The pain that follows nerve injury is chronic and consistently refractory to available analgesics. These neuropathic pain syndromes include deafferentation pain, diabetic, cancer and ischemic neuropathies, phantom limb pain, trigeminal neuralgia, postherpetic neuralgias and nerve injury caused by surgery or trauma. Neuropathic pain is not only chronic and intractable, it is debilitating and causes extreme physical, psychological and social distress. The broad, long-term objective of our research is to elucidate mechanisms responsible for the generation and maintenance of neuropathic pain. This knowledge will enable development of new medications to treat neuropathic pain without the added liability of drug abuse. To investigate mechanisms of neuropathic pain, our laboratory developed and characterized reliable rat neuropathy models termed sciatic cryoneurolysis (SCN) and spinal nerve cryoneurolysis (SPCN). The models produce a focal nerve lesion by exposure and freezing of the sciatic nerve (SCN) or the more proximal L5 spinal nerve (SPCN). The models have proved ideal for the study of neuropathic pain due to creation of predictable and robust pain behaviors. Using both our neurolysis models and the chronic constriction injury model (Bennett and Xie, 1988), we have found evidence that immune cell activation and immune cell products (cytokines) contribute to generation of chronic pain states. In this proposal, the cryoneurolysis models will be used with other neuropathic pain models to test our hypothesis and compare different models of neuropathic pain in one laboratory. The central hypothesis--spinal cytokine activation leads to neuropathic pain--will be tested using methods established in my laboratory and the following specific aims: 1). Characterize spinal proinflammatory cytokine expression (IL-1, IL-6 and TNF-a) and glial activation in nerve injury and acute inflammatory animals Models. 2) identify the origin of altered cytokine expression in the spinal cord following nerve injury. 3) Evaluate cytokine manipulations as a technique to diminish pain responses using specific cytokine antagonists and endogenous ~anti-cytokines.~ Quantitative immunocytochemistry, in situ hybridization, specific pharmacological agents and nociceptive behavioral assays will be used to resolve these specific aims. When completed, these studies will provide: Information on the kinetics of spinal inflammatory cytokine expression and glial activation following distinct nerve injuries known to produce differential neuropathic behaviors Data on the origin of increased spinal expression of specific cytokines Preliminary data to support new pharmacological approaches to neuropathic pain A foundation for further understanding the neuroimmune response of nerve injury and the relationship to other central nervous system inflammatory disease states. Data to guide future studies that evaluate the role of cytokines and neuroimmune activation in chronic pain.
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