title: Olivocochlear innervation in the mouse: immunocytochemical maps, crossed versus uncrossed contributions, and transmitter colocalization.
abstract: To further understand the roles and origins of gamma-aminobutyric acid (GABA) and calcitonin gene-related peptide (CGRP) in the efferent innervation of the cochlea, we first produced in the mouse an immunocytochemical map of the efferent terminals that contain acetylcholine (ACh), CGRP, and GABA. Olivocochlear (OC) terminals in inner and outer hair cell (IHC and OHC) regions were analyzed quantitatively along the cochlear spiral via light-microscopic observation of cochlear wholemounts immunostained with antibodies to glutamic acid decarboxylase (GAD), vesicular acetylcholine transporter (VAT), or the peptide CGRP. Further immunochemical characterization was performed in mice with chronic OC transection at the floor of the fourth ventricle to distinguish crossed from uncrossed contributions and, indirectly, the contributions of lateral versus medial components of the OC system. The results in mouse showed that (1) there are prominent GABAergic, cholinergic, and CGRPergic innervations in the OHC and IHC regions, (2) GABA and CGRP are extensively colocalized with ACh in all OC terminals in the IHC and OHC areas, (3) the longitudinal gradient of OC innervation peaks roughly at the 10-kHz region in the OHC area and is more uniform along the cochlear spiral in the IHC area, (4) in contrast to other mammalian species there is no radial gradient of OC innervation of the OHCs, and (5) all OHC efferent terminals arise from the medial OC system and terminals in the IHC area arise from the lateral OC system.
authors.affiliation: Department of Otology and Laryngology, Harvard Medical School and Eaton-Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114-3096, USA. sfm@epl.meei.harvard.edu
authors.forename: Stéphane F
authors.initials: SF
authors.lastname: Maison
authors.forename: Joe C
authors.initials: JC
authors.lastname: Adams
authors.forename: M Charles
authors.initials: MC
authors.lastname: Liberman
mesh_terms: D000109:Acetylcholine / Q000032:analysis; D000818:Animals; D001306:Auditory Pathways / Q000033:anatomy & histology; D019771:Axotomy; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D002352:Carrier Proteins / Q000032:analysis; D003051:Cochlea / Q000737:chemistry / Q000294:innervation*; D003056:Cochlear Nerve / Q000033:anatomy & histology* / Q000737:chemistry; D004525:Efferent Pathways / Q000033:anatomy & histology*; D005260:Female; D005968:Glutamate Decarboxylase / Q000032:analysis; D006198:Hair Cells, Auditory / Q000737:chemistry*; D006199:Hair Cells, Auditory, Inner / Q000737:chemistry; D018072:Hair Cells, Auditory, Outer / Q000737:chemistry; D007150:Immunohistochemistry; D008297:Male; D026901:Membrane Transport Proteins; D051379:Mice; D008808:Mice, Inbred CBA; D009847:Olivary Nucleus / Q000033:anatomy & histology; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid / Q000032:analysis
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C493460:Slc18a3 protein, mouse; D050494:Vesicular Acetylcholine Transport Proteins; D033921:Vesicular Transport Proteins; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; D015740:Calcitonin Gene-Related Peptide; D000109:Acetylcholine