title: Behavioral economics of food reinforcement and the effects of prefeeding, extinction, and eticlopride in dopamine D2 receptor mutant mice.
abstract: BACKGROUND
  Several studies have investigated the reinforcing effects of food in genetically engineered mice lacking dopamine D(2) receptors (DA D(2)Rs); however, behavioral economic analyses quantifying reinforcement have not been conducted.
  
  
  OBJECTIVE
  The role of DA D(2)Rs in food reinforcement was examined by comparing responding under various fixed-ratio (FR) schedules of reinforcement, and effects of extinction, satiation, and the DA D(2)R antagonist eticlopride, in mice with and without genetic deletions of the receptor.
  
  
  RESULTS
  Response rates of DA D(2)R knockout (KO) mice were generally lower than those of littermate wild-type (WT) and heterozygous (HET) mice. The demand curve (consumption vs. FR value) for KO mice decreased more steeply than that of HET or WT mice, suggesting that reinforcing effectiveness is decreased with DA D(2)R deletion. Prefeeding decreased, whereas extinction increased overall response rates as a proportion of baseline, with no significant genotype differences. Both (+)- and (-)-eticlopride dose-dependently decreased responding in all genotypes with (-)-eticlopride more potent than (+)-eticlopride in all but KO mice. The enantiomers were equipotent in KO mice, and similar in potency to (+)-eticlopride in WT and HET mice.
  
  
  CONCLUSIONS
  That prefeeding and extinction did not vary across genotypes indicates a lack of involvement of DA D(2)Rs in these processes. Differences between (-)-eticlopride effects and extinction indicate that DA D(2)R blockade does not mimic extinction. The maintenance of responding in KO mice indicates that the DA D(2)R is not necessary for reinforcement. However, the economic analysis indicates that the DA D(2)R contributes substantially to the effectiveness of food reinforcement.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Division of Behavioral Biology, Johns Hopkins University, Ross 469, 720 Rutland Ave, Baltimore, MD 21205, USA. psoto@jhmi.edu
authors.forename: Paul L
authors.initials: PL
authors.lastname: Soto
authors.forename: David K
authors.initials: DK
authors.lastname: Grandy
authors.forename: Steven R
authors.initials: SR
authors.lastname: Hursh
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Katz
mesh_terms: D000818:Animals; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D005108:Extinction, Psychological / Q000187:drug effects* / Q000502:physiology; D005247:Feeding Behavior / Q000187:drug effects / Q000502:physiology; D005502:Food; D006579:Heterozygote; D006720:Homozygote; D051379:Mice; D018345:Mice, Knockout; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000502:physiology; D012055:Reinforcement Schedule; D012457:Salicylamides / Q000494:pharmacology*
chemical_list: D065127:Dopamine D2 Receptor Antagonists; D017448:Receptors, Dopamine D2; D012457:Salicylamides; C045989:eticlopride