Chronic sazetidine-A at behaviorally active doses does not increase nicotinic cholinergic receptors in rodent brain

J Pharmacol Exp Ther. 2012 Nov;343(2):441-50. doi: 10.1124/jpet.112.198085. Epub 2012 Aug 16.

Abstract

Chronic nicotine administration increases α4β2 neuronal nicotinic acetylcholine receptor (nAChR) density in brain. This up-regulation probably contributes to the development and/or maintenance of nicotine dependence. nAChR up-regulation is believed to be triggered at the ligand binding site, so it is not surprising that other nicotinic ligands also up-regulate nAChRs in the brain. These other ligands include varenicline, which is currently used for smoking cessation therapy. Sazetidine-A (saz-A) is a newer nicotinic ligand that binds with high affinity and selectivity at α4β2* nAChRs. In behavioral studies, saz-A decreases nicotine self-administration and increases performance on tasks of attention. We report here that, unlike nicotine and varenicline, chronic administration of saz-A at behaviorally active and even higher doses does not up-regulate nAChRs in rodent brains. We used a newly developed method involving radioligand binding to measure the concentrations and nAChR occupancy of saz-A, nicotine, and varenicline in brains from chronically treated rats. Our results indicate that saz-A reached concentrations in the brain that were ∼150 times its affinity for α4β2* nAChRs and occupied at least 75% of nAChRs. Thus, chronic administration of saz-A did not up-regulate nAChRs despite it reaching brain concentrations that are known to bind and desensitize virtually all α4β2* nAChRs in brain. These findings reinforce a model of nicotine addiction based on desensitization of up-regulated nAChRs and introduce a potential new strategy for smoking cessation therapy in which drugs such as saz-A can promote smoking cessation without maintaining nAChR up-regulation, thereby potentially increasing the rate of long-term abstinence from nicotine.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Azetidines / administration & dosage
  • Azetidines / blood
  • Azetidines / pharmacology*
  • Behavior, Animal / drug effects*
  • Benzazepines / administration & dosage
  • Benzazepines / blood
  • Benzazepines / pharmacology
  • Binding Sites
  • Brain Chemistry / drug effects*
  • Cerebral Cortex / cytology
  • Cerebral Cortex / drug effects
  • Cerebral Cortex / metabolism
  • Dose-Response Relationship, Drug
  • Female
  • Male
  • Membranes / drug effects
  • Membranes / metabolism
  • Neurons / drug effects
  • Neurons / metabolism
  • Nicotine / administration & dosage
  • Nicotine / blood
  • Nicotine / pharmacology
  • Nicotinic Agonists / administration & dosage
  • Nicotinic Agonists / blood
  • Nicotinic Agonists / pharmacology
  • Pregnancy
  • Pyridines / administration & dosage
  • Pyridines / blood
  • Pyridines / pharmacology*
  • Quinoxalines / administration & dosage
  • Quinoxalines / blood
  • Quinoxalines / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Nicotinic / drug effects*
  • Self Administration
  • Up-Regulation / drug effects
  • Varenicline

Substances

  • Azetidines
  • Benzazepines
  • Nicotinic Agonists
  • Pyridines
  • Quinoxalines
  • Receptors, Nicotinic
  • sazetidine-A
  • Nicotine
  • Varenicline