Abstract
Using the inactive isomer of a receptor ligand to define nonspecific binding in vivo may not be an accurate method. Diastereomers of the muscarinic acetylcholine receptor (mAChR) ligand IQNB (3-quinuclidinyl-4-iodobenzilale) were used in vivo to ascertain the conditions necessary for determining nonspecific binding with an inactive ligand. A 1 μM blocking dose of QNB was administered 1 h prior to the (S,S)-[I-125]IQNB. The rats were sacrificed 1 or 3 h after the (S,S)-[I-125]IQNB injection. The brains were dissected into 9 regions containing mAChRs in a range from 21-251 nM and the data were converted to % dose/g tissue. Rats sacrificed one hour after the (S,S)-[I-125]IQNB injection had a difference in binding between the QNB-blocked and control groups with the largest differences found in the regions with the highest mAChRs. In rats sacrificed three hours after the (S,S)-[I-125]IQNB injection no regions had any differences in the binding of (S,S)-[I-125]IQNB. The difference in the amount of (S,S)-[I-125]IQNB bound under control conditions and with the QNB block is the amount of specific binding. We conclude that three hours after (S,S)-[I-125]IQNB injection its binding can be considered nonspecific.
Article PDF
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
McRee, R., Boulay, S., Cohen, V. et al. (S,S)-[I-125]IQNB Specific Binding to Rat Brain Muscarinic Receptors In Vivo. Neuropsychopharmacol 11, 276 (1994). https://doi.org/10.1038/sj.npp.1380178
Published:
Issue Date:
DOI: https://doi.org/10.1038/sj.npp.1380178