Bassareo V, Di Chiara G
Department of Toxicology, University of Cagliari, Italy.
J Neurosci. 1997 Jan 15;17(2):851-61. doi: 10.1523/JNEUROSCI.17-02-00851.1997.
Feeding a novel food (Fonzies) to rats fed ad libitum with standard food increased extracellular dopamine (DA) in the medial prefrontal cortex (PFCX) and in the medial nucleus accumbens (NAc). Previous Fonzies feeding, although it did not affect the increase of extracellular DA in the PFCX in response to Fonzies feeding, blunted that increase in the NAc (habituation); recovery from habituation in the NAc was complete 5 d after previous Fonzies feeding. Predictive association of an otherwise neutral stimulus extrinsic to Fonzies (empty plastic box) with Fonzies feeding resulted in the acquisition by the stimulus of the property to elicit incentive responses directed toward the stimulus and to increase extracellular DA in the PFCX. However, the same stimulus, or a more complex stimulus including intrinsic stimuli (Fonzies-filled plastic box), failed to acquire the ability to modify extracellular DA in the NAc. Pseudoconditioning, i.e., nonpredictive association of the extrinsic stimulus (empty box) with Fonzies feeding, did not result in acquisition by the stimulus of the property to elicit incentive responses and to increase extracellular DA in the PFCX. Repeated nonreinforced presentation of previously conditioned extrinsic stimuli (empty box) resulted in extinction of the property to elicit incentive responses and to increase extracellular DA in the PFCX. These results indicate that in rats fed ad libitum, phasic activation of mesocortical and mesolimbic DA systems by motivational stimuli is differentially influenced by associative (conditioning) and nonassociative (habituation) learning mechanisms and is differentially related to acquisition and expression of incentive motivation.
给自由采食标准食物的大鼠喂食一种新食物（Fonzies），会增加内侧前额叶皮质（PFCX）和伏隔核内侧（NAc）的细胞外多巴胺（DA）。先前喂食过Fonzies，虽然这并不影响PFCX中细胞外DA对Fonzies喂食的增加反应，但会减弱NAc中的这种增加（习惯化）；在先前喂食Fonzies 5天后，NAc中的习惯化恢复完全。将Fonzies之外原本中性的外部刺激（空塑料盒）与Fonzies喂食进行预测性关联，导致该刺激获得了引发针对该刺激的激励反应并增加PFCX中细胞外DA的特性。然而，相同的刺激，或包括内在刺激（装有Fonzies的塑料盒）的更复杂刺激，未能获得改变NAc中细胞外DA的能力。假条件作用，即外部刺激（空盒子）与Fonzies喂食的非预测性关联，不会导致该刺激获得引发激励反应并增加PFCX中细胞外DA的特性。对先前已条件化的外部刺激（空盒子）进行重复的非强化呈现，会导致引发激励反应并增加PFCX中细胞外DA的特性消失。这些结果表明，在自由采食的大鼠中，动机性刺激对中皮质和中边缘DA系统的相位激活受到联想（条件作用）和非联想（习惯化）学习机制的不同影响，并且与激励动机的获得和表达存在不同的关系。
