Injury to the brain of spinal cord can result in debilitating loss of function, because severed axons within the central nervous system (CNS) can not regenerate. Severed axons within the peripheral nervous system (PNS), however, can regenerate quite well. This difference is not due to the intrinsic ability of the axons, but to the difference in the environment between the central and peripheral nervous systems. Schwann cells within the PNS are known to be intimately involved in mediating axonal regeneration. After injury, Schwann cells (unlike glia within the CNS) substantially upregulated their expression of many axon growth promoting molecules such as the cellular adhesion molecules and neurotrophins. This proposal will examine whether gene therapy can be used to increase the growth supportive environment within the CNS and increase the potential for axonal regeneration. To accomplish this task, recombinant adenovirus will be used to transfer cDNAs encoding cellular adhesion molecules (NILE/L1, NCAM, and N-cadherin) and neurotrophins (NT-3, NGF, and bFGF) into strocytes in tissue culture and within the dorsal spinal cord. Tissue culture experiments will be used to examine neurite outgrowth over astrocytes or spinal cord cryosections transfected with individual or multiple cellular adhesion molecules. To examine axonal regeneration in vivo, the dorsal root entry zone model will be used since there severed sensory axons fail to regenerate into the spinal cord. Recombinant adenoviruses will then be injected into the dorsal spinal cord segments corresponding to the lesion . Regeneration will be assessed in rats transfected with individual as well as combinations of one cellular adhesion molecule and one neurotrophin. The extent of axonal regeneration will be determined by recovery of either nociceptive or proprioceptive function using several behavioral assays in correspondence with HRP tract tracing. Spinal cords will also be assayed by immunohistology to examine the relationship between regenerating axons and transgene expression. These experiments will elicit a better understanding of how the growth promotive status of the environment influences axonal regeneration and if different cellular adhesion molecules or neurotrophins selectively influence the growth of either nocicpeive of proprioceptive sensory axons.
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