title: Unmyelinated auditory type I spiral ganglion neurons in congenic Ly5.1 mice.
abstract: With the exception of humans, the somata of type I spiral ganglion neurons (SGNs) of most mammalian species are heavily myelinated. In an earlier study, we used Ly5.1 congenic mice as transplant recipients to investigate the role of hematopoietic stem cells in the adult mouse inner ear. An unanticipated finding was that a large percentage of the SGNs in this strain were unmyelinated. Further characterization of the auditory phenotype of young adult Ly5.1 mice in the present study revealed several unusual characteristics, including 1) large aggregates of unmyelinated SGNs in the apical and middle turns, 2) symmetrical junction-like contacts between the unmyelinated neurons, 3) abnormal expression patterns for CNPase and connexin 29 in the SGN clusters, 4) reduced SGN density in the basal cochlea without a corresponding loss of sensory hair cells, 5) significantly delayed auditory brainstem response (ABR) wave I latencies at low and middle frequencies compared with control mice with similar ABR threshold, and 6) elevated ABR thresholds and deceased wave I amplitudes at high frequencies. Taken together, these data suggest a defect in Schwann cells that leads to incomplete myelinization of SGNs during cochlear development. The Ly5.1 mouse strain appears to be the only rodent model so far identified with a high degree of the "human-like" feature of unmyelinated SGNs that aggregate into neural clusters. Thus, this strain may provide a suitable animal platform for modeling human auditory information processing such as synchronous neural activity and other auditory response properties.
authors.affiliation: Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
authors.forename: Vinu
authors.initials: V
authors.lastname: Jyothi
authors.forename: Manna
authors.initials: M
authors.lastname: Li
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Kilpatrick
authors.forename: Nancy
authors.initials: N
authors.lastname: Smythe
authors.forename: Amanda C
authors.initials: AC
authors.lastname: LaRue
authors.forename: Daohong
authors.initials: D
authors.lastname: Zhou
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Schulte
authors.forename: Richard A
authors.initials: RA
authors.lastname: Schmiedt
authors.forename: Hainan
authors.initials: H
authors.lastname: Lang
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D003051:Cochlea / Q000166:cytology / Q000254:growth & development / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006198:Hair Cells, Auditory / Q000378:metabolism / Q000648:ultrastructure; D006801:Humans; D051379:Mice; D020297:Mice, Congenic; D008815:Mice, Inbred Strains; D009186:Myelin Sheath / Q000378:metabolism*; D009457:Neuroglia / Q000378:metabolism / Q000648:ultrastructure; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure*; D012583:Schwann Cells / Q000166:cytology / Q000502:physiology; D013136:Spiral Ganglion / Q000166:cytology*
chemical_list: D015415:Biomarkers