Cytoarchitecture of the cochlear nucleus in the hedgehog and tree shrew

The superior olivary complex of the hedgehog (Paraechinus hypomelas) differs from most mammals in having a large lateral superior olive but no medial superior olive. In an attempt to determine if this structural difference would be reflected in the organization of the cochlear nucleus, we compared, in Nissl preparations, the cytoarchitecture of the cochlear nucleus of the hedgehog with that of the tree shrew (Tupaia glis), another insectivore which does have a medial superior olive. While in both species most of the major cell types seen in the cat [Osen, J. Comp. Neurol. 136, 453–484 (1969)] were evident, a striking difference was found in the organization of the anteroventral cochlear nucleus. In the tree shrew this nucleus is subdivided into an anterior portion which contains large spherical cells and an adjacent posterior region which contains smaller spherical cells. In the hedgehog a region of large spherical cells could not be found; the absence of this area of the anteroventral cochlear nucleus may be related to the absence of the medial superior olive. [Supported by a grant from the National Science Foundation.]