Spinal cord injury (SCI) generates a cascade of events that lead to inhibition of axonal regeneration. These molecular and biochemical changes represents the presence of repulsive factors that may restrict or block neurite outgrowth after CNS trauma. Members of the Eph subfamily of receptor tyrosine kinases (RTKs)have been associated with axonal pathfinding, target recognition and synapse formati on during development. It has been shown that these roles are accomplished by repulsive interactions caused after ligands binding. However, the role of EphAs in inhibiting axonal outgrowth in adult injured spinal cord is unknown. The expression of some of these receptors after injury was examined with standardized semi-quantitative RT-PCRanalysis. Results showed that several EphA's RTKs were induced after the injury and this enhanced expression persisted for several days. The expression of the EphA's after SCI were localized by immunocytochemistry and the results indicated that at the lesion epicenter, the immunoreactivity was focused in the lateral and ventral region of the white matter. These results suggest that these EphA's may be involved in the establishment of the non-permissive environment for axonal regeneration after CNS trauma. It is the objective of this proposal to block EphA's gene expression with antisense technology, reducing the nonpermissive environment generated after contusion to the spinal cord. Behavioral (BBB, grid walking, narrow-beam crossing, righting reflex and climbing test), physiological (transcranial magnetic motor evoked potentials) and anatomical tracing studies will be performed to monitor axonal regeneration and functional recovery after blockade of these repulsive proteins in SCI. In addition, neurotrophic factors will be used together with the antisense oligonucleotides to enhance the axonal outgrowth across the injury site. Establishing the EphA recept or roles, both on the regenerating fibers and in the local microenvironment, may lead to novel therapeutic strategies to enhance regeneration and functional recovery after SCI.