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The Journal of Neuroscience, September 30, 2009, 29(39):12145-12158; doi:10.1523/JNEUROSCI.0897-09.2009

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Development/Plasticity/Repair
Spinal Interneuron Axons Spontaneously Regenerate after Spinal Cord Injury in the Adult Feline

Keith K. Fenrich and P. Ken Rose

Canadian Institute for Health Research Group in Sensory-Motor Integration, Department of Physiology, Center for Neuroscience, Queen's University, Kingston, Ontario, Canada K7L 3N6

Correspondence should be addressed to Keith K. Fenrich, Department of Physiology, Queen's University, Kingston, Ontario, Canada, K7L 3N6. Email: keith{at}biomed.queensu.ca

It is well established that long, descending axons of the adult mammalian spinal cord do not regenerate after a spinal cord injury (SCI). These axons do not regenerate because they do not mount an adequate regenerative response and growth is inhibited at the injury site by growth cone collapsing molecules, such as chondroitin sulfate proteoglycans (CSPGs). However, whether axons of axotomized spinal interneurons regenerate through the inhibitory environment of an SCI site remains unknown. Here, we show that cut axons from adult mammalian spinal interneurons can regenerate through an SCI site and form new synaptic connections in vivo. Using morphological and immunohistochemical analyses, we found that after a midsagittal transection of the adult feline spinal cord, axons of propriospinal commissural interneurons can grow across the lesion despite a close proximity of their growth cones to CSPGs. Furthermore, using immunohistochemical and electrophysiological analyses, we found that the regenerated axons conduct action potentials and form functional synaptic connections with motoneurons, thus providing new circuits that cross the transected commissures. Our results show that interneurons of the adult mammalian spinal cord are capable of spontaneous regeneration after injury and suggest that elucidating the mechanisms that allow these axons to regenerate may lead to useful new therapeutic strategies for restoring function after injury to the adult CNS.

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Received Feb. 22, 2009; revised Aug. 4, 2009; accepted Aug. 20, 2009.

Correspondence should be addressed to Keith K. Fenrich, Department of Physiology, Queen's University, Kingston, Ontario, Canada, K7L 3N6. Email: keith{at}biomed.queensu.ca

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