Identification of a novel nicotinic binding site in mouse brain using [(125)I]-epibatidine.
[(125)I]-Epibatidine binds to multiple nicotinic acetylcholine receptor (nAChR) subtypes with high affinity. In this study, [(125)I]-epibatidine was used to label and characterize a novel nAChR subtype found in mouse brain inferior colliculus, interpeduncular nucleus, and olfactory bulb homogenates. Binding of [(125)I]-epibatidine was saturable and apparently monophasic in each brain region (K:(D:)=71+/-12 pM mean+/-s.e.mean across regions) but inhibition of [(125)I]-epibatidine binding (200 pM) by A85380, cytisine and (-)-nicotine was biphasic, indicating the presence of multiple binding sites. The sites with lower agonist affinity comprised 30.0+/-2.2, 58.6+/-0.1 and 48.7+/-3.3% of specific [(125)I]-epibatidine (200 pM) binding in inferior colliculus, interpeduncular nucleus, and olfactory bulb homogenates, respectively. The affinity difference between A85380-sensitive and -resistant binding sites was particularly marked (approximately 1000 fold). Thus A85380 was used to differentiate agonist-sensitive and -resistant sites. The pharmacological profiles of the A85380-resistant sites in each region were assessed with inhibition binding experiments, using 14 agonists and five antagonists. The profiles were indistinguishable across regions, implying that A85380-resistant [(125)I]-epibatidine binding sites in inferior colliculus, interpeduncular nucleus, and olfactory bulb represent a single nAChR subtype. The pharmacological profile of the A85380-resistant sites is very different from that previously reported for high affinity (-)-[(3)H]-nicotine-, [(125)I]-alpha-bungarotoxin-, or [(125)I]-alpha-conotoxin MII-binding sites, suggesting that they represent a novel nAChR population in mouse brain.
Whiteaker
P
P
Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado, CO 80303 USA.
Jimenez
M
M
McIntosh
J M
JM
Collins
A C
AC
Marks
M J
MJ
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D001384:Azetidines / Q000378:metabolism; D001392:Azocines; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism*; D007457:Iodine Radioisotopes; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009538:Nicotine / Q000378:metabolism; D018722:Nicotinic Agonists / Q000378:metabolism*; D011725:Pyridines / Q000378:metabolism*; D011807:Quinolizines; D011978:Receptors, Nicotinic / Q000032:analysis / Q000378:metabolism*; D000093843:Quinolizidine Alkaloids
D000470:Alkaloids; D001384:Azetidines; D001392:Azocines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D007457:Iodine Radioisotopes; D009538:Nicotine; D018722:Nicotinic Agonists; D011725:Pyridines; D011807:Quinolizines; D011978:Receptors, Nicotinic; C104288:A 85380; C004712:cytisine; D000093843:Quinolizidine Alkaloids; C082748:epibatidine