Influence of neurotrophins on the synaptogenesis of inner hair cells in the deaf Bronx waltzer (bv) XXXX organ of Corti in culture.

@entity9140 @entity9139 @entity1246 @entity19 @entity16843 @entity528
The Bronx waltzer (bv) deaf @entity19 is characterized by massive degeneration of the primary auditory receptors, the inner hair cells, which occurs during the time of expected afferent synaptogenesis. The process is associated with degeneration and protracted division of the normally postmitotic afferent @entity528 . To investigate the potential role of neurotrophins in the afferent synaptogenesis of inner hair cells, we exposed bv newborn cochleas in organotypic culture to @entity9140 ( @entity9140 ), @entity9139 ( @entity9139 ) and nerve growth factor (NGF), and also to @entity1246 ( @entity1246 ), for up to 8 days. The study was done using light and electron microscopy. Only about 20% of the inner hair cells survived in culture, regardless of the treatment, similar to the number in the intact mutant in our colony. Depending on the exogenous treatment, this population consisted of either innervated ultrastructurally normal cells or denervated dedifferentiated cells wrapped-in lieu of nerve endings-by the supporting inner phalangeal and border cells. In the control and @entity1246 cultures, inner hair cells were mostly denervated. @entity9140 and @entity9139 alone or combined increased synaptogenesis and hair cell survival only during the first 3 days (by about 10%); however, the cells became denervated by 8 @entity16843 ( @entity16843 ). Only NGF induced stable innervation and differentiation of neurosensory relationships, including supernumerary innervation characteristic of the intact bv. Denervation among the remaining 20% of inner hair cells induced a reactive wrapping by inner phalangeal and border cells which evidently extended inner hair cell survival. Immunocytochemical studies of these reactive supporting cells were done in the intact (8 @entity16843 ) mutant cochlea. The supporting cells that provide sustenance to the denervated inner hair cells displayed strong @entity9140 (and possibly @entity9139 ) immunoreactivity. Subsequently, we revealed the presence of all three neurotrophins in the inner hair cell region of the developing (1-8 @entity16843 ) cochlea of the normal ICR @entity19 . The inner hair cells expressed all three neurotrophins; @entity9140 prevailed in the inner phalangeal cells, @entity9139 in the pillar cells and inner phalangeal cells, and NGF in the pillar cells. IN CONCLUSION: initially, the 80% loss of inner hair cells is apparently caused by their failed afferent synaptogenesis. Exogenous neurotrophins influence synaptogenesis in the bv in culture, but NGF alone is successful in promoting stable neurosensory relationships. The presence of neurotrophins in supporting cells in the normal and degenerating cochlea indicates their role in the sustenance of inner hair cells.
