EFFECTS OF DIHYDREXIDINE, A FULL DOPAMINE D-1 RECEPTOR AGONIST, ON DELAYED-RESPONSE PERFORMANCE IN CHRONIC LOW-DOSE MPTP-TREATED MONKEYS

Monkeys exposed to low doses of the neurotoxin 1-methyl-4-phenyl-1,2,3 ,6-tetrahydropyridine (MPTP) over long periods of time develop cogniti ve deficits without severe parkinsonian motor signs. In the present st udy we assessed the effects of the selective and full dopamine D-1 rec eptor agonist dihydrexidine on delayed response deficits in chronic lo w dose (CLD) MPTP-treated monkeys. Dihydrexidine caused a dose-depende nt improvement in task performance, that could be blocked by the D-1 r eceptor antagonist SCH-23390. In addition to reducing the number of mi stakes made during delayed response performance, dihydrexidine also im proved task persistence. These data suggest that dihydrexidine may be useful in treating cognitive as well as motor deficits of parkinsonism .