Àrea de Psicobiologia, Campus de Riu Sec, Universitat Jaume I, 12071 Castelló, Spain.
Dept. of Neurology, University of Miami, Miller School of Medicine, Miami, FL 33136, USA.
Pharmacol Biochem Behav. 2018 Jun;169:27-34. doi: 10.1016/j.pbb.2018.04.004. Epub 2018 Apr 13.
Motivated behavior is characterized by activation and high work output. Nucleus accumbens (Nacb) modulates behavioral activation and effort-based decision-making. Caffeine is widely consumed because of its energizing properties. This methylxanthine is a non-selective adenosine A/A receptor antagonist. Adenosine receptors are highly concentrated in Nacb. Adenosine agonists injected into Nacb, shift preference towards low effort alternatives. The present studies characterized effort-related effects of caffeine in a concurrent progressive ratio (PROG)/free reinforcer choice procedure that requires high levels of work output, and generates great variability among different animals. Male Sprague-Dawley rats received an acute dose of caffeine (2.5-20.0 mg/kg, IP) and 30 min later were tested in operant boxes. One group was food-restricted and had to lever pressed for high carbohydrate pellets, another group was non-food-restricted and lever pressed for a high sucrose solution. Caffeine (2.5 and 5.0 mg/kg) increased lever pressing in food-restricted animals that were already high responders. However, in non-restricted animals, caffeine (5.0 and 10.0 mg/kg) increased work output only among low responders. In fact, caffeine (10.0 and 20.0 mg/kg) in non-restricted animals, reduced lever pressing among high responders in the PROG task, and also in a different group of animals lever pressing in an easy task (fixed ratio 7 schedule) that uniformly generates high levels of responding. Caffeine did not modify sucrose preference or consumption under free access conditions. Thus, when animals do not have a homeostatic need, caffeine can help those not very intrinsically motivated to work harder for a more palatable reward. However, caffeine can disrupt performance of animals intrinsically motivated to work hard for a better reward.
动机性行为的特点是激活和高工作输出。伏隔核（Nacb）调节行为激活和基于努力的决策。咖啡因因其提神作用而被广泛消费。这种甲基黄嘌呤是一种非选择性腺苷 A/A 受体拮抗剂。腺苷受体在 Nacb 中高度集中。将腺苷激动剂注入 Nacb 会使动物倾向于选择低努力的替代物。本研究在需要高工作输出的同时进行的递增比率（PROG）/自由强化选择程序中，描述了咖啡因与努力相关的影响，该程序在不同动物之间产生了很大的变异性。雄性 Sprague-Dawley 大鼠接受单次急性剂量的咖啡因（2.5-20.0mg/kg，IP），30 分钟后在操作箱中进行测试。一组动物进行食物限制，必须按压杠杆以获得高碳水化合物丸，另一组动物不受食物限制，按压杠杆以获得高蔗糖溶液。咖啡因（2.5 和 5.0mg/kg）增加了已经是高反应者的食物限制动物的按压杠杆次数。然而，在非限制动物中，咖啡因（5.0 和 10.0mg/kg）仅在低反应者中增加了工作输出。事实上，在非限制动物中，咖啡因（10.0 和 20.0mg/kg）在 PROG 任务中降低了高反应者的按压杠杆次数，并且在另一组动物的简单任务（固定比率 7 时间表）中也降低了按压杠杆次数，该任务均匀地产生高水平的反应。在自由获得条件下，咖啡因不会改变蔗糖偏好或消耗。因此，当动物没有生理需求时，咖啡因可以帮助那些内在动力不强的动物为更美味的奖励更加努力工作。然而，咖啡因会破坏那些为了更好的奖励而努力工作的动物的表现。
