Organization of the superior olivary complex in the guinea pig. I. Cytoarchitecture, cytochrome oxidase histochemistry, and dendritic morphology.

The superior olivary complex is a prominent component of the auditory system. It consists of the lateral and medial superior olivary nuclei and a large number of smaller cell groups known as the periolivary nuclei, which are sources of both ascending and descending projections. The goal of this study was to establish criteria for identifying the periolivary nuclei in the guinea pig. Use of Nissl stains, the Golgi impregnation technique, and cytochrome oxidase histochemistry allowed us to distinguish eleven periolivary nuclei on the basis of differences in the types of cells they contain, in the distribution of cell types, and in the cytochrome oxidase staining characteristics of both the cells and the neuropil. The nuclei, named according to their position with respect to the lateral and medial superior olivary nuclei, can be divided into four groups: (1) a lateral group comprising the lateral nucleus of the trapezoid body and the anterolateral and posteroventral periolivary nuclei, (2) a dorsal group comprising the dorsal and dorsolateral periolivary nuclei, (3) a ventral group comprising the ventral nucleus of the trapezoid body and the anteroventral, ventromedial and rostral periolivary nuclei, and (4) a medial group comprising the medial nucleus of the trapezoid body and the superior paraolivary nucleus. Cytological distinctions among the periolivary nuclei are consistent with other evidence that they serve different functions and highlight the need for detailed study of their connections, immunocytochemistry and physiological response properties.