Identification of a novel nicotinic binding site in mouse brain using [(125)I]-epibatidine

Br J Pharmacol. 2000 Oct;131(4):729-39. doi: 10.1038/sj.bjp.0703616.


[(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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alkaloids / pharmacology
  • Animals
  • Autoradiography
  • Azetidines / metabolism
  • Azocines
  • Binding Sites
  • Brain / metabolism*
  • Bridged Bicyclo Compounds, Heterocyclic / metabolism*
  • Iodine Radioisotopes
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Nicotine / metabolism
  • Nicotinic Agonists / metabolism*
  • Pyridines / metabolism*
  • Quinolizines
  • Receptors, Nicotinic / analysis
  • Receptors, Nicotinic / metabolism*


  • A 85380
  • Alkaloids
  • Azetidines
  • Azocines
  • Bridged Bicyclo Compounds, Heterocyclic
  • Iodine Radioisotopes
  • Nicotinic Agonists
  • Pyridines
  • Quinolizines
  • Receptors, Nicotinic
  • cytisine
  • Nicotine
  • epibatidine