[Light- and electronmicroscopic investigations of the development of the stria vascularis in the ductus cochlearis of the guinea pig fetus]. / Licht- und elektronenmikroskopische Untersuchungen zur Entwicklung der Stria vascularis im Ductus cochlearis von Meerschweinchenfeten.

Our studies on exactly dated guinea pig fetuses show: Already in early stages of development (37th day), in the anlage of the vascular stria vesicular invaginations of the apical plasmalemma of epithelial cells are noted and regarded as a sign of an exchange of substances between epithelial cells and the endolymph. As to the direction of substance transport, the morphological finding allows no decision. From the 42nd to the 44th day of development, the subepithelial basal lamina becomes progressively indistinct. From the 45th day onward, the basal lamina is not yet demonstrable. The largest part of the chromophobe cells of the vascular stria derives from the mesenchyme. The question, whether some of the chromophobe cells are of epithelial origin, as some authors propose, will hopefully be clarified in further studies.

Maturation of junctional complexes during embryonic and early postnatal development of inner ear secretory epithelia.

The development and maturation of tight junctions in secretory epithelia of the inner ear, i.e., the stria vascularis in the cochlea and the dark cell epithelium around the vestibular organs, have been analyzed with the freeze-fracture technique. Inner ears were followed from the otocyst stage to the mature stage (mouse; gestational age 20 to 21 days). Before epithelial cells differentiate into specific tissues, tight junctions have a loose network of sealing elements with zero to four sealing strands. During and after cytodifferentiation, the numbers of strands increase both in the marginal cells of the stria vascularis and in the dark cells around the vestibular organs. Large intra- and intercellular variations in the numbers of sealing strands of the tight junction occur prior to birth in both types of secretory epithelia. In the dark cells the mature structure of the tight junction with five to eight sealing elements is reached at birth. Maturation of marginal cell junctions occurs during the first few days postnatally. Thus, the tight junctions are morphologically mature before the development of the high potassium concentration in the endolymph.