Effects of propranolol on behavior maintained under fixed-ratio schedules of cocaine injection or food presentation in squirrel monkeys.

Behavior of squirrel monkeys was maintained under comparable 30-response fixed-ratio schedules of cocaine injection or fooc presentation. Every 30th key press in the presence of a green light produced an intravenous injection of 25 mug/kg of cocaine in one group of monkeys or delivery of a food pellet in a second group of monkeys. Each cocaine injection or food presentation was followed by a 1-minute timeout period, during which the green light was absent and responses had no programmed consequences. Responding at a mean rate of more than 1/sec was maintained in the presence of the green light during each daily session. Propranolol doses from 0.3 to 3.0 mg/kg i.m. had no effect on food-maintained responding but decreased cocaine-maintained responding by approximately 30%. The selective disruption of cocaine-maintained responding by propranolol appeared to depend on the cumulative cocaine dose. Decreases in cocaine-maintained responding after propranolol became increasingly pronounced as the session progressed. Similar progressive decreases in cocaine-maintained responding were produced by increasing the dose of cocaine per injection.