Central projections of spinal dorsal roots in the monkey. I. Cervical and upper thoracic dorsal roots

Abstract A study of the central distribution of cervical and upper thoracic dorsal roots (DR) was made in 18 monkeys subjected to 31 dorsal rhizotomies. Degeneration was studied in multiple spinal and medullary sections stained by the Nauta technic. Dorsal roots C2 through T7 project fibers to: (1) portions of laminae III and IV, (2) the intermediomedial nucleus, and (3) portions of laminae VII, VIII and IX. DR C5 through T1 project fibers to medial parts of lamina VI. DR fibers reach cell groups of lamina IX via different trajectories, one of which is dominant in the brachial enlargement. Fibers project to the spinal accessory nucleus from C2 through C5 DR, while portions of the dorsal nucleus receive fibers from C5 to T7 DR. Ascending fibers in the fasciculus cuneatus: (1) arise from C1 through T7 DR, (2) exhibit only general segregation due to overlap, and (3) project somatotopically throughout the extent of the cuneate (CN) and accessory cuneate (ACN) nuclei. Fiber terminations in CN and ACN are: (1) similar for C1 through T1 DR, and (2) distinctive for T2 through T7 DR. The upper five cervical DR project fibers to: (1) the supraspinal nucleus, and (2) both the central cervical and intermediate nuclei. Cytological and degeneration studies suggest that the central cervical and intermediate nuclei constitute parts of the same cell column.