EFFECTS OF EXCITOTOXIC INJURY ON SPINAL SENSORY PATHWAYS

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The condition of pain following spinal cord injury (SCI) is one of many challenges facing patients coping with the physical and life threatening consequences of SCI. This condition continues to challenge health professionals with an incidence of 60-80 percent for all SCI patients. Nearly 40 percent of these patients report severe pain to the extent they would trade any chance of functional recovery for relief of pain. Without research directed towards understanding the mechanisms responsible for this condition it is unlikely that effective treatments will be developed. To this end, the focus of this proposal is directed towards evaluating the cellular events responsible for the development of spontaneous and evoked pain behaviors in a model developed to study the pathophysiological, biochemical, and molecular cascades responsible for different pain states associated with SCI. Over the past five years the excitotoxic model of SCI, which relies upon the intraspinal injection of the AMPA/metabotropic receptor agonist quisqualic acid (QUIS), has been used to simulate injury evoked elevations of glutamate and produce a pathological sequella similar to that following ischemic and traumatic SCI. The experiments of Specific Aim 1 will evaluate the relationship between the astrocytic, microglial, and neuronal responses to excitotoxic injury and the onset of spontaneous and evoked pain behaviors. The main focus of these experiments will be directed towards correlating the temporal profile of these responses along the longitudinal axis of the cord with the onset of pain behaviors following QUIS injections. Specific Aim 2 will focus on establishing a physiological correlate between cellular responses at different distances from the injury epicenter and changes in the functional state of sensory neurons following excitotoxic lesions. In Specific Aims 1-2 efforts will be made to evaluate the effects of the anti-inflammatory agent IL-10 and/or the iNOS inhibitor and NMDA antagonist agmatine on the relationship between the onset of pain behaviors and the cellular response and physiological changes following QUIS injury. Specific Aim 3 will focus on an evaluation of the biochemical changes following QUIS injections with a special emphasis on the initiating events responsible for the anatomical and functional changes in sensory circuits that underlie the onset of persistent pain following SCI. Of special interest will be the role of cytoskeletal proteins in the regulation of membrane fluidity and distribution of glutamate binding sites along with the role of inflammatory mediators in producing plastic changes in spinal sensory neurons. The long range goal of the proposed research is to understand the pathophysiological and biochemical mechanisms responsible for the progressive tissue damage in SCI, and to provide new directions for the development of therapeutic interventions for the prevention and treatment of chronic pain following injury.