Age-related changes in human muscarinic acetylcholine receptors measured by positron emission tomography.

The effects of age on the binding parameters of [11C]N- methyl-4-piperidylbenzilate ([11C]NMPB), a specific muscarinic cholinergic receptor ligand, were studied. Eighteen healthy male volunteers (18-75 years old) participated. Regional radioactivity in the brain was followed for 60 min by positron emission tomography (PET). Uptake of [11C]NMPB continuously increased in all brain areas with the exception of the cerebellum. For the quantification of receptor binding, a compartment model, in which radioactivity in the cerebellum was used as an input function, was used. The binding parameter, K3, of muscarinic acetylcholine receptors in eight brain regions (pons, hippocampus, frontal cortex, striatum, temporal cortex, thalamus, occipital cortex, parietal cortex) showed an age-related decrease of about 45% over the age range.