Stereotyped behaviour in response to the selective D-2 dopamine receptor agonist RU 24213 is enhanced by pretreatment with the selective D-1 agonist SK&F 38393.

When given alone, 2.5 mg/kg of the selective D-2 agonist RU 24213 was a threshold dose for the induction of weak stereotyped behaviour, while 15 mg/kg of the selective D-1 agonist SK&F 38393 failed to induce stereotypy. Responses to 2.5 mg/kg RU 24213 were dose-dependently potentiated by 3.0-15.0 mg/kg SK&F 38393, and compulsive stereotypy was only evident in animals receiving the combination treatment. Increasing D-1 dopaminergic activity appears to promote the expression of behaviours initiated through D-2 receptor stimulation.