EFFECTS OF TRIHEXYPHENIDYL AND L-DOPA ON BRAIN MUSCARINIC CHOLINERGICRECEPTOR-BINDING MEASURED BY POSITRON EMISSION TOMOGRAPHY

The effects of pharmacological intervention on brain muscarinic cholin ergic receptor (mAChR) binding were assessed in seven patients with Pa rkinson's disease by positron emission tomography and carbon-11 labell ed N-methyl-4-piperidyl benzilate ([C-11]NMPB). [C-11]NMPB was injecte d twice, approximately 2 hours apart, in each patient, to assess the e ffect of single doses of 4 mg of trihexyphenidyl (n = 5) or 400 mg of L-dopa with 57 mg of benserazide (n = 2) on the binding parameter of m AChRs (K3). There was a mean 28% inhibition of K3 values in the brain in the presence of trihexyphenidyl, which was assumed to reflect mAChR occupancy. No significant change in K3 was observed in the presence o f L-dopa. This study demonstrates the feasibility of measuring mAChR o ccupancy by an anticholinergic medication with PET.