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This study provides a morphologic characterization of the human superior olivary complex as revealed by immunohistochemistry by using antibodies against the calcium binding proteins parvalbumin, calbindin, calretinin, and the nonphosphorylated neurofilament H SMI-32. By combining these markers, it was possible to establish the neuronal architecture and details of the morphologic organization (including axonal terminals) of the different nuclei. The medial superior olivary nucleus is formed by a sheet of parallel-oriented cells. A clear segregation of axon terminals was noticed on the medially and laterally oriented dendrites of the mostly bipolar neurons. The lateral superior olivary nucleus lacked a distinct nuclear shape but was formed by several patches of rather irregularly arranged neurons. Calretinin or parvalbumin immunoreactive afferent terminals were observed which contacted somata or dendrites of these neurons. The immunolabeling also revealed the boundaries of the dorsal periolivary nucleus and morphologic detail of its neurons. A coherent nuclear structure that could be addressed as the medial nucleus of the trapezoid body was not identified by any single one or by combinations of the markers used. The data were also used to establish a three-dimensional-reconstruction of the three major subnuclei of the superior olivary complex. The results are discussed with respect to the possible role of the superior olivary complex in the processing of spatial acoustic information in the azimuthal plane.

The auditory brainstem nuclei, angularis (NA), magnocellularis (NM), and laminaris (NL) of the chicken, Gallus, contain terminals that stain for antibodies against the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). Some of these terminals originate from cells surrounding nucleus magnocellularis. Results from this study indicate that the majority of the GABAergic terminals found in NA, NM and NL originate from the superior olivary nucleus (SON). Injections of cholera toxin and horseradish peroxidase show that superior olivary nucleus (SON) neurons, which respond to pure tones, project bilaterally to NA, NM, and NL. NA and NL are reciprocally connected with the SON. More NA cells project to the SON than NL cells. While SON neurons project to NM, NM neurons do not project axons back to the SON. The configuration of SON terminals in NA, NM and NL matches the pattern of GABA-immunoreactive puncta seen in these three nuclei: they surround individual NM cells, congregate in the dendritic neuropil of NL, and blanket the NA. The data indicate that NA, NM and NL may be affected by two different inhibitory cell types: local interneurons and SON neurons. Patterns of connectivity described in this report suggest that the activity of NA cells could influence NM and NL cell physiology. Specifically, increases in NA cell activity could augment the effects of GABAergic SON neurons on NM and NL. Hence, binaural perception in the chicken may be more dependent upon changes in intensity cues than previously believed.

The objective of the present study was, by using the Mongolian gerbil (Meriones unguiculatus) as an animal model, to provide data on the growth dynamics of central auditory and visual nuclei and to relate the growth of these structures to the growth of the entire brain. So far, no such systematic study has been performed in any mammalian species. The knowledge of the rates of development of central nervous sensory structures might be useful for understanding the contribution of the central nervous system to maturation of sensory processing. Increases in volumes of nuclei and changes in their shape were analyzed for animals at the day of birth (P0); at postnatal days P7, P15, P22, P28; and in the third month (P90). The auditory nuclei investigated were the cochlear nucleus, the superior olivary complex, the nuclei of the lateral lemniscus, the inferior colliculus, and the medial geniculate body. From the visual system, the superior colliculus and the lateral geniculate body were studied. At P15 (shortly after the onset of central auditory responsiveness), the volumes of all auditory nuclei examined reached only 60–70% of their adult sizes; i.e., they showed considerable growth afterwards. At the same time (shortly before the animals open their eyes), the visual nuclei had almost reached their adult sizes (superior colliculus, 91%; lateral geniculate nucleus, 97%). These data demonstrate that different sensory nuclei contribute in highly different fashions to brain growth. There are system-specific differences in growth dynamics between central auditory and visual nuclei. However, the absolute growth of nuclei in both sensory systems relates to the brain regions. The data do not support the idea of a peripheral-to-central gradient in the growth of central auditory nuclei. © 1994 Wiley-Liss, Inc.