NADPH-diaphorase reveals presumptive sympathetic primary afferents in the developing human spinal cord

Numerous studies have elucidated two visceral afferent pathways in the spin al cord of mammals, the lateral collateral pathway (LCP) and the medial col lateral pathway (MCP). The present study utilized NADPH-diaphorase histoche mistry to visualize afferent pathways in the developing human thoracolumbar spinal cord. Diaphorase-positive fiber bundles, strikingly similar to the previously defined LCP and MCP, were observed coursing along the lateral an d medial aspects of the dorsal horn to the base of the dorsal horn, the int ermediate gray, and/or the dorsal commissure. Furthermore, some axons formi ng the MCP crossed in the dorsal commissure to the contralateral side of th e spinal cord. In addition, axons projecting in the LCP often appeared to t erminate within clusters of diaphorase-labeled sympathetic preganglionic ne urons, supporting the concept that monosynaptic connections may exist betwe en primary afferents and autonomic motor neurons. Thus, nitric oxide may be involved in both afferent and efferent neurons in reflex pathways of the h uman sympathetic nervous system. (C) 2000 Elsevier Science B.V. All rights reserved.