A Quantitative Analysis of the Afferent Innervation of the Organ of Corti in Guinea Pig

Morrison, Donald; Schindler, Robert A.; Wersäll, Jan

doi:10.3109/00016487509124649

Cited by 97 publications

(29 citation statements)

References 11 publications

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“…These neurons respond to sound and transmit this information to the cochlear nucleus via their fast-conducting fibers (reviewed by Ruggero 1992). The type II neurons make up the remaining small percentage of primary auditory neurons (Spoendlin 1969;Morrison et al 1975;Kiang et al 1984;Brown 1987;Romand and Romand 1987), and their thin fibers provide a presumably slow-conducting pathway into the brain. The function of these neurons is unknown because physiological studies suggest that they do not respond to sounds typically used as search stimuli (Robertson 1984;Brown 1994;Robertson et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Postsynaptic Targets of Type II Auditory Nerve Fibers in the Cochlear Nucleus.

Benson

Brown

2004

JARO

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Type II auditory nerve fibers, which provide the primary afferent innervation of outer hair cells of the cochlea, project thin fibers centrally and form synapses in the cochlear nucleus. We investigated the postsynaptic targets of these synapses, which are unknown. Using serial-section electron microscopy of fibers labeled with horseradish peroxidase, we examined the border of the granule-cell lamina in mice, an area of type II termination that receives branches having swellings with complex shapes. About 70% of the swellings examined with the electron microscope formed morphological synapses, which is a much higher value than found in previous studies of type II swellings in other parts of the cochlear nucleus. The high percentage of synapses enabled a number of postsynaptic targets to be identified. Most of the targets were small dendrites. Two of these dendrites were traced to their somata of origin, which were cochlear-nucleus ''small cells'' situated at the border of the granule-cell lamina. These cells did not appear to receive any terminals containing synaptic vesicles that were large and round, indicating a lack of input from type I auditory nerve fibers. Nor did type II swellings or targets participate in the synaptic glomeruli formed by mossy terminals and the dendrites of granule cells. Other type II synapses were axosomatic and their targets were large cells, which were presumed multipolar cells and one cell with characteristics of a globular bushy cell. These large cells almost certainly receive additional input from type I auditory nerve fibers, which provide the afferent innervation of the cochlear inner hair cells. A few type II postsynaptic targets-the two small cells as well as a large dendrite-received synapses that had accompanying postsynaptic bodies, a likely marker for synapses of medial olivocochlear branches. These targets thus probably receive convergent input from type II fibers and medial olivocochlear branches. The diverse nature of the type II targets and the examples of segregated convergence of other inputs illustrates the synaptic complexity of type II input to the cochlear nucleus.

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Section: Introductionmentioning

confidence: 99%

Postsynaptic Targets of Type II Auditory Nerve Fibers in the Cochlear Nucleus.

Benson

Brown

2004

JARO

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“…The upper tunnel crossing fibers are efferent (9, 16), and other efferents may cross at the tunnel floor (17). Large synaptic terminals on outer hair cells are endings ofupper tunnel crossing fibers (9,12,16) The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertiseinent" in accordance with 18 U. S. C. §1734 solely to indicate this fact.…”

Section: Introductionmentioning

confidence: 99%

“…The outer hair cells make relatively few synapses with auditory nerve boutons from about 10% of the spiral ganglion cells (7)(8)(9). The auditory receptor organ also receives efferent, centrifugal innervation from the brainstem, through olivocochlear neurons.…”

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“…Inner hair cells and auditory nerve dendrites under inner hair cells receive efferent innervation from the inner spiral bundle (15). The upper tunnel crossing fibers are efferent (9,16), and other efferents may cross at the tunnel floor (17). Large synaptic terminals on outer hair cells are endings ofupper tunnel crossing fibers (9,12,16) and are efferent (18,19).…”

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confidence: 99%

“…In the organ ofCorti, each inner hair cell synapses with about 20 auditory nerve boutons from about 90% of the total spiral ganglion cell population (7)(8)(9). The outer hair cells make relatively few synapses with auditory nerve boutons from about 10% of the spiral ganglion cells (7)(8)(9).…”

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Enkephalin-like immunoreactivity of olivocochlear nerve fibers in cochlea of guinea pig and cat

Fex

Altschuler

1981

Proc. Natl. Acad. Sci. U.S.A.

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The distribution ofenkephalin-like immunoreactivity in the cochlea ofthe guinea pig and cat was studied. Indirect immunofluorescence immunohistochemistry using antisera generated against a methionine enkephalin-bovine thyroglobulin conjugate was applied to surface preparations of the organ of Corti and cryostat sections of the whole of the cochlea. In the cochlear osseous spiral lamina, immunofluorescence was localized to unmyelinated fibers ofthe intraganglionic spiral bundle. In the organ of Corti, immunofluorescence was localized to a small number of fibers at inner hair cells, the inner spiral bundle, and tunnel spiral bundle, to tunnel crossing fibers at the level of the tunnel floor, to an occasional spiral outer fiber, and to the synaptic region ofouter hair cells in the three rows of the basal turn of the cochlea. Less immunofluorescence was found in this region as one progressed towards the apex, with none seen at the apex. At the most apical region the inner spiral bundle became patchy and the tunnel spiral bundle developed arcades. There was no immunofluorescence found in spiral ganglion cells, in auditory nerve fibers, or in the hair cells of the organ of Corti. The findings were the same in cat as in guinea pig, the latter being studied in more detail. It was concluded that efferent, olivocochlear neurons ofthe cochlea, synapsing predominantly with primary auditory nerve fibers from the inner sensory cells or with the sensory cells, contain enkephalin-like immunoreactivity. Also, the findings indicate that endings of olivocochlear neurons that synapse predominantly with outer hair cells contain enkephalin-like immunoreactivity. It has previously been shown that ofivocochlear neurons are likely to be cholinergic.Methionine enkephalin and leucine enkephalin are opioid pentapeptides originally isolated from the whole brain (1, 2). Immunohistochemical mapping of enkephalin-like immunoreactivity in the central nervous system was done (3-5), and it was noted that in certain regions enkephalin-like immunoreactivity and opiate receptors had a similar distribution (3, 5). A much entertained working hypothesis is that enkephalins may act as neurotransmitters or modulate the action of neurotransmitters (6).In the organ ofCorti, each inner hair cell synapses with about 20 auditory nerve boutons from about 90% of the total spiral ganglion cell population (7-9). The outer hair cells make relatively few synapses with auditory nerve boutons from about 10% of the spiral ganglion cells (7-9). The auditory receptor organ also receives efferent, centrifugal innervation from the brainstem, through olivocochlear neurons. In the cochlea, myelinated and unmyelinated olivocochlear fibers spiral in the fascicles ofthe intraganglionic bundle (10, 11) and then fan out to the organ of Corti. In the organ of Corti, such fibers form the inner spiral bundle and the tunnel spiral bundle (12)(13)(14). Inner hair cells and auditory nerve dendrites under inner hair cells receive efferent innervation from the inner spiral bundl...

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