INVIVO VISUALIZATION OF ACETYLCHOLINESTERASE WITH POSITRON EMISSION TOMOGRAPHY

THE cerebral distribution of [C-11]physostigmine, an acetylcholinester ase inhibitor, was studied with autoradiography in rats and positron e mission tomography in primates. In rat brain [C-11]physostigmine radio activity was exactly superimposable to acetylcholinesterase activity, being highest in the basal ganglia, moderate in the cortex and hippoca mpus, and low in the cerebellum. In primate brain, the early blood-flo w dependent distribution of [C-11]physostigmine was followed by a rapi d redistribution to acetylcholinesterase-rich regions such as the stri atum. The cerebral uptake of [C-11]physostigmine was significantly red uced by competition with an excess of unlabeled physostigmine. These r esults suggest that [C-11]physostigmine is a promising new ligand for in vivo imaging of acetylcholinesterase activity with PET.