Nicotine enhances responding with conditioned reinforcement.

Abstract

The mesolimbic dopamine system has been implicated in the primary reinforcing properties of drugs of abuse as well as in enhanced responding with conditioned reinforcement produced by psychomotor stimulant drugs. Despite clinical observations that nicotine self-administration (i.e. smoking) depends strongly upon conditioned reinforcement (i.e. cues support smoking behavior), little is known about whether nicotine directly affects motivational processes. In these experiments, we investigated whether acute nicotine would influence responding with conditioned reinforcement and the degree to which pretreatment with the nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine would modify any nicotine-induced behavioral effects. After subjects had been trained to associate an initially neutral stimulus with water reward, they received acute nicotine (43,25-350 micro g/kg SC; -5 min) or saline injections and were tested on the acquisition of a new response for conditioned reinforcement paradigm. In separate experiments, the effect of pretreatment with the nicotinic acetylcholine receptor antagonist mecamylamine (300 or 1000 micro g/kg SC; -20 min) alone, or in combination with nicotine (350 micro g/kg SC; -5 min), on conditioned reinforcement was also examined. Acute nicotine injection produced a selective enhancement of responding with conditioned reinforcement (i.e. on the CR lever), without producing non-selective increases in overall responding. The effect of nicotine (350 micro g/kg SC; -5 min) was selectively blocked by mecamylamine (300 micro g/kg). These findings demonstrate that acute exposure to nicotine augments the control over behavior by a conditioned reinforcer, suggesting that nicotine may enhance motivational processes.