- cGMP-dependent signaling pathways in spinal pain processing (2009)
- Oral presentation from 4th International Conference of cGMP Generators, Effectors and Therapeutic Implications ; Regensburg, Germany. 19–21 June 2009 Background: An exaggerated pain sensitivity is the dominant feature of inflammatory and neuropathic pain both in the clinical setting and in experimental animal models. It manifests as pain in response to normally innocuous stimuli (allodynia), increased response to noxious stimuli (hyperalgesia) or spontaneous pain, and can persist long after the initial injury is resolved. Research over the last decades has revealed that several signaling pathways in the spinal cord essentially contribute to the pain sensitization. To test the contribution of cGMP produced by NO-sensitive guanylyl cyclase (NO-GC) to pain sensitization, we investigated the localization of NO-GC in the spinal cord and in dorsal root ganglia, and we characterized the nociceptive behavior of mice deficient in NO-GC (GC-KO mice). Results: We show that NO-GC (β1 subunit) is distinctly expressed in neurons of the mouse spinal cord, while its distribution in dorsal root ganglia is restricted to non-neuronal cells. GC-KO mice exhibited a considerably reduced nociceptive behavior in models of inflammatory or neuropathic pain, but their responses to acute pain were not impaired. Moreover, GC-KO mice failed to develop pain sensitization induced by spinal administration of drugs releasing NO. Surprisingly, during spinal nociceptive processing cGMP produced by NO-GC may activate signaling pathways different from cGMP-dependent protein kinase I (cGKI), while cGKI can be activated by natriuretic peptide receptor-B (NPR-B) dependent cGMP production. Conclusion: Taken together, our results provide evidence that NO-GC has a dominant role in the development of exaggerated pain sensitivity during inflammatory and neuropathic pain. Furthermore, beside the NO-mediated cGMP synthesis, cGMP produced by NPR-B contributes to pain sensitization by activation of cGKI.
- Prostaglandin D2 is involved in the mechanisms underlying fever in rats (2007)
- Prostaglandin D2 (PGD2) is involved in a variety of physiological and pathophysiological processes, but its role in fever is poorly understood and the data obtained so far are rather controversial. Here we investigated the effects of central PGD2 delivery and of systemic prostaglandin D synthase (PGDS) or cyclooxygenase (COX) inhibition on core body temperature (TC) and on prostaglandin levels in the cerebrospinal fluid (CSF) of rats. Both PGE2 and PGD2 were detectable in CSF samples from control rats (6.2 ± 1.1 and 17.3 ± 3.1 pg/ml, respectively). Lipopolysaccharide (LPS) injection (50 μg i.p.) induced fever during the 5-hour observation period. Five hours after LPS injection, the levels of PGE2 and PGD2 were increased in the CSF about 90-fold (541.0 ± 47.5 pg/ml) and 5-fold (95.4 ± 23.1 pg/ml), respectively. Administration of PGD2 (50 - 500 ng) into the cisterna magna (i.c.m) evoked a delayed fever response in a dose-dependent manner that was accompanied by increased levels of PGE2 in the CSF. RT-PCR analyses revealed that the increased levels of PGE2 after PGD2 administration were not caused by up-regulation of COX-2 or microsomal prostaglandin E synthase 1 (mPGES-1) in the hypothalamus. Interestingly, i.c.m. pretreatment of animals with PGD2 considerably sustained the pyrogenic effects of i.c.m. administered PGE2. Pretreatment with a novel PGDS inhibitor, EDJ300520 (10 – 40 mg/kg p.o.), 1 h prior to the LPS injection impaired the LPS-induced increase of both PGD2 and PGE2 in the CSF and inhibited the fever response. In contrast, administration of EDJ300520 3 h after LPS injection did not ameliorate the LPS-induced fever. Accordingly, the concentration of PGE2 in the CSF was not decreased after EDJ300520 treatment. However, the CSF levels of PGD2 were reduced after administration of a high dose of EDJ300520 (40 mg/kg). We also investigated the effects of antipyretic drugs on the CSF levels of PGE2 and PGD2 during LPS-induced fever. Four antipyretic drugs with different mechanisms of action were used, including ibuprofen (5 - 20 mg/kg), celecoxib (10 - 50 mg/kg), SC560 5 - 20 mg/kg), and paracetamol (50 - 150 mg/kg). Each drug was used in three different doses and was orally administered 3 h after the LPS injection. All drugs were capable to attenuate the LPS-induced fever. The decrease of TC paralleled the reduction of PGE2 levels in the CSF. Of note, there was a tendency to reduced PGD2 levels in the CSF after treatment with the antipyretic drugs. However, only SC560 and the high dose of celecoxib (50 mg/kg) reduced the PGD2 levels significantly. In summary, our experiments underscore the pivotal role of PGE2 as the principal downstream mediator of fever. Moreover, we demonstrate that PGD2 is also involved in the mechanisms underlying fever. Our data suggest that PGD2 exerts an indirect pyrogenic effect by modulating the availability of PGE2 in the CSF. Additional studies are needed to explore the exact mechanism by
- Cysteine-rich protein 2 is a downstream effector of cGMP-dependent protein kinase I in nociception : poster presentation (2007)
- The experience of pain is mediated by a specialized sensory system, the nociceptive system. There is considerable evidence that the cGMP/cGMP kinase I (cGKI) signaling pathway modulates the nociceptive processing within the spinal cord. However, downstream targets of cGKI in this context have not been identified to date. In this study we investigated whether cysteine-rich protein 2 (CRP2) is a downstream effector of cGKI in the spinal cord and is involved in nociceptive processing. Immunohistochemistry of the mouse spinal cord revealed that CRP2 is expressed in superficial laminae of the dorsal horn. CRP2 is colocalized with cGKI and with markers of primary afferent C fibers. Importantly, the majority of CRP2 mRNA-positive dorsal root ganglion (DRG) neurons express cGKI and CRP2 is phosphorylated in a cGMP-dependent manner. To elucidate the functional role of CRP2 in nociception, we investigated the nociceptive behavior of CRP2-deficient (CRP2-/-) mice. Touch perception and acute thermal nociception were unaltered in CRP2-/- mice. However, CRP2-/- mice showed an increased nociceptive behavior in models of persistent pain as compared to wild type mice. Intrathecal administration of cGKI activating cGMP analogs increased the nociceptive behavior in wild type but not in CRP2-/- mice, indicating that the presence of CRP2 was essential for cGMP/cGKI-mediated nociception. These data indicate that CRP2 is a new downstream effector of cGKI-mediated spinal nociceptive processing and point to an inhibitory role of CRP2 in the generation of inflammatory pain.