Department of Psychology, University of Connecticut, Storrs, CT 06269-1020, USA.
Neuroscience. 2011 Nov 24;196:178-88. doi: 10.1016/j.neuroscience.2011.07.078. Epub 2011 Aug 25.
Nucleus accumbens dopamine (DA) is a critical component of the brain circuitry regulating behavioral output during reinforcement-seeking behavior. Several studies have investigated the characteristics of accumbens DA release during the performance of well-learned operant behaviors, but relatively few have focused on the initial acquisition of particular instrumental behaviors or operant schedules. The present experiments focused on the initial acquisition of operant performance on a reinforcement schedule by studying the transition from a fixed ratio 1 (FR1) schedule to another operant schedule with a higher ratio requirement (i.e. fixed ratio 5 [FR5]). Microdialysis sessions were conducted in different groups of rats that were tested on either the FR1 schedule; the first, second, or third day of FR5 training; or after weeks of FR5 training. Consistent with previous studies, well-trained rats performing on the FR5 schedule after weeks of training showed significant increases in extracellular DA in both core and shell subregions of nucleus accumbens during the behavioral session. On the first day of FR5 training, there was a substantial increase in DA release in nucleus accumbens shell (i.e. approximately 300% of baseline). In contrast, accumbens core DA release was greatest on the second day of FR5 training. In parallel experiments, DA release in core and shell subregions did not significantly increase during free consumption of the same high carbohydrate food pellets that were used in the operant experiments, despite the very high levels of food intake in experienced rats. However, in rats exposed to the high-carbohydrate food for the first time, there was a tendency for extracellular DA to show a small increase. These results demonstrate that transient increases in accumbens DA release occur during the initial acquisition of ratio performance, and suggest that core and shell subregions show different temporal patterns during acquisition of instrumental behavior.
伏隔核多巴胺（DA）是调节强化寻求行为中行为输出的大脑回路的关键组成部分。几项研究调查了在执行熟练操作性行为期间伏隔核 DA 释放的特征，但相对较少的研究集中在特定工具性行为或操作性方案的初始获得上。本实验通过研究从固定比率 1（FR1）方案过渡到具有更高比率要求的另一种操作性方案（即固定比率 5[FR5]），重点研究了在强化方案上获得操作性表现的初始阶段。在不同组的大鼠中进行了微透析会议，这些大鼠在 FR1 方案上进行测试；在 FR5 训练的第一天、第二天或第三天；或在 FR5 训练数周后。与先前的研究一致，经过数周训练后在 FR5 方案上表现良好的大鼠在行为会议期间显示核心和壳区伏隔核中的细胞外 DA 显著增加。在 FR5 训练的第一天，伏隔核壳中的 DA 释放有大幅度增加（即大约基线的 300%）。相比之下，在 FR5 训练的第二天，accumbens 核心的 DA 释放最大。在平行实验中，尽管经验丰富的大鼠的食物摄入量非常高，但在自由消耗相同的高碳水化合物食物丸时，核心和壳区的 DA 释放并没有显著增加。然而，在第一次接触高碳水化合物食物的大鼠中，细胞外 DA 有轻微增加的趋势。这些结果表明，在比率表现的初始获得期间，伏隔核 DA 释放会短暂增加，并且表明核心和壳区在工具性行为的获得过程中表现出不同的时间模式。
