Effects of D1 dopamine agonists on schedule-controlled behavior in the squirrel monkey

Behavioral effects of several dopamine D1 receptor agonists were compared with those of cocaine and (+)-amphetamine in squirrel monkeys trained to press a response key under a fixed-interval schedule of electric shock presentation. Cocaine (0.03 to 0.3mg/kg) and (+)-amphetamine (0.01 to 0.1mg/kg) at low to intermediate doses increased rates of responding under the fixed-interval schedule; at higher doses each of these drugs decreased response rates. In contrast, neither full nor partial 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-controlled behavior in primates support 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 further suggest that those characteristic stimulant effects are more probably due to stimulation of other dopamine receptors.