Muscarinic and dopaminergic receptors in the aging human brain.

[3H]1-Quinuclidinyl(phenyl)-4-benzilate ([3H]QNB), [3H]spiroperidol and [3H]flupenthixol were used to label brain muscarinic, dopamine D2 and D1 receptors, respectively, in altogether 78 patients aged from 4 to 93 years. The binding of [3H]QNB declined with age in the frontal cortex, hippocampus, caudate nucleus and putamen. Scatchard analysis showed that the reduced binding was due to a decline in the number of receptors. The binding of the dopaminergic ligands was determined in the caudate nucleus, putamen, pallidum and substantia nigra. [3H]Spiroperidol binding showed age-dependent decline in all the brain areas examined, while no change was seen in [3H]flupenthixol binding in any brain area studied. Also the decrease in [3H]spiroperidol binding was due to the reduced number of receptors. The results of this study suggest that aging is more likely to affect certain neurotransmitter receptor systems than certain brain areas.