The human olivocochlear system: Organization and development

The goals of the present study were to identify ol ivocochlear neurons in t he human brainstem, to establish the time course of their early development and to compare the organization of the human olivocochlear system to that of other mammals. To accomplish these goals, we used immunohistochemistry f or choline acetyltransferase (ChAT) and calcitonin gene-related peptide (CG RP) in postmortem brainstems of human subjects ranging in age from 16 fetal weeks to 17 years. By immunostaining, we identified two classes of cells i n the superior olivary complex: both classes were seen to be present from t he twenty-first fetal week to the seventeenth year. Neurons which are immun ostained only for ChAT are located primarily in the dorsomedial, ventral an d ventrolateral sectors of the periolivary region. These neurons are predom inantly bipolar or multipolar cells, and are probably homologous to medial olivocochlear neurons in other species. A second population of cells is imm unoreactive for both ChAT and CGRP. This population includes a cluster of m ostly small oval neurons, located on the dorsal edge of the olivary complex , and a variable number of cells found along the margin of the lateral oliv ary nucleus. These ChAT- and CGRP-immunoreactive cells are likely to be hom ologous to the lateral olivocochlear system in other mammals. With increasi ng age, the dorsal cluster of small cells shifts from its original cap-like position over the lateral olivary nucleus to become an extended column of cells lying among the fibers of the olivocochlear bundle.