Synaptic organization in the dorsal cochlear nucleus of the cat: a light and electron microscopic study.

Abstract

AbstractThis report describes some observations of the synaptic organization of one region of the cat dorsal cochlear nucleus (DCN). The large “fusiform cell” and its innervation from the cochlea are emphasized. The morphology of the mature fusiform cell and its postnatal development are described in rapid Golgi impregnations of perfusion‐fixed littermate cats. The mature features are correlated with profiles of fusiform cell bodies, apical dendrites, and basal dendritic trunks in electron micrographs from adult cat brains. Small neurons and granule cells are also identified in electron micrographs. In Golgi impregnations, axons of small cells and granule cells may terminate upon fusiform cells. Six classes of axons can be distinguished in rapid Golgi impregnations of the DCN. Two classes are of cochlear origin. One axonal class arises from small cells. The sources of the remaining axonal classes have not been identified in this study. Primary afferents can terminate as large, mossy endings in the DCN neuropil. They can also participate in axonal nests along with axons and dendrites of small cells. In electron micrographs, four synaptic endings can be distinguished. Primary cochlear fibers end in large terminals with asymmetrical synaptic complexes and round, clear vesicles. Primary axons can end in glomeruli, resembling those of the cerebellum, or in synaptic nests which are conglomerates of neuronal processes including other types of endings. The origins of the other synaptic types are not yet known. According to this study, primary afferent input could influence fusiform cells directly or indirectly, via small cells and granule cells.