Embryogenesis of the inner ear. II. The late differentiation of the mammalian crista ampullaris in vivo and in vitro.

The embryonic development of the crista ampullaris of the CBA/CBA mouse was followed both in organ culture of explanted inner ears of the 16th gestational day and in vivo from the 16th gestational day until the 21st day, an age corresponding to birth. Cytodifferentiation of the sensory epithelium of the crista ampullaris occurs during this period. At partus, there is a rather mature crista with well developed hair cells and 1-2 layers of supporting cells. Innervation and differentiation into type I and type II hair cells have started prior to partus but occur mainly post partum. The in vitro development followed that of the in vivo but with a slight delay, especially concerning the later stages of the in vitro development. At the time corresponding to partus, differentiation of hair cells is almost identical in the two groups but innervation is delayed in the in vitro group of inner ears. Because of the very high reproducibility/stability in vitro and morphologic maturation of both hair cells and gross structure of the crista ampullaris, organ culture of the 16th gestational day inner ear explant is a suitable model in the study of the late embryonic development under normal and pathological conditions.