The neuronal architecture of the anteroventral cochlear nucleus of the cat in the region of the cochlear nerve root: Horseradish peroxidase labelling of identified cell types

Abstract

Golgi impregnations of the posterior part of the cat's anteroventral cochlear nucleus have revealed two types of neurons, bushy cells with short bush-like dendrites and stellate cells with long, tapered processes; Nissl stains have revealed globular and multipolar cell bodies with dispersed and clumped ribosomal patterns, respectively. In the present study, we injected horseradish peroxidase into the trapezoid body. Ipsilaterally, retrograde, diffuse labelling of neurons, presumably through damaged fibers, yielded Golgi-like profiles of numerous bushy cells with typical dendrites and with thick axons projecting toward the trapezoid body. Stellate cells were almost never labelled in this way. Anterograde diffuse labelling of thick axons demonstrated calyx endings in the contralateral medial nucleus of the trapezoid body. In the electron-microscope, the perikarya of diffusely-filled bushy neurons were found to have the dispersed ribosomal pattern and the kinds of synaptic endings typical of globular cells, including large profiles of end-bulbs from cochlear nerve axons. After injections restricted to the medial trapezoid nucleus, granularly-labelled cells in the cochlear nucleus were almost completely confined to the contralateral side; Nissl counterstaining showed them to be globular cells in the posterior part of the anteroventral cochlear nucleus. After larger injections, involving surrounding regions of the superior olivary complex, granular labelling occurred throughout the ventral cochlear nucleus on both sides. There is also evidence that stellate cells in Golgi impregnations correspond to multipolar cell bodies in Nissl stains. We conclude that bushy cells typically correspond to globular cells, which receive end-bulbs from the cochlea and send thick axons to the contralateral medial trapezoid nucleus, where they form calyces on principal cells. Principal cells, in turn, are known to project to the lateral superior olive and to one of the nuclei of origin of the crossed olivo-cochlear bundle, which feeds back to the cochlea. In this circuit, correlations between synaptic patterns and particular physiological signal transfer characteristics can be suggested. These could be related to binaural intensity interactions in the lateral superior olive and to a regulatory loop involving the olivo-cochlear bundles.