Development of Spiral Ganglion Neurons

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This MRI Research Planning Grant is for one year to obtain pilot data on innervation f the inner ear. The sensory receptor cells in the cochlea of the mammalian ear are of two types, the inner hair cells (IHC) and the far more numerous outer hair cells (OHC). These receptor cells are innervated by nerve cells (neurons) that have their cell bodies in a structure called the spiral ganglion of the ear. Adult animals have two types of spiral ganglion cells, based on their contacts with one or the other type of hair cells, the diameter of their fibers, and size and shape of their cell bodies. It remains puzzling that the OHC, representing roughly 3/4 of all the hair cells, receive contacts from fewer than one-tenth of all the ganglion cells. It is not clear how the neurons develop into these two classes. In newborn animals, some studies suggest that these cells are morphologically different from the adult neurons, and are initially a homogeneous population. This planning grant is a preliminary step toward clarifying the anatomy and ultra- structure of the spiral ganglion neurons that contact OHCs in newborn rodents. Both light microscopy and electron microscopy will be used, in conjunction with dye-filling techniques for single cells, and specific antibody staining. The analysis of these data will provide a basis for a later full proposal to pursue the development of these neurons. This project is on a group of cells important in understanding mechanisms of hearing. The data will provide a needed baseline to allow preparation of a full research project on development of these cells.