The Cells of Origin of the Dorsal Column Postsynaptic Projection in the Lumbosacral Enlargements of Cats and Monkeys

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Abstract
Dorsal column postsynaptic (DCPS) neurons in the lumbosacral enlargements of cats and macaque monkeys [Macaca mulatta and M. fascicularis] were retrogradely labeled by placing HRP [horseradish peroxidase] on their severed axons within the dorsal columns. The enlargements of both species contained 800-1100 labeled DCPS neurons. The DCPS projection was as large as the feline spinocervical tract. Most of these neurons probably projected to the dorsal column nuclei, and thereby constituted one of the major sources of somatosensory input to the brain. In the cat, DCPS neurons were concentrated in a band, centered in lamina IV, that swept down through laminae V-VI along the medial border of the dorsal horn. A 2nd concentration of labeled cells was found in dorsomedial lamina VII. In the monkey, DCPS neurons were concentrated in a relatively broader band in laminae III-IV, and scattered cells were consistently observed throughout laminae V-VII and X and in the dorsolateral white matter. The prominence of the monkey''s DCPS projection suggests that humans also had such a projection.