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Chemotropic guidance facilitates axonal regeneration and synapse formation after spinal cord injury

Nature Neuroscience volume 12, pages 1106–1113 (2009)Cite this article

Abstract

A principal objective of spinal cord injury (SCI) research is the restoration of axonal connectivity to denervated targets. We tested the hypothesis that chemotropic mechanisms would guide regenerating spinal cord axons to appropriate brainstem targets. We subjected rats to cervical level 1 (C1) lesions and combinatorial treatments to elicit axonal bridging into and beyond lesion sites. Lentiviral vectors expressing neurotrophin-3 (NT-3) were then injected into an appropriate brainstem target, the nucleus gracilis, and an inappropriate target, the reticular formation. NT-3 expression in the correct target led to reinnervation of the nucleus gracilis in a dose-related fashion, whereas NT-3 expression in the reticular formation led to mistargeting of regenerating axons. Axons regenerating into the nucleus gracilis formed axodendritic synapses containing rounded vesicles, reflective of pre-injury synaptic architecture. Thus, we report for the first time, to the best of our knowledge, the reinnervation of brainstem targets after SCI and an essential role for chemotropic axon guidance in target selection.

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Figure 1: Experimental procedure.
Figure 2: Transected ascending sensory axons extend toward Lenti–NT-3–transduced cells in the denervated nucleus gracilis.
Figure 3: Comparison of axon growth into the nucleus gracilis after viral GFP or NT-3 delivery with or without conditioning lesions.
Figure 4: Quantification of CTB-labeled axons and reporter gene expression in the nucleus gracilis.
Figure 5: Lesioned axons regenerate to ectopic regions when NT-3 is ectopically expressed.
Figure 6: Regenerating axons form new synapses in the denervated nucleus gracilis.
Figure 7: Electrophysiological responses in the nucleus gracilis evoked by sciatic nerve stimulation in intact and C1-injured rats.

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Acknowledgements

We thank L. Ma and B. Sjöstrand for technical assistance and J. Silver for helpful suggestions. This work was supported by the US National Institutes of Health (NS09881 and NS54883), the Veterans Administration, the International Spinal Research Trust, Wings for Life, the Dr. Miriam and Sheldon G. Adelson Medical Research Foundation and the Bernard and Anne Spitzer Charitable Trust.

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Authors and Affiliations

  1. Department of Neurosciences, University of California, San Diego, La Jolla, California, USA

    Laura Taylor Alto, James M Conner, Edmund R Hollis II, Armin Blesch & Mark H Tuszynski

  2. Department of Neurology, University of California, Los Angeles, California, USA

    Leif A Havton

  3. Veterans Administration Medical Center, San Diego, California, USA

    Mark H Tuszynski

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  1. Laura Taylor Alto
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Contributions

L.T.A. designed the experiments, performed surgery, labeled tissue, analyzed data and wrote the manuscript. L.A.H. performed ultrastructural studies and analysis. J.M.C. carried out electrophysiological analyses. E.R.H. examined the myelination state of regenerated axons. A.B. and M.H.T. designed experiments, performed surgery, analyzed data and wrote the manuscript.

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Correspondence to Armin Blesch or Mark H Tuszynski.

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Alto, L., Havton, L., Conner, J. et al. Chemotropic guidance facilitates axonal regeneration and synapse formation after spinal cord injury. Nat Neurosci 12, 1106–1113 (2009). https://doi.org/10.1038/nn.2365

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