Fiber degeneration following lesions in the posteroventral cochlear nucleus of the cat

Abstract

The results of studying fiber projections of the anteroventral cochlear nucleus (AVCN) by the Nauta and protargol methods were described in a previous paper. In the present study using similar methods, lesions in the posteroventral cochlear nucleus (PVCN) produced degeneration in the intermediate acoustic stria of Held and in the trapezoid body. Neither of these tracts projects to principal nuclei of the superior olivary complex, but rather they have overlapping projections to ipsilateral periolivary cell groups which partially surround the lateral superior olivary nucleus. Contralaterally, axons in the stria of Held project to: ( i) The dorsomedial periolivary cell group; ( ii) the anterolateral periolivary cell group; ( iii) the ventral nucleus of the lateral lemniscus; and ( iv) the inferior colliculus. Fibers in the trapezoid body project to the contralateral ventromedial periolivary cell group. The possibility that these projections represent, in part, inputs to cells which give rise to the olivocochlear bundle is discussed. In contrast to AVCN which projects to the lateral and medial superior olivary nuclei proper, PVCN projects to adjacent periolivary cell groups, but both AVCN and PVCN project in an overlapping fashion to the ventral nucleus of the lateral lemniscus; bilaterally. This result lends further support to the idea that the cochlear nucleus is a complex of subnuclei each of which has specific sets of projections.