title: Differential influence of morphine sensitization on accumbens shell and core dopamine responses to morphine- and food-conditioned stimuli.
abstract: BACKGROUND
  Sensitization of the incentive and dopamine (DA) stimulant properties of drug-conditioned stimuli (CSs) by repeated exposure to drugs of abuse has been assigned an important role in the genesis of drug addiction.
  
  
  OBJECTIVE
  To test in rats if morphine-induced sensitization potentiates incentive and DA-releasing properties in the nucleus accumbens (NAc) shell and core elicited by presentation of a morphine-conditioned stimulus(CS) and if this property generalizes to a non-drug-(palatable food, Fonzies)-CS.
  
  
  METHODS
  Controls and rats previously sensitized by morphine were trained via three daily sessions consisting of a 10-min presentation of CS (Fonzies filled box, FB) followed by s.c. saline and morphine (1 mg/kg) or by standard food and Fonzies. Rats were implanted with microdialysis probes and the next-day incentive reactions and NAc shell and core DA were monitored during CS presentation and subsequent morphine (1 mg/kg) administration or Fonzies feeding.
  
  
  RESULTS
  Morphine sensitization increased incentive and NAc shell and core DA responses to morphine-CS. Morphine conditioning per se increased incentive reactions and NAc shell but not core DA responses to FB presentation. Morphine sensitization potentiated incentive responses but did not affect NAc shell and core DA responses to Fonzies-CS. Fonzies conditioning increased incentive reactions and NAc core but not shell DA responses to FB presentation.
  
  
  CONCLUSIONS
  These observations confirm the prediction of the incentive sensitization theory in the case of drug-CS but not of non-drug-CS. NAc DA might be differentially involved in the expression of incentive sensitization of drug- and non-drug-CSs, thus providing a clue for the abnormal incentive properties of drug CSs.
authors.affiliation: Department of Biomedical Sciences, National Institute of Neuroscience, University of Cagliari, Via Ospedale 72, Cagliari, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bassareo
authors.forename: Flavia
authors.initials: F
authors.lastname: Cucca
authors.forename: Cristina
authors.initials: C
authors.lastname: Cadoni
authors.forename: Paolo
authors.initials: P
authors.lastname: Musio
authors.forename: Gaetano
authors.initials: G
authors.lastname: Di Chiara
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001931:Brain Mapping; D003213:Conditioning, Psychological / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism*; D005502:Food; D013287:Illicit Drugs / Q000009:adverse effects*; D008297:Male; D009020:Morphine / Q000009:adverse effects*; D009021:Morphine Dependence / Q000378:metabolism / Q000523:psychology; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D013287:Illicit Drugs; D009020:Morphine; D004298:Dopamine