title: Extensive spinal decussation and bilateral termination of cervical corticospinal projections in rhesus monkeys.
abstract: 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 (approximately 12,000 axons) than were labeled in all descending components of the CST (approximately 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.
authors.affiliation: Department of Neurosciences, University of California, San Diego, La Jolla, California 92093-0626, USA.
authors.forename: Ephron S
authors.initials: ES
authors.lastname: Rosenzweig
authors.forename: John H
authors.initials: JH
authors.lastname: Brock
authors.forename: Maya D
authors.initials: MD
authors.lastname: Culbertson
authors.forename: Paul
authors.initials: P
authors.lastname: Lu
authors.forename: Rod
authors.initials: R
authors.lastname: Moseanko
authors.forename: V Reggie
authors.initials: VR
authors.lastname: Edgerton
authors.forename: Leif A
authors.initials: LA
authors.lastname: Havton
authors.forename: Mark H
authors.initials: MH
authors.lastname: Tuszynski
mesh_terms: D000818:Animals; D001369:Axons; D001710:Biotin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism; D003911:Dextrans / Q000008:administration & dosage / Q000378:metabolism; D005260:Female; D005456:Fluorescent Dyes / Q000008:administration & dosage / Q000378:metabolism; D008253:Macaca mulatta / Q000033:anatomy & histology*; D008297:Male; D008845:Microinjections; D009044:Motor Cortex / Q000033:anatomy & histology* / Q000166:cytology; D009411:Nerve Endings; D009412:Nerve Fibers; D009434:Neural Pathways / Q000033:anatomy & histology* / Q000166:cytology; D011712:Pyramidal Tracts / Q000033:anatomy & histology* / Q000166:cytology; D013116:Spinal Cord / Q000033:anatomy & histology* / Q000166:cytology
chemical_list: D003911:Dextrans; D005456:Fluorescent Dyes; C076397:biotinylated dextran amine; D001710:Biotin