Development and evaluation of muscarinic cholinergic receptor ligands n-[11c]ethyl-4piperidyl benzilate and n-[11c]propyl-4-piperidyl benzilate: a pet study in comparison with n[11c]methyl-4-piperidyl benzilate in the conscious monkey brain

The muscarinic cholinergic receptor ligands N-[11C]ethyl-4-piperidyl benzilate (4-EPB) and N-[11C]propyl-4-piperidyl benzilate (4-PPB) were developed and evaluated in comparison with N-[11C]methyl-4-piperidyl benzilate (4-MPB) in the conscious monkey brain using positron emission tomography (PET). Time-activity curves of [11C]4-EPB, unlike [11C]4MPB, showed peaks within 91 min in regions rich in muscarinic receptors. [11C]4-PPB showed no specific binding even in the regions rich in these receptors. These observation demonstrated that increases in [11C]alkyl chain length could alter the kinetic properties of receptor ligands for PET.