Projections of caudal fasciculus gracilis to nucleus gracilis and other medullary structures, and Clarke's nucleus in the rat

Abstract

The extent of the projection of fasciculus gracilis from low thoracic (T12–13) spinal cord, to nucleus gracilis (NG) was studied by the Nauta-Gygax method in the rat in order to: (1) help define projection fields of fasciculus gracilis hindlimb and tail afferents along the longitudinal extent of NG; and (2) broaden the comparative data on the projection of the lower body to NG via fasciculus gracilis, already known in cat and monkey. Results showed that: (1) degenerated fasciculus gracilis axons are situated mainly dorsal to the corticospinal fibers, in the dorsal funiculus; (2) terminal projection fields were located at all levels of ipsilateral NG — caudal to the obex, terminal debris was confined to the medial two-thirds of NG — rostrad of the obex, in oral NG, degeneration was of finer caliber and projection fields more diffuse; and (3) ipsilateral degeneration was also seen at the level of a portion of Clarke's nucleus, and, in commissural and lateral cuneate nuclei and medial reticular formation in medulla.