Distribution of primary cochlear afferents in the bulbar nuclei of the rat: a horseradish peroxidase (HRP) study in parasagittal sections.

HRP was injected into the cochleae of 25 young albino rats in order to trace the primary afferents to the bulbar cochlear nuclei. Besides the classic V-shaped pattern and unconnected with it, HRP labelling revealed two plexuses stemming directly from the axons of the cochlear root. The plexuses cover the posterior area of the posteroventral cochlear nucleus (posterior plexus) and the anterolaterodorsal area of the anteroventral cochlear nucleus (anterior plexus). The fibres giving rise to these two plexuses were previously grouped in two bundles which have been called the posterior and anterior bundles, respectively. The origin of the anterior bundle is typically seen with the fibres stemming out at right angles; the origin and course of the posterior bundle, which characteristically cross over, is also a typical feature.