The nucleus accumbens (NAc) is critical for regulating the appetitive and consummatory phases of motivated behavior. These experiments examined the effects of dopamine and opioid receptor manipulations within the NAc during an effort-based choice task that allowed for simultaneous assessment of both phases of motivation. Male Sprague-Dawley rats received bilateral guide cannulas targeting the NAc core and were tested in 1-hr sessions with free access to rat chow and the choice to work for sugar pellets on a progressive ratio 2 (PR2) reinforcement schedule. Individual groups of rats were tested following stimulation or blockade of NAc D1-like or D2-like receptors, stimulation of µ-, δ-, or κ-opioid receptors, or antagonism of opioid receptors. Behavior was examined under ad libitum conditions and following 23-hr food restriction. NAc blockade of the D1-like receptors or stimulation of the D2 receptor reduced break point for earning sugar pellets; D2 receptor stimulation also modestly lowered chow intake. NAc µ-opioid receptor stimulation increased intake of the freely-available chow while simultaneously reducing break point for the sugar pellets. In non-restricted conditions, δ-opioid receptor stimulation increased both food intake and breakpoint. There were no effects of stimulating NAc D1 or κ receptors, nor did blocking D2 or opioid receptors affect task behavior. These data support prior literature linking dopamine to appetitive motivational processes, and suggest that µ- and δ-opioid receptors affect food-directed motivation differentially. Specifically, µ-opioid receptors shifted behavior towards consumption, and δ-opioid receptor enhanced both sugar-seeking and consumption of the pabulum chow when animals were not food restricted.

伏隔核 (NAc) 对于调节动机行为的食欲和完成阶段至关重要。这些实验检查了在基于努力的选择任务期间 NAc 内多巴胺和阿片受体操作的影响，该任务允许同时评估动机的两个阶段。雄性 Sprague-Dawley 大鼠接受了针对 NAc 核心的双边引导插管，并在 1 小时的会议中进行了测试，可免费获得大鼠食物，并选择在渐进比率 2 (PR2) 强化计划中为糖丸工作。在刺激或阻断 NAc D1 样或 D2 样受体、刺激 μ-、δ-或 κ-阿片受体或拮抗阿片受体后，对各组大鼠进行测试。行为被随意检查条件和遵循 23 小时食物限制。NAc 阻断 D1 样受体或刺激 D2 受体降低了获得糖丸的折点；D2 受体刺激也适度降低了食物摄入量。NAc µ-阿片受体刺激增加了可自由获取的食物的摄入量，同时降低了糖丸的断点。在非限制条件下，δ-阿片受体刺激增加了食物摄入量和断点。没有刺激 NAc D1 或 κ 受体的作用，阻断 D2 或阿片受体也没有影响任务行为。这些数据支持将多巴胺与食欲动机过程联系起来的先前文献，并表明 μ- 和 δ-阿片受体对食物导向的动机有不同的影响。具体而言，μ-阿片受体将行为转向消费，