Central projections of brachial and lumbar dorsal roots in reptiles

The central distributions of single lumbar and brachial dorsal roots have been determined in the reptiles: Caiman sclerops, Ctenosaura hemophila and Iguana iguana. Degeneration resulting from root transections was assessed by means of the uranyl nitrate modification of the Nauta method. All dorsal root projections were entirely ipsilateral to the side of the damaged roots. A projection to the ventral horn was found in the lizards, but not in Caiman. A nuclear column, apparently homologous with Clarke's column of mammals, was observed in Ctenosaura and Caiman. A somatotopically organized dorsal column projection to gracile and cuneate nuclei was found in Ctenosaura and Caiman. No evidence was obtained for a projection to a lateral cuneate nucleus or to areas rostral to the level of the dorsal column nuclei. The findings are contrasted with previous descriptions of dorsal root projections in reptiles, as well as with the pattern of dorsal root distribution reported for amphibians and for mammals.