An HRP study in the cat of brainstem projections to the spinal cord, with particular reference to sacral afferents.

Cells of origin of the spinal projections from the brainstem of the cat have been studied by means of retrograde axonal transport of horseradish peroxidase (HRP). Following injections of HRP into various levels of the spinal cord, many labeled cells were found in several structures in the brainstem. The labeled cells occurred in the raphe nuclei, reticular formation, vestibular complex, and nuclei of the dorsolateral pontine tegmentum. In the dorsolateral pontine tegmentum, many labeled cells were found in the nuclei of locus coeruleus, subcoeruleus and Kölliker-Fuse. In the coeruleus and subcoeruleus, the greatest number of labeled cells were found, when HRP was injected into the sacral cord. No difference emerged, however, in the number of labeled cells appearing in the Kölliker-Fuse nucleus after injection of the enzyme into different levels of the spinal cord. It appears that neurons in the lateral vestibular nucleus which project to different levels of the spinal cord are located in different parts of this nucleus.