Muscarinic acetylcholine receptors (mAChRs) are involved in regulating many fundamental central and peripheral functions. Because abnormal mAChR signaling has been implicated in numerous pathophysiological conditions Levine et al (1999), Levine et al (2001), elucidating the physiological and pathophysiological roles of the individual mAChR subtypes is of considerable therapeutic interest. Complications in studying such pathophysiological roles occur because of the lack of ligands that can block or activate specific mAChR subtypes with a high degree of selectivity Wess (1996), Caulfield and Birdsall (1998). Moreover, most organs or tissues express multiple mAChRs, complicating further the interpretation of experimental data obtained with muscarinic ligands.