The afferent and sympathetic components of the lumbar spinal outflow to the colon and pelvic organs in the cat. II. The lumbar splanchnic nerves.

The cell bodies of the lumbar sensory and sympathetic pre- and postganglionic neurons that project to the inferior mesenteric ganglion in the lumbar splanchnic nerves of the cat have been labeled retrogradely with horseradish peroxidase applied to the central end of their cut axons near the inferior mesenteric ganglion. The numbers, segmental distribution, location, and size of these labeled somata have been determined quantitatively. After all the lumbar splanchnic nerves on one side of an animal were labeled, most labeled cell bodies were situated ipsilaterally in dorsal root ganglia, ganglia of the lumbar sympathetic trunk, and spinal cord segments L2-L5, with the maximum numbers in L3 and L4. A few labeled somata lay contralaterally or rostral to L2. After labeling of only one lumbar splanchnic nerve, the majority of cell bodies were found in the labeled segment, but a few were also present up to three segments rostral or caudal. These variations could always be attributed to extraspinal connections usually via the lumbar sympathetic trunk. Cross-sectional areas of labeled afferent somata were small relative to those of the entire population of dorsal root ganglion cells. Preganglionic cell bodies were labeled in the intermediate gray matter extending from its lateral border ventrolaterally across to the central canal. Two regions of high density were observed: one laterally just medial to the edge of the white matter and the other lateral to the central canal. The dorsolateral group lay somewhat medial and caudal to the usual limits of the intermediolateral column. Labeled preganglionic neurons were on the average larger than the unlabeled cells in the inferior mesenteric ganglion, with the group lying medially being larger than those that were laterally positioned. From the data, it is estimated that about 4,600 afferent axons, about 4,600 preganglionic axons, and about 2,800 postganglionic axons travel in the lumbar splanchnic nerves to the inferior mesenteric ganglion of the cat.