Worsened motor test performance following acute apomorphine injection in previously untreated patients with Parkinson's disease

Abstract

Instrumental tests and clinical rating assess motor disability in Parkinson's disease (PD) patients. Previous long-term dopaminergic substitution influences the behaviour following acute dopaminergic stimulation. Objective of this study was to investigate the motor response following an apomorphine application in previously untreated-, treated- and before treated PD patients, who received placebo. Outcomes of instrumental tests worsened in previously untreated-, but not in before treated PD patients after apomorphine injection and in the PD subjects under the placebo condition. Generally, rating scores of motor symptoms significantly improved after apomorphine administration, whereas placebo application showed no effects. Tolerance to sedative effects of apomorphine in treated PD patients or sensitivity of employed motor tests to presynaptic dopaminergic autoreceptor mediated inhibition of endogenous dopamine release or postsynaptic dopaminergic overstimulation with resulting decreased cognitive function in previously untreated PD patients hypothetically caused this discrepancy between outcomes of subjective clinical rating and objective motor test performance.