PET shows that striatal dopamine D1 and D2 receptors are differentially affected in AD

OBJECTIVE: To study dopamine D1 and D2 receptors in the putamen and the caudate nucleus in patients with AD and age-matched healthy controls by means of PET. METHODS: A dopamine D1 receptor antagonist ([11C]NNC 756) and a D2 receptor antagonist ([11C]raclopride) were used as ligands. The uptake of these ligands was calculated as a distribution volume ratio of the putamen and the caudate nucleus to the cerebellum. RESULTS: The mean [11C]NNC 756 uptake in AD was reduced by 14% from the mean control value both in the putamen (p = 0.004) and the caudate nucleus (p = 0.009). There was no significant reduction in the mean [11C]raclopride uptake in either the putamen or the caudate nucleus in AD. There was no correlation between [11C]NNC 756 or [11C]raclopride uptake and Mini-Mental State Examination or motor Unified PD Rating Scale scores in patients with AD. CONCLUSIONS: There are changes in striatal D1 but not in D2 receptors in AD.