title: Differential effects on natural reward processing in rats after repeated heroin.
abstract: BACKGROUND
  Heroin users report reward deficits as well as reward enhancements (to drug stimuli). To better understand the causal relation between chronic heroin and alterations in natural reward processing, we used experimental techniques in animal models.
  
  
  METHODS
  Separate groups of rats were trained in several food reward paradigms: conditioned place preference (CPP), food-reinforced lever pressing under a progressive ratio schedule of reinforcement, free feeding, and lever pressing with conditioned reinforcement. After training, the rats were subjected to 10 daily heroin (2 mg/kg) or saline vehicle injections and tested at 3, 15, and 30 days post-treatment.
  
  
  RESULTS
  Repeated heroin treatment abolished the CPP and significantly reduced break points for food reward at 3, 15, and 30 days post-treatment. Repeated heroin did not affect free feeding. Finally, repeated heroin significantly enhanced responding for a food-based conditioned reinforcer.
  
  
  CONCLUSIONS
  Repeated heroin decreases the attractiveness of food-associated cues and reduces motivation to work for natural reward. However, it appears to enhance natural conditioned reward processes that involve the acquisition of novel responding. Thus, repeated heroin appears to produce differential effects on natural reward processing depending on the nature of the reward-directed behavior.
authors.affiliation: The Graduate Center, City University of New York, New York, NY, USA.
authors.forename: Ewa
authors.initials: E
authors.lastname: Galaj
authors.forename: Ivonne
authors.initials: I
authors.lastname: Cruz
authors.forename: Jordan
authors.initials: J
authors.lastname: Schachar
authors.forename: Matthew
authors.initials: M
authors.lastname: Koziolek
authors.forename: Robert
authors.initials: R
authors.lastname: Ranaldi
mesh_terms: D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects* / Q000502:physiology; D003932:Heroin / Q000008:administration & dosage*; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D012055:Reinforcement Schedule
chemical_list: D003932:Heroin