Cochlear Motion Across the Reticular Lamina Implies It Is Not a Stiff Plate
Key findings
- In this study, high-resolution optical coherence tomography was used in gerbils to measure motion in the organ of Corti at different radial locations across the reticular lamina surface, at the tops and bottoms of the three rows of outer hair cells (OHCs)
- In vivo, the motion of the reticular lamina varied radially: the third-row gain was more than three times greater than that of the first-row, whereas motion at the bottom of OHCs remained similar
- Postmortem, the measured points moved together approximately in phase
- The reticular lamina seems to bend and/or stretch in vivo, not move as a stiff plate as has been assumed for over a century
- Determining the specifics of reticular lamina motion is key to understanding cochlear amplification via OHC stimulation and sound transduction via inner hair cell stimulation
Outer hair cells (OHCs) in the cochlea have an instrumental role in amplifying sound. Each OHC has an attached Deiters' cell and Deiters' cell phalangeal process, which form a Y-shaped building block between the reticular lamina and basilar membrane within the organ of Corti.
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Sunil Puria, PhD, Amelia Peabody Scientist in the Eaton-Peabody Laboratories at Mass Eye and Ear, previously showed that longitudinal and radial angles of the phalangeal processes in the Y-shaped structures vary across three rows of OHCs.
Recently developed optical technology permitted earlier observations that the phasing of the OHC motion required to amplify the motion of the basilar membrane arises from radial motion of the reticular lamina. Dr. Puria and postdoctoral research fellow Nam Hyun Cho, PhD, speculated that the Y-shaped structures below the reticular lamina may be involved in creating that motion.
In Scientific Reports, the researchers report the first definitive measurements of the reticular lamina in the gerbil basal region and the first in vivo evidence of motion across all three OHC rows.
Methods
Most studies that have measured motion in the organ of Corti concentrated on motion in the direction in which the OHC force acts against the basilar membrane, which is expected to produce cochlear amplification.
Using high-resolution optical coherence tomography in gerbils, the researchers measured motion at various depths along that same direction. However, they also measured at different radial locations across the reticular lamina surface, at the tops and bottoms of the three rows of individual OHCs.
Results
In vivo, the motion of the reticular lamina varied radially. The third-row gain was more than three times greater than that of the first-row, whereas motion at the bottom of OHCs remained similar.
Postmortem, the measured points moved together approximately in phase.
Why It Matters
The findings imply the reticular lamina is much more flexible than the Deiters' cells that are connected to OHCs at their bottom surfaces. In vivo, the reticular lamina may bend and/or stretch, not move as a stiff plate as assumed for more than a century. Determining the specifics of reticular lamina motion is key to understanding cochlear amplification via OHC stimulation and sound transduction via inner hair cell stimulation.
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