Staining of the dorsal root projection to the cat's dorsal horn by anterograde movement of horseradish peroxidase.

A modification of the horseradish peroxidase method was used to stain selectively dorsal root fibers entering the spinal cord of the cat. This technique stains intact terminal arborizations. Using this method to examine the primary afferent supply to lamina II of the lumbosacral segments, we observed that both thick primary afferent collaterals (2-3 mum), entering by way of the dorsal column, and thinner primary afferent collaterals (<1 mum), entering by way of Lissauer's tract, form terminals in lamina II. The terminals derived from the thick primary afferent collaterals were concentrated in the ventral portion of lamina II.