Operant responding for a visual reinforcer in rats is enhanced by noncontingent nicotine: implications for nicotine self-administration and reinforcement.
BACKGROUND
Current conceptualizations of drug reinforcement assume that drug-taking behavior is a consequence of the contingent, temporal relationship between the behavior and drug reward. However, stimulant drugs also potentiate the rewarding effects of other reinforcers when administered noncontingently.


OBJECTIVE
These studies were designed to determine whether noncontingent nicotine enhances the reinforcing properties of a nonpharmacological reinforcer and whether this direct effect facilitates operant behavior within the context of a nicotine self-administration procedure.


METHODS
Rats self-administered nicotine or food, or received noncontingent nicotine, saline, or food either with or without a response-contingent, unconditioned reinforcing visual stimulus (VS).


RESULTS
Noncontingent nicotine, whether delivered as discrete injections based on a pattern of self-administered nicotine or as a continuous infusion, increased response rates maintained by the VS. There were no significant differences in responding by animals that received contingent compared with noncontingent nicotine when a VS was available. This increase was not observed in the absence of the VS or as a consequence of noncontingent food delivery. Operant behavior was equally attenuated and reinstated by the removal and subsequent replacement of contingent and noncontingent nicotine. Nicotine supported self-administration in the absence of response-contingent, nicotine-paired stimuli; however, response rates were drastically reduced compared with nicotine self-administration with the VS.


CONCLUSIONS
Nicotine influences operant behavior in two ways: by acting as a primary reinforcer when it is contingent upon behavior, and by directly potentiating the reinforcing properties of other stimuli through a nonassociative mechanism. Nicotine self-administration and smoking may be largely dependent upon this later action.
Donny
Eric C
EC
Department of Psychiatry, Behavioral Pharmacology Research Unit, Johns Hopkins University School of Medicine, Baltimore, Md., USA.
Chaudhri
Nadia
N
Caggiula
Anthony R
AR
Evans-Martin
F Fay
FF
Booth
Sheri
S
Gharib
Maysa A
MA
Clements
Laure A
LA
Sved
Alan F
AF
D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects*; D008297:Male; D009538:Nicotine / Q000008:administration & dosage* / Q000494:pharmacology; D010775:Photic Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012201:Reward; D012646:Self Administration
D009538:Nicotine