THE ROLE OF THE NEUROTROPHINS IN MATURATION AND MAINTENANCE OF POSTNATAL AUDITORY INNERVATION

Auditory hair cells produce trophic factors that directly affect matur ation and survival of auditory neurons. These factors include two memb ers of the neurotrophin family: brain-derived neurotrophic factor (BDN F) and neurotrophin-3 (NT-3). Loss of hair cells as a result of either noise trauma or ototoxic damage, results In the degeneration of audit ory neurons. An in vitro model of early postnatal rat organ of Corti/s piral ganglion explants was used to study the effects of deprivation a nd supplementation of nerve growth factor (NGF), BDNF, and NT-3 on neu ronal survival. Immunolocalization of receptors for these neurotrophin s correlated with their effectiveness as promoters of neuronal surviva l. BDNF affected early neuronal survival, whereas NT-3 was the most im portant survival factor for maturing auditory neurons. NGF was shown t o maintain axonal morphology. Our results support the hypothesis that changes in the expression of these neurotrophins and their specific re ceptors in the maturing cochlea may control the postnatal processes of neuronal apoptosis and maturation of the innervation of both inner an d outer hair cells. The results suggest that these growth factors have potential for preventing neuronal degeneration as well as enhancing t he repair of damaged neuronal processes in the traumatized auditory sy stem.