Presynaptic and postsynaptic dopaminergic binding densities in the nigrostriatal and mesocortical systems in early Parkinson's disease: A double‐tracer positron emission tomography study

To investigate changes in the relation between presynaptic and postsynaptic dopaminergic functions in vivo in both nigrostriatal and mesocortical systems in Parkinson's disease (PD), 10 drug‐naive early PD patients were studied twice using positron emission tomography with [11C]CFT (dopamine transporter probe) followed by [11C]SCH 23390 (D1 receptor probe). Regional binding potentials (k3/k4) of [11C]CFT and [11C]SCH 23390 in the striatum (nigrostriatal system) and the orbitofrontal cortex (mesocortical system) were estimated by compartment analyses. Levels of [11C]CFT k3/k4 in the two projection areas were shown to be significantly lower in PD, whereas [11C]SCH 23390 levels remained unchanged. Regression analysis showed that estimates of CFT k3/k4 were positively correlated with those of SCH 23390 k3/k4 in the striatum in normal control, whereas the two binding estimates were less positively correlated in the caudate and inversely correlated in the putamen in PD. No significant correlation was observed in the orbitofrontal cortex in both groups. These results indicated that dopamine transporters and D1 receptors change in parallel in the normal striatal synapses, but the association becomes asymmetrical because of reduction in presynaptic and relative elevation in postsynaptic markers in PD. Alterations in synaptic parallel regulation in the nigrostriatal system might reflect early pathophysiology in the parkinsonian brain.