The segmental origin of preganglionic axons in the upper thoracic rami of the cat.

Sympathetic preganglionic neurones have been identified in the thoracic spinal cord of cats after selective application of horseradish peroxidase (HRP) to the cut axons of the individual white rami of T1 to T3. The labelled neurones were restricted rostrocaudally to the length of a single segment, although this did not correspond exactly with the point of exit of the corresponding spinal root. The results do not support the concept of an intraspinal pathway of preganglionic axons in this region and one possible explanation for the difference between these data and those of others is discussed.