Corticorubral projections in the rat

In a series of young adult albino rats the terminal projections of corticorubral fibers were studied by light and electron microscopic methods following unilateral sensorimotor cortex suction ablation. Degenerating axons could be traced from the ipsilateral cerebral peduncle to the periphery of the red nucleus. Within the red nucleus the degeneration was sparse. No degeneration was seen contralaterally. With the electron microscope degenerating axons showed electron dense axoplasm and seemed devoid of their normal complement of organelles. Electron‐dense degenerating synaptic terminals, one to two per grid square, were found in the more rostral portions of the red nucleus. These terminals were of the asymmetrical type with increased density of the post‐synaptic membrane and made contact with small to medium sized dendrites. No degenerating axosomatic or axoaxonal knobs were seen. No degenerating terminals were seen in the caudal regions of the red nucleus. This study finds that following ablation of the sensorimotor cortex in the rat there is a projection to the ipsilateral red nucleus and that the contacts are primarily of the axodendritic type as revealed by the electron microscope.