A PET study with [11-C]raclopride in Parkinson's disease: preliminary results on the effect of amantadine on the dopaminergic system

Amantadine has been proved to be beneficial in Parkinson's disease. Althoug h it is still uncertain which neurochemical events are modified at therapeu tic doses, an increase in dopaminergic tone secondary to NMDA receptor bloc kade and a direct inhibition of the glutamatergic overactivity have been su ggested to be involved in its clinical effects. The aim of this study was t o evaluate the effects of amantadine on the dopaminergic system by measurin g the in vivo binding of [11-C]raclopride to D2 dopamine receptors in the b asal ganglia of 6 patients with idiopathic Parkinson's disease. Each patien t underwent a PET study, before and after 14 days of treatment with amantad ine (200 mg/day). Repeated treatment with therapeutic doses of amantadine i nduced a moderate increase in the in vivo binding of [11-C]raclopride in th e putamen of PD patients. This observation indicates that in PD patients, 2 00 mg/day amantadine does not produce an increase in extracellular levels o f dopamine sufficiently to inhibit raclopride binding or that, if present, is it masked by a concurrent increase in receptor availability, as recently reported in rat striatum.