Mingote Susana, Weber Suzanne M, Ishiwari Keita, Correa Mercè, Salamone John D
Department of Psychology, University of Connecticut, Storrs, CT 06269-1020, USA.
Eur J Neurosci. 2005 Mar;21(6):1749-57. doi: 10.1111/j.1460-9568.2005.03972.x.
Accumbens dopamine (DA) depletions produce deficits that are related to the ratio requirement of the operant schedule; however, it is also possible that time without reinforcement is a factor. The present study examined the effects of accumbens DA depletions in rats using variable interval (VI) schedules with additional fixed ratio (FR) requirements. Four VI schedules were used (VI 60/FR 1, VI 120/FR 1, VI 60/FR 10, VI 120/FR 10). Attachment of the additional work requirement increased response rates under control conditions. After surgery, there was no interaction between interval level (i.e. 60 vs. 120 s) and DA depletion, but there was a significant interaction between ratio requirement (i.e. 1 vs. 10) and DA depletion within the first week after surgery. DA depletions substantially impaired performance on the schedules with added FR 10 requirements, an effect that was largely dependent upon a reduction in fast responses (i.e. inter-response times less than 1.0 s). There was little effect of DA depletion on overall responding on VI 60/FR 1 and VI 120/FR 1 schedules. DA depletions also increased the tendency to take long pauses in responding (i.e. > 20.0 s), and this effect was evident across all schedules tested. Thus, accumbens DA depletions interact with work requirements and blunt the rate-enhancing effects of moderate size ratios, and also enhance the tendency to pause. Attachment of ratio requirements to interval schedules is a work-related response cost that provides a challenge to the organism, and DA in nucleus accumbens appears to be necessary for adapting to this challenge.
伏隔核多巴胺（DA）耗竭会产生与操作性条件反射程序的比率要求相关的缺陷；然而，无强化时间也可能是一个因素。本研究使用具有额外固定比率（FR）要求的可变间隔（VI）程序，研究了大鼠伏隔核DA耗竭的影响。使用了四种VI程序（VI 60/FR 1、VI 120/FR 1、VI 60/FR 10、VI 120/FR 10）。附加工作要求的加入在对照条件下提高了反应率。手术后，间隔水平（即60秒与120秒）与DA耗竭之间没有相互作用，但在手术后第一周内，比率要求（即1与10）与DA耗竭之间存在显著的相互作用。DA耗竭严重损害了添加FR 10要求的程序中的表现，这种影响在很大程度上取决于快速反应（即反应间隔时间小于1.0秒）的减少。DA耗竭对VI 60/FR 1和VI 120/FR 1程序的总体反应影响很小。DA耗竭还增加了反应中长时间停顿（即>20.0秒）的倾向，并且在所有测试的程序中这种影响都很明显。因此，伏隔核DA耗竭与工作要求相互作用，削弱了中等规模比率的速率增强作用，并且还增强了停顿的倾向。将比率要求附加到间隔程序是一种与工作相关的反应成本，这对生物体构成了挑战，伏隔核中的DA似乎是适应这一挑战所必需的。
