Ishiwari Keita, Weber Suzanne M, Mingote Susana, Correa Mercè, Salamone John D
Department of Psychology, University of Connecticut, Storrs, CT 06269-1020, USA.
Behav Brain Res. 2004 May 5;151(1-2):83-91. doi: 10.1016/j.bbr.2003.08.007.
It has been suggested that depletions of accumbens dopamine (DA) make rats more sensitive to work-related response costs. One way of controlling work costs in operant tasks has been to use fixed-ratio (FR) schedules with different ratio requirements. In addition to using ratio requirements to control response costs, investigators also can employ different force requirements. In the present study, different groups of rats were trained on two schedules (FR 1 and FR 5) and weights were placed on the levers 2 days each week. In the FR 5 studies, two different weights were used (32 or 64 g), while three different weights were used in the FR 1 studies (32, 64, or 96 g). After baseline training, rats received intra-accumbens injections of either 6-OHDA to deplete DA, or ascorbate vehicle as the control. The effects of DA depletions were highly schedule-dependent. DA-depleted animals on the FR 5 schedule showed reductions in responding across the different weight conditions. In contrast, DA depletion did not significantly suppress FR 1 responding under any conditions. Addition of weights to the levers reduced responding on the FR 1 and FR 5 schedules, but did not enhance sensitivity to DA depletion. Thus, rats with accumbens DA depletions were sensitive to different ratio requirements, yet they were relatively insensitive to different force requirements within the range tested. These studies indicate that DA depletions make animals sensitive to temporal or rate components of work that greatly influence responding on ratio schedules.
有人提出，伏隔核多巴胺（DA）的耗竭会使大鼠对与工作相关的反应代价更加敏感。在操作性任务中控制工作代价的一种方法是使用具有不同比率要求的固定比率（FR）时间表。除了使用比率要求来控制反应代价外，研究人员还可以采用不同的用力要求。在本研究中，不同组的大鼠在两种时间表（FR 1和FR 5）上接受训练，并且每周有两天在杠杆上放置重物。在FR 5研究中，使用了两种不同的重量（32或64克），而在FR 1研究中使用了三种不同的重量（32、64或96克）。在基线训练后，大鼠接受伏隔核内注射6-OHDA以耗尽DA，或注射抗坏血酸载体作为对照。DA耗竭的影响高度依赖于时间表。处于FR 5时间表的DA耗尽动物在不同重量条件下的反应均有所减少。相比之下，在任何条件下，DA耗竭都不会显著抑制FR 1反应。在杠杆上增加重量会降低FR 1和FR 5时间表上的反应，但不会增强对DA耗竭的敏感性。因此，伏隔核DA耗尽的大鼠对不同的比率要求敏感，但在测试范围内它们对不同的用力要求相对不敏感。这些研究表明，DA耗竭使动物对工作的时间或速率成分敏感，而这些成分会极大地影响比率时间表上的反应。
