Stereocilia Morphology Research Articles

An electrophysiologic study of the guinea pig inner ear following low pressure barotrauma

We examined electrophysiologic and morphologic changes following low pressure barotrauma in 25 guinea pigs. Compound action potentials (CAPs), cochlear microphonics (CMs), and transiently evoked otoacoustic emissions (TEOAEs) were elicited by tone bursts (1, 2, 4 and 8 kHz) or non-linear clicks immediately following barotrauma. CAP threshold elevations were observed in 19 out of 25 cochleas, mainly at lower stimulus frequencies. Furthermore, CM and TEOAE thresholds were significantly increased, while CAP and CM amplitudes demonstrated reductions at all stimulus frequencies and intensities. CAP N1 latencies exhibited slight elongations at all stimulus frequencies and intensities. The regression coefficient between the mean CAP thresholds of four stimulus frequencies and TEOAE thresholds was statistically significant. Scanning electron microscopy (SEM) study of six electrophysiologically abnormal cochleas revealed altered stereocilia morphology in four, but no changes in two. We hypothesize that low pressure barotrauma can injure inner ear hair cells through an early threshold shift secondary to dislocation of the basement membrane.

Fluid-structure interaction of the stereocilia bundle in relation to mechanotransduction.

Current hypotheses regarding mechanotransduction rely upon motion of the stereocilia relative to the apical surface of the hair cell. The viscosity of the surrounding endolymphatic fluid will, however, attenuate stereocilia motion at higher frequencies of excitation. To investigate stereocilia motion for physiologically reasonable deflections and frequencies of excitation, the fluid-structure interaction of the stereocilia bundle is considered analytically. Solutions in the frequency domain are determined for stereocilia bundle dimensions at several locations along the cochlear duct of the chinchilla. Results indicate that motion of the stereocilia is analogous to that of a low-pass filter. Comparison of these solutions with Greenwood's frequency-place map demonstrates that motion of the stereocilia bundle exists without substantial attenuation at least up to frequencies appropriate for the location of the corresponding hair cell along the cochlear duct. The variation in stereocilia morphology within the mammalian cochlea thus appears to provide a collection of low-pass mechanoreceptors, arranged in order of increasing corner frequency across the auditory spectrum.

High-resolution scanning-electron microscopy of stereocilia using the osmium-thiocarbohydrazide coating technique

Further observations on the detailed morphology of stereocilia have been made using high-resolution scanning-electron microscopy of osmium-thiocarbohydrazide-coated guinea pig cochleae. Three types of cross-link have been observed between stereocilia. Side-to-side and row-to-row linkages are composed of a filamentous network whilst upward-pointing links are a fine single strand, often with a terminal widening. The stereocilia have rough surfaces. These features are observed on both inner and outer hair cells despite reported sensitivity to long periods of osmium fixation. We suggest that osmium sensitivity may be altered by the buffering conditions used during preparation.The observations on osmium-coated material correspond more closely with those made using transmission-electron microscopy than those made using other scanning-electron microscopical preparation techniques, since gold-coating artefacts are absent and the degree of specimen collapse is less. This has enabled us to observe fine details of the links and their attachments which have not been reported previously in SEM.