Comparing the effects of scopolamine on operant and aggressive responses in squirrel monkeys.

The anticholinergic drug, scopolamine, causes disinhibition or an increase in responses that an animal normally suppresses. Experiment 1 confirmed this effect in squirrel monkeys. Experiment 2 explored the implications of drug-produced disinhibition on aggressive interactions. In Experiment 1, scopolamine produced increased unreinforced responding on a DRL schedule and increased responding during unreinforced (Time Out) periods. In contrast, the peripheral control drug, methyl scopolamine, caused decreased responding in both situations. In Experiment 2, social rank and drug treatment interacted. When space was restricted so that the opportunity for social interactions was maximized, scopolamine consistently increased aggressiveness in the dominant monkey and decreased aggressiveness in a submissive monkey. When space was increased so that the opportunity for social interactions was minimized, scopolamine caused decreased aggressive responses in all monkeys. Neither the effective dosage nor the drug's effect on the operant task could be easily generalized to aggressive responses.