Identification of the sympathetic preganglionic pathway to the cat stellate ganglion

Both intraspinal and segmental preganglionic pathways to sympathetic ganglia have been proposed based on different methods of horseradish peroxidase application. The present study mapped the projections of preganglionic neurons to the stellate ganglion in the cat by horseradish peroxidase injection into ganglia with various white rami intact. Central and peripheral cut ends of the severed white rami were tied to eliminate leakage of peroxidase from the ganglia. In control cats with all white rami intact, an average of 9186 neurons were labeled in the spinal cord ipsilateral to the injection from C8 to T9; the highest density of labeling occurred in the first and second thoracic segments. In cats with single white rami intact (T1, T2, or T3), neurons were labeled only in the spinal cord segment that corresponded to the intact ramus and one segment rostral to it. In additional experiments, the spinal cord was hemisected a few segments below, and ipsilateral to the injected ganglion with all rami intact. In these cats neurons were labeled with a similar distribution to control cats, indicating that the preganglionic pathway was extraspinal. Finally, experiments were performed on cats with a single ramus intact, but without ligatures around the cut rami. The distribution of neuronal labeling was similar to control cats (labeled cells from C8 to T9). These results demonstrate that peroxidase leakage from the stellate ganglion can result in an artifactual labeling which would indicate an intraspinal preganglionic pathway. Thus, the present experiments support a segmental distribution of upper thoracic sympathetic preganglionic neurons to the stellate ganglion in the cat, and do not provide evidence for long intraspinal pathways of preganglionic neurons before exit from the cord.