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  • Title: In vivo autoradiographic and dissection evaluation of isomers of 125I-labeled 1-azabicyclo[2.2.2] oct-3-yl-alpha-(1-iodo-1-propen-3-yl)-alpha-phenylacetate (IQNP).
    Author: Rayeq MR, Boulay SF, Sood VK, McPherson DW, Knapp FF, Zeeberg BR.
    Journal: Recept Signal Transduct; 1996; 6(1):13-34. PubMed ID: 8933619.
    Abstract:
    (R,S)-[125I]IQNB has been used extensively in in vivo studies in rats and has been of utility in demonstrating the in vivo subtype selectivity of nonradioactive ligands in competition studies. Radiolabeled Z- and E-(-,-)-1-azabicyclo[2.2.2]oct-3-yl alpha-hydroxy-alpha-(1-iodo-1-propen-3-yl)-alpha-phenylacetate (Z- and E-[-,-]-[125I]IQNP) are analogs of (R,S)-[125I]IQNB. Preliminary rat brain regional dissection studies have indicated that Z- and E-(-,-)-[125I]IQNP, in general, are distributed similarly to (R,S)-[125I]IQNB. An important observation is that Z-(-,-)-[125I]IQNP binds to the muscarinic receptors in those brain regions enriched in the m2 subtype with approximately a two- to fivefold higher percent dose/g compared to (R,S)-[125I]IQNB. These observations are confirmed here by in vivo autoradiographic comparison of the time-courses of (R,S)-[125I]IQNB, Z-(-,-)-[125I]IQNP, and E-(-,-)-[125I]IQNP. Thus, in vivo competition studies against Z-(-,-)-[125I]IQNP would provide a potentially more sensitive and accurate probe for demonstrating the in vivo m2 selectivity of the nonradioactive ligands. In addition, Z-(-,-)-[123I]IQNP would potentially be useful for SPECT imaging of muscarinic receptor loss in neurodegenerative diseases.
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