Diabetes mellitus is a serious and widespread disease in the western world. Neuropathy is the most common of the complications associated with protracted diabetes and the most notable presentation in many patients is some form of abnormal pain perception. This may range from continuous or episodic spontaneous pain to exaggerated pain in response to a mildly painful (hyperalgesia) or innocuous (allodynia) stimulus. The mechanisms underlying painful diabetic neuropathy are not known and there is no targeted therapy available, so that treatment is often restricted to sedatives that impede normal daily function. The objective of this research proposal is to investigate the etiology of sensory dysfunction using the diabetic rat model and cells grown in conditions of elevated glucose. Our previous findings show that diabetic rats exhibit behavioral indices of hyperalgesia and allodynia. This includes a protracted response to spinal delivery of substance P, suggesting that there is a component to hyperalgesia that lies beyond the peripheral nervous system. We have produced preliminary data that shows an increase in spinal levels of the enzyme cyclooxygenase-2 (COX-2), which has been implicated in a number of neuropathic pain states by its ability to produce prostaglandins. Our primary hypothesis is that hyperglycemia induces COX-2 protein and activity in the spinal cord, which leads to exaggerated prostaglindin release in response to sensory input and thereby promotes a spinally mediated hyperalgesia. We will test this hypothesis using diabetic rats exposed to the noxious sensory stimuli of either paw formalin injection or intrathecal excitatory neurotransmitters and make measurements using a variety of behavioral, morphologic, physiologic, biochemical and molecular techniques. We will also use selective pharmacologic agents to define the etiology of increased COX-2 expression in diabetic rats and also in cultured spinal cells (astrocytes and neurons). It is hoped that these studies will prompt development of therapeutics targeted at preventing or alleviating painful diabetic neuropathy.
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