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PET and: markers for the pre- and postsynaptic neurons were used to study the dopamine system in vivo in Huntington's disease. The radioligands used were [11C]SCH 23390 for D1-receptors, [11C]raclopride for D2-receptors and [11C]beta-CIT for dopamine transporters. Five patients with Huntington's disease and five matched controls were recruited. Brain anatomy was examined by MRI. The findings in patients were as follows. Postsynaptic D1- and D2-receptor densities were similarly reduced in the striatum. A reduction in D1-receptor density was shown in the temporal cortex; it draws attention to the cortical degeneration in relation to the cognitive deficits observed in Huntington's disease. The reduction of D1- and D2-receptor binding potentials in the striatum correlated significantly with increasing duration of illness. The correlation between the duration of illness and decline of D1- and D2-receptors make these receptors valuable as quantitative markers for the Huntington's disease degenerative process. Besides postsynaptic changes, a significant 50% decrease of [11C]beta-CIT binding to the dopamine transporter was found in the striatum. A reduced striatal blood flow in Huntington's disease cannot be excluded and could account for a small part of the decrease in [11C]beta-CIT binding. We suggest that the finding reflects a loss of presynaptic terminals or a reduced expression of dopamine transporter in the nigrostriatal dopaminergic system in Huntington's disease.

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