the number of barrier crossings the animals could perform. Instead, the present results indicate that nucleus accumbens dopamine depletions affected the relative allocation of barrier climbing responses if alternative food sources were available.

Anhedonia or anergia? Effects of haloperidol and nucleus accumbens dopamine depletion on instrumental response selection in a T-maze cost/benefit procedure

Two experiments were conducted to study the role of dopamine in the performance of a novel cost/benefit procedure. Rats were trained on a T-maze task in which one arm contained a high reinforcement density (4 x 45 mg Bioserve pellets) and the other arm contained a low reinforcement density (2 x 45 mg pellets). Different groups of rats were trained either with unobstructed access to both arms from the start area, or under a condition in which a large vertical barrier (44 cm) was placed in the arm that contained the high density of food reinforcement. In the first experiment, rats trained under each procedure received injections of 0.1 mg/kg haloperidol and tartaric acid vehicle as a control procedure. Analysis of variance indicated that there was a significant effect of the barrier on maze arm choice, a significant effect of haloperidol, and a significant drug x barrier interaction. Haloperidol did not affect arm choice in rats tested without the barrier present, but this drug significantly reduced the number of selections of the arm with high reinforcement density when the barrier was present. In the second experiment, groups of rats were trained as described above, and then received intraaccumbens injections of 6-hydroxydopamine or ascorbate vehicle. Nucleus accumbens dopamine depletions produced by 6-hydroxydopamine decreased the number of selections of the arm with high reinforcement density when the barrier was present, but had no effect on arm choice when the barrier was not present.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex motor and sensorimotor functions of striatal and accumbens dopamine: involvement in instrumental behavior processes

The suggestions that dopamine (DA) systems are involved in "motor control" and "reward" represent the classic working hypotheses on the behavioral functions of these systems. The research generated by these hypotheses has yielded results that are far more complicated than the simplest form of either hypothesis would indicate. Pharmacological or lesion-induced interference with DA function does not suppress all aspects of movement control, nor all aspects of reward, nor all aspects of motivation. The deficits produced by interference with DA systems are selective and dissociative in nature, affecting some aspects of motor or motivational function, but leaving others basically intact. In some sense the hypotheses that DA is involved in "motor" or "reward" or "motivational" processes are partly correct, but the processes to which these terms refer are too broad to offer an accurate and detailed description of the behavioral functions of brain DA. A review of the literature on the behavioral pharmacology of DA suggests that the behaviors most easily disrupted by DA antagonists are highly activated and complex learned instrumental responses that are elicited or supported by mild conditioned stimuli, and maintained for considerable periods of time. It is proposed that DA in accumbens and striatum modulates the ability of neocortical and limbic areas involved in sensory, associative, and affective processes to influence complex aspects of motor function, and also modulates the execution of complex motor acts organized by the neocortex. Thus, interference with DA systems produces a "subcortical apraxia", which dissociates complex stimulus processes from complex motor processes, but leaves aspects of those processes intact.

Distinguishing between haloperidol's and decamethonium's disruptive effects on operant behavior in rats: use of measurements that complement response rate

The behavioral effects of haloperidol (0.04 to 0.16 mg/kg) and nonparalytic doses of decamethonium (0.2 to 0.8 mg/kg) were studied with operant methods that permitted the measurement of response rate, peak force of response, duration of response, and duration of the rat's head entry into the reinforcement dipper well. Type of operant response topography (forelimb press or forelimb grasp-and-pull) and peak force (low or high) required for reinforcement delivery were independent variables. The low-force, press-topography condition yielded qualitatively different profiles for the two drugs. Haloperidol increased peak force and duration of operant response, increased maximum head entry duration, and temporally dissociated forelimb and head entry behavior. Decamethonium decreased force and duration of operant response, did not appreciably affect maximum head entry duration, and did not influence the normal temporal coupling of forelimb and head entry responses. The haloperidol effects were seen as reflections of pseudo-Parkinsonism, not muscle weakness, which appeared to be the primary source of decamethonium's behavioral effects.

Dopamine and depression: a review of recent evidence. II. Theoretical approaches

This paper discusses 3 behavioural approaches to depression, 'learned helplessness', reward system dysfunction and reduced responsiveness to the environment, and the role of dopamine (DA) in their related animal models. The meso-limbic and nigrostriatal DA system appears to be related primarily to responsiveness to the environment. This conclusion is discussed in relation to the clinical symptomatology of depression.