Mechanisms of Secondary Damage after Spinal Cord Injury

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DESCRIPTION (provided by applicant): Spinal cord damage produces a wave of secondary injury that produces continuing damage over the hours and days following insult. It appears that an early phase of secondary injury is related to excitotoxic cell death and the presence of inflammatory cytokines like tumor necrosis factor-alpha (TNF-a). We have found that TNF-a and kainic acid (KA), a glutamate agonist, combine to produce much more cell death in the spinal gray matter than either substance alone. This effect is blocked by an AMPA/KA receptor (AMPAR) antagonist, CNQX (Hermann et al, 2001). TNF-a also appears to rapidly increase the number of AMPARs expressed on the surface of hippocampal neurons in culture, and increases glutamatergic post-synaptic activity, probably through modulation of constitutive AMPAR trafficking (E. Beattie et al, 2002). Our hypothesis is that in the minutes following spinal cord contusion, both glutamate and TNF-a levels rise. The TNF increase results in the rapid increase in AMPARs available on the cell surface. This increases the susceptibility of spinal neurons to glutamate-induced cell death. We propose the following specific aims: 1) Determine whether TNF-a injected into motoneuron pools will increase the cell surface expression of AMPARs using confocal techniques for measuring this effect and compare the time course of this effect with this with MN death induced by co-injections of TNF and glutamate agonists (kainic acid, KA), 2) We will compare the results of injections from aim 1 to mild contusion lesions that we know produce similar MN cell death to determine if injury also results in increases in cell surface AMPARs, 3) We will determine whether blockade of TNF-a action by co-injection of soluble TNFR or blocking antibodies reduces both cell death induced by co-injection of KA and increased surface expression of AMPARs, and whether these treatments can reduce secondary injury after mild cervical SCI. In the fourth aim, we will extend these studies to include oligodendrocytes of the white matter tracts. The same strategies will be used as for gray matter neurons. These studies should provide evidence to test whether this novel interaction between a cytokine and a neurotransmitter may be involved in the exacerbation of secondary injury following SCI. If so, it may be a new target for therapies.