Mechanisms of Neuropathic Pain in Demylenated Nerves

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Inflammatory responses in injured nerves are likely to be key contributing factors in the generation and maintenance of neuropathic pain in inflammatory demyelinating disorders such as Guillain-Barre' Syndrome. Neuropathic pain is a common feature in individuals suffering from the acute phase of Guillain-Barre Syndrome (upwards of 89% of patients) and recovery from the acute phase of Guillain-Barre Syndrome (i.e. remyelination of peripheral axons) does not provide pain relief. In fact, residual neuropathy affecting large- and medium-sized myelinated fibers endures long after the acute attack of Guillain-Barre' syndrome in approximately half of all tested patients. Reported neuropathies include increases in the threshold required for vibration and cold sensation, in addition to neuropathic pain. The positive sensory symptoms of vibration and cold can potentially be explained by delayed remyelination of large and medium diameter fibers. However, the unremitting nature of the neuropathic pain associated with peripheral nerves suggests that factors and/or receptors inherent to the peripheral nerve may be contributing to long-term peripheral sensitization. The aim of this proposal is to examine the cellular and molecular mechanisms underlying the peripheral sensitization by investigating the production of inflammation-associated pro-algesic factors which may directly sensitize sensory nerve fibers and cell bodies. We will determine whether the chronic cutaneous hyperalgesia exhibited by animals subjected to focal nerve demyelination is correlated with the degree of inflammatory response by activated cell types in the peripheral nervous system and the resultant production of the peripherally-derived pro-inflammatory mediators TNFot, IL-1P, and/or MCP-1. In addition, we will identify the cellular sources of cytokine/chemokine production and/or their respective receptors. The cellular sources, inflammatory mediators and their receptors are potential targets for future drug therapies. Verification of the pharmaceutical effects of pro-inflammatory mediators from identified cells may be accomplished by assaying the activation state of the transcription factor, NFvcB, which is central to the regulation of the inflammatory mediators. The combination of this model of an inflammatory demyelinating disease with these techniques offer an unprecedented ability to study the potential influences of cytokine/chemokine(s) on cutaneous hyperalgesia in the rodent. These behavioral, cellular, and biochemical observations will directly advance our fundamental insights into cellular basis of neuropathic pain that accompanies both Guillain-Barre' Syndrome and chronic inflammatory pain processes.