Neurotrophins Support Spinal Cord Learning and Rehabilitation

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Recent studies showing that the injured spinal cord has the capacity to learn motor tasks, suggest that spinal learning is an intrinsic component of functional recovery. The physiological and molecular mechanisms by which repeated activity can enhance locomotor learning in spinal cord injured subjects remain elusive. Our current research clearly indicates that exercise has an effect on select molecular systems involved with synaptic plasticity underlying learning and memory. In particular, exercise elevates BDNF in the spinal cord. Several studies have demonstrated the potent effect of BDNF on synaptic facilitation and neuronal excitability, indicating that BDNF has the capacity to mediate higher order neural function such as learning and memory. In fact, we have recently shown that exercise-induced BDNF production facilitates hippocampal learning. In addition, a large body of work has demonstrated the therapeutic potential of BDNF to attenuate neural loss associated with neural trauma or disease. Therefore, a central theme of this proposal is to examine the relationship between exercise-induced BDNF and learning in the spinal cord. We propose studies to determine how exercise can facilitate learning in the spinal cord by activating signaling systems under the modulation of endogenous BDNF and NT-3. To accomplish this goal, we will rely on our experience gained from pioneering the current understanding of the involvement of exercise-induced BDNF in mediating synaptic plasticity and learning. We will use a well-defined quantitative behavioral paradigm to assess spinal cord learning. We hypothesize that exercise and learning share molecular mechanisms and that BDNF plays a central role in modulating these mechanisms in the injured spinal cord. The highlight of these studies is the possibility to evaluate the effects of exercise on learning, in conjunction with its effects on stepping performance in the same animals. We will take advantage of the pharmacology of the serotonergic system to facilitate locomotion in complete transected animals, and its close interaction with the BDNF system. Success in the proposed investigations should provide new strategies for the development of treatments to improve functional recovery after spinal cord injury.