Spinal cord injury is a catastrophic event that dramatically alters the lifestyle of the victim and subjects the individual to a lifetime of reduced mobility, recurrent medical problems and chronic neuropathic pain. The ultimate severity of the injury is not only determined by the initial damage produced by the tramna, but also by a cascade of biochemical events that further erodes the integrity of the spinal cord over the course of several days. One of these pathways leads to a dramatic increase in the concentration and release of the opioid peptide dynorphin. Dynorphin is a neurotoxic peptide that damages neurons in the spinal cord by activating the N-methyl-D-aspartate (NMDA) subclass of excitatory amino acid receptors. The damage produced by dynorphin can produce symptoms in non-traumatized spinal cord ranging from chronic allodynia (pain to normally non-painful stimuli) to full paralysis. Thus, it is likely that dynorphin contributes significantly to the post trauma spinal cord damage. The ultimate goal of this project is to understand how dynorphin contributes to spinal cord injury. ? The mechanism by which dynorphin activates NMDA receptors is currently not known. In this proposal the hypothesis that will be tested is that dynorphin activates low activity or quiescent NMDA receptors that lack the exon-5 coded region of the NR1 subunit (NRla). Whole cell patch clamp experiments will be conducted in cultured spinal cord neurons, spinal cord slices, and cell lines transfected with known combinations of NMDA receptor subunits. These experiments will demonstrate that 1) dynorphin enhances the activity of a subset of NMDA receptors, 2) the NRla subunit is critical for dynorphin enhancing NMDA receptor function, and 3) the low activity NRla containing NMDA receptors are responsible for dynorphin's enhancement of synaptic activity in the spinal cord. These experiments will identify the mechanism for dynorphin's neurotoxicity as well as identify potential pharmacological targets for intervention in the critical post trauma period of spinal cord injury. ? ?
