Neurons lying in the white matter of the upper cervical spinal cord project to the intermediolateral cell column

Neurons lying in the white matter of the upper cervical spinal cord become transneuronally labelled following pseudorabies virus injections into the kidney or stellate ganglion, suggesting that they project directly to sympathetic preganglionic neurons. In the present study, we extend these findings and report here that i) neurons in both the lateral spinal nucleus and lateral funiculus become transneuronally labelled after pseudorabies virus injections into the superior cervical ganglion, stellate ganglion, celiac ganglion, or adrenal gland and ii) both of these two cell groups project directly to the sympathetic preganglionic neurons as demonstrated with the Phaseolus vulgaris leuco-agglutinin axonal tracing method. In addition, lateral funiculus neurons project to the cervical and upper thoracic dorsal horn (lamina V), intermediate gray matter (laminae VII and X), and ventral horn. The lateral spinal nucleus also projects to the medial part of laminae I and II, V, VII. To verify that pseudorabies virus-infected lateral funiculus and lateral spinal nucleus cells have a neuronal phenotype, we demonstrated that these cells also can be immunostained with antibodies directed against a neuron specific marker, neuronal nuclear protein called NeuN, but not with antibodies against glial acidic fibrillary protein or oligodendroglia. In summary, this report provides the first evidence that two descending sympathetic projection systems arise from neurons lying within the white matter of the cervical spinal cord.