title: Corticospinal sprouting differs according to spinal injury location and cortical origin in macaque monkeys.
abstract: The primate corticospinal tract (CST), the major descending pathway mediating voluntary hand movements, comprises nine or more functional subdivisions. The role of subcomponents other than that from primary motor cortex, however, is not well understood. We have previously shown that following a cervical dorsal rhizotomy (Darian-Smith et al., 2013), CST projections originating from primary somatosensory (S1) and motor (M1) cortex responded quite differently to injury. Terminal projections from the S1 (areas 3b/1/2) shrank to <60% of the contralateral side, while M1 CST projections remained robust or expanded (>110%). Here, we asked what happens when a central lesion is added to the equation, to better simulate clinical injury. Monkeys (n = 6) received either a unilateral (1) dorsal root lesion (DRL), (2) or a combined DRL/dorsal column lesion (DRL/DCL), or (3) a DRL/DCL where the DCL was made 4 months following the initial DRL. Electrophysiological recordings were made in S1 4 months postlesion in the first two groups, and 6 weeks after the DCL in the third lesion group, to identify the reorganized region of D1-D3 (thumb, index finger, and middle finger) representation. Anterograde tracers were then injected bilaterally to assess spinal terminal labeling. Remarkably, in all DRL/DCL animals, terminal projections from the S1 and M1 extended bilaterally and caudally well beyond terminal territories in normal animals or following a DRL. These data were highly significant. Extensive sprouting from the S1 CST has not been reported previously, and these data raise important questions about S1 CST involvement in recovery following spinal injury.
authors.affiliation: Department of Comparative Medicine, Stanford University School of Medicine, Stanford, California 94305-5342 cdarian@stanford.edu.
authors.forename: Corinna
authors.identifier: http://orcid.org/0000-0002-4753-4574
authors.initials: C
authors.lastname: Darian-Smith
authors.affiliation: Department of Comparative Medicine, Stanford University School of Medicine, Stanford, California 94305-5342.
authors.forename: Alayna
authors.initials: A
authors.lastname: Lilak
authors.affiliation: Department of Comparative Medicine, Stanford University School of Medicine, Stanford, California 94305-5342.
authors.forename: Joseph
authors.initials: J
authors.lastname: Garner
authors.affiliation: Department of Comparative Medicine, Stanford University School of Medicine, Stanford, California 94305-5342.
authors.forename: Karen-Amanda
authors.initials: KA
authors.lastname: Irvine
mesh_terms: D000818:Animals; D008252:Macaca fascicularis; D008297:Male; D009415:Nerve Net / Q000473:pathology / Q000503:physiopathology; D009416:Nerve Regeneration / Q000502:physiology*; D009473:Neuronal Plasticity; D011712:Pyramidal Tracts / Q000473:pathology* / Q000503:physiopathology*; D066191:Sensorimotor Cortex / Q000473:pathology* / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000473:pathology* / Q000503:physiopathology*
keywords: axonal sprouting; corticospinal pathway; motor cortex; nonhuman primate; somatosensory cortex; spinal cord injury