The long term goal of the research is a detailed description of the synaptic organization of the cochlear nucleus, the complex of cell group that receive the central projections of the auditory nerve, in terms of the specific neuronal types that it comprises. The research is designed to develop classifications of cell types, based on morphological features that may be functionally significant, and to then describe the synaptic interactions of each cell type with auditory nerve terminals, with other cochlear nuclear cells, and with inputs from other parts of the central auditory system. The objective is to gain an understanding of the cytological and connectional principles that form the morphological basis for stimulus coding by sensory neurons. Neuroanatomical methods based on the anterograde and retrograde axonal transport of radioactive amino acids and horseradish peroxidase, respectively, will be used to trace the connections of the neurons in the cochlear nucleus at both the light and electron microscopic levels. In the electron microscope, specific cell types can be identified when they are marked with retrogradely transported horseradish peroxidase, and specific terminal types can be identified when they are marked with radioactively labelled amino acids. Correlations of the results of the light and electron microscopic findings will allow descriptions of the cochlear nucleus in terms of the synaptic connections formed among specific types of neurons. The proposed work, in providing a detailed description of the neuroanatomy of parts of the auditory system, will provide information essential for a complete description of the ways in which the system processes acoustic stimuli. The results may be used as a common framework by workers in auditory physiology, neurochemistry, and behavior for correlating and comparing their results.