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Extensive spinal decussation and bilateral termination of cervical corticospinal projections in rhesus monkeys
Author(s) -
Rosenzweig Ephron S.,
Brock John H.,
Culbertson Maya D.,
Lu Paul,
Moseanko Rod,
Edgerton V. Reggie,
Havton Leif A.,
Tuszynski Mark H.
Publication year - 2009
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.21940
Subject(s) - spinal cord , biotinylated dextran amine , anatomy , decussation , biology , corticospinal tract , pyramidal tracts , neuroscience , primate , anterograde tracing , white matter , central nervous system , axon , medicine , magnetic resonance imaging , radiology , diffusion mri
To examine neuroanatomical mechanisms underlying fine motor control of the primate hand, adult rhesus monkeys underwent injections of biotinylated dextran amine (BDA) into the right motor cortex. Spinal axonal anatomy was examined using detailed serial‐section reconstruction and modified stereological quantification. Eighty‐seven percent of corticospinal tract (CST) axons decussated in the medullary pyramids and descended through the contralateral dorsolateral tract of the spinal cord. Eleven percent of CST axons projected through the dorsolateral CST ipsilateral to the hemisphere of origin, and 2% of axons projected through the ipsilateral ventromedial CST. Notably, corticospinal axons decussated extensively across the spinal cord midline. Remarkably, nearly 2‐fold more CST axons decussated across the cervical spinal cord midline (≈12,000 axons) than were labeled in all descending components of the CST (≈6,700 axons). These findings suggest that CST axons extend multiple segmental collaterals. Furthermore, serial‐section reconstructions revealed that individual axons descending in either the ipsilateral or contralateral dorsolateral CST can: 1) terminate in the gray matter ipsilateral to the hemisphere of origin; 2) terminate in the gray matter contralateral to the hemisphere of origin; or 3) branch in the spinal cord and terminate on both sides of the spinal cord. These results reveal a previously unappreciated degree of bilaterality and complexity of corticospinal projections in the primate spinal cord. This bilaterality is more extensive than that of the rat CST, and may resemble human CST organization. Thus, augmentation of sprouting of these extensive bilateral CST projections may provide a novel target for enhancing recovery after spinal cord injury. J. Comp. Neurol. 513:151–163, 2009. © 2009 Wiley‐Liss, Inc.