Autoradiography of H-3-pirenzepine and H-3-AFDX-384 in Mouse Brain Regions: Possible Insights into M-1, M-2, and M-4 Muscarinic Receptors Distribution

0489164 - ÚEB 2019 RIV CH eng J - Journal Article
Valuskova, P. - Farar, V. - Forczek, Sándor - Křížová, I. - Mysliveček, J.
Autoradiography of H-3-pirenzepine and H-3-AFDX-384 in Mouse Brain Regions: Possible Insights into M-1, M-2, and M-4 Muscarinic Receptors Distribution.
Frontiers in Pharmacology. Roč. 9, FEB 20 (2018), č. článku 124. ISSN 1663-9812. E-ISSN 1663-9812
Institutional support: RVO:61389030
Keywords : 3 h-afdx-384 * 3 H-pirenzepine * 3 h-qnb * Autoradiography * M muscarinic receptor 1 * M muscarinic receptor 2 * M muscarinic receptor 4
OECD category: Neurosciences (including psychophysiology
Impact factor: 3.845, year: 2018

Autoradiography helps to determine the distribution and density of muscarinic receptor (MR) binding sites in the brain. However, it relies on the selectivity of radioligands toward their target. 3 H-Pirenzepine is commonly believed to label predominantly M 1 MR, 3 H-AFDX-384 is considered as M 2 MR selective ligand. Here we performed series of autoradiographies with 3 H-AFDX-384 (2 nM), and 3 H-pirenzepine (5 nM) in WT, M 1 KO, M 2 KO, and M 4 KO mice to address the ligand selectivity. Labeling with 3 H-pirenzepine using M 1 KO, M 2 KO, and M 4 KO brain sections showed the high selectivity toward M 1 MR. Selectivity of 3 H-AFDX-384 toward M 2 MR varies among brain regions and depends on individual MR subtype proportion. All binding sites in the medulla oblongata and pons, correspond to M 2 MR. In caudate putamen, nucleus accumbens and olfactory tubercle, 77.7, 74.2, and 74.6% of 3 H-AFDX-384 binding sites, respectively, are represented by M 4 MR and M 2 MR constitute only a minor portion. In cortex and hippocampus, 3 H-AFDX-384 labels almost similar amounts of M 2 MR and M 4 MR alongside significant amounts of non-M 2 /non-M 4 MR. In cortex, the proportion of 3 H-AFDX-384 binding sites attributable to M 2 MR can be increased by blocking M 4 MR with MT3 toxin without affecting non-M 4 MR. PD102807, which is considered as a highly selective M 4 MR antagonist failed to improve the discrimination of M 2 MR. Autoradiography with 3 H-QNB showed genotype specific loss of binding sites. In conclusion: while 3 H-pirenzepine showed the high selectivity toward M 1 MR, 3 H-AFDX-384 binding sites represent different populations of MR subtypes in a brain-region-specific manner. This finding has to be taken into account when interpreting the binding data.
Permanent Link: http://hdl.handle.net/11104/0283632