Embryonic Development of the Specific Vestibular Hair Cell Pathology in A Strain of the Waltzing Guinea Pig

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Abstract
The cytodifferentiation and maturation of vestibular hair cells, and the pathological development of vestibular type I hair cells, were followed in a strain of the waltzing guinea pig. The hair cells are first identified on the 30th gestational day. During the next 7–10 days the number of hair cells increases considerably in parallel with cytodifferentiation: the development of stereocilia, the cuticular plate, the afferent nerve terminals and the formation of synaptic contacts. On the 48th gestational day efferent nerve terminals are identified as are also a large number of fully developed nerve calyces. Differentiation into hair cells type I and type II was clearly evident at this stage. The first pathological finding appeared on the 38th gestational day as fusion of stereocilia. Actin filament rods in type I hair cells are identified with certainty on the 60th gestational day. In parallel with the in vivo development, inner ear explants (30–50th gestational days) were cultured in vitro. In this material actin filament rods were found already in 30th gestational day explants cultured 8 days in vitro. At this stage also hair cell protrusion and sensory hair fusion occurred.