Identification and somatotopic organization of nuclei projecting via the dorsolateral funiculus in rats: A retrograde tracing study using HRP slow-release gels

Horseradish peroxidase (HRP) in slow-release gel was unilaterally implanted in the transected dorsolateral funiculus (DLF) of either cervical, midthoracic, lumbar or sacral spinal cord levels of adult male rats. Cell mappings were made of all brain areas projecting through the DLF. Following cervical implants, dense labelling was observed within a band along the dorsolateral border of the inferior olive, locus coeruleus, the paralemniscal reticular formation, the mesencephalic central gray, the red nucleus and the paraventricular nucleus of the hypothalamus. The DLF projection from the central gray consisted of a rostrocaudal line of cells extending from the level of the mesen-/diencephalic junction to the rostral red nucleus. The somatotopic organization of labelled nuclei was assessed by comparing the pattern of filled cells following HRP implants at various cord levels. The potential role of these areas in pain modulation was discussed in light of their descending projections through the DLF of the spinal cord.