Morphology of cochlear root neurons in the rat.

The morphology of large neurons in the cochlear nerve root of albino rat has been studied with a variety of techniques including Nissl and cell-myelin staining, Golgi impregnation, horseradish peroxidase back-filling of severed axons, transmission electron microscopy, and morphometry. The cells, called root neurons, resemble the globular cells of the ventral cochlear nucleus in having an oval cell body, an eccentric nucleus, an axon that projects centrally via the trapezoid body, and in receiving many primary-like axosomatic boutons. The root neurons, however, are larger than globular cells, and they have at least two types of dendrites oriented, respectively, parallel and across the cochlear nerve fibres. The soma, moreover, has less finely dispersed Nissl material, is less completely covered with terminals, and receives a smaller proportion of presumably inhibitory synapses. So far, this particular type of neuron has been observed only in rat and mouse.