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|Title:||D3 Receptors in Incentive Learning and Drug Addiction|
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|Authors/Affiliations:||1 Richard J. Beninger*|
1 Queen's University, Departments of Psychology & Psychiatry, Kingston, ON, Canada
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|Content:||Objective: Dopamine D3 receptors (Drd3) have been implicated in the control of responding by drug-related conditioned incentive stimuli. I will review relevant studies and what they imply about the role of Drd3 in learning.|
Materials and Methods: Recent studies have investigated the effects of Drd3 partial agonists or antagonists on the control of self-administration of intravenous (IV) cocaine, IV morphine and oral ethanol on reward-rich and lean schedules, in reinstatement tests, on second order schedules and on the acquisition and expression of conditioned place preference (CPP) and conditioned activity. For comparison, related studies where conditioned stimuli are based on natural reward also will be considered.
Results: When self-administration depends more heavily on conditioned cues for its maintenance, for example on second-order schedules or lean ratio schedules, Drd3 partial agonists or antagonists reduce responding; although data are limited, similar effects may be seen for responding for cues based on drugs or natural rewards. Drd3 agents also block the ability of conditioned cues to reinstate responding for cocaine or food. Drd3 antagonists more consistently block expression than acquisition of CPP or conditioned activity based on rewarding drugs.
Conclusions: Collectively, results suggest that Drd3 plays a more important role in the expression than in the acquisition of conditioned respondes. The mechanism mediating the role of Drd3 in the control of responding by conditioned incentive stimuli remains unknown but it has been found that Drd3 receptors increase in number in the nucleus accumbens during conditioning. Further studies are needed to identify the mechanisms underlying the role of dopamine and of dopamine receptor subtypes in reward-related incentive learning.
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