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The development of vestibulocochlear efferents and cochlear afferents in mice.
- Source :
-
International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience [Int J Dev Neurosci] 1997 Jul; Vol. 15 (4-5), pp. 671-92. - Publication Year :
- 1997
-
Abstract
- We have reinvestigated the embryonic development of the vestibulocochlear system in mice using anterograde and retrograde tracing techniques. Our studies reveal that rhombomeres 4 and 5 include five motor neuron populations. One of these, the abducens nucleus, will not be dealt with here. Rhombomere 4 gives rise to three of the remaining populations: the facial branchial motor neurons; the vestibular efferents; and the cochlear efferents. The migration of the facial branchial motor neurons away from the otic efferents is completed by 13.5 days post coitum (dpc). Subsequently the otic efferents separate into the vestibular and cochlear efferents, and complete their migration by 14.5 dpc. In addition to their common origin, all three populations have perikarya that migrate via translocation through secondary processes, form a continuous column upon completion of their migrations, and form axonal tracts that run in the internal facial genu. Some otic efferent axons travel with the facial branchial motor nerve from the internal facial genu and exit the brain with that nerve. These data suggest that facial branchial motor neurons and otic efferents are derived from a common precursor population and use similar cues for pathway recognition within the brain. In contrast, rhombomere 5 gives rise to the fourth population to be considered here, the superior salivatory nucleus, a visceral motor neuron group. Other differences between this group and those derived from rhombomere 4 include perikaryal migration as a result of translocation first through primary processes and only then through secondary processes, a final location lateral to the branchial motor/otic efferent column, and axonal tracts that are completely segregated from those of the facial branchial and otic efferents throughout their course inside the brain. Analysis of the peripheral distribution of the cochlear efferents and afferents show that efferents reach the spiral ganglion at 12.5 dpc when postmitotic ganglion cells are migrating away from the cochlear anlage. The efferents begin to form the intraganglionic spiral bundle by 14.5 dpc and the inner spiral bundle by 16.5 dpc in the basal turn. They have extensive collaterals among supporting cells of the greater epithelial ridge from 16.5 dpc onwards. Afferents and efferents in the basal turn of the cochlea extend through all three rows of outer hair cells by 18.5 dpc. Selective labeling of afferent fibers at 20.5 dpc (postnatal day 1) shows that although some afferents are still in early developmental stages, some type II spiral ganglion cells already extend for long distances along the outer hair cells, and some type I spiral ganglion cells end on a single inner hair cell. These data support previous evidence that in mice the early outgrowth of afferent and efferent fibers is essentially achieved by birth.
- Subjects :
- Animals
Axons physiology
Axons ultrastructure
Brachial Plexus cytology
Brachial Plexus embryology
Carbocyanines
Cell Differentiation physiology
Cochlea cytology
Dextrans
Facial Nerve cytology
Facial Nerve embryology
Female
Mice
Motor Neurons physiology
Pregnancy
Rhombencephalon cytology
Rhombencephalon embryology
Vestibule, Labyrinth cytology
Cochlea embryology
Neurons, Afferent physiology
Neurons, Efferent physiology
Vestibule, Labyrinth embryology
Subjects
Details
- Language :
- English
- ISSN :
- 0736-5748
- Volume :
- 15
- Issue :
- 4-5
- Database :
- MEDLINE
- Journal :
- International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience
- Publication Type :
- Academic Journal
- Accession number :
- 9263042
- Full Text :
- https://doi.org/10.1016/s0736-5748(96)00120-7