title: Influence of morphine sensitization on the responsiveness of mesolimbic and mesocortical dopamine transmission to appetitive and aversive gustatory stimuli.
abstract: BACKGROUND
  Repeated treatment with morphine has been shown to sensitize rats to its stimulant effects on motor activity and mesolimbic dopamine (DA) transmission.
  
  
  OBJECTIVE
  The aim of this study is to investigate if morphine sensitization is associated to changes in the behavioral reactions to appetitive and aversive taste stimuli and in the response of in vivo DA transmission in the nucleus accumbens (NAc) shell and core and medial prefrontal cortex (PFCX) to the same stimuli.
  
  
  METHODS
  Rats were administered twice a day for three consecutive days with increasing doses of morphine [10, 20, and 40 mg/kg, subcutaneously (sc)] or with saline. After 15 days of withdrawal, rats were infused intraorally with either an appetitive (sweet chocolate, 1 ml) or an aversive solution (quinine HCl 5 × 10(-4) M, 1 ml). The behavioral taste reactions were recorded during microdialysis of DA in the NAc shell and core and PFCX.
  
  
  RESULTS
  Opiate sensitization did not affect behavioral reactions to intraoral chocolate or quinine. In rats naive to the taste stimuli, morphine sensitization was associated to potentiation of stimulatory DA response to appetitive and aversive taste stimuli in the NAc core. Morphine sensitization reciprocally affected habituation of DA responsiveness after one trial exposure to appetitive and aversive taste stimuli (abolition it in the shell, induction in the PFCX). No habituation of DA responsiveness to taste was observed in the NAc core in controls as well as in morphine-sensitized rats.
  
  
  CONCLUSIONS
  These results suggest that opiate sensitization is associated to differential adaptive changes of the responsiveness of DA transmission to taste stimuli in DA terminal areas.
authors.affiliation: Department of Toxicology, University of Cagliari, Via Ospedale 72, Cagliari, Italy. deluca@unica.it
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: De Luca
authors.forename: Zisis
authors.initials: Z
authors.lastname: Bimpisidis
authors.forename: Valentina
authors.initials: V
authors.lastname: Bassareo
authors.forename: Gaetano
authors.initials: G
authors.lastname: Di Chiara
mesh_terms: D000818:Animals; D001070:Appetitive Behavior / Q000187:drug effects*; D002099:Cacao; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D009020:Morphine / Q000494:pharmacology*; D009021:Morphine Dependence / Q000378:metabolism / Q000503:physiopathology; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D017397:Prefrontal Cortex / Q000187:drug effects* / Q000378:metabolism; D011803:Quinine; D051381:Rats; D017207:Rats, Sprague-Dawley; D013239:Stereotyped Behavior / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*; D055697:Taste Perception / Q000187:drug effects*
chemical_list: D009020:Morphine; D011803:Quinine; D004298:Dopamine