Untreated chronic pain leads to reorganization of neuronal circuits within the central nervous system (CNS), central sensitization, and enhanced pain. Chronic pain patients are often depressed, with higher morbidity probability. In animal models of chronic inflammation, paw and joint inflammation is accompanied by both thermal and mechanical hyperalgesia as well as increased nitric oxide (NO) production in plasma and joint synovial tissue. Nitric oxide is synthesized from arginine by NO synthase (NOS) which is found in at least three isoforms, constitutive endothelial (ceNOS) and neuronal (cnNOS) and inducible (iNOS). Although a major source of increased NO in inflammation is likely due to activity of iNOS is peripheral cells involved in the immune response, increased NOS activity is also found in spinal cord, the first relay site for pain processing. The relative activities of spinal iNOS and cnNOS in inflammatory pain and their contributions to hyperalgesia and inflammation are not known. The proposed studies are designed to test the hypothesis that spinal cnNOS activity contributes to both the inflammation and the hyperalgesia observed in chronic inflammatory pain. Chronic inflammation will be induced by administration of peptidoglycan/polysaccharide (PG/PS) or complete Freund s adjuvant (CFA) into rats, treatments that produce chronic inflammation of the limbs.
Specific aims are to (1) selectively inhibit activity of spinal cnNOS with selective inhibitors or antisense oligodeoxynucleotide (ODN) administered directly into the spinal cord and measuring peripheral inflammation and thermal and mechanical nociception. Expression of spinal cnNOS protein in spinal cord slices and dorsal root ganglia will be measured by immunocytochemistry at various time points during development and maintenance of inflammation. Total NOS activity is spinal cord homogenates will also be determined by measuring conversion of arginine to citrulline. These results will be compared to those obtained with spinal injection of missense ODN or vehicle. (2) develop a technique using a NO-sensitive microelectrode to measure real time in situ release of NO in the spinal cord of anesthetized rats. This technique will be used to measure spinal NO release following noxious mechanical stimulation of both inflamed and non-inflamed hindpaws. Effects of cnNOS inhibition on this release will be measured. Results of these studies will provide information about the role of spinal NO in initiation, development and maintenance or peripheral chronic inflammation and hyperalgesia. This information can be used to develop new drugs to treat chronic inflammatory pain or other types of chronic pain.
