Vol. 290, Issue 2, 917-922, August 1999

Quantitative Autoradiography with Short-Lived Positron Emission Tomography Tracers: A Study on Muscarinic Acetylcholine Receptors with N-[¹¹C]methyl-4-piperidylbenzilate¹

Sven Sihver , Wiebke Sihver , Mats Bergström , A. Urban Höglund, Pernilla Sjöberg, Bengt Långström and Yasuyoshi Watanabe

Department of Neuroscience, Unit of Pharmacology (S.S., W.S., Y.W.) and Department of Physiology, Unit of Comparative Medicine (U.H.), Faculty of Medicine, Uppsala University, Uppsala, Sweden; Subfemtomole Biorecognition Project, Japan Science and Technology Corporation, Toyonaka, Osaka, Japan (S.S., W.S., M.B., B.L., Y.W.); Uppsala University PET Centre, University Hospital, Uppsala, Sweden (M.B., P.S., B.L.); and Osaka Bioscience Institute, Suita-shi, Osaka, Japan (Y.W.)

The present work demonstrates quantitative autoradiography by using positron emission tomography tracers and storage phosphorimaging plates. The uptake and association of [¹¹C]N-methyl-4-piperidylbenzilate was measured in rat brain tissue cryosections of various thicknesses. The signal increased with increasing section thickness, but only in 10-µm-thick sections did the binding reach the steady state during a 50-min observation time. This violation of the equilibrium condition, potentially combined with perfusion limitations, leads to erroneous increased binding-site density and decreased affinity in the 25- and 50-µm-thick sections. For better imaging of receptor distribution it is reasonable to use thicker sections. For quantitative analysis of receptor-binding parameters, the specific properties of ligands at different thicknesses of cryosections need to be considered. Evidence is provided that the nonselective muscarinic antagonist N-methyl-4-piperidylbenzilate binds preferentially to the M₄ subtype of muscarinic acetylcholine receptors.