The cells of origin of the dorsal column postsynaptic projection in the lumbosacral enlargements of cats and monkeys

Dorsal column postsynaptic (DCPS) neurons in the lumbosacral enlargements of cats and macaque monkeys were retrogradely labeled by placing HRP on their severed axons within the dorsal columns. The enlargements of both species contained 800-1,100 labeled DCPS neurons. The DCPS projection is thus as large as the feline spinocervical tract. It is very probable that most of these neurons project to the dorsal column nuclei and thereby constitute 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 second 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 have such a projection.