In the cochlea, as in other regions of the nervous system, innervating fibers arrive at their targets with astonishing accuracy, often bypassing unsuitable connections en route. Such specificity during development is of prime importance in assuring normal auditory function, but the mechanisms which generate that specificity have not been well- studied. In other developing tissues, interactions between adhesive molecules on nerve fibers and in their microenvironments are thought to direct or facilitate neurite guidance. As part of the long range goal to elucidate biochemical mechanisms of neuronal connectivity in the cochlea, this project will synthesize information on cell-surface molecules, extracellular matrix molecules, cochlear development, cochlear anatomy and developmental neurobiology and use immunocytochemistry, in situ hybridization, tissue culture, and mutant animals to address questions of axonal guidance in the cochlea. Specifically this project will determine 1) by light microscopy, whether the lack of the extracellular matrix molecule tenascin in a transgenic mouse alters neural development in the cochlea; 2) by immunocytochemistry, whether the distributions of the extracellular matrix proteins laminin and thrombospondin coincide with directional choices made by growth cones; 3) by immunocytochemistry, whether neurites growing in different regions possess different complements of extracellular matrix receptors; 4) by blocking the functions of specific molecules with antibodies in cochlear organ culture, whether extracellular matrix and receptor proteins function in neurite guidance; 5) by spiral ganglion explant culture on defined substrata, whether spiral ganglion cell neurites have preferences for specific substrata whether the neurites are capable of choosing between the substrata; 6) by in situ hybridization, whether subclasses of spiral ganglion neurons possess characteristic complements of adhesive molecules. The questions asked in this project are important for understanding normal and abnormal neural development in the cochlea and thus are important for understanding causes of human deafness. But in addition, the results will be pertinent to questions of neural regeneration. They will be relevant to experimental attempts to encourage reestablishment of functional fiber networks in the cochlea after nerve damage.
