title: The phenolic monoterpenoid carvacrol inhibits the binding of nicotine to the housefly nicotinic acetylcholine receptor.
abstract: BACKGROUND
  The phenolic monoterpenoid carvacrol, which is found in many plant essential oils (thyme, oregano and Alaska yellow cedar), is highly active against pest arthropods, but its mechanisms of action are not fully understood. Here, carvacrol is shown to bind in a membrane preparation containing insect nicotinic acetylcholine receptors (nAChRs). [(14) C]-Nicotine binding assays with Musca domestica (housefly) nAChRs were used in this study to demonstrate carvacrol's binding to nAChRs, thereby acting as a modulator of the receptors.
  
  
  RESULTS
  Carvacrol showed a concentration-dependent inhibition of [(14) C]-nicotine binding in a membrane preparation of housefly heads containing nAChRs, with IC50 = 1.4 μM, in a non-competitive pattern. Binding studies with neonicotinoid insecticides revealed that imidacloprid and thiamethoxam did not inhibit the binding of [(14) C]-nicotine, while dinotefuran, from the guanidine subclass of neonicotinoids, inhibited nicotine binding like carvacrol.
  
  
  CONCLUSIONS
  Carvacrol binds to housefly nAChRs at a binding site distinct from nicotine and acetylcholine, and the nAChRs are a possible target of carvacrol for its insecticidal activity.
authors.affiliation: Pesticide Toxicology Laboratory, Department of Entomology, Iowa State University of Science and Technology, Ames, IA, USA.
authors.forename: Fan
authors.initials: F
authors.lastname: Tong
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Gross
authors.forename: Marc C
authors.initials: MC
authors.lastname: Dolan
authors.forename: Joel R
authors.initials: JR
authors.lastname: Coats
mesh_terms: D000818:Animals; D001665:Binding Sites; D000081007:Cymenes; D015536:Down-Regulation / Q000187:drug effects*; D006793:Houseflies / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D007300:Insect Control; D019476:Insect Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D007306:Insecticides / Q000737:chemistry / Q000494:pharmacology*; D039821:Monoterpenes / Q000737:chemistry / Q000494:pharmacology*; D009538:Nicotine / Q000737:chemistry / Q000378:metabolism*; D018733:Nicotinic Antagonists / Q000737:chemistry / Q000494:pharmacology; D010636:Phenols / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000378:metabolism
chemical_list: D000081007:Cymenes; D019476:Insect Proteins; D007306:Insecticides; D039821:Monoterpenes; D018733:Nicotinic Antagonists; D010636:Phenols; D011978:Receptors, Nicotinic; D009538:Nicotine; C073316:carvacrol