Video-enhanced DIC images of the noise-damaged and regenerated chick tectorial membrane.

Exposure of the chick cochlea to acoustic overstimulation results in a loss of hair cells and a disruption of the tectorial membrane. With time, new hair cells are produced to replace those that are lost and, concurrently, a new tectorial membrane is regenerated. Previous studies of tectorial membrane regeneration examined tissues that were fixed and processed for scanning and transmission electron microscopy. This processing results in a considerable shrinkage of the membrane, and, therefore, it was unclear how the noise damage and subsequent regeneration affected the unfixed, in situ structure of the tectorial membrane. We have recently developed techniques for studying the unfixed tectorial membrane with video-enhanced differential-interference-contrast (DIC) light microscopy. Exposure to a 1500-Hz pure tone at 120 dB SPL for 24 h causes localized damage to the hair cells and tectorial membrane in the mid-proximal region of the basilar papilla. Examination of the unfixed membrane immediately after noise exposure shows that the damage to the tectorial membrane is actually caused by the acoustic trauma and is not an artifact of fixation. After 14 days of recovery, a thick, honeycomb of new matrix has grown from the supporting cells in the basilar papilla and has formed new connections with the stereocilia of surviving and regenerating hair cells. Moreover, this new honeycomb has fused with the remainder of the surrounding, undamaged tectorial membrane, thus reestablishing a continuity in the structure of the membrane across both the damaged and undamaged regions of the basilar papilla.