Axons from non-cochlear sources in the anteroventral cochlear nucleus of the cat. A study with the rapid Golgi method.

Six groups of non-cochlear axons which project to the anteroventral cochlear nucleus of the cat can be identified in rapid Golgi preparations. The axons in three of these groups enter the anteroventral cochlear nucleus from its medial border, most of the fibers coming from the trapezoid body. Group I axons terminate in the anterior part of the anterior division of the anteroventral cochlear nucleus. Group II axons terminate in a portion of the small cell cap and in part of the posteroventral cochlear nucleus; they supply some endings to the dorsal part of the posterior division of the anteroventral nucleus as well. Group III axons end diffusely throughout the anterior division but not in the posterior division. Two groups of axons travel from caudal parts of the cochlear nucleus to the anteroventral part within the small cell cap. Group IV axons end in the dorsal part of the posterior division. Group V axons terminate in the dorsal part of the anterior division. Group VI axons course through the granule cell layer and form endings there but not in the anteroventral cochlear nucleus proper. The axons of each group form characteristic patterns of terminal branches, which give the different parts of the anteroventral cochlear nucleus a distinctive appearance in rapid Golgi preparations.Each subdivision of the anteroventral cochlear nucleus receives cochlear input. However, the present findings demonstrate differential non-cochlear inputs to the various subdivisions, implying that non-cochlear influences on the activity of the neurons may not be the same throughout the nucleus. Moreover, each subdivision contains several types of neurons and the non-cochlear inputs may project to all or to only some of these cell types. Thus, the arrangements of the non-primary inputs to the neurons of the cochlear nuclear complex introduce another level of complexity to its synaptic organization.