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Synaptic arrangements between inner hair cells and tunnel fibers in the mouse cochlea
Author(s) -
Sobkowicz Hanna M.,
August Benjamin K.,
Slapnick Susan M.
Publication year - 2004
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/syn.20026
Subject(s) - efferent , hair cell , organ of corti , inner ear , anatomy , cochlea , efferent nerve , synapse , spiral ganglion , ribbon synapse , outer hair cells , neuroscience , biology , chemistry , afferent , synaptic vesicle , vesicle , genetics , membrane
Abstract Hair cells, the sensory cells of the organ of Corti, receive afferent innervation from the spiral ganglion neurons and efferent innervation from the superior olivary complex. The inner and outer hair cells are innervated by distinctive fiber systems. Our electron microscopical studies demonstrate, however, that inner hair cells, in addition to their own innervation, are also synaptically engaged with the fibers destined specifically to innervate outer hair cells, within both the afferent and efferent innervation. Serial sections of the afferent tunnel fibers (destined to innervate outer hair cells) in the apical turn demonstrate that, while crossing toward the tunnel of Corti, they receive en passant synapses from inner hair cells. Each inner hair cell (in a series of five in the apical turn) was innervated by two tunnel fibers, one on each side. We show here for the first time that, in the adult, the afferent tunnel fibers receive a ribbon synapse from inner hair cells and form reciprocal contacts on their spines. Vesiculated efferent fibers from the inner pillar bundle (which carries the innervation to outer hair cells) form triadic synapses with inner hair cells and their synaptic afferent dendrites; the vesiculated terminals of the lateral olivocochlear fibers from the inner spiral bundle synapse extensively on the afferent tunnel fibers, forming triadic synapses with both afferent tunnel fibers and their synaptic inner hair cells. This intense synaptic activity involving inner hair cells and both afferent and efferent tunnel fibers, at their crossroad, implies functional connections between both inner and outer hair cells in the process of hearing. Synapse 52:299–315, 2004. © 2004 Wiley‐Liss, Inc.