FORMATION OF THE COCHLEA IN THE CHICKEN-EMBRYO - SEQUENCE OF INNERVATION AND LOCALIZATION OF BASAL LAMINA-ASSOCIATED MOLECULES

The purpose of this study was to determine the temporal and spatial gradients in the innervation of the chicken cochlea, the basilar papilla, as it develops in the early embryo. A series of white Leghorn chick embryos (Hamburger-Hamilton Stage 20-43) were prepared for serial sectioning and stained by Toluidine blue or by antibodies to fibronectin or laminin. Light microscopic observations were made on the first fiber bundles to reach each region of the basilar papilla. There is a distinct temporo-spatial pattern of the ingrowth of fiber bundles to the developing basilar papilla. The primary pattern is not described as any simple linear gradient. Fiber ingrowth begins proximally, shifts to a distal and then to a mid-proximal region. The fiber ingrowth correlates temporally and spatially with disruption of fibronectin and laminin staining of the basal lamina where fiber bundles are penetrating. This pattern may reflect not only the sequence of fiber ingrowth but also the displacement of cells and fibers in the elongating basilar papilla, which grows as a result of a contemporaneous mitotic activity throughout the structure rather than progressing from one end to the other.