Increased function of pronociceptive TRPV1 at the level of the joint in a rat model of osteoarthritis pain

Objectives Blockade of transient receptor potential vanilloid 1 (TRPV1) with systemic antagonists attenuates osteoarthritis (OA) pain behaviour in rat models, but on-target-mediated hyperthermia has halted clinical trials. The present study investigated the potential for targeting TRPV1 receptors within the OA joint in order to produce analgesia. Methods The presence of TRPV1 receptors in human synovium was detected using western blotting and immunohistochemistry. In a rat model of OA, joint levels of an endogenous ligand for TRPV1, 12- ydroxyeicosatetraenoic acid (12-HETE), were quantified using liquid chromatography-tandem mass spectrometry (LCMS/MS). Effects of peripheral administration of the TRPV1 receptor antagonist JNJ-17203212 on afferent fibre activity, pain behaviour and core body temperature were investigated. Effects of a spinal administration of JNJ-17203212 on dorsal horn neuronal responses were studied. Results We demonstrate increased TRPV1 immunoreactivity in human OA synovium, confirming the diseased joint as a potential therapeutic target for TRPV1-mediated analgesia. In a model of OA pain, we report increased joint levels of 12-HETE, and the sensitisation of joint afferent neurones to mechanical stimulation of the knee. Local administration of JNJ- 17203212 reversed this sensitisation of joint afferents and inhibited pain behaviour (weight-bearing asymmetry), to a comparable extent as systemic JNJ- 17203212, in this model of OA pain, but did not alter core body temperature. There was no evidence for increased TRPV1 function in the spinal cord in this model of OA pain. Conclusions Our data provide a clinical and mechanistic rationale for the future investigation of the therapeutic benefits of intra-articular administration of TRPV1 antagonists for the treatment of OA pain

A role for PPARα in the medial prefrontal cortex in formalin-evoked nociceptive responding in rats

Background and Purpose The nuclear hormone receptor, PPARα, and its endogenous ligands, are involved in pain modulation. PPARα is expressed in the medial prefrontal cortex (mPFC), a key brain region involved in both the cognitive-affective component of pain and in descending modulation of pain. However, the role of PPARα in the mPFC in pain responding has not been investigated. Here, we investigated the effects of pharmacological modulation of PPARα in the rat mPFC on formalin-evoked nociceptive behaviour and the impact of formalin-induced nociception on components of PPARα signalling in the mPFC. Experimental Approach The effects of intra-mPFC microinjection of a PPARα agonist (GW7647) or a PPARα antagonist (GW6471) on formalin-evoked nociceptive behaviour in rats were studied. Quantitative real-time PCR and LC-MS/MS were used to study the effects of intraplantar injection of formalin on PPARα mRNA expression and levels of endogenous ligands, respectively, in the mPFC. Key Results Intra-mPFC administration of GW6471, but not GW7647, resulted in delayed onset of the early second phase of formalin-evoked nociceptive behaviour. Furthermore, formalin-evoked nociceptive behaviour was associated with significant reductions in mPFC levels of endogenous PPARα ligands (N-palmitoylethanolamide and N-oleoylethanolamide) and a 70% reduction in PPARα mRNA but not protein expression. Conclusions and Implications These data suggest that endogenous ligands may act at PPARα in the mPFC to play a facilitatory/permissive role in second phase formalin-evoked nociceptive behaviour in rats.This work was funded by grants from Science Foundation Ireland (10/IN.1/B2976) and The Irish Research Council for Science, Engineering and Technologypeer-reviewe

A role for pparα in the medial prefrontal cortex in formalin-evoked nociceptive responding in rats

Background and PurposeThe nuclear hormone receptor, PPAR, and its endogenous ligands, are involved in pain modulation. PPAR is expressed in the medial prefrontal cortex (mPFC), a key brain region involved in both the cognitive-affective component of pain and in descending modulation of pain. However, the role of PPAR in the mPFC in pain responding has not been investigated. Here, we investigated the effects of pharmacological modulation of PPAR in the rat mPFC on formalin-evoked nociceptive behaviour and the impact of formalin-induced nociception on components of PPAR signalling in the mPFC. Experimental ApproachThe effects of intra-mPFC microinjection of a PPAR agonist (GW7647) or a PPAR antagonist (GW6471) on formalin-evoked nociceptive behaviour in rats were studied. Quantitative real-time PCR and LC-MS/MS were used to study the effects of intraplantar injection of formalin on PPAR mRNA expression and levels of endogenous ligands, respectively, in the mPFC. Key ResultsIntra-mPFC administration of GW6471, but not GW7647, resulted in delayed onset of the early second phase of formalin-evoked nociceptive behaviour. Furthermore, formalin-evoked nociceptive behaviour was associated with significant reductions in mPFC levels of endogenous PPAR ligands (N-palmitoylethanolamide and N-oleoylethanolamide) and a 70% reduction in PPAR mRNA but not protein expression. Conclusions and ImplicationsThese data suggest that endogenous ligands may act at PPAR in the mPFC to play a facilitatory/permissive role in second phase formalin-evoked nociceptive behaviour in rats. Linked ArticlesThis article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visi

A role for pparα in the medial prefrontal cortex in formalin-evoked nociceptive responding in rats

Background and PurposeThe nuclear hormone receptor, PPAR, and its endogenous ligands, are involved in pain modulation. PPAR is expressed in the medial prefrontal cortex (mPFC), a key brain region involved in both the cognitive-affective component of pain and in descending modulation of pain. However, the role of PPAR in the mPFC in pain responding has not been investigated. Here, we investigated the effects of pharmacological modulation of PPAR in the rat mPFC on formalin-evoked nociceptive behaviour and the impact of formalin-induced nociception on components of PPAR signalling in the mPFC. Experimental ApproachThe effects of intra-mPFC microinjection of a PPAR agonist (GW7647) or a PPAR antagonist (GW6471) on formalin-evoked nociceptive behaviour in rats were studied. Quantitative real-time PCR and LC-MS/MS were used to study the effects of intraplantar injection of formalin on PPAR mRNA expression and levels of endogenous ligands, respectively, in the mPFC. Key ResultsIntra-mPFC administration of GW6471, but not GW7647, resulted in delayed onset of the early second phase of formalin-evoked nociceptive behaviour. Furthermore, formalin-evoked nociceptive behaviour was associated with significant reductions in mPFC levels of endogenous PPAR ligands (N-palmitoylethanolamide and N-oleoylethanolamide) and a 70% reduction in PPAR mRNA but not protein expression. Conclusions and ImplicationsThese data suggest that endogenous ligands may act at PPAR in the mPFC to play a facilitatory/permissive role in second phase formalin-evoked nociceptive behaviour in rats. Linked ArticlesThis article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visi

Ability of Vital and Fluorescent Staining in the Differentiation of <i>Schistosoma haematobium</i> Live and Dead Eggs

This study reports (for the first time) the staining ability of vital (0.4% trypan blue and 1% neutral red) and fluorescent (Hoechst 33258) dyes to differentiate between live and dead Schistosoma haematobium (S. haematobium) eggs in human urine samples. Since S. haematobium egg is important in disease pathology, diagnosis, transmission, and drug development research, it is essential to be able to easily distinguish live eggs from dead ones. Staining is considered a way of enhancing the identification of live and dead eggs. Urine samples from school children were examined for the presence of S. haematobium eggs. Vital and fluorescent dyes were used to stain the samples that contained S. haematobium eggs, after which they were observed using light and fluorescent microscopes, respectively. The Hoechst 33258 provided a good staining outcome for differentiation between live and dead eggs, followed by 0.4% Trypan blue. Regarding the 1% neutral red stain, even though it provided some evidence of which egg was alive or dead, the distinction was not very clear; therefore, it could be useful when used in combination with other stains for egg viability determination. The benefits of this study will include assessing the effect of drugs on S. haematobium eggs in Schistosomiasis research