EFFECTS OF D1 DOPAMINE AGONISTS ON SCHEDULE-CONTROLLED BEHAVIOR IN THE SQUIRREL-MONKEY

Behavioral effects of several dopamine D1 receptor agonists were compa red with those of cocaine and (+)-amphetamine in squirrel monkeys trai ned to press a response key under a fixed-interval schedule of electri c shock presentation. Cocaine (0.03 to 0.3 mg/kg) and (+)-amphetamine (0.01 to 0.1 mg/kg) at low to intermediate doses increased rates of re sponding under the fixed-interval schedule; at higher doses each of th ese drugs decreased response rates. In contrast, neither full nor part ial D1 receptor agonists produced reliable increases in response rates . Rather, these drugs decreased rates of responding in a dose-related manner. These results with schedule-controled behavior in primates sup port earlier findings in rodents that indicate that D1 agonist actions result in effects quite different from the characteristic psychomotor stimulant effects produced by cocaine or (+)-amphetamine; and they fu rther suggest that those characteristic stimulant effects are more pro bably due to stimulation of other dopamine receptors.