Spinal projections of cat primary afferent fibers innervating lumbar facet joints and multifidus muscle.

The spinal projections of small-caliber (presumably nociceptive) afferents arising from lumbar spinal joints and muscles were examined using anterograde transport of WGA-HRP. Injections of WGA-HRP into these structures gave rise to similar, rostro-caudally extensive patterns of spinal labeling indicating that many afferents innervating one facet joint or paraspinal muscle terminate bilaterally in laminae I-II, V-VIII, and X of the lumbar, sacral, and thoracic spinal cord. These diffuse patterns of terminal arborization are reminiscent of visceral input and contrast with the more restricted unilateral terminal fields reported for afferents innervating more distal hindlimb tissues.