Light and electron microscopical studies of the GABA innervation of the dorsal column nuclei and the lateral cervical nucleus in the primate species Macaca fascicularis and Papio anubis.

In 4 monkeys of the species Macaca fascicularis (2 animals) and Papio anubis (2 animals) the three dorsal column nuclei and the lateral cervical nucleus have been investigated immunocytochemically with antiserum against gamma-aminobutyric acid (GABA). Light microscopic studies demonstrated the presence of GABA-positive cells in the gracile nucleus, the internal cuneate nucleus and the lateral cervical nucleus but not in the external cuneate nucleus. Although labeled cells seemed fairly evenly spread in the nuclei there was an increased amount between the clusters of the internal cuneate nucleus and in the border zone between the gracile and the cuneate nucleus. Electron microscopical investigation showed GABA labeling in fairly small neurons with relatively large cell nuclei and low somatic bouton covering. GABA-positive terminals with rounded synaptic vesicles were present in all the investigated nuclei also the external cuneate one. No apparent difference in number of such boutons in the different nuclei or parts of the nuclei was found. GABA-positive boutons mostly synapsed with dendrites but in the dorsal column nuclei also with other larger boutons. Axosomatic contacts between labeled terminals and neuronal perikarya were more common in the lateral cervical nucleus than in the dorsal column nuclei. 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 the GABA labeled cells is rather evenly spread over the nucleus in the monkey whereas in the cat they are concentrated to the ventromedial region.