Increased density of dopamine D2 receptors in the putamen, but not in the caudate nucleus in early Parkinson's disease: a PET study with [ 11C]raclopride

Abstract

Striatal dopamine D2 receptors were studied, using positron emission tomography (PET), in 10 patients with early Parkinson's disease without any antiparkinsonian medication and in 14 healthy controls. [ 11C]Raclopride was used as ligand and an equilibrium method was applied. The maximum count of receptors ( B max) and their dissociation constant ( K d) were calculated according to the Scatchard principle. In parkinsonian patients, the B max of D2 receptors was increased in the putamen contralateral to the predominant symptoms, as compared to the opposite putamen, by 33% ( p = 0.0008). In the caudate nucleus no significant side to side differences was noted. On comparison with age-matched healthy controls, B max values in the putamen ( p = 0.0012) but not in the caudate nucleus contralateral to the side of predominant clinical symptoms were increased in PD patients. The K d values were unchanged. The difference in putaminal B max values between the opposite hemispheres correlated with the difference in the severity of parkinsonian motor symptoms between the two body sides ( r = 0.69, p = 0.03). The present results show that there is both a relative and absolute increase in the number of dopamine D2 receptors in the putamen, but not in the caudate nucleus in early Parkinson's disease.