Neuron types in the central nucleus of the inferior colliculus that project to the medial geniculate body

Abstract

At least four neuron types, distinguished on the basis of dendritic and cell body morphology, were labeled in the central nucleus of the inferior colliculus after horseradish peroxidase injections into the medial geniculate body of the cat. Most labeled cells had disc-shaped dendritic fields whose orientation and arrangement into layers were important identifying features. Most labeled cells were small or medium-sized disc-shaped cells with dendritic fields and cell bodies of corresponding size. These cell types appeared to have dispersed Nissl substance and infrequent axosomatic endings. Large disc-shaped cells, identified by their large dendritic fields and somata, were also labeled. These may have had a different Nissl pattern, including both perinuclear cisterns and clumps of granular endoplasmic reticulum, and numerous axosomatic synaptic endings. Stellate cells, which constituted the fourth labeled cell type, were distinguished by their spherical dendritic fields composed of dendrites radiating in all directions, especially across the layers formed by the disc-shaped cells. Stellate cells probably corresponded to neurons with stacks or clumps of granular endoplasmic reticulum, an irregular nuclear envelope, and frequent axosomatic contacts. These results suggest that many of the cell types previously identified in studies using the Golgi method send their axons to the medical geniculate body. The results also raise the possibility that Nissl pattern and dendritic morphology of central nucleus cell types are related. The presence of several types of neurons in the central nucleus with axons ascending to the thalamus may provide a structural basis for some type of parallel information processing in this part of the central auditory system.