Maintenance and suppression of behavior by intravenous nicotine injections in squirrel monkeys.

Nicotine appears to be a contributing factor in maintaining cigarette smoking, but experimental evidence for its reinforcing effects is scarce. Indeed, it has been suggested that in some situations nicotine may have noxious properties, which limit smoking behavior. These ideas were explored by comparing the effects of intravenous injections of nicotine on behavior of squirrel monkeys under two experimental procedures. Under a fixed-interval schedule of nicotine self-administration, responding was well maintained by injections of 30-300 microgram/kg of nicotine. Nicotine-maintained responding could be reduced by presession treatment with the nicotine antagonist, mecamylamine, or by substitution of saline for nicotine. In a second experiment, responding was maintained under a two-component fixed-ratio schedule of food presentation in which responses during one component (punishment component) also resulted in injections of 10-30 microgram/kg of nicotine. Nicotine markedly suppressed responding during the punishment component but not during the alternating nonpunishment components. The suppressant effects of nicotine could be reversed by presession treatment with either mecamylamine or the antianxiety drug chlordiazepoxide, or by substitution of saline for nicotine. Nicotine had pronounced effects both as a reinforcer and as a punisher; the nature of the effects depended on the schedule under which nicotine was administered.