Relations between auditory nerve endings and cell types in the cat's anteroventral cochlear nucleus seen with the Golgi method and Nomarski optics.

Rapid Golgi impregnations of the ascending branches of the auditory nerve fibers and of the types of neurons in the anteroventral cochlear nucleus (AVCN) were studied. Entire ascending branches could be observed, some of these branches project to each subdivision, others do not. There are two main typesof large neurons: the bushy and stellate cells. Criteria were established for identifying unimpregnated bushy and stellate perikarya by means of Nomarski optics, and these criteria were checked by Momarski observations on neurons which had either impregnated dendrites and unimpregnated cell bodies or impregnated portions of perikarya. In this way, the relations of unimpregnated cell bodies to auditory nerve endings were observed. Furthermore, with Nomarski optics, the cytoarchitectonic subdivisions of AVCN could be determined. Differences in the end-bulbs and collateral endings formed by the auditory nerve fibers were distinguished in three of the cytoarchitectonic subdivisions of the AVCN. End-bulbs in the anterior division were much larger than those in the dorsal and ventral parts of the posterior division. The large end-bulbs of Held in the anterior division of the AVCN were consistently associated with the perikarya of bushy cells and not with those of stellate cells. The large end-bulbs are not observed in the posterior division. Thus, bushy cells in the posterior division, although morphologically similar to those in the anterior division, must have a different synaptic organization. This difference may correspond to electrophysiological distinctions in the time-patterns of response recorded in these regions following acoustic stimulation.