Tyrosine Hydroxylase Expression in Type II Cochlear Afferents in Mice.
Acoustic information propagates from the ear to the brain via spiral ganglion neurons that innervate hair cells in the cochlea. These afferents include unmyelinated type II fibers that constitute 5 % of the total, the majority being myelinated type I neurons. Lack of specific genetic markers of type II afferents in the cochlea has been a roadblock in studying their functional role. Unexpectedly, type II afferents were visualized by reporter proteins induced by tyrosine hydroxylase (TH)-driven Cre recombinase. The present study was designed to determine whether TH-driven Cre recombinase (TH-2A-CreER) provides a selective and reliable tool for identification and genetic manipulation of type II rather than type I cochlear afferents. The "TH-2A-CreER neurons" radiated from the spiral lamina, crossed the tunnel of Corti, turned towards the base of the cochlea, and traveled beneath the rows of outer hair cells. Neither the processes nor the somata of TH-2A-CreER neurons were labeled by antibodies that specifically labeled type I afferents and medial efferents. TH-2A-CreER-positive processes partially co-labeled with antibodies to peripherin, a known marker of type II afferents. Individual TH-2A-CreER neurons gave off short branches contacting 7-25 outer hair cells (OHCs). Only a fraction of TH-2A-CreER boutons were associated with CtBP2-immunopositive ribbons. These results show that TH-2A-CreER provides a selective marker for type II versus type I afferents and can be used to describe the morphology and arborization pattern of type II cochlear afferents in the mouse cochlea.
The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD, 21205, USA.
Pankhuri
http://orcid.org/0000-0003-3585-8851
P
Vyas
The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD, 21205, USA.
Jingjing Sherry
JS
Wu
Department of Neurobiology, Howard Hughes Medical Institute, Harvard Medical School, 220 Longwood Avenue, Boston, MA, 02115, USA.
Amanda
A
Zimmerman
The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD, 21205, USA. pfuchs1@jhmi.edu.
Paul
P
Fuchs
The Center for Hearing and Balance, Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 824, Baltimore, MD, 21205, USA. eglowat1@jhmi.edu.
Elisabeth
E
Glowatzki
D000818:Animals; D003051:Cochlea / Q000294:innervation*; D005260:Female; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D009475:Neurons, Afferent / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D064531:Peripherins / Q000032:analysis; D013629:Tamoxifen / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000032:analysis*
D064531:Peripherins; D013629:Tamoxifen; D014446:Tyrosine 3-Monooxygenase
afferent; cochlea; dopamine; hair cells; hearing; type II fiber
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