Cousins M S, Salamone J D
Department of Psychology, University of Connecticut, Storrs 06269-1020.
Pharmacol Biochem Behav. 1994 Sep;49(1):85-91. doi: 10.1016/0091-3057(94)90460-x.
Rats were tested on days 1, 3, and 5 of a 5-day test week in an operant chamber in which they could either lever press on a fixed-ratio 5 (FR5) schedule to obtain food pellets (Bioserve) or approach and consume lab chow that was also available in the chamber (Teklad Premier). Rats typically pressed at high rates to obtain the food pellets and ate little of the lab chow. On days 2 and 4 of each week lab chow was not concurrently available, and rats could only lever press on the FR5 schedule for pellets to obtain food. Dopamine depletions produced by intraaccumbens injections of the neurotoxic agent 6-hydroxydopamine produced a dramatic decrease in lever pressing and increase in chow consumption on days when lab chow was available. Lever pressing was not significantly reduced in dopamine-depleted rats on days when chow was not available, although there was a significant correlation between lever pressing and accumbens dopamine levels. These results suggest that nucleus accumbens dopamine depletions do not produce a general deficit in food motivation. Moreover, accumbens dopamine depletions do not appear to produce severe deficits in fine motor control that impair the execution of individual motor acts involved in lever pressing. Rather, the present results are consistent with the notion that accumbens dopamine sets constraints upon which food-related response is selected in a particular situation, and that these depletions alter the relative allocation of food-related responses.
在为期5天的测试周的第1天、第3天和第5天，将大鼠置于一个操作性条件反射箱中进行测试。在该箱子中，大鼠可以按照固定比例5（FR5）的时间表按压杠杆以获取食丸（Bioserve公司生产），或者接近并食用箱内提供的实验室饲料（Teklad Premier品牌）。大鼠通常会以较高的频率按压杠杆来获取食丸，而很少吃实验室饲料。在每周的第2天和第4天，不同时提供实验室饲料，大鼠只能按照FR5时间表按压杠杆以获取食丸来获取食物。通过向伏隔核内注射神经毒性剂6-羟基多巴胺造成多巴胺耗竭，在提供实验室饲料的日子里，导致杠杆按压行为显著减少，而饲料消耗量增加。在不提供饲料的日子里，多巴胺耗竭的大鼠的杠杆按压行为没有显著减少，尽管杠杆按压行为与伏隔核多巴胺水平之间存在显著相关性。这些结果表明，伏隔核多巴胺耗竭不会导致食物动机方面的普遍缺陷。此外，伏隔核多巴胺耗竭似乎不会导致精细运动控制方面的严重缺陷，从而损害参与杠杆按压的单个运动行为的执行。相反，目前的结果与以下观点一致：伏隔核多巴胺在特定情况下对选择哪种与食物相关的反应施加限制，并且这些耗竭会改变与食物相关反应的相对分配。
