Synaptic Relationships in the Granule-Cell Associated Systems in Dorsal Cochlear Nucleus

Abstract

The dorsal cochlear nucleus (DCN) is the most complex part of the cochlear nucleus, from the standpoint of interneuronal circuitry (Lorente de Nó, 1981; Osen et al., 1990). Figure 1 shows a summary of part of the DCN’s circuitry. The principal cells of the nucleus are the pyramidal and giant cells, which project their axons to the contralateral inferior colliculus (Adams, 1979; Osen, 1972). The DCN is layered, with three layers running parallel to its free surface; the pyramidal cell somata form the second layer; these cells are bipolar, as indicated schematically in the figure, with apical dendrites in the superficial layer and basal dendrites in the deep layer (Blackstad et al., 1984; Kane, 1974; Smith and Rhode, 1985). The apical and basal dendrites of pyramidal cells encounter two different afferent systems. In the deep layer, there are primarily auditory affrents, including auditory nerve fibers (not shown; Osen, 1970) and collaterals of multipolar cells from PVCN (Oertel et al., 1990; Smith and Rhode, 1989). In addition to pyramidal basal dendrites, these afferent systems contact the other DCN principal cell type, giant cells, as well as vertical cells, which are an inhibitory interneuron (Saint Marie et al, 1991; Wenthold et al., 1987; Wickesberg and Oertel, 1990).