Association between Striatal Subregions and Extrastriatal Regions in Dopamine D1 Receptor Expression: A Positron Emission Tomography Study

The mesencephalic dopamine (DA) system is the main DA system related to affective and cognitive functions. The system consists of two different cell groups, A9 and A10, which originate from different regions of the midbrain. The striatum is the main input from the midbrain, and is functionally organized into associative, sensorimotor and limbic subdivisions. At present, there have been few studies investigating the associations of DA functions between striatal subdivisions and extrastriatal regions. The aim of this study was to investigate the relationship of DA D(1) receptor (D(1)R) expression between striatal subdivisions and extrastriatal regions in humans using positron emission tomography (PET) with voxel-by-voxel whole brain analysis. The PET study was performed on 30 healthy subjects using [(11)C]SCH23390 to measure D(1)R expression. Parametric images of binding potentials (BP(ND)) were created using the simplified reference tissue model. Regions of interest were defined for striatal subdivisions. Multiple regression analysis was undertaken to determine extrastriatal regions that were associated with each striatal subdivision in BP(ND) using statistical parametric mapping 5. The BP(ND) values of associative, sensorimotor and limbic subdivisions were similarly correlated with those of multiple brain regions. Regarding the interrelationships among striatal subdivisions, mutual correlations were found among associative, sensorimotor and limbic subdivisions in BP(ND) as well. The relationships in BP(ND) between striatal subdivisions and extra-striatal regions suggest that differential striatal subdivisions and extrastriatal regions have a similar biological basis of D(1)R expression. Different DA projections from the midbrain did not explain the associations between striatal subdivisions and extrastriatal regions in D(1)R expression, and the DA-related neural networks among the midbrain, striatum and the other regions would contribute to a similar D(1)R expression pattern throughout the whole brain.