Neural Interaction in the Human Spiral Ganglion: A TEM study

Abstract

A TEM study was performed on freshly fixed human spiral ganglions (HSG) collected during skull base surgery. This technique gives well preserved tissue for ultrastructural analysis. Unlike spiral ganglion cells in mature animals so far studied, most HSG cells lack a myelin coat, but are surrounded by a thin rim of Schwann cell (SC) cytoplasm. In the region of maximal innervation density (upper basal and middle turn), HSG cells were frequently ensheathed by the same Schwann cell, forming a "unit-like" structure. In this region the cells often showed signs of physical interaction where the SCs were frequently incompletely developed ("gaps") so that the cell membranes of adjacent ganglion cells (sometimes as many as four in one section plane) were in direct apposition. In one thin section as many as 20 of 100 ganglion cells were found to face the cell membrane, at any point, of an adjacent cell. At these "gaps" in the SC, complexes of cell membrane specializations occurred between individual HSG cells. The same nerve junctions were also found between unmyelinated nerve fibres and the body of large ganglion cells. Our findings may challenge the view that afferent information in the acoustic nerve is conveyed uninterrupted to the CNS at the level of the spiral ganglion.

The Human Spiral Ganglion: New Insights into Ultrastructure, Survival Rate and Implications for Cochlear Implants

“…The fi ne structure of the human spiral ganglion differs from that of other mammalian species studied so far [Kimura et al, 1979;Ota and Kimura, 1980;Arnold, 1987;Tylstedt et al, 1997;Rask-Andersen et al, 2000b]. Unlike in most animals the perikarya of the human spiral ganglion are unmyelinated.…”

“…This adds insights into the surface structure of the modiolar wall and its relation to the spiral ganglion. We previously published results from transmission electron microscopy (TEM) studies of the human spiral ganglion using surgically obtained tissue , 2000aTylstedt et al, 1997;Tylstedt and RaskAndersen, 2001] and on the organ of Corti using SEM [Glueckert et al, 2005]. This represents the fi rst such study to detail the morphology and characteristics of the human spiral ganglion using SEM and sectioned material.…”

Expression of TrkB and BDNF in human cochlea—an immunohistochemical study

“…The cultured guinea pig inner ear neurons that also express TrkB might serve as an in vitro model for human cochlear neuron in regeneration studies. Nevertheless, the unique connexin protein expression (Liu et al 2009a), the lack of myelination around the neuronal somata, and the specific electron-dense structure associated with the cell membrane in human SGNs (Tylstedt et al 1997;Tylstedt and Rask-Andersen 2001) indicate possible differences in the survival and regeneration conditions and patterns between human and animal inner ear neurons. In rat cochlea influenced by ototoxic drugs, the expression of the TrkB receptor (Tan and Shepherd 2006) and TrkB mRNA transcript (Wissel et al 2006) has been found to be down-regulated.…”

Application of Mouse Models to Research in Hearing and Balance

“…In humans, where most spiral ganglion cell bodies are unmyelinated (Tylstedt et al 1997;Tylstedt and Rask-Andersen 2001;Glueckert et al 2005), this feature may promote survival and sound responsiveness in neurons that have become disconnected from their hair cell targets. In B6 mice, aggregates are observed principally in the apical half of the cochlea and appear to multiply with age.…”