PROJECTIONS OF THIN (TYPE-II) AND THICK (TYPE-I) AUDITORY-NERVE FIBERS INTO THE COCHLEAR NUCLEUS OF THE MOUSE

被引:72
作者
BROWN, MC
LEDWITH, JV
机构
[1] HARVARD UNIV, SCH MED, DEPT PHYSIOL, BOSTON, MA 02115 USA
[2] HARVARD UNIV, SCH MED, DEPT OTOLARYNGOL, BOSTON, MA 02115 USA
关键词
Afferent; Granule cell; Outer hair cell; Unmyelinated;
D O I
10.1016/0378-5955(90)90098-A
中图分类号
R36 [病理学]; R76 [耳鼻咽喉科学];
学科分类号
100104 ; 100213 ;
摘要
Injections of horseradish peroxidase into the mouse spiral ganglion were used to label type-I and type-II afferent fibers. Axons presumed to be from type-II spiral ganglion cells because of their small diameter (< 0.7 μm) and lack of nodes of Ranvier were traced to their terminations in the cochlear nucleus. Thicker fibers presumed to be from type-I ganglion cells were also reconstructed. Type-I and type-II axons labeled by basal turn injections bifurcate together in the dorsal part of the auditory nerve root, forming a branch that ascends into the anteroventral cochlear nucleus and a branch that descends into the posteroventral cochlear nucleus. Type-I fibers formed many collaterals ending in terminal swellings whereas type-II fibers were almost unbranched. Swellings from type-I and type-II fibers were often formed alongside one another. Examples of this proximity include terminal swellings of root collaterals in the auditory nerve root, as well as type-II en passant swellings and type-I terminal swellings throughout the ventral cochlear nucleus. The projections are dissimilar, however, since every type-II fiber projects at least one collateral to the granule-cell lamina. These collaterals usually end in neuropil forming the border between the ventral cochlear nucleus and the granule-cell lamina. In this border region, the type-II terminals overlap with those of branches from thick axons of the olivocochlear (efferent) bundle. Type-II fibers also differ from type-I fibers by only rarely coursing into the dorsal cochlear nucleus and by forming very few terminal swellings. En passant swellings, however, are numerous on type-II fibers, with ellipsoidal-shaped swellings prominent in the nerve root and angular and complex-shaped swellings common nearer the terminals. We suggest that the latter swellings are associated with type-II synapses whereas the ellipsoidal swellings represent non-synaptic structures. © 1990.
引用
收藏
页码:105 / 118
页数:14
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