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Recovery of locomotion after partial spinal cord lesions in cats: assessment using behavioral, electrophysiological and imaging techniques.

This short review summarizes experimental findings made after spinal cord injury, mainly in cats. After a complete spinal injury, cats re-express hindlimb locomotion after 2-3 weeks because of a spinal locomotor circuitry named the central pattern generator or CPG. To investigate whether such circuits are also implicated in the recovery of locomotion after partial spinal lesions, we have used a dual spinal lesion paradigm. Essentially, after an initial unilateral hemisection, cats spontaneously recover quadrupedal locomotion. When a complete section is then performed 3 weeks after this hemisection, cats can walk with the hindlimbs within 24 hours compared to 2-3 weeks in cats with single complete spinal lesions demonstrating the importance of spinal mechanisms after partial lesions. Using kinematic and electromyographic methods to evaluate the changes throughout the dual lesion paradigm, we could show that the spinal cord reorganizes spontaneously without locomotor training or with training provided between the partial and complete spinal lesion. To assess spinal lesions we have used histology and magnetic resonance imaging (MRI). We will describe some advanced MRI techniques such as diffusion and magnetization transfer, which provide higher specificity to axon degeneration and demyelination. Examples of advanced MRI techniques in cats and humans are described, including the current limitations and perspectives.