STRUCTURAL MATURATION OF THE INTERFACE REGION BETWEEN THE STRIA VASCULARIS AND SPIRAL LIGAMENT IN THE NEONATAL RAT COCHLEA

The ultrastructural morphology of the interface region between the str ia vascularis (SV) and spiral ligament (SL) was examined in the neonat al rat cochlea via transmission electron microscopy, At postnatal day (PND) 3, morphology of both basal cells and fibrocytes was simple and immature. Only a small number of fibrocytes was observed in the SL. In tercellular junctions between basal cells and fibrocytes, and between adjacent fibrocytes, were few. At PND 7, the number of fibrocytes incr eased, and more organelles appeared within their cytoplasm. From PND 1 1 to 14, nuclei of the basal cells appeared to be more spindle-shaped and contained more heterochromatin. The cytoplasm of the fibrocytes wa s pale, and a greater number of cytoplasmic vesicles and mitochondria emerged. More intercellular junctions were observed between basal cell s and fibrocytes at the interface region and between fibrocytes in the SL, By PND 21, the morphology of basal cells and fibrocytes and their intercellular junctions appeared to be adult-like. These morphologica l observations correlate with previous reports on the functional matur ation of the developing rat cochlea.