Abstract
We present preliminary functional data from human vestibular hair cells and primary afferent calyx terminals during fetal development. Whole-cell recordings were obtained from hair cells or calyx terminals in semi-intact cristae prepared from human fetuses aged between 11 and 18 weeks gestation (WG). During early fetal development (11–14 WG), hair cells expressed whole-cell conductances that were qualitatively similar but quantitatively smaller than those observed previously in mature rodent type II hair cells. As development progressed (15–18 WG), peak outward conductances increased in putative type II hair cells but did not reach amplitudes observed in adult human hair cells. Type I hair cells express a specific low-voltage activating conductance, G K,L. A similar current was first observed at 15 WG but remained relatively small, even at 18 WG. The presence of a “collapsing” tail current indicates a maturing type I hair cell phenotype and suggests the presence of a surrounding calyx afferent terminal. We were also able to record from calyx afferent terminals in 15–18 WG cristae. In voltage clamp, these terminals exhibited fast inactivating inward as well as slower outward conductances, and in current clamp, discharged a single action potential during depolarizing steps. Together, these data suggest the major functional characteristics of type I and type II hair cells and calyx terminals are present by 18 WG. Our study also describes a new preparation for the functional investigation of key events that occur during maturation of human vestibular organs.
Highlights
Most of our understanding about the cellular development of human peripheral vestibular organs comes from anatomical studies, which have documented their early growth and maturation (Sans and Dechesne 1985, 1987)
Anatomical differentiation of human vestibular hair cells and supporting cells begins at the end of the embryonic period when fetal crown-rump length (CRL) is between 16.5 and 26 mm or approximately 8–9 weeks gestation (WG, Dechesne et al 1987)
Whole-cell patch clamp recordings were obtained from hair cells and calyx afferent terminals in 31 semi-intact preparations of human fetal vestibular cristae
Summary
Most of our understanding about the cellular development of human peripheral vestibular organs comes from anatomical studies, which have documented their early growth and maturation (Sans and Dechesne 1985, 1987). Anatomical differentiation of human vestibular hair cells and supporting cells begins at the end of the embryonic period when fetal crown-rump length (CRL) is between 16.5 and 26 mm or approximately 8–9 weeks gestation (WG, Dechesne et al 1987). At this stage, hair cells have short, polarized hair bundles and exhibit anatomical features, including synaptic bodies, which are consistent with synapse development (Sans and Dechesne 1985). Invading primary afferent fibers are juxtaposed with these nascent hair cells and exhibit postsynaptic densities (Sans and Dechesne 1985). Limited anatomical data are available for human tissue beyond this time
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