In recent years much effort has been expended on the effort to understand the mechanisms that govern the growth of neuronal axons to their appropriate targets. While tremendous strides have been made, the determination of the specificity and nature of the cues that govern the development of axonal projections remains one of the central problems in neurobiology today. Transplantation provides a unique method for manipulating the environment in which these projections develop. Transplantation of sensory tissue to the brain has proven to be a useful model for examining factors involved in the development of projections to the central nervous system. The intracranial transplantation of retinae has provided a model system that has been instrumental in elucidating various factors involved in the survival of retinal ganglion cells and the growth of their axons toward the proper targets within the central visual system. Much less is known about target seeking by cochlear spiral ganglion cells during development. Spiral ganglion cells send their axons to the cochlear nucleus complex, where highly ordered, tonotopic connections are formed. Can transplantation of the embryonic inner ear be utilized in a manner similar to the embryonic retina, to elucidate factors involved in the development of these highly ordered connections? Can critical sensory components of the inner ear survive isolation and transplantation? The preliminary results presented here suggest that, under certain conditions, the inner ear can be transplanted and will develop organotypic sensory surfaces. The primary goals of this study are to improve this organotypic development and to evaluate the potential of intracranial transplantation of the inner ear to unlock some the secrets governing the development of projections within the auditory system. The techniques of intraocular cotransplantation will be used to test new approaches to manipulating auditory development with growth factors. The results of these experiments will guide intracranial transplantation of the inner ear and the subsequent search for axonal connections. Such findings will increase our understanding of the mechanisms underlying the proper development of the auditory system and through this, our knowledge of certain types of neural deafness. A greater understanding of these areas may eventually lead to new methods of ameliorating deafness.
