Structure of the reticular lamina and repair after noise injury.

Laser Scanning Confocal Microscopy (LSCM) and specific labeling techniques were employed to examine the distributing of F-actin and microtubules in the reticular lamina of the guinea pig and monkey organ of Corti. Actin specific label was found in the circumferential belt of adherens junction at the borders between cells in the reticular lamina, and in the cuticular plate of hair cells. The distribution of actin in the adherens junction belt was asymmetric. Actin label was not found in the fonticulus, where the microtubule organizing center resides. Actin free areas were also found between the junctional actin and the cuticular plate. Microtubule specific label was very intense in supporting cells. In normal hair cells, the spatial distribution of tubulin at the reticular lamina is mutually exclusive with that of actin. After noise exposure, a belt of actin was found in the central portion of degenerating outer hair cells, possibly representing a constricted circumferential junction. Expanded supporting cells replaced degenerating hair cells and maintained the confluence of the reticular lamina during the dynamic process of scar formation. A complex network of actin-rich cables appeared at sites of degenerating inner hair cells, suggesting that more than two supporting cells are involved in scar formation for inner hair cells. LSCM proved an attractive method for analysis of the organ of Corti since preparation of the tissue is relatively rapid, preparation artefacts are minimized, different markers in the same specimen may be co-localized and out-of focus fluorescence blurring is eliminated.