Abstract
Unraveling the cellular and molecular mechanisms of spinal cord injury is fundamental for our possibility to develop successful therapeutic approaches. These approaches need to address the issues of the emergence of a non-permissive environment for axonal growth in the spinal cord, in combination with a failure of injured neurons to mount an effective regeneration program. Experimental in vivo models are of critical importance for exploring the potential clinical relevance of mechanistic findings and therapeutic innovations. However, the highly complex organization of the spinal cord, comprising multiple types of neurons, which form local neural networks, as well as short and long-ranging ascending or descending pathways, complicates detailed dissection of mechanistic processes, as well as identification/verification of therapeutic targets. Inducing different types of dorsal root injury at specific proximo-distal locations provide opportunities to distinguish key components underlying spinal cord regeneration failure. Crushing or cutting the dorsal root allows detailed analysis of the regeneration program of the sensory neurons, as well as of the glial response at the dorsal root-spinal cord interface without direct trauma to the spinal cord. At the same time, a lesion at this interface creates a localized injury of the spinal cord itself, but with an initial neuronal injury affecting only the axons of dorsal root ganglion neurons, and still a glial cell response closely resembling the one seen after direct spinal cord injury. In this review, we provide examples of previous research on dorsal root injury models and how these models can help future exploration of mechanisms and potential therapies for spinal cord injury repair.
Highlights
Published: 25 August 2021Dorsal root ganglion (DRG) neurons are pseudounipolar cells with a single process, bifurcating in a peripherally and a centrally directed branch
Since myelination in the central nervous system (CNS) is triggered at axonal diameters smaller than in the peripheral nervous system (PNS) [5], large non-myelinated sensory axons in the PNS are likely to become myelinated after their entry into the spinal cord [6]
Becomes a barrier for axonal ingrowth, give examples of previous and current research exploring how to overcome this barrier in the adult nervous system, and how future spinal cord injury research can benefit from using dorsal root injury models
Summary
Dorsal root ganglion (DRG) neurons are pseudounipolar cells with a single process, bifurcating in a peripherally and a centrally directed branch. The regenerative response of the central process of DRG neurons is markedly weaker than what follows after an injury to their peripheral process These two factors contribute to the failure of injured dorsal root axons to re-enter the spinal cord in a similar way a non-permissive environment and attenuated growth response obstruct functional regeneration in the injured spinal cord. The most centrally located dorsal root injury, dorsal root avulsion, will damage the DREZ, including its central glial component, and thereby constitute a true CNS injury, but isolated to the dorsal root axons and their immediate surroundings [13] In this brief review, we describe how DREZ becomes a barrier for axonal ingrowth, give examples of previous and current research exploring how to overcome this barrier in the adult nervous system, and how future spinal cord injury research can benefit from using dorsal root injury models
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