title: New operant model of reinstatement of food-seeking behavior in mice.
abstract: BACKGROUND
  A major problem in treating obesity is the high rate of relapse to abnormal food-taking behavior when maintaining diet.
  
  
  OBJECTIVE
  The present study evaluates the reinstatement of extinguished palatable food-seeking behavior induced by cues previously associated with the palatable food, re-exposure to this food, or stress. The participation of the opioid and dopamine mechanisms in the acquisition, extinction, and cue-induced reinstatement was also investigated.
  
  
  METHODS
  C57BL/6 mice were first trained on a fixed-ratio-1 schedule of reinforcement to obtain chocolate-flavored pellets during 20 days, which was associated to a stimulus light. Operant behavior was then extinguished during 20 daily sessions. mRNA levels of opioid peptide precursors and dopamine receptors were evaluated in the brain by in situ hybridization and RT-PCR techniques.
  
  
  RESULTS
  A reinstatement of food-seeking behavior was only obtained after exposure to the food-associated cue. A down-regulation of prodynorphin mRNA was found in the dorsal striatum and nucleus accumbens after the acquisition, extinction, and reinstatement of the operant behavior. Extinction and reinstatement of this operant response enhanced proenkephalin mRNA in the dorsal striatum and/or the nucleus accumbens core. Down-regulation of D2 receptor expression was observed in the dorsal striatum and nucleus accumbens after reinstatement. An up-regulation of PDYN mRNA expression was found in the hypothalamus after extinction and reinstatement.
  
  
  CONCLUSIONS
  This study provides a new operant model in mice for the evaluation of food-taking behavior and reveals specific changes in the dopamine and opioid system associated to the behavioral responses directed to obtain a natural reward.
authors.affiliation: Departament de Ciencies Experimentals i de la Salut, Universitat Pompeu Fabra, PRBB, Barcelona, Spain.
authors.forename: Elena
authors.initials: E
authors.lastname: Martín-García
authors.forename: Aurelijus
authors.initials: A
authors.lastname: Burokas
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Kostrzewa
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Gieryk
authors.forename: Michal
authors.initials: M
authors.lastname: Korostynski
authors.forename: Barbara
authors.initials: B
authors.lastname: Ziolkowska
authors.forename: Barbara
authors.initials: B
authors.lastname: Przewlocka
authors.forename: Ryszard
authors.initials: R
authors.lastname: Przewlocki
authors.forename: Rafael
authors.initials: R
authors.lastname: Maldonado
mesh_terms: D000818:Animals; D016739:Behavior, Addictive; D001921:Brain / Q000378:metabolism / Q000503:physiopathology; D003216:Conditioning, Operant / Q000502:physiology*; D004195:Disease Models, Animal; D005247:Feeding Behavior / Q000502:physiology*; D001068:Feeding and Eating Disorders / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology; D005502:Food; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018847:Opioid Peptides / Q000378:metabolism; D011954:Receptors, Dopamine / Q000378:metabolism; D012008:Recurrence; D013315:Stress, Psychological / Q000378:metabolism / Q000503:physiopathology* / Q000523:psychology
chemical_list: D018847:Opioid Peptides; D011954:Receptors, Dopamine