Axonal regeneration and development of de novo axons from distal dendrites of adult feline commissural interneurons after a proximal axotomy

Keith K Fenrich, Nicole Skelton, Victoria E MacDermid, Claire Francesca Meehan, Stacey Armstrong, Monica S Neuber-Hess, P Ken Rose

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Abstract

Following proximal axotomy, several types of neurons sprout de novo axons from distal dendrites. These processes may represent a means of forming new circuits following spinal cord injury. However, it is not know whether mammalian spinal interneurons, axotomized as a result of a spinal cord injury, develop de novo axons. Our goal was to determine whether spinal commissural interneurons (CINs), axotomized by 3-4-mm midsagittal transection at C3, form de novo axons from distal dendrites. All experiments were performed on adult cats. CINs in C3 were stained with extracellular injections of Neurobiotin at 4-5 weeks post injury. The somata of axotomized CINs were identified by the presence of immunoreactivity for the axonal growth-associated protein-43 (GAP-43). Nearly half of the CINs had de novo axons that emerged from distal dendrites. These axons lacked immunoreactivity for the dendritic protein, microtubule-associated protein2a/b (MAP2a/b); some had GAP-43-immunoreactive terminals; and nearly all had morphological features typical of axons. Dendrites of other CINs did not give rise to de novo axons. These CINs did, however, each have a long axon-like process (L-ALP) that projected directly from the soma or a very proximal dendrite. L-ALPs were devoid of MAP2a/b immunoreactivity. Some of these L-ALPs projected through the lesion and formed bouton-like swellings. These results suggest that proximally axotomized spinal interneurons have the potential to form new connections via de novo axons that emerge from distal dendrites. Others may be capable of regeneration of their original axon.
Original languageEnglish
JournalJournal of Comparative Neurology
Volume502
Issue number6
Pages (from-to)1079-97
Number of pages19
ISSN0021-9967
DOIs
Publication statusPublished - 2007

Keywords

  • Age Factors
  • Animals
  • Axotomy
  • Biological Markers
  • Biotin
  • Cats
  • Dendrites
  • Disease Models, Animal
  • Functional Laterality
  • GAP-43 Protein
  • Growth Cones
  • Immunohistochemistry
  • Interneurons
  • Microtubule-Associated Proteins
  • Nerve Regeneration
  • Neuronal Plasticity
  • Presynaptic Terminals
  • Recovery of Function
  • Reproducibility of Results
  • Spinal Cord Injuries

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