Choice reaction time after levodopa challenge in parkinsonian patients

Various types of choice reaction time paradigms demonstrated deficits in th e preparation and execution of movements in parkinsonian subjects. These st udies showed controversial results, since they included parkinsonian indivi duals being: (previously untreated); (ii) off; (iii) on anti-parkinsonian m edication. Moreover, these trials do not take into consideration the acute effects of levodopa administration. Objective of this study was to determin e the effect of long-term dopaminergic substitution therapy within a standa rdized levodopa challenge test in combination with a repeatedly performed c hoice reaction rime task in parkinsonian individuals. Parkinsonian particip ants consisted of previously untreated, so-called "de-novo" patients and of individuals, who were chronically substituted with dopaminergic drugs, but were taken off medication for at least 12 h. All participants took 250 mg levodopa/benserazide after assessment of baseline data. Then we repeatedly measured choice reaction- and movement time within the next 90 min. No sign ificant change of the assessed task data appeared in the "de-novo" group, b ut reaction- and movement time significantly shortened in previously treate d subjects. Sedative effects of levodopa and/or dopaminergic overstimulatio n hypothetically explain the results of the previously untreated patients, whereas long-term dopaminergic substitution therapy hypothetically causes t olerance to these phenomena in treated parkinsonian individuals. Future stu dies on parkinsonian subjects should discuss their results on the basic pat hophysiology or basal ganglia dysfunction in the light of a putative impact of long-term anti-parkinsonian drug therapy. (C) 2000 Elsevier Science B.V . All rights reserved.