Light and electron microscopic study of neurones in the feline lateral cervical nucleus with a descending projection.

Nerve cells in the feline lateral cervical nucleus (LCN) with a descending projection were labelled by injections of horseradish peroxidase, in most cases conjugated to wheat germ agglutinin. After small injections into different spinal cord segments in 16 cats the labelled cells were found mainly in the rostral and ventral portions of the ipsilateral LCN, without a detectable topographic organization. Massive bilateral injections were made into the cervical or lumbar enlargement in 6 cats. Unilateral lesions of the dorsolateral funiculus rostral to the injections generally prevented labelling of LCN cells on the same side. The other side was used to calculate the total number of descending LCN neurones and it was estimated that approximately 500 cells projected down the spinal cord. Comparison with the number of labelled cells after the small injections revealed that the descending LCN neurones projected to an average of at least two spinal segments. Quantitative ultrastructural analyses were made of 17 descending neurones from 7 cats subjected to massive unilateral injections into the cervical or lumbar enlargement. The labelled cells constituted a fairly homogeneous population with respect to the investigated somatic and dendritic features. The morphology and relative frequency of the descending neurones indicate that they may constitute parts of the subpopulation of small LCN cells that have previously been assumed to consist of locally ramifying interneurones.