Current medical imaging modalities, such as MRI and CT, do not provide high enough resolution to detect many
changes within the cochlea that cause hearing loss. We sought to develop the technique of optical coherence
tomography (OCT) to image the cochlea noninvasively and within its native environment. We used spectral domain
OCT with 950 nm as the center wavelength and a bandwidth of ~100 nm to image freshly excised normal mouse cochlea
at different developmental ages. The OCT system has an axial resolution of ~4 μm (in air) and a lateral resolution of
~10 μm. When we imaged normal adult mouse cochleae through the round window membrane, Reissner's membrane,
the basilar membrane, the tectorial membrane, the spiral ligament, the spiral limbus, and the modiolus could be clearly
identified. When we imaged intact adult cochleae, we were able to image through ~130 μm of bone and tissue to see up
to a depth of ~600 μm, and all of the previously identified structures were still visible. Imaging of early postnatal mice
during the timeline of cochlear development permitted visualization of the expected structural differences from adult
cochleae. Therefore, we conclude that spectral domain OCT is an effective technique for noninvasive imaging of the
murine cochlea.
Mice are an excellent model for studying mammalian hearing and transgenic mouse models of human hearing, loss are commonly available. However, the mouse cochlea is substantially smaller than other animal models routinely used to study cochlear physiology. This makes study of their hair cells difficult. We develop a novel methodology to optically image calcium within living hair cells left undisturbed within the excised mouse cochlea. Fresh cochleae are harvested, left intact within their otic capsule bone, and fixed in a recording chamber. The bone overlying the cochlear epithelium is opened and Reissner's membrane is incised. A fluorescent calcium indicator is applied to the preparation. A custom-built upright two-photon microscope was used to image the preparation using 3-D scanning. We are able to image about one third of a cochlear turn simultaneously, in either the apical or basal regions. Within one hour of animal sacrifice, we find that outer hair cells demonstrate increased fluorescence compared with surrounding supporting cells. This methodology is then used to visualize hair cell calcium changes during mechanotransduction over a region of the epithelium. Because the epithelium is left within the cochlea, dissection trauma is minimized and artifactual changes in hair cell physiology are expected to be reduced.
Mice are an excellent model for studying mammalian hearing and transgenic mouse models of human hearing loss
are commonly available for research. However, the mouse cochlea is substantially smaller than other animal models
routinely used to study cochlear physiology. This makes the study of their hair cells difficult. We developed a novel
methodology to optically image calcium within living hair cells left undisturbed within the excised mouse cochlea.
Fresh cochleae were harvested, left intact within their otic capsule bone, and glued upright in a recording chamber. The
bone overlying the region of the cochlear epithelium to be studied was opened and Reissner's membrane was incised. A
fluorescent indicator was applied to the preparation to image intracellular calcium. A custom-built upright two-photon
microscope was used to image the preparation using three dimensional scanning. We were able to image about 1/3 of a
cochlear turn simultaneously, in either the apical or basal regions. Within one hour of animal sacrifice, we found that
outer hair cells demonstrated increased fluorescence compared with surrounding supporting cells. Thus, this
methodology can be used to visualize hair cell calcium changes and mechanotransduction over a region of the epithelium.
Because the epithelium is left within the cochlea, dissection trauma is minimized and artifactual changes in hair cell
physiology are reduced.
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