[PET study of cholinergic system in the brain]

Area of Science:

• Neuroscience
• Radiochemistry
• Medical Imaging

Background:

• Acetylcholinesterase (AChE) is a key enzyme in the cholinergic system.
• Measuring AChE activity non-invasively is crucial for understanding neurodegenerative disorders.

Purpose of the Study:

• To develop and validate a Positron Emission Tomography (PET) method using carbon-11 labeled N-methyl-4-piperidyl acetate to quantify brain acetylcholinesterase (AChE) activity.
• To assess age-related changes in AChE activity and its alterations in neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease (PD), and progressive supranuclear palsy (PSP).

Main Methods:

• Developed a PET imaging technique with C-11 N-methyl-4-piperidyl acetate to measure AChE activity.
• Performed kinetic analysis of brain and plasma radioactivity to derive the rate constant k3 as an index of AChE activity.
• Compared k3 values across different brain regions in healthy volunteers and patients with AD, PD, and PSP.

Main Results:

• Established regional AChE activity ratios in the healthy brain (cortex/thalamus/cerebellum/striatum: 1/3/8/10).
• Found no significant age-related decline in cerebral cortical AChE activity in healthy individuals.
• Observed significant reductions in AChE activity in the cerebral cortex and hippocampus in AD patients (-24%), in the cerebral cortex in PD patients (-18%), and in the thalamus in PSP patients (-38%).

Conclusions:

• The developed PET method provides a reliable index (k3) for quantifying central AChE activity.
• AChE activity is preserved in the aged cerebral cortex.
• The technique is valuable for detecting cholinergic deficits in neurodegenerative diseases, aiding in diagnosis and understanding disease mechanisms.