PET mapping of extrastriatal D2-like dopamine receptors in the human brain using an anatomic standardization...

The Computerized Brain Atlas (CBA) transforms PET images of individual subjects into a standard brain anatomy. We have previously applied this to PET images with [(11)C]raclopride and confirmed that the D2 dopamine receptors in the striatum can be evaluated accurately with a standard brain anatomy. There is growing evidence that extrastriatal D2 receptors, in spite of their low density, have pathophysiological significance for schizophrenia. We used the CBA to explore the extrastriatal distribution of D2 receptors in 13 healthy subjects using [11C]FLB 457, a substituted benzamide with very high affinity for D2 and D3 receptors. There was good agreement between the specific binding ratios from CBA quantification of standardized images and those from region-of-interest analyses of original images. The highest levels of binding were observed in the putamen and caudate nucleus, followed by the globus pallidus and nucleus accumbens. Besides the basal ganglia, the hypothalamus and nucleus ruber also showed high levels of binding. Intermediate levels were found in the substantia nigra, nucleus subthalami, amygdala, and thalamus. Interestingly, there was very heterogeneous binding among the thalamic nuclei. The anterior and mediodorsal nuclei showed relatively high binding. The cerebral cortices showed lower levels with significant regional differences. Binding was highest in the temporal cortex and hippocampus followed by the anterior cingulate gyrus, and the parietal and frontal cortices, but was lowest in the occipital cortex. The use of CBA for analysis of [11C]FLB 457 binding makes it possible to build a normal database for the extrastriatal D2 receptors in the living human brain. The heterogeneous distribution of D2 receptors provides an attractive opportunity for new research on the pathophysiology and drug treatment of schizophrenia.