Bassareo V, Di Chiara G
Department of Toxicology and CNR, Center for Neuropharmacology, University of Cagliari, Italy.
Neuroscience. 1999 Mar;89(3):637-41. doi: 10.1016/s0306-4522(98)00583-1.
The nucleus accumbens septi is the major target of mesolimbic dopamine neurons originating in the ventral tegmental area of the mesencephalon. Studies involving experimental manipulation of dopamine transmission by drugs and by lesions, as well as in vivo monitoring of extracellular dopamine concentrations, have provided evidence that the dopamine transmission of the nucleus accumbens plays an important role in behaviour motivated by conventional (e.g., food, sex) and drug reinforcers. Motivated behaviour is distinguished into an appetitive (preparatory/anticipatory) phase consisting of flexible response patterns intended to search and approach the reward itself, and a consummatory phase, consisting of fixed response patterns (eating, drinking, copulating, etc.) finalized to the utilization of the biological resources of the reward (caloric, metabolic, genetic, etc.). While some studies reported a stimulation of dopamine transmission in the nucleus accumbens in relation to appetitive as well as consummatory behaviour, other studies reported a relationship exclusively with consummatory behaviour. Therefore, the precise relationship between dopamine transmission in the nucleus accumbens and specific phases of motivated behaviour is debated. On the basis of topographical, histochemical and connectional evidence, the nucleus accumbens has been subdivided into two compartments, a medioventral "shell" and a laterodorsal "core". This heterogeneity may be relevant to the current debate over the role of nucleus accumbens dopamine in behaviour. Thus, one might hypothesize that, depending on the specific compartment of the nucleus accumbens where dopamine transmission is monitored, a different relationship with specific stimuli which motivate behaviour is obtained. In order to verify this possibility we monitored by microdialysis the changes in dopamine transmission in the nucleus accumbens shell and core during appetitive and consummatory phases of behaviour motivated by food. As food we utilized a palatable snack food (Fonzies) whose consumption has been shown in previous studies from our laboratory to release dopamine in the nucleus accumbens shell and in the medial prefrontal cortex. Unpredicted consumption of Fonzies preferentially stimulated dopamine transmission in the shell as compared to the core. Appetitive food stimuli (perforated Fonzies-filled boxes) phasically stimulated dopamine transmission in the core but not in the shell and sensitized the dopamine response to feeding in the core but inhibited that in the shell. These clear-cut differences between nucleus accumbens shell and core suggest that phasic dopamine transmission in each compartment of the nucleus accumbens subserves different roles in motivated behaviour.
伏隔核是起源于中脑腹侧被盖区的中脑边缘多巴胺能神经元的主要靶点。涉及通过药物和损伤对多巴胺传递进行实验性操纵，以及对细胞外多巴胺浓度进行体内监测的研究表明，伏隔核的多巴胺传递在由传统（如食物、性）和药物强化物驱动的行为中起重要作用。动机行为可分为一个欲求（准备/预期）阶段，该阶段由旨在寻找并接近奖励本身的灵活反应模式组成，以及一个完成阶段，该阶段由最终利用奖励的生物资源（热量、代谢、遗传等）的固定反应模式（进食、饮水、交配等）组成。虽然一些研究报告称，伏隔核中的多巴胺传递与欲求行为以及完成行为均有关，但其他研究报告称仅与完成行为有关。因此，伏隔核中的多巴胺传递与动机行为特定阶段之间的确切关系存在争议。基于地形学、组织化学和连接证据，伏隔核已被细分为两个部分，一个是内侧腹侧的“壳”和一个外侧背侧的“核”。这种异质性可能与当前关于伏隔核多巴胺在行为中的作用的争论相关。因此，有人可能会假设，根据监测多巴胺传递的伏隔核的特定部分，会获得与驱动行为的特定刺激的不同关系。为了验证这种可能性，我们通过微透析监测了在食物驱动行为的欲求阶段和完成阶段伏隔核壳和核中多巴胺传递的变化。作为食物，我们使用了一种美味的休闲食品（Fonzies），我们实验室之前的研究表明，食用这种食品会在伏隔核壳和内侧前额叶皮质释放多巴胺。与核相比，意外食用Fonzies优先刺激了壳中的多巴胺传递。欲求性食物刺激（装有穿孔Fonzies的盒子）阶段性地刺激了核中的多巴胺传递，但未刺激壳中的多巴胺传递，并使核中对进食的多巴胺反应敏感化，但抑制了壳中的反应。伏隔核壳和核之间这些明显的差异表明，伏隔核每个部分的阶段性多巴胺传递在动机行为中发挥不同的作用。
