Abstract
For several decades, it has been suggested that dopamine (DA), especially in nucleus accumbens, mediates the primary reinforcing characteristics of natural stimuli such as food, as well as drugs of abuse. Yet, several fundamental aspects of primary food reinforcement, motivation, and appetite are left intact after interference with accumbens DA transmission. Recent studies have shown that accumbens DA is involved in responsiveness to conditioned stimuli and activational aspects of motivation. In concurrent choice tasks, accumbens DA depletions cause animals to reallocate their choice behavior in the direction of instrumental behaviors that involve less effort. Also, an emerging body of evidence has demonstrated that the effects of accumbens DA depletions on instrumental food-seeking behavior can vary greatly depending upon the task. For example, some schedules of reinforcement are insensitive to the effects of DA depletions, whereas others are highly sensitive (e.g., large fixed ratios). Accumbens DA depletions slow the rate of operant responding, blunt the rate-facilitating effects of moderate-sized ratios, and enhance the rate-suppressing effects of very large ratios (i.e., produce ratio strain). Accumbens DA may be important for enabling rats to overcome behavioral constraints, such as work-related response costs, and may be critical for the behavioral organization and conditioning processes that enable animals to engage in vigorous responses, such as barrier climbing, or to emit large numbers of responses in ratio schedules in the absence of primary reinforcement. The involvement of accumbens DA in activational aspects of motivation has implications for energy-related disorders in psychiatry, as well as aspects of drug-seeking behavior.
Footnotes
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↵1 Present address: Àrea de Psicobiologia, Campus de Riu Sec, Universitat Jaume I, 12079 Castelló, Spain.
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Much of the research described in this article was supported by a series of grants to J.S. by the National Science Foundation of the United States.
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DOI: 10.1124/jpet.102.035063
- Abbreviations:
- DA
- dopamine
- FR
- fixed ratio
- SCH 23390
- R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine
- VI
- variable interval
- FI
- fixed interval
- SKF 83566
- (±)-7-bromo-1-(fluoresceinyl thioureido)phenyl-8-hydroxy-3-methyl-2,3,4,5,-tetrahydro-1H-benzazepine
- Received October 8, 2002.
- Accepted December 10, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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