Preferences for tastes paired with a nicotine antagonist in rats chronically treated with nicotine

The present report addressed the hypothesis that withdrawal from chronic nicotine treatment activates the same motivational processes as withdrawal from chronic opiate treatment. Conditioning produced by the nicotine antagonist mecamylamine in nicotine-treated animals was studied and compared to the well-known potentiation by opiate treatment of the aversive conditioning produced by the opiate antagonist naloxone. A sensitive two-flavor, three-trial, taste conditioning procedure was used and it was found that chronic treatment using Alzet minipumps for 1 month with nicotine (8 or 16 mg/kg/day) potentiated the ability of mecamylamine to produce taste conditioning. Thus, in nicotine-placebo control animals, only 1.0 mg/kg mecamylamine (s.c.) produced significant conditioning, whereas in nicotine-treated animals 0.5 and 1.0 mg/kg mecamylamine was effective. However, in contrast to chronic opiate treatment, which increases the aversive effect of an opiate antagonist (as confirmed here using treatment for one month with 0.25 mg/kg/day fentanyl and taste conditioning with 0.1 mg/kg naloxone, s.c.), the nicotine treatment changed the valence of the mecamylamine conditioning. The nicotine-naive animals avoided the mecamylamine-paired flavor, whereas the nicotine-exposed subjects preferred it. These findings indicated that there may be important differences between nicotine and opiate withdrawal. Not all effects of nicotine withdrawal in models of addiction can be assumed to be negatively motivating.