title: Operant responding for conditioned and unconditioned reinforcers in rats is differentially enhanced by the primary reinforcing and reinforcement-enhancing effects of nicotine.
abstract: BACKGROUND
  Nicotine self-administration in rats is modest when response-contingent nicotine infusions are delivered alone (primary reinforcement) but robust when nicotine infusions are combined with a mildly reinforcing non-pharmacological stimulus. Furthermore, response-independent (non-contingent) nicotine administration also elevates responding for that same non-pharmacological stimulus, suggesting that in addition to primary reinforcement, nicotine can enhance the incentive value of other reinforcers.
  
  
  OBJECTIVE
  In this study, we tested the hypothesis that the reinforcement-enhancing effects of non-contingent nicotine are more dependent on the reinforcing strength of the non-pharmacological stimulus than are the effects of contingent nicotine.
  
  
  METHODS
  A weakly reinforcing light-tone stimulus was established as a conditioned reinforcer by repeated pairings with sucrose for some rats, or by delivery in an explicitly unpaired design with sucrose to other rats. Subsequently, both groups lever pressed for the stimulus with contingent nicotine, non-contingent nicotine (0.06 mg kg(-1) per infusion, freebase), or non-contingent saline, according to fixed ratio and progressive ratio reinforcement schedules.
  
  
  RESULTS
  Compared to sucrose-unpaired training, repeated association with sucrose established the light-tone stimulus as a robust conditioned reinforcer. Contingent and non-contingent nicotine equally elevated responding for this conditioned stimulus. Conversely, for the less reinforcing (sucrose-unpaired) stimulus contingent nicotine more effectively elevated behavior compared to non-contingent nicotine.
  
  
  CONCLUSIONS
  The reinforcement-enhancing effect of nicotine increases behavior controlled by both conditioned and unconditioned reinforcers; however, for less salient stimuli associative processes derived from the primary reinforcing effects of contingent nicotine may also be important. These data suggest that nicotine present in tobacco may differentially modulate stimulus-driven behavior in smokers.
authors.affiliation: Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA. nchaudhri@gallo.ucsf.edu
authors.forename: Nadia
authors.initials: N
authors.lastname: Chaudhri
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Caggiula
authors.forename: Eric C
authors.initials: EC
authors.lastname: Donny
authors.forename: Sheri
authors.initials: S
authors.lastname: Booth
authors.forename: Maysa
authors.initials: M
authors.lastname: Gharib
authors.forename: Laure
authors.initials: L
authors.lastname: Craven
authors.forename: Matthew I
authors.initials: MI
authors.lastname: Palmatier
authors.forename: Xiu
authors.initials: X
authors.lastname: Liu
authors.forename: Alan F
authors.initials: AF
authors.lastname: Sved
mesh_terms: D000818:Animals; D001245:Association Learning / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects*; D008297:Male; D009042:Motivation; D009538:Nicotine / Q000008:administration & dosage / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012054:Reinforcement, Psychology; D012646:Self Administration; D013395:Sucrose / Q000008:administration & dosage; D013997:Time Factors; D014029:Tobacco Use Disorder / Q000523:psychology*
chemical_list: D018722:Nicotinic Agonists; D013395:Sucrose; D009538:Nicotine