Dissociating the primary reinforcing and reinforcement-enhancing effects of nicotine using a rat self-administration paradigm with concurrently available drug and environmental reinforcers
Nicotine has two effects on reinforcement in traditional self-administration paradigms. It serves as a primary reinforcer by increasing the probability of behaviors that result in nicotine delivery. However, nicotine also potently enhances behaviors that result in the delivery of nonpharmacological reinforcers.
The present study sought to dissociate these two effects of nicotine on reinforcement.
For one group of rats (2 lever), a nonpharmacological reinforcer [visual stimulus (VS)] was available for pressing one lever. Nicotine infusions were available for pressing a different lever. A second group (NIC + VS) received more traditional self-administration training; both the VS and nicotine were delivered for pressing a single active lever. Control groups received either nicotine infusions (NIC only) or VS presentations (VS only) for pressing the active lever.
Nicotine alone was a weak reinforcer; the VS alone was slightly more reinforcing than nicotine. When these two reinforcers were combined (NIC + VS), response rates were synergistically increased. For the 2-lever group, responding on the nicotine lever was weak, matching the response rates of rats receiving nicotine alone. However, responding on the VS lever was potently enhanced in this group; equaling the response rates for rats receiving both reinforcers for making a single response (NIC + VS).
These data indicate that the reinforcement-enhancing effects of nicotine are very potent even when only moderate quantities of the drug are self-administered. Moreover, they provide the first demonstration that the reinforcement-enhancing and primary reinforcing effects of nicotine can be dissociated behaviorally.
KeywordsNicotine Self-administration Reinforcement Concurrent schedule Stimuli Acetylcholine
The authors would like to thank Dr. Neil Levens for his thoughtful comments on a previous version of this manuscript. All experiments followed the “Principles of laboratory animal care” (NIH #85-23, revised 1985) and were approved by the University of Pittsburgh Institutional Animal Care and Use Committee (assurance #A3187-01). This research was supported by NIH grants DA-10464, DA-12655, and DA-19278.
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