DECREASE IN HUMAN STRIATAL DOPAMINE-D2 RECEPTOR DENSITY WITH AGE - A PET STUDY WITH [C-11] RACLOPRIDE

The effect of age on human striatal dopamine D2 receptors was investigated with positron emission tomography (PET) using [C-11]raclopride as a radioligand. Twenty-one healthy volunteers aged from 20 to 81 years were studied. An equilibrium method was applied and two separate PET scans with different specific activities of [C-11]raclopride were performed. The maximal number of receptors (B(max)) and their dissociation constant (K(d)) were calculated using Scatchard analysis. There was an age-dependent decline in the B(max) (r = -0.49; p = 0.02) of striatal D2 receptors while the K(d) remained unchanged. The results show that there is an age-related loss of striatal D2 receptors, which, together with other changes in the brain nigrostriatal dopaminergic system, may contribute to extrapyramidal symptoms associated with aging.