NEUROTROPHINS AND THE DEVELOPMENT OF COCHLEAR INNERVATION

The rapid progress in the past few years concerning neurotrophic facto r research, has greatly stimulated advances in developmental neurobiol ogy-of hearing. We have summarized evidence that neurotrophins are exp ressed by auditory sensory epithelia during the time at which ganglion cells with neurotrophin receptors send their processes to these epith elia. Recent findings have led to the identification of BDNF and NT3 a s responsible substances. Since no NGF mRNA nor the NGF high affinity receptor component trkA mRNA were detectable during the development of cochlear structures, this factor is not likely to be an important neu rotrophin at this level. By their biological activity, neurotrophins c ould be responsible for chemotrophic, differentiation, survival, and m aintenance functions at the afferent as well as at the efferent level of the inner ear development.