Rubrospinal neurons fail to respond to brain-derived neurotrophic factor applied to the spinal cord injury site 2 months after cervical axotomy.
Numerous experimental therapies to promote axonal regeneration have shown promise in animal models of acute spinal cord injury, but their effectiveness is often found to diminish with a delay in administration. We evaluated whether brain-derived neurotrophic factor (BDNF) application to the spinal cord injury site 2 months after cervical axotomy could promote a regenerative response in chronically axotomized rubrospinal neurons. BDNF was applied to the spinal cord in three different concentrations 2 months after cervical axotomy of the rubrospinal tract. The red nucleus was examined for reversal of neuronal atrophy, GAP43 and Talpha1 tubulin mRNA expression, and trkB receptor immunoreactivity. A peripheral nerve transplant paradigm was used to measure axonal regeneration into peripheral nerve transplants. Rubrospinal axons were anterogradely traced and trkB receptor immunohistochemistry performed on the injured spinal cord. We found that BDNF treatment did not reverse rubrospinal neuronal atrophy, nor promote GAP-43 and Talpha1 tubulin mRNA expression, nor promote axonal regeneration into peripheral nerve transplants. TrkB receptor immunohistochemistry demonstrated immunoreactivity on the neuronal cell bodies, but not on anterogradely labeled rubrospinal axons at the injury site. These findings suggest that the poor response of rubrospinal neurons to BDNF applied to the spinal cord injury site 2 months after cervical axotomy is not related to the dose of BDNF administered, but rather to the loss of trkB receptors on the injured axons over time. Such obstacles to axonal regeneration will be important to identify in the development of therapeutic strategies for chronically injured individuals.
International Collaboration on Repair Discoveries (ICORD), University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4. briankkwon@yahoo.ca
Brian K
BK
Kwon
Jie
J
Liu
Loren
L
Oschipok
Joshua
J
Teh
Zhuo Wei
ZW
Liu
Wolfram
W
Tetzlaff
D000818:Animals; D019771:Axotomy / Q000009:adverse effects* / Q000379:methods; D001710:Biotin / Q000031:analogs & derivatives* / Q000378:metabolism; D001933:Brain Stem / Q000166:cytology; D019208:Brain-Derived Neurotrophic Factor / Q000627:therapeutic use*; D003911:Dextrans / Q000378:metabolism; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000378:metabolism; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D007150:Immunohistochemistry / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D008297:Male; D009416:Nerve Regeneration / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010751:Phosphopyruvate Hydratase / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020813:Receptor, trkB / Q000378:metabolism; D012012:Red Nucleus / Q000166:cytology* / Q000187:drug effects; D013119:Spinal Cord Injuries / Q000188:drug therapy*; D013266:Stilbamidines / Q000378:metabolism; D013997:Time Factors; D014404:Tubulin / Q000235:genetics / Q000378:metabolism
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D019208:Brain-Derived Neurotrophic Factor; D003911:Dextrans; D005456:Fluorescent Dyes; D019922:GAP-43 Protein; D013266:Stilbamidines; D014404:Tubulin; C076397:biotinylated dextran amine; D001710:Biotin; D020813:Receptor, trkB; D010751:Phosphopyruvate Hydratase