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Phosphorylation of IB through IB kinase (IKK) is the first step in nuclear factor B (NF-B) activation and upregulation of NF-Bresponsive genes. Hence, inhibition of IKK activity may be expected to prevent injury-, infection-, or stress-induced upregulation of various proinflammatory genes and may thereby reduce hyperalgesia and inflammation. In the present study, we tested this hypothesis using a specific and potent IKK inhibitor (S1627). In an IKK assay, S1627 inhibited IKK activity with an IC 50 value of 10.0 Ϯ 1.2 nM. In cell culture experiments, S1627 inhibited interleukin (IL)-1␤-stimulated nuclear translocation and DNA-binding of NF-B. Plasma concentration time courses after intraperitoneal injection revealed a short half-life of 2.8 hr in rats. Repeated intraperitoneal injections were, therefore, chosen as the dosing regimen. S1627 reversed thermal and mechanical hyperalgesia at 3ϫ 30 mg/kg in the zymosan-induced paw inflammation model and reduced the inflammatory paw edema at 3ϫ 40 mg/kg. S1627 also significantly reduced tactile and cold allodynia in the chronic constriction injury model of neuropathic pain at 30 mg/kg once daily. The drug had no effect on acute inflammatory nociception in the formalin test and did not affect responses to heat and tactile stimuli in naive animals. As hypothesized, S1627 prevented the zymosan-induced nuclear translocation of NF-B in the spinal cord and the upregulation of NF-B-responsive genes including cyclooxygenase-2, tumor necrosis factor-␣, and IL-1␤. Our data indicate that IKK may prove an interesting novel drug target in the treatment of pathological pain and inflammation.

Nociceptin/orphanin FQ (N/OFQ) and nocistatin (NST) are two recently identified neuropeptides with opposing effects on several CNS functions, including spinal nociception. The cellular mechanisms that underlie this antagonism are not known. Here, we have investigated the effects of both peptides on synaptic transmission mediated by the three fast neurotransmitters l-glutamate, glycine, and GABA in the superficial layers of the rat spinal cord horn, which constitute the first important site of integration of nociceptive information in the pain pathway. NST selectively reduced transmitter release from inhibitory interneurons via a presynaptic Bordetella pertussis toxin-sensitive mechanism but left excitatory glutamatergic transmission unaffected. In contrast, N/OFQ only inhibited excitatory transmission. In the rat formalin test, an animal model of tonic pain in which N/OFQ exerts antinociceptive activity, NST induced profound hyperalgesia after intrathecal application. Similar to glycine and GABA(A) receptor antagonists, NST had no significant effects in the rat tail-flick test, a model of acute thermal pain. Our results provide a cellular basis for the antagonism of N/OFQ and NST and suggest the existence of a so far unidentified membrane receptor for NST. In addition, they support a role of NST as an endogenous inhibitor of glycinergic and GABAergic neurotransmission in the sensory part of the spinal cord and as a mediator of spinal hyperalgesia.

It is widely accepted that peripheral injury increases spinal inducible cyclooxygenase (COX-2) expression and prostaglandin E 2 (PGE 2 ) formation as key mediators of nociceptive sensitization. Here, we used inducible nitric oxide synthase (iNOS) genedeficient (iNOSϪ/Ϫ) mice to determine the contribution of iNOSderived nitric oxide (NO) to this process. iNOSϪ/Ϫ mice exhibited reduced thermal hyperalgesia after zymosan injection. Spinal NO and PGE 2 formation both remained at baseline levels, in contrast to wild-type (wt) mice. In wt mice reduced hyperalgesia similar to that seen in iNOSϪ/Ϫ mice was induced by local spinal, but not by systemic treatment with the iNOS inhibitor L-NIL, suggesting that the reduced heat sensitization in iNOSϪ/Ϫ mice was attributable to the lack of spinal rather than peripheral iNOS. Two additional observations indicate that the antinociceptive effects of iNOS inhibition are dependent on a loss of stimulation of PG synthesis. First, intrathecal injection of the COX inhibitor indomethacin, which exerted pronounced antinociceptive effects in wt mice, was completely ineffective in iNOSϪ/Ϫ mice. Second, treatment with the NO donor RE-2047 not only completely restored spinal PG production and thermal sensitization in iNOSϪ/Ϫ mice but also its sensitivity to indomethacin. In both types of mice induction of thermal hyperalgesia was accompanied by similar increases in COX-1 and COX-2 mRNA expression. The stimulation of PG production by NO therefore involves an increase in enzymatic activity, rather than an alteration of COX gene expression. These results indicate that NO derived from spinal iNOS acts as a fast inductor of spinal thermal hyperalgesia. Key words: nitric oxide; inducible nitric oxide synthase; zymosan; thermal hyperalgesia; paw edema; spinal microdialysis; L-NIL; RE-2047; prostaglandins; cyclooxygenaseAcute tissue damage is often accompanied by the fast development of hyperalgesia and allodynia (Andrew and Greenspan, 1999). Both peripheral mechanisms at the site of injury and central processes particularly in the spinal cord contribute to this phenomenon. Prostaglandins (PGs) Brune, 1994) as well as nitric oxide (NO) (Lawand et al., 1997) are produced in response to tissue damage peripherally and centrally. Whereas PGs are generally accepted to play a dominant role in nociceptive sensitization (Bley et al., 1998), the role of NO is less clear. Also some authors claim of an anti-nociceptive action of NO (Goettl and Larson, 1996;Hamalainen and Lovick, 1997), most favor a pronociceptive activity Kawabata et al., 1994;Chen and Levine, 1999). Part of this controversy may arise from the existence of three different isoenzymes of NO synthase (NOS) (Gonzalez-Hernandez and Rustioni, 1999), which may have distinct effects on nociception, and from the lack of specific inhibitors for these different isoforms. In the CNS including the spinal cord, NO is thought to be primarily produced by the neuronal isoform of NOS (nNOS) (Downen et al., 1999). However, endothelial NOS is also found in neur...