title: Menthol Alone Upregulates Midbrain nAChRs, Alters nAChR Subtype Stoichiometry, Alters Dopamine Neuron Firing Frequency, and Prevents Nicotine Reward.
abstract: Upregulation of β2 subunit-containing (β2*) nicotinic acetylcholine receptors (nAChRs) is implicated in several aspects of nicotine addiction, and menthol cigarette smokers tend to upregulate β2* nAChRs more than nonmenthol cigarette smokers. We investigated the effect of long-term menthol alone on midbrain neurons containing nAChRs. In midbrain dopaminergic (DA) neurons from mice containing fluorescent nAChR subunits, menthol alone increased the number of α4 and α6 nAChR subunits, but this upregulation did not occur in midbrain GABAergic neurons. Thus, chronic menthol produces a cell-type-selective upregulation of α4* nAChRs, complementing that of chronic nicotine alone, which upregulates α4 subunit-containing (α4*) nAChRs in GABAergic but not DA neurons. In mouse brain slices and cultured midbrain neurons, menthol reduced DA neuron firing frequency and altered DA neuron excitability following nAChR activation. Furthermore, menthol exposure before nicotine abolished nicotine reward-related behavior in mice. In neuroblastoma cells transfected with fluorescent nAChR subunits, exposure to 500 nm menthol alone also increased nAChR number and favored the formation of (α4)3(β2)2 nAChRs; this contrasts with the action of nicotine itself, which favors (α4)2(β2)3 nAChRs. Menthol alone also increases the number of α6β2 receptors that exclude the β3 subunit. Thus, menthol stabilizes lower-sensitivity α4* and α6 subunit-containing nAChRs, possibly by acting as a chemical chaperone. The abolition of nicotine reward-related behavior may be mediated through menthol's ability to stabilize lower-sensitivity nAChRs and alter DA neuron excitability. We conclude that menthol is more than a tobacco flavorant: administered alone chronically, it alters midbrain DA neurons of the nicotine reward-related pathway.
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Brandon J
authors.identifier: http://orcid.org/0000-0003-0381-028X
authors.initials: BJ
authors.lastname: Henderson
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Teagan R
authors.initials: TR
authors.lastname: Wall
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Beverley M
authors.initials: BM
authors.lastname: Henley
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Charlene H
authors.initials: CH
authors.lastname: Kim
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Weston A
authors.initials: WA
authors.lastname: Nichols
authors.affiliation: National Institute on Aging, Baltimore, Maryland 21224.
authors.forename: Ruin
authors.initials: R
authors.lastname: Moaddel
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and.
authors.forename: Cheng
authors.identifier: http://orcid.org/0000-0001-9649-7450
authors.initials: C
authors.lastname: Xiao
authors.affiliation: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, and Lester@Caltech.edu.
authors.forename: Henry A
authors.identifier: http://orcid.org/0000-0002-5470-5255
authors.initials: HA
authors.lastname: Lester
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D059290:Dopaminergic Neurons / Q000187:drug effects* / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects / Q000235:genetics; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008610:Menthol / Q000494:pharmacology*; D008636:Mesencephalon / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009447:Neuroblastoma / Q000473:pathology; D009538:Nicotine / Q000008:administration & dosage*; D018722:Nicotinic Agonists / Q000008:administration & dosage; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*; D012201:Reward; D013997:Time Factors; D015854:Up-Regulation / Q000187:drug effects* / Q000235:genetics
chemical_list: D008164:Luminescent Proteins; D018722:Nicotinic Agonists; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D008610:Menthol; D009538:Nicotine; D000109:Acetylcholine
keywords: dopamine neuron; electrophysiology; menthol; nicotine; nicotinic receptor; reward