Experimental spinal cord injury : development of protection and repair strategies in rats

Abstract: Spinal cord injury typically results in neurological deficits that can not be reversed, often leaving patients bound to a wheelchair. Current treatment strategies are not very successful. Despite many promising experimental strategies, clinical translation has so far been very limited. This thesis describes gene regulation patterns of important inhibitory/growth promoting molecules and the possible effects of training and environmental enrichment on the outcome of experimental spinal cord injury. The thesis also reports improved recovery from spinal cord injury following local intrathecal blockade of the epidermal growth factor receptor. Potential mechanisms by which transplantation of Schwann cells from a novel source may improve outcome after spinal cord injury are discussed. Finally, magnetic resonance imaging is used to monitor metabolic changes in the brain and spinal cord after injury. The inability of the spinal cord and brain to regenerate has been partly attributed to the presence of inhibitory factors, some of which may increase their presence after injury. Inhibitory factors such as Nogo or chondroitin sulfate proteoglycans ultimately activate the small GTPase RhoA which leads to growth cone collapse and prevents regeneration. Inhibition of RhoA has been shown to enhance recovery after experimental spinal cord injury. We investigated mRNA regulation patterns of 6 members of the Rho family in the spinal cord and dorsal root ganglia. We found specific changes of temporal and spatial expression patterns in response to spinal cord injury, suggesting different roles of these GTPases after injury. Physiotherapy and rehabilitation are well established methods used after spinal cord injury. Environmental enrichment and exercise may even be neuroprotective. We tested the effects of moderate environmental enrichment and voluntary wheel running either before or after injury on the outcome of incomplete spinal cord injury in rats. However, no benefical effects were detected. Similarly, voluntary wheel running did not change the outcome after spinal cord injury in terms of recovery or behavior. While these results suggest that voluntary wheel running and moderate environmental enrichment have very limited effects, if any, on the outcome of experimental spinal cord injury, they do not contradict the fact that voluntary and guided training can be a useful tool in human spinal cord injury rehabilitation. Epidermal growth factor receptor activation triggers astrocytes into becoming reactive astrocytes, to form scar-like tissue and to secrete growth inhibitory molecules and inhibition of EGFR has been shown to promote neurite growth in vivo and in vitro. Blocking a Nogo receptor interacting mechanism or modulating the astrocytic response may be the underlying mechanism. We found that local delivery of an irreversible EGFR inhibitor after contusion injury in rats led to markedly better functional and structural outcome. Motor and sensory functions are improved and bladder function is restored faster. The fact that EGFR inhibitors are in clinical use as treatment for certain cancers, may help pave the way for clinical trials of such compounds also in spinal cord injury. Schwann cells are one of the most investigated cell types for transplantation in experimental spinal cord injury models, although understanding of the beneficial mechanisms is limited. Here we used a new source of Schwann cells, derived from the boundary cap neural crest stem cells. Cells were differentiated in vitro and transplanted 1 week after contusion injury into rats. We found significant functional improvement of both moderate and severe contusion injury, together with more tissue sparing, axonal outgrowth and Sox10+ glia recruitment. Although cells survived poorly after injury, we found they need to be transplanted alive to produce beneficial effects. Endogenous Schwann cells were found in higher numbers in transplanted animals. We also found that ependymal cells could be a source of oligodendrocytes/ Schwann-like cells after injury. To evaluate experimental spinal cord injury a variety of sensorimotor tests and imaging techniques are used. Typically, these tests do not generate information about metabolic processes in the CNS. Here, we investigated proton magnetic resonance spectroscopy as a new tool to obtain neurochemical profiles in vivo in the CNS after spinal cord injury. We found significant changes of several metabolites in both spinal cord and motorcortex. Changed metabolite patterns were detected in motor cortex and spinal cord. This enabled us to make prediction models with high sensitivity and specificity. We suggest that proton magnetic resonance spectroscopy is a useful tool to monitor metabolic changes in CNS tissue after spinal cord injury and evaluate experimental protection and repair strategies.

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