Reciprocal responsiveness of nucleus accumbens shell and core dopamine to food- and drug-conditioned stimuli.
BACKGROUND
Drugs of abuse and palatable food share the ability to stimulate dopamine (DA) transmission in the nucleus accumbens shell. However, while the stimulation of shell DA by food undergoes habituation, that by drugs of abuse does not.


OBJECTIVE
This study aims to directly compare the changes of extracellular DA, by microdialysis, in shell and core and prefrontal cortex (PFCX) in response to food- and drug-conditioned stimuli (CSs).


METHODS
Rats were trace-conditioned by Fonzies box (FB) or vanilla box (VB; CS), followed by food: Fonzies, intraoral chocolate solution (food-unconditioned stimulus (US)) and morphine (1.0 mg/Kg sc; drug US). Control (unconditioned) rats received standard food instead of Fonzies, tap water instead of chocolate, saline instead of morphine.


RESULTS
Food-CSs increased core but not shell DA, while drug-CSs did the opposite. Food and drug-CSs both increased PFCX DA. Exposure to food-CSs potentiated core and PFCX DA response to food while shell responsiveness was dependent upon the relative CS and US nature. If the CS was intrinsic to the food US (CS = FB/US = Fonzies) the response of shell DA to the US was abolished. If the CS was extrinsic to the food US (CS = FB/US = chocolate; CS = VB/US = Fonzies), shell DA increased in response to the US. Exposure to the drug-CS potentiated the DA response to the drug-US in the shell and in the PFCX, but not in the core.


CONCLUSIONS
Drug-CSs differentially activate DA as compared to food-CSs in shell and core and differentially affect DA response to the US in these areas. These differences might be relevant for the role of DA in the mechanism of drug addiction.
Department of Toxicology, CNR Institute of Neuroscience, Section of Cagliari, National Institute of Neuroscience, University of Cagliari, Via Ospedale 72, 09124, Cagliari, Italy.
Valentina
V
Bassareo
Paolo
P
Musio
Gaetano
G
Di Chiara
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal; D002099:Cacao; D003214:Conditioning, Classical / Q000187:drug effects* / Q000502:physiology; D004298:Dopamine / Q000378:metabolism*; D005502:Food; D008297:Male; D017551:Microdialysis / Q000379:methods; D009020:Morphine / Q000008:administration & dosage*; D009294:Narcotics / Q000008:administration & dosage*; D009714:Nucleus Accumbens / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D017397:Prefrontal Cortex / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D013549:Sweetening Agents / Q000008:administration & dosage
D009294:Narcotics; D013549:Sweetening Agents; D009020:Morphine; D004298:Dopamine