Postlesional regeneration of vestibular hair cells in adult animals

In mammals, the destruction of mature hair cells-(HCs) of the inner ear pro duces balance disorders and irreversible deafness. Since both avian and mam malian HCs were believed to be produced prior to birth, HC regeneration was not thought to occur. However, during the last decade, research has indica ted that vestibular HCs can-reappear after lesions of the neurosensory epit helia, whereas cochlear HCs do not regenerate. Repair of the neurosensory e pithelium is associated with division of epithelial Supporting cells, In vi tro, this proliferation is stimulated by growth factors acting on tyrosine kinase receptors, but the effect of each growth factor varies depending on the maturation stage and on the species. New HCs may arise either from diff erentiation of proliferating cells or from transdifferentiation of differen tiated supporting cells, The differentiation process can affect two subsets of HCs (type 1 and type 2 HC) which differ in their regenerating potential , since one can become physiologically mature, while the other will display immature physiological features.