Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California Los Angeles, Los Angeles, CA 90024, USA.
Neuroscience. 2009 Oct 20;163(3):770-80. doi: 10.1016/j.neuroscience.2009.06.071. Epub 2009 Jul 18.
Considerable evidence suggests that in instrumental conditioning rats learn the relationship between actions and their consequences, or outcomes. Such goal-directed actions are sensitive to changes in outcome value. The present study assessed the role of the endogenous opioid system in goal-directed reward learning. In two experiments, rats were trained to lever press for food pellets either under vehicle or naloxone-induced opioid receptor blockade. Specific satiety procedures were used for outcome devaluation, and the effect of this devaluation on instrumental responding was then tested in extinction. In Experiment 1 outcome devaluation resulted in a reduction in lever pressing in rats that were trained after vehicle injections, indicating that actions in these rats were goal-directed. In contrast, actions in rats trained under naloxone were insensitive to outcome devaluation when tested off drug, suggesting that lever pressing had become habitual in these rats. Interestingly, in Experiment 2 naloxone-induced habitual behavior was shown to be specific to the context in which the training occurred under naloxone; rats showed normal sensitivity to outcome devaluation when tested in an alternate vehicle-trained context. Additionally, in Experiment 2 we found that the acute administration of naloxone on test had no effect in itself, indicating that opioid receptor-related processes contribute to the acquisition of goal-directed actions and not to their general performance. These data suggest that an intact endogenous opioid system is necessary for normal goal-directed learning and more importantly, reveal that a compromised endogenous opioid system during learning enhances the habitual control of actions.
大量证据表明，在工具性条件反射中，老鼠学会了动作与其后果（或结果）之间的关系。这种有目标的行为对结果价值的变化很敏感。本研究评估了内源性阿片系统在目标导向奖励学习中的作用。在两项实验中，老鼠被训练在车辆或纳洛酮诱导的阿片受体阻断剂下按压杠杆以获取食物丸。采用特定的饱腹感程序对结果进行贬值，然后在消退中测试这种贬值对工具反应的影响。在实验 1 中，结果贬值导致在接受车辆注射后接受训练的老鼠按压杠杆的次数减少，这表明这些老鼠的动作是有目标的。相比之下，在纳洛酮下接受训练的老鼠在停药后对结果贬值没有反应，这表明这些老鼠的按压杠杆已经成为习惯。有趣的是，在实验 2 中，纳洛酮诱导的习惯性行为表现出对纳洛酮下训练发生的环境的特异性；当在替代的车辆训练环境中进行测试时，老鼠对结果贬值表现出正常的敏感性。此外，在实验 2 中，我们发现纳洛酮的急性给药本身没有影响，这表明阿片受体相关过程有助于获得有目标的动作，而不是它们的一般表现。这些数据表明，完整的内源性阿片系统是正常目标导向学习所必需的，更重要的是，揭示了学习过程中受损的内源性阿片系统增强了动作的习惯性控制。
