Suppression of behavior by intravenous injections of nicotine or by electric shocks in squirrel monkeys: effects of chlordiazepoxide and mecamylamine.

Squirrel monkeys responded under a two-component fixed-ratio schedule of food presentation with both nonpunishment and punishment components. In both components of the multiple schedule, every 30th key-pressing response resulted in food presentation. In the punishment component, the first response in each 30-response fixed ratio also produced either an i.v. injection of nicotine (10-30 micrograms/kg) or an electric shock (1-5 mA). Response-produced nicotine injections or electric shocks functioned similarly to suppress responding by over 70% in the punishment component. Presession treatment with chlordiazepoxide (5.6-10 mg/kg i.m.) markedly increased responding that had been suppressed by either nicotine injection or electric shock. In contrast, presession treatment with the nicotinic antagonist, mecamylamine (0.1-0.3 mg/kg i.m.) increased responding that had been suppressed by nicotine injection but did not increase responding that had been suppressed by electric shock. Thus, chlordiazepoxide appeared to have general rate-increasing effects on suppressed responding, regardless of the nature of the event suppressing responding, whereas mecamylamine appeared to selectively antagonize the suppressant effects of nicotine. Doses of chloridazepoxide and mecamylamine that increased suppressed responding in punishment components either had little effect on or slightly increased responding in nonpunishment components. These results show that under suitable environmental conditions response-produced i.v. injection of nicotine can function effectively as a punisher.