Rats prefer cocaine over nicotine in a two-lever self-administration choice test.
Smoking is considered the leading cause of preventable death in the United States, but studies in animals suggest that nicotine is only weakly reinforcing. The maintenance of a dangerous habit by a weakly reinforcing agent has been the topic of some dispute. Using a two-lever "choice" self-administration procedure developed in our laboratory, we evaluated drug preferences as an index of relative reward strength for nicotine versus cocaine in nicotine-trained rats. Rats were initially exposed to each drug separately in single-lever self-administration sessions and then allowed to choose between them in a two-lever choice test session offering both drugs. When offered choices between different nicotine doses [8, 25, and 75 microg/kg/injection (inj), free base], rats responded approximately equally for any dose, regardless of which doses were compared. Rats clearly preferred 267 or 800 microg/kg/inj cocaine hydrochloride to any of the nicotine doses. These results indicate that cocaine has greater reward strength than nicotine and supports previous findings that self-administering rats seek to maximize reward magnitude regardless of the self-administered drug or training history. It is possible that dependence elevates nicotine's reward magnitude or nicotine addiction may rely more importantly upon negative rather than pure positive reinforcement.
Manzardo
A M
AM
College of Medicine, Department of Pharmacology, University of California-Irvine, Irvine, CA 92697-4625, USA. manzardo@scripps.edu
Stein
L
L
Belluzzi
J D
JD
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology; D003042:Cocaine / Q000494:pharmacology*; D019970:Cocaine-Related Disorders / Q000503:physiopathology*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007260:Infusion Pumps; D008297:Male; D009538:Nicotine / Q000494:pharmacology*; D018722:Nicotinic Agonists / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012054:Reinforcement, Psychology; D012201:Reward; D012646:Self Administration; D014029:Tobacco Use Disorder / Q000503:physiopathology*
D018765:Dopamine Uptake Inhibitors; D018722:Nicotinic Agonists; D009538:Nicotine; D003042:Cocaine