Neurons of the lateral spinal nucleus in the rat spinal cord – A Golgi study

The neurons of the lateral spinal nucleus in the spinal cord of young adult rats were studied in transverse and longitudinal planes using the Golgi-Kopsch method and electron microscope. The perikarya were mainly polygonal or spindle shaped, and measured 20 to 35 μm in the longest diameter. They formed a dense column in the dorsolateral funiculus underneath the pial surface. The dendrites followed three patterns. Several of them turned laterally and approached the surface of the spinal cord. Another group of dendrites ran longitudinally within the column of the perikarya. A third group of dendrites turned medially or ventromedially and coursed towards the reticulated portion of the gray matter. Medium-sized neurons located at the margin of this latter portion of the spinal cord sent some of their straight dendrites into the dorsolateral funiculus. Thus, the dendrites of these two populations of neurons appeared as rungs of a ladder in longitudinally-cut spinal cord specimens. Only the initial portions of the axons of the LSN neurons could be impregnated. They originated with a regular axon hillock from either the perikaryon or from one of the primary dendrites and became unimpregnated after a 20 to 40 μm long course, indicating their myelinated character. Preliminary ultrastructural observations revealed that the laterally directed dendrites of the neurons in the lateral spinal nucleus approached the free surface of the spinal cord and ended immediately underneath the pia mater. Large numbers of fine, unmyelinated fibers were found in the dorsolateral funiculus coursing perpendicular to the laterally and medially oriented dendrites.