Neurons have the intrinsic ability to regenerate after injury to the adult mammalian spinal cord as demonstrated by transplantation of either peripheral nerves, Schwann cells, or fetal spinal cord tissue. These axons regenerate into and throughout these transplants, but fail to grow significant distances back into the adult central nervous system (CNS). Axons that do regenerate into the adult CNS are randomly organized and not directed specifically towards their targets. Several hypotheses indicate that changes in the growth promoting state, either by active inhibition or the lack of a good growth supportive substrate, produce an environment that is refractory to axonal regeneration. This application is designed to examine the hypothesis that a selective expression of growth-supportive and guidance molecules can be used to increase axonal regeneration and direct these axons to select target regions. To test this hypothesis, we will examine axonal growth in two models. The first is the well-established dorsal root entry zone model to examine regeneration from separate sensory populations through the dorsal root entry zone (DREZ) and into the spinal cord. We have previously demonstrated robust axonal regeneration into both appropriate and aberrant targets. The first two specific aims will use this model. The second is a novel in vivo guidance model that uses an expression pathway to guide axonal growth from neuronal transplants towards a distant target location. We propose to accomplish the following specific aims: 1) to determine if co-expression of nerve growth factor (NGF) and semaphorin 3a within the adult spinal cord will direct the regeneration of sensory axons to appropriate target locations. 2) To enhance proprioceptive axonal regeneration by selective expression of neurotrophin (NT)-3 or tyrosine kinase (trk) C-receptor. 3) To direct the growth of axons from a neuronal transplant along a complex pathway to a distant target location. 4) To generate an expression pathway that can induce axonal growth from a transplant, through or around a lesion site, and towards a distant target location. For the proposed experiments, recombinant adenovirus will be used to transfer cellular adhesion molecules (CAMs), laminin neurotrophins, or chemorepulsive (e.g., semaphorin 3a) into the endogenous CNS environment. Regeneration of sensory axons through the DREZ and into the spinal cord will be examined using behavioral assessments for functional recovery and tract tracing techniques. This grant application is designed to better define the molecular mechanisms that influence axonal regeneration and guidance within the adult CNS, with the ultimate goal of inducing axonal regeneration in the spinal cord to appropriate locations, while discouraging aberrant connections.
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