title: Dopaminergic innervation of the mouse inner ear: evidence for a separate cytochemical group of cochlear efferent fibers.
abstract: Immunostaining mouse cochleas for tyrosine hydroxylase (TH) and dopamine beta-hydroxylase suggests that there is a rich adrenergic innervation throughout the auditory nerve trunk and a small dopaminergic innervation of the sensory cell areas. Surgical cuts in the brainstem confirm these dopaminergic fibers as part of the olivocochlear efferent bundle. Within the sensory epithelium, TH-positive terminals are seen only in the inner hair cell area, where they intermingle with other olivocochlear terminals expressing cholinergic markers (vesicular acetylcholine transporter; VAT). Double immunostaining suggests little colocalization of TH and VAT; quantification of terminal volumes suggests that TH-positive fibers constitute only 10-20% of the efferent innervation of the inner hair cell area. Immunostaining of mouse brainstem revealed a small population of TH-positive cells in and around the lateral superior olive. Consistent with cochlear projections, double staining for the cholinergic marker acetylcholinesterase suggested that TH-positive somata are not cholinergic and vice versa. All observations are consistent with the view that a small dopaminergic subgroup of lateral olivocochlear neurons 1) projects to the inner hair cell area, 2) is distinct from the larger cholinergic group projecting there, and 3) may correspond to lateral olivocochlear "shell" neurons described by others (Warr et al. [1997] Hear. Res 108:89-111).
authors.affiliation: Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114.
authors.forename: Keith N
authors.initials: KN
authors.lastname: Darrow
authors.forename: Emmanuel J
authors.initials: EJ
authors.lastname: Simons
authors.forename: Leslie
authors.initials: L
authors.lastname: Dodds
authors.forename: M Charles
authors.initials: MC
authors.lastname: Liberman
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D003051:Cochlea / Q000166:cytology / Q000294:innervation* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D004299:Dopamine beta-Hydroxylase / Q000378:metabolism; D004525:Efferent Pathways / Q000166:cytology / Q000378:metabolism*; D006199:Hair Cells, Auditory, Inner / Q000166:cytology / Q000378:metabolism; D006309:Hearing / Q000502:physiology; D006319:Hearing Loss, Sensorineural / Q000378:metabolism / Q000503:physiopathology; D007150:Immunohistochemistry; D051379:Mice; D008808:Mice, Inbred CBA; D009433:Neural Inhibition / Q000502:physiology; D011149:Pons / Q000166:cytology / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D050494:Vesicular Acetylcholine Transport Proteins / Q000378:metabolism
chemical_list: C493460:Slc18a3 protein, mouse; D050494:Vesicular Acetylcholine Transport Proteins; D014446:Tyrosine 3-Monooxygenase; D004299:Dopamine beta-Hydroxylase; D000109:Acetylcholine; D004298:Dopamine