title: Dopamine efflux in the nucleus accumbens during within-session extinction, outcome-dependent, and habit-based instrumental responding for food reward.
abstract: BACKGROUND
  Dopamine (DA) activity in the nucleus accumbens (NAc) is related to the general motivational effects of rewarding stimuli. Dickinson and colleagues have shown that initial acquisition of instrumental responding reflects action-outcome relationships based on instrumental incentive learning, which establishes the value of an outcome. Given that the sensitivity of responding to outcome devaluation is not affected by NAc lesions, it is unlikely that incentive learning during the action-outcome phase is mediated by DA activity in the NAc.
  
  
  OBJECTIVE
  DA efflux in the NAc after limited and extended training was compared on the assumption that comparable changes would be observed during both action-outcome- and habit-based phases of instrumental responding for food. This study also tested the hypothesis that increase in NAc DA activity is correlated with instrumental responding during extinction maintained by a conditioned stimulus paired with food.
  
  
  METHODS
  Rats were trained to lever press for food (random-interval 30 s schedule). On the 5th and 16th day of training, microdialysis samples were collected from the NAc or mediodorsal striatum (a control site for generalized activity) during instrumental responding in extinction and then for food reward, and analyzed for DA content using high performance liquid chromatography.
  
  
  RESULTS
  Increase in DA efflux in the NAc accompanied responding for food pellets on both days 5 and 16, with the magnitude of increase significantly enhanced on day 16. DA efflux was also significantly elevated during responding in extinction only on day 16.
  
  
  CONCLUSIONS
  These results support a role for NAc DA activity in Pavlovian, but not instrumental, incentive learning.
authors.affiliation: Department of Psychiatry, University of British Columbia, 2255 Wesbrook Mall, Vancouver, British Columbia, V6T 2A1, Canada.
authors.forename: Soyon
authors.initials: S
authors.lastname: Ahn
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Phillips
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002851:Chromatography, High Pressure Liquid; D003216:Conditioning, Operant; D004298:Dopamine / Q000378:metabolism*; D005108:Extinction, Psychological; D005247:Feeding Behavior; D006040:Goals; D006184:Habits; D008297:Male; D017551:Microdialysis; D009042:Motivation; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009714:Nucleus Accumbens / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D012201:Reward; D013997:Time Factors; D035501:Uncertainty
chemical_list: D018377:Neurotransmitter Agents; D004298:Dopamine