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Operant responding for conditioned and unconditioned reinforcers in rats is differentially enhanced by the primary reinforcing and reinforcement-enhancing effects of nicotine
Authors:Nadia Chaudhri  Anthony R. Caggiula  Eric C. Donny  Sheri Booth  Maysa Gharib  Laure Craven  Matthew I. Palmatier  Xiu Liu  Alan F. Sved
Affiliation:(1) Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA;(2) Department of Psychology, University of Pittsburgh, Pittsburgh, PA, USA;(3) Ernest Gallo Clinic and Research Center, University of California at San Francisco, Suite 200, 5858 Horton Street, Emeryville, CA 94608, USA
Abstract:Rationale 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.Objectives 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.Materials and 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.
Keywords:Acetylcholine  Self‑  administration  Reinforcement  Operant  Nicotine  Tobacco  Pavlovian  Rats  Nonpharmacological stimulus  Smoking
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