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Localization of efferent neurotransmitters in the inner ear of the homozygous Bronx waltzer mutant mouse.
- Source :
-
Hearing research [Hear Res] 2002 May; Vol. 167 (1-2), pp. 136-55. - Publication Year :
- 2002
-
Abstract
- Naturally occurring mutant mice provide an excellent model for the study of genetic malformations of the inner ear. Mice homozygous for the Bronx waltzer (bv/bv) mutation are severely hearing impaired or deaf and exhibit a 'waltzing' gait. Functional aspects of cochlear and vestibular efferents in the bv/bv mutant mouse are not well known. The present study was designed to evaluate several candidates of efferent neurotransmitters or neuromodulators including choline acetyltransferase (ChAT), gamma-aminobutyric acid (GABA), and calcitonin gene-related peptide (CGRP) in the inner ear of the bv/bv mutant mouse. Ultrastructural investigations at both light and electron microscopic level were performed. Ultrastructural morphologic evaluations of the cochlea and the vestibular end-organs were also undertaken. It is demonstrated that ChAT, GABA and CGRP immunoreactivities are present in the cochlea and in vestibular end-organs of bv/bv mutant mice. In the organ of Corti, immunoreactivity of ChAT, GABA and CGRP is confined to the inner spiral fibers, tunnel-crossing fibers, and the vesiculated nerve endings synapsing with outer hair cells. Interestingly, immunoreactivity was detectable even where inner hair cells appeared missing. Results also revealed malformations of the outer hair cells with synaptic contacts to efferent nerve endings consistently intact. In the neurosensory epithelia of the vestibular end-organs, the presence of ChAT, GABA, and CGRP immunoreactivity was localized at the vestibular efferents, with the exception of the macula of saccule. In one 8-month-old macula of utricle where the depletion of hair cells appeared highest, ChAT immunostaining was still discernible. Ultrastructural investigation demonstrated that vesiculated efferent nerve endings make synaptic contact with the outer hair cells in the organ of Corti and with type II hair cells in the vestibular end-organs. The present study provides further support that the efferent system in the bv/bv mutant inner ear is morphologically as well as functionally mature. These findings also demonstrate that if and when the onset of efferent degeneration in the bv/bv mutant inner ear occurs, it transpires subsequent to pathological conditions in the hair cells. The present findings give further indication that the efferent systems of the bv/bv mutant inner ear are independent of the afferent systems in many aspects including development, maturation as well as degeneration.
- Subjects :
- Animals
Auditory Pathways metabolism
Calcitonin Gene-Related Peptide metabolism
Choline O-Acetyltransferase metabolism
Cochlea metabolism
Cochlea ultrastructure
Ear, Inner ultrastructure
Efferent Pathways metabolism
Female
Hair Cells, Auditory, Inner abnormalities
Hair Cells, Auditory, Inner metabolism
Hair Cells, Auditory, Inner ultrastructure
Hair Cells, Auditory, Outer abnormalities
Hair Cells, Auditory, Outer metabolism
Hair Cells, Auditory, Outer ultrastructure
Immunohistochemistry
Male
Mice
Mice, Inbred CBA
Mice, Mutant Strains
Microscopy, Electron
Vestibule, Labyrinth abnormalities
Vestibule, Labyrinth metabolism
Vestibule, Labyrinth ultrastructure
gamma-Aminobutyric Acid metabolism
Ear, Inner abnormalities
Ear, Inner metabolism
Neurotransmitter Agents metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 0378-5955
- Volume :
- 167
- Issue :
- 1-2
- Database :
- MEDLINE
- Journal :
- Hearing research
- Publication Type :
- Academic Journal
- Accession number :
- 12117537
- Full Text :
- https://doi.org/10.1016/s0378-5955(02)00382-9