Light and electron microscopical studies of the substance P innervation of the dorsal column nuclei and the lateral cervical nucleus in the primate.

In 2 monkeys of the species Macaca fascicularis the three dorsal column nuclei and the lateral cervical nucleus have been investigated immunocytochemically with antiserum against Substance P. The Substance P labeling was widely spread but rather sparse. It occurred in small structures of the size of boutons in the gracile, main cuneate and lateral cervical nucleus. The most intensive labeling of the gracile nucleus was found in the dorsal border of the nucleus and the lateral part of the caudal division. At the border between the spinal trigeminal nucleus and the triangular part of the cuneate nucleus Substance P labeling was also increased but mainly localized to the former nucleus. In the pars rotunda and the caudal part of the main cuneate nucleus there was a more intense labeling laterally especially at the obex level. In the lateral cervical nucleus Substance P positive structures seemed evenly spread and somewhat more numerous than in the gracile and main cuneate nucleus. Electron microscopy demonstrated Substance P positive boutons, which were fairly large and mostly in synaptic contact with dendrites. The results from the different nuclei in the monkey were compared with the results of similar investigations in the cat. It is concluded that there are important species differences especially on the light microscopical level in the lateral cervical nucleus. Thus Substance P terminals are evenly spread over the nucleus in the monkey whereas in the cat those structures are concentrated to the ventromedial region.