Lamellar arrangement of neuronal somata in the dorsal root ganglion of the cat.

The retrograde transport of horseradish peroxidase (HRP) was used to study the distribution of perikarya in the dorsal root ganglia (DRGs). Injections of HRP subcutaneously into a small area of the foreleg, flank, perineum, the central pad of the forepaw, muscles of the foreleg, the wall of the urinary bladder, and mucosa of the rectum resulted in many retrogradely labeled perikarya in one DRG. Labeled perikarya were distributed in the ganglia proximally to distal elongated slabs or columns, especially in cases of subcutaneous injections. A similar slab, or columnar distribution, of HRP-labeled perikarya was noticed when the tracer was injected into the spinal cord preceded by the transection of all dorsal root filaments but one. Perikarya located along the lateral border of the ganglion were labeled through rostral filaments, and perikarya distributed along the medial border were labeled through caudal filaments. A segmental somatotopic map has been conceived for the DRG as an intermediate territory between the periphery and the spinal cord.