Connections of the superior olive in the chicken.

The avian superior olive (OS) is known to be a station in the auditory pathway, although its anatomic connections remain uncertain. The afferent and efferent connections of OS neurons in the chicken were identified with wheat germ agglutinin conjugated to horse radish peroxidase (WGA-HRP) injected into the OS nucleus. Projections to the OS originate bilaterally in the cochlear nuclei (nucleus angularis) and the nucleus laminaris. Anterogradely labelled axon terminals were found in the ipsilateral nucleus magnocellularis, the contralateral intermediate nucleus of the lateral lemniscus, and the shell portion of the central nucleus of the inferior colliculus. Retrograde transport of [3H]-glycine from the OS was also charted. Glycine-transporting cells were found ipsilaterally in the nucleus angularis and the nucleus laminaris. Neuronal soma in a newly identified nucleus of the trapezoid body (NTB) were found to actively concentrate glycine, although the neurons probably do not synapse within the OS. Anatomically, the avian OS would appear to be part of the interaural intensity difference pathway; however, our data and published information are insufficient to establish a homology to the human lateral superior olive.