INCORPORATION OF D-[H-3]-GLUCOSAMINE AND L-[H-3]-FUCOSE INTO THE DEVELOPING RAT COCHLEA

The uptake of two tritiated carbohydrates, D-[H-3]-glucosamine and L-[H-3]-fucose, to the developing rat cochlea was examined using light and electron microscopic radioautography. Both carbohydrates, administered to in vitro developing rat cochleas, shared a similar ultrastructural labeling pattern on the microvilli and apical cell region and on the tectorial membrane (TM) fibrils. On embryonic day 18, the radiolabeling appeared on the apical surface of the undifferentiated epithelium that will develop into both spiral limbus and Kolliker's organ (KO), while on postnatal day (PD) 1, it was only located on the apical surface of the KO. When D-[H-3]-glucosamine was administered in vivo to newborn rats, the radiolabeling was observed in the TM covering the KO at PD 3. Lastly, D-[H-3]-glucosamine administered in vivo to PD 7 rats, appeared at PD 9 in the TM region lying just above the organ of Corti. The present findings support the previously suggested leading role of the spiral limbus and KO in the secretion of the TM during cochlear development. The secretion of carbohydrates, and probably of other matrix components, starts on the spiral limbus and KO region and progressively extends to the organ of Corti.