Alterations in hair bundle micromechanics during in vitro and vivo overstimulation of chick cochlear hair cells.

Format:

Book

Thesis/Dissertation

Author/Creator:

Duncan, Robert Keith.

Contributor:

University of Pennsylvania.

Language:

English

Subjects (All):

Biomedical engineering.

Cytology.

Neurosciences.

0317.

0379.

0541.

Local Subjects:

0317.

0379.

0541.

Physical Description:

257 pages

Contained In:

Dissertation Abstracts International 60-04B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

Inner ear hair cells are critical elements along the auditory pathway, and these cells exhibit a wide range of pathologies in noise-induced hearing loss. The specialized tuft of sensory stereocilia extending from the apical hair cell surface is a primary site of injury, and structural damage to this hair bundle leads to alterations in mechanoelectrical transduction. This thesis addresses the alterations to hair bundle micromechanics following injury from in vitro and in vivo overstimulation of chick cochlear hair cells. In order to assess changes in hair bundle micromechanics, a number of preliminary studies were performed. The motion of the tallest and shortest stereocilia was characterized in an in vitro preparation, and it was found that the shortest stereocilia consistently moved through greater excursions than the tallest stereocilia, regardless of stimulation frequency or intensity. Moreover, while the tallest stereocilia moved symmetrically about the rest position, the motion of the shortest hairs was decidedly asymmetric with greater excitatory than inhibitory deflections. Both relative stereocilia motion and short hair asymmetry were diminished following treatment with a calcium-free external culture medium shown to destroy interconnecting tip links. It was concluded that tip links, which have also been associated with transduction, were responsible for the relative and asymmetric motion. Observations of hair bundle motion provided an assay for inferring the presence of tip links after noise exposure. In addition, a lumped-parameter model of hair bundle micromechanics supported the notion that tip link destruction, and not injury to stereocilium stiffness, would result in the reduction of relative motion. In a final set of experiments, hair bundles were subjected to in vitro and in vivo overstimulation. In vitro exposure produced a loss in bundle stiffness that subsequently recovered. Relative motion and short hair asymmetry were unchanged following overstimulation, and therefore tip links were intact and undamaged. Thus, the site of injury was the stereocilia. Intense in vivo sound exposures injured both tip links and stereocilium stiffness. Finally, it was demonstrated that hair bundles with curvilinear profiles were more susceptible to injury from in vitro overstimulation.

Notes:

Source: Dissertation Abstracts International, Volume: 60-04, Section: B, page: 1725.

Adviser: James C. Saunders.

Thesis (Ph.D.)--University of Pennsylvania, 1999.

Local Notes:

School code: 0175.

ISBN:

9780599258822

Access Restriction:

Restricted for use by site license.