title: Pharmacologically distinct nicotinic acetylcholine receptors drive efferent-mediated excitation in calyx-bearing vestibular afferents.
abstract: Electrical stimulation of vestibular efferent neurons rapidly excites the resting discharge of calyx/dimorphic (CD) afferents. In turtle, this excitation arises when acetylcholine (ACh), released from efferent terminals, directly depolarizes calyceal endings by activating nicotinic ACh receptors (nAChRs). Although molecular biological data from the peripheral vestibular system implicate most of the known nAChR subunits, specific information about those contributing to efferent-mediated excitation of CD afferents is lacking. We sought to identify the nAChR subunits that underlie the rapid excitation of CD afferents and whether they differ from α9α10 nAChRs on type II hair cells that drive efferent-mediated inhibition in adjacent bouton afferents. We recorded from CD and bouton afferents innervating the turtle posterior crista during electrical stimulation of vestibular efferents while applying several subtype-selective nAChR agonists and antagonists. The α9α10 nAChR antagonists, α-bungarotoxin and α-conotoxin RgIA, blocked efferent-mediated inhibition in bouton afferents while leaving efferent-mediated excitation in CD units largely intact. Conversely, 5-iodo-A-85380, sazetidine-A, varenicline, α-conotoxin MII, and bPiDDB (N,N-dodecane-1,12-diyl-bis-3-picolinium dibromide) blocked efferent-mediated excitation in CD afferents without affecting efferent-mediated inhibition in bouton afferents. This pharmacological profile suggested that calyceal nAChRs contain α6 and β2, but not α9, nAChR subunits. Selective blockade of efferent-mediated excitation in CD afferents distinguished dimorphic from calyx afferents by revealing type II hair cell input. Dimorphic afferents differed in having higher mean discharge rates and a mean efferent-mediated excitation that was smaller in amplitude yet longer in duration. Molecular biological data demonstrated the expression of α9 in turtle hair cells and α4 and β2 in associated vestibular ganglia.
authors.affiliation: Department of Otolaryngology, Department of Neurobiology and Anatomy, and Department of Pharmacology and Physiology, University of Rochester, Rochester, New York 14642, joseph_holt@urmc.rochester.edu.
authors.forename: J Chris
authors.identifier: http://orcid.org/0000-0001-7908-083X
authors.initials: JC
authors.lastname: Holt
authors.affiliation: Department of Otolaryngology.
authors.forename: Kevin
authors.initials: K
authors.lastname: Kewin
authors.affiliation: Department of Otolaryngology.
authors.forename: Paivi M
authors.identifier: http://orcid.org/0000-0002-2498-5970
authors.initials: PM
authors.lastname: Jordan
authors.affiliation: Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612.
authors.forename: Peter
authors.initials: P
authors.lastname: Cameron
authors.affiliation: Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612.
authors.forename: Marcin
authors.initials: M
authors.lastname: Klapczynski
authors.affiliation: Department of Psychiatry, University of Utah, Salt Lake City, Utah 84112.
authors.forename: J Michael
authors.initials: JM
authors.lastname: McIntosh
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, and.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Crooks
authors.affiliation: College of Pharmacy, University of Kentucky, Lexington, Kentucky 40536.
authors.forename: Linda P
authors.initials: LP
authors.lastname: Dwoskin
authors.affiliation: Department of Anatomy and Cell Biology, University of Illinois at Chicago, Chicago, Illinois 60612.
authors.forename: Anna
authors.identifier: http://orcid.org/0000-0001-6259-0294
authors.initials: A
authors.lastname: Lysakowski
mesh_terms: D000818:Animals; D001384:Azetidines / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D002038:Bungarotoxins / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D018680:Cholinergic Antagonists / Q000494:pharmacology; D020916:Conotoxins / Q000494:pharmacology; D005260:Female; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010847:Picolines / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000502:physiology; D021122:Protein Subunits / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011950:Receptors, Cholinergic / Q000378:metabolism*; D014426:Turtles; D000068580:Varenicline; D014725:Vestibular Nerve / Q000166:cytology / Q000378:metabolism* / Q000502:physiology
chemical_list: C426745:5-iodo-3-(2-azetidinylmethoxy)pyridine; D001384:Azetidines; D001552:Benzazepines; D002038:Bungarotoxins; D018679:Cholinergic Agonists; D018680:Cholinergic Antagonists; D020916:Conotoxins; C513964:N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide; D010847:Picolines; D021122:Protein Subunits; D011725:Pyridines; D011810:Quinoxalines; D011950:Receptors, Cholinergic; C514816:sazetidine-A; D000068580:Varenicline
keywords: ACh; calyx; vestibular afferent; vestibular efferent; α6 nAChR; α9 nAChR