Differential responsiveness of dopamine transmission to food-stimuli in nucleus accumbens shell/core compartments

The nucleus accumbens septi is the major target of mesolimbic dopamine neur ons originating in the ventral tegmental area of the mesencephalon.(3) Stud ies involving experimental manipulation of dopamine transmission by drugs a nd by lesions, as well as in vivo monitoring of extracellular dopamine conc entrations, have provided evidence that the dopamine transmission of the nu cleus accumbens plays an important role in behaviour motivated by conventio nal (e.g., food, sex)(22,23,29) and drug reinforcers.(6,14) Motivated behav iour is distinguished into an appetitive (preparatory/anticipatory) phase c onsisting of flexible response patterns intended to search and approach the reward itself, and a consummatory phase, consisting of fixed response patt erns (eating, drinking, copulating, etc.) finalized to the utilization of t he biological resources of the reward (caloric, metabolic, genetic, etc.)(1 3) While some studies reported a stimulation of dopamine transmission in th e nucleus accumbens in relation to appetitive as well as consummatory behav iour,(7,19) other studies reported a relationship exclusively with consumma tory behaviour.(10,16,20,28) Therefore, the precise relationship between do pamine transmission in the nucleus accumbens and specific phases of motivat ed behaviour is debated. On the basis of topographical, histochemical and c onnectional evidence, the nucleus accumbens has been subdivided into two co mpartments, medioventral "shell" and a laterodorsal "core".(1,8,9,11) This heterogeneity may be relevant to the current debate over the role of nucleu s accumbens dopamine in behaviour. Thus, one might hypothesize that, depend ing on the specific compartment of the nucleus accumbens where dopamine tra nsmission is monitored, a different relationship with specific stimuli whic h motivate behaviour is obtained. In order to verify this possibility we mo nitored by microdialysis(4,27) 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 lab oratory to release dopamine in the nucleus accumbens shell and in the media l prefrontal cortex.(2) Unpredicted consumption of Fonzies preferentially s timulated dopamine transmission in the shell as compared to the core. Appet itive food stimuli (perforated Fonzies-filled boxes) phasically stimulated dopamine transmission in the core but not in the shell and sensitized the d opamine response to feeding in the core but inhibited that in the shell. Th ese clear-cut differences between nucleus accumbens shell and core suggest that phasic dopamine transmission in each compartment of the nucleus accumb ens subserves different roles in motivated behaviour. (C) 1999 IBRO. Publis hed by Elsevier Science Ltd.