ASYMMETRICAL PRESYNAPTIC AND POSTSYNAPTIC CHANGES IN THE STRIATAL DOPAMINE PROJECTION IN DOPA NAIVE PARKINSONISM - DIAGNOSTIC IMPLICATIONS OF THE D2 RECEPTOR STATUS

Nine L-dopa naive patients with clinically diagnosed parkinsonism were studied using positron emission tomography with 6-L-[F-18]fluorodopa ([F-18]dopa, a pre-synaptic tracer) and [C-11]raclopride (which binds to D2 receptors). Putamen [F-18]dopa uptake was reduced in all patient s, confirming a loss of function affecting the nigrostriatal projectio n. In eight patients the putamen with the lowest [F-18]dopa uptake (al ways contralateral to the clinically most affected side) had the highe st [C-11]raclopride binding, suggesting upregulation of the post-synap tic D2 receptors. In the ninth patient [C-11]raclopride binding was lo wer in the putamen with the lowest [F-18]dopa uptake, indicating an ad ditional post-synaptic deficit. All nine patients were shown to be L-d opa responsive. The subsequent clinical course of the former eight pat ients has been typical of idiopathic Parkinson's disease, whilst the n inth patient has developed postural hypotension, urinary incontinence and respiratory stridor typical of multiple system atrophy. Reduced [C -11]raclopride binding in L-dopa naive parkinsonian patients might ser ve as a useful early marker of this condition.