The role of nitric oxide and prostaglandin signaling pathways in spinal nociceptive processing in chronic inflammation

Resveratrol Inhibition of the WNT/β-Catenin Pathway following Discogenic Low Back Pain

Low back pain (LBP) management is an important clinical issue. Inadequate LBP control has consequences on the mental and physical health of patients. Thus, acquiring new information on LBP mechanism would increase the available therapeutic tools. Resveratrol is a natural compound with many beneficial effects. In this study, we investigated the role of resveratrol on behavioral changes, inflammation and oxidative stress induced by LBP. Ten microliters of Complete Freund’s adjuvant (CFA) was injected in the lumbar intervertebral disk of Sprague Dawley rats to induce degeneration, and resveratrol was administered daily. Behavioral analyses were performed on day zero, three, five and seven, and the animals were sacrificed to evaluate the molecular pathways involved. Resveratrol administration alleviated hyperalgesia, motor disfunction and allodynia. Resveratrol administration significantly reduced the loss of notochordal cells and degenerative changes in the intervertebral disk. From the molecular point of view, resveratrol reduced the 5th/6th lumbar (L5–6) spinal activation of the WNT pathway, reducing the expression of WNT3a and cysteine-rich domain frizzled (FZ)8 and the accumulation of cytosolic and nuclear β-catenin. Moreover, resveratrol reduced the levels of TNF-α and IL-18 that are target genes strictly downstream of the WNT/β-catenin pathway. It also showed important anti-inflammatory activities by reducing the activation of the NFkB pathway, the expression of iNOS and COX-2, and the levels of PGE2 in the lumbar spinal cord. Moreover, resveratrol reduced the oxidative stress associated with inflammation and pain, as shown by the observed reduced lipid peroxidation and increased GSH, SOD, and CAT activities. Therefore, resveratrol administration controlled the WNT/β-catenin pathway and the related inflammatory and oxidative alterations, thus alleviating the behavioral changes induced by LBP.

Contralateral monoarthritis exacerbated chronic constriction injury-induced pain hypersensitivity through upregulating inducible nitric oxide synthase

Introduction

High comorbidity of osteoarthritis (OA) and neuropathic pain has been reported in aged patients. Evidence shows that central sensitization of pain processing occurs in late-phase OA and may facilitate the development of neuropathic pain. Few studies reveal whether acute monoarthritis (MA) aggravates neuropathic pain on the opposite side of the body from the injury.

Methods

To address whether neuropathic pain is affected by contralateral MA through distinct inflammatory pathway, MA was induced by intra-articular injection of complete Freund’s adjuvant (CFA) into the right tibiotarsal joint, and neuropathic pain was established by chronic constriction injury (CCI) of the left sciatic nerve.

Results

We observed that MA aggravated mechanical allodynia and thermal hyperalgesia in CCI rats. Furthermore, MA affected the other side of the spinal cord in multiple aspects, including the upregulation of iNOS mRNA and the enhancement of forskolin-induced facilitation of excitatory synaptic transmission in the spinal cord dorsal horn substantia gelatinosa neurons.

Discussion

Interestingly, intrathecal injection of 1400W, an antagonist of iNOS, attenuated intensity of pain behaviors in CCI rats with contralateral MA to similar levels in CCI rats without MA, and also normalized the facilitatory effect of forskolin on excitatory synaptic transmission in the spinal cord dorsal horn neurons in contralateral MA rats. Therefore, contralateral MA worsened CCI-induced pain hypersensitivity probably through upregulating iNOS and enhancing the facilitation of synaptic transmission following CCI.

Conclusion

Inhibiting the iNOS might be a potential therapeutic strategy for concurrent OA and neuropathic pain.

The Mammary Microenvironment in Mastitis in Humans, Dairy Ruminants, Rabbits and Rodents: A One Health Focus

The One Health concept promotes integrated evaluation of human, animal, and environmental health questions to expedite advances benefiting all species. A recognition of the multi-species impact of mastitis as a painful condition with welfare implications leads us to suggest that mastitis is an ideal target for a One Health approach. In this review, we will evaluate the role of the mammary microenvironment in mastitis in humans, ruminants and rabbits, where appropriate also drawing on studies utilising laboratory animal models. We will examine subclinical mastitis, clinical lactational mastitis, and involution-associated, or dry period, mastitis, highlighting important anatomical and immunological species differences. We will synthesise knowledge gained across different species, comparing and contrasting disease presentation. Subclinical mastitis (SCM) is characterised by elevated Na/K ratio, and increased milk IL-8 concentrations. SCM affecting the breastfeeding mother may result in modulation of infant mucosal immune system development, whilst in ruminants notable milk production losses may ensue. In the case of clinical lactational mastitis, we will focus on mastitis caused by Staphylococcus aureus and Escherichia coli. Understanding of the pathogenesis of involution-associated mastitis requires characterization of the structural and molecular changes occurring during involution and we will review these changes across species. We speculate that milk accumulation may act as a nidus for infection, and that the involution 'wound healing phenotype' may render the tissue susceptible to bacterial infection. We will discuss the impact of concurrent pregnancy and a 'parallel pregnancy and involution signature' during bovine mammary involution.

Genetic variations in interleukin-8 and interleukin-10 are associated with pain, depressed mood, and fatigue in lung cancer patients

CONTEXT

A report by the National Cancer Institute identified that an important gap in symptom research is the investigation of multiple symptoms of cancer that might identify common biological mechanisms among cancer-related symptoms.

OBJECTIVES

We applied novel statistical methods to assess whether variants of 37 inflammation genes may serve as biologic markers of risk for severe pain, depressed mood, and fatigue in non-Hispanic white patients with non-small cell lung cancer.

METHODS

Pain, fatigue, and depressed mood were assessed before cancer treatment. We used a generalized, multivariate, classification tree approach to explore the influence of single-nucleotide polymorphisms in the inflammation genes in pain, depressed mood, and fatigue in lung cancer patients.

RESULTS

Among patients with advanced-stage disease, interleukin (IL)-8-T251A was the most relevant genetic factor for pain (odds ratio [OR] = 2.18, 95% CI = 1.34-3.55, P = 0.001), depressed mood (OR = 0.37, 95% CI = 0.14-1.0), and fatigue (OR = 2.07, 95% CI = 1.16-3.70). Among those with early-stage non-small cell lung cancer, variants in the IL-10 receptor were relevant for fatigue among women. Specifically, women with Lys_Glu or Glu_Glu genotype in the IL-10 gene had a 0.49 times lower risk of severe fatigue compared with those with Lys_Lys genotype (OR = 0.49, 95% CI = 0.25-0.92, P = 0.027). Among men with early-stage lung cancer, a marginal significance was observed for IL-1A C-889T, C/T, or T/T genotypes. These men had a lower risk of severe fatigue compared with those with C/C genotype (OR = 0.38, 95% CI = 0.13-1.06).

CONCLUSION

The interaction of multiple inflammation genes, along with nongenetic factors, underlies the occurrence of symptoms. IL-8 and IL-10 may serve as potential targets for treating multiple symptoms of cancer.

Symptom clusters of pain, depressed mood, and fatigue in lung cancer: assessing the role of cytokine genes

PURPOSE

Symptom clusters, the multiple, co-occurring symptoms experienced by cancer patients, are debilitating and affects quality of life. We assessed if a panel of immune-response genes may underlie the co-occurrence of severe pain, depressed mood, and fatigue and help identify patients with severe versus non-severe symptom clusters.

METHODS

Symptoms were assessed at presentation, prior to cancer treatment in 599 newly diagnosed lung cancer patients. We applied cluster analyses to determine the patients with severe versus non-severe symptom clusters of pain, depressed mood, and fatigue.

RESULTS

Two homogenous clusters were identified. One hundred sixteen patients (19 %) comprised the severe symptom cluster, reporting high intensity of pain, depressed mood, and fatigue and 183 (30 %) patients reported low intensity of these symptoms. Using Bayesian model averaging methodology, we found that of the 55 single nucleotide polymorphisms assessed, an additive effect of mutant alleles in endothelial nitric oxide synthase (-1474 T/A) (posterior probability of inclusion (PPI) = 0.78, odds ratio (OR) = 0.54, 95 % credible interval (CI) = (0.31, 0.93)); IL1B T-31C (PPI = 0.72, OR = 0.55, 95 % CI = (0.31, 0.97)); TNFR2 Met(196)Arg (PPI = 0.70, OR = 1.85, 95 % CI = (1.03, 3.36)); PTGS2 exon 10+837T > C (PPI = 0.69, OR = 0.54, 95 % CI = (0.28, 0.99)); and IL10RB Lys(47)Glu (PPI = 0.68; OR = 1.74; 95 % CI = (1.04, 2.92)) were predictive for symptom clusters.

CONCLUSIONS

Genetic polymorphisms may facilitate identification of high-risk patients and development of individualized symptom therapies.

Masseter inflammation differentially regulates three nitric oxide synthases in the rat trigeminal subnucleus caudalis

OBJECTIVE

The aim of the present study was to evaluate changes in expression levels of three nitric oxide synthases (NOSs), namely inducible NOS (iNOS), neuronal NOS (nNOS) and endothelial NOS (eNOS), in the subnucleus caudalis of the trigeminal sensory nuclear complex (Vc) under experimental myositis conditions.

DESIGN

Male Sprague Dawley rats were injected with an inflammatory agent, complete Freund's adjuvant (CFA), or capsaicin in the masseter muscle. The brainstem region containing the Vc was extracted at both immediate (30 and 60 min) and longer (1, 3, 7 days) time points to examine the changes in the three NOS protein levels via the Western blot technique. Subsequently, the RT-PCR experiments were carried out to verify the changes in iNOS mRNA.

RESULTS

Following the injections of CFA, there were no significant changes in the level of the three NOS proteins at the immediate time points. However, there was a significant upregulation of iNOS mRNA and protein 3 days after CFA-induced inflammation. Neither nNOS nor eNOS showed significant changes in the protein level at any of the longer time points. Capsaicin injection in the masseter, which we recently reported to upregulate all three NOS at the immediate time points, did not result in significant changes at longer time points.

CONCLUSION

Acute and chronic muscle inflammation differentially modulates the expression of the three NOS in the Vc. These data suggest that the contribution of each NOS in craniofacial muscle pain processing under inflammatory conditions may be anticipated with distinct temporal profiles.

Chronic stress induces transient spinal neuroinflammation, triggering sensory hypersensitivity and long-lasting anxiety-induced hyperalgesia

Chronic stressful events induce biochemical, physiological and psychological changes, resulting in stress-related neuropsychiatric disorders, such as anxiety or depression. Using repeated social defeat as a stressful event model, we show that this preclinical paradigm induces a transient increase in the expression of the genes encoding the pro-inflammatory molecules iNOS and COX-2. We provide the first demonstration that chronic stress affects spinal plasticity through a mechanism involving local neuroinflammation. The functional consequences of such neuroinflammation are associated with a transient decrease in the mechanical nociceptive threshold. Administration of the cholecystokinin(CCK)-2 receptor antagonist, CI-988, directly into the Rostral Ventromedial Medulla reverses the chronic stress-induced decrease in the nociceptive threshold. These data strongly suggest that chronic stress induces a spinal neuroinflammation associated with transient sensory hypersensitivity involving the activation of CCK-dependent nociceptive descending facilitatory pathways. Pharmacological data show that chronic social stress-induced long-lasting state of anxiety is not responsible for maintaining the spinal neuroinflammation and, therefore, for the associated sensory hypersensitivity. Conversely, an evaluation of pain-related behavior in the formalin model indicates that anxiety is directly related to prolonged hyperalgesia prevented by systemic benzodiazepine or CCK-2 receptor antagonist treatments. The present study highlights the adverse effects of chronic stress on spinal neuroinflammation triggering sensory hypersensitivity. Exploration of this phenomenon points out the divergence between pain sensitivity and anxiety-induced hyperalgesia, which is in agreement with clinical observations. Altogether, these data open up new perspectives for clinical research devoted to the evaluation and treatment of pain in anxio-depressive patients.

Complete Freund's adjuvant-induced intervertebral discitis as an animal model for discogenic low back pain

BACKGROUND

Although numerous animal models for low back pain associated with intervertebral disk (IVD) degeneration have been proposed, insufficient data have been provided to make any conclusions regarding pain. Our aim in this study was to determine the reliability of complete Freund's adjuvant (CFA) injection into the rat spine as an animal model representing human discogenic pain.

METHODS

We studied IVD degenerative changes with pain development after a 10-microL CFA injection into the L5-6 IVD of adult rats using behavioral, histologic, and biochemical studies. Serial histologic changes were analyzed to detect degenerative changes. Expression of calcitonin gene-related peptide (CGRP), prostaglandin E (PGE), and inducible nitric oxide synthase (iNOS) were determined using immunohistochemistry or real-time polymerase chain reaction as support data for pain development. In addition, CGRP immunoreactivity (ir) at the IVD was considered indirect evidence of neural ingrowth into the IVD.

RESULTS

There was a significant increase of the hindpaw withdrawal response in the CFA group until 7 wk postoperatively (P < 0.05). Histologic analyses revealed progressive degenerative changes of the disks without any damage in adjacent structures, including nerve roots. In the CGRP-ir staining study, the bilateral dorsal horns and IVD had positive ir after intradiscal CFA injection. CGRP mRNA expression was increased in the dorsal root ganglion (DRG) at 2 and 4 wk, whereas PGE and iNOS mRNAs were markedly increased at 2 wk. The increment of CGRP expression was higher in allodynic rats compared with nonallodynic rats.

CONCLUSION

Intradiscal CFA injection led to chronic disk degeneration with allodynia, which was suggested by pain behavior and expression of pain-related mediators. The increment of CGRP, PGE, and iNOS also suggest pain-related signal processing between the IVD and the neural pathway in this animal model. This animal model may be useful for future research related to the pathophysiology and development of novel treatment for spine-related pain.

Capnellene, a natural marine compound derived from soft coral, attenuates chronic constriction injury-induced neuropathic pain in rats

BACKGROUND AND PURPOSE

Natural compounds obtained from marine organisms have received considerable attention as potential sources of novel drugs for treatment of human inflammatory diseases. Capnellene, isolated from the marine soft coral Capnella imbricate, 4,4,6a-trimethyl-3-methylene-decahydro-cyclopenta[]pentalene-2,3a-diol (GB9) exhibited anti-inflammatory actions on activated macrophages in vitro. Here we have assessed the anti-neuroinflammatory properties of GB9 and its acetylated derivative, acetic acid 3a-hydroxy-4,4,6a-trimethyl-3-methylene-decahydro-cyclopenta[]pentalen-2-yl ester (GB10).

EXPERIMENTAL APPROACH

Effects of GB9 or GB10 on the expression of inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2) in interferon-gamma (IFN-gamma)-stimulated mouse microglial BV2 cells were measured by Western blot. The in vivo effects of these compounds were examined in the chronic constriction injury (CCI) rat model of neuropathic pain, measuring thermal hyperalgesia, and microglial activation and COX-2 protein in lumbar spinal cord, by immunohistochemistry.

KEY RESULTS

In BV2 cells, GB9 and GB10 inhibited the expression of iNOS and COX-2, stimulated by IFN-gamma. Intrathecal administration of GB9 and GB10 inhibited CCI-induced nociceptive sensitization and thermal hyperalgesia in a dose-dependent manner. Intraperitoneal injection of GB9 inhibited CCI-induced thermal hyperalgesia and also inhibited CCI-induced activation of microglial cells and up-regulation of COX-2 in the dorsal horn of the lumbar spinal cord ipsilateral to the injury.

CONCLUSION AND IMPLICATIONS

Taken together, these data indicate that the marine-derived capnellenes, GB9 and GB10, had anti-neuroinflammatory and anti-nociceptive properties in IFN-gamma-stimulated microglial cells and in neuropathic rats respectively. Therefore, capnellene may serve as a useful lead compound in the search for new therapeutic agents for treatment of neuroinflammatory diseases.

Histochemical characterization, distribution and morphometric analysis of NADPH diaphorase neurons in the spinal cord of the agouti

We evaluated the neuropil distribution of the enzymes NADPH diaphorase (NADPH-d) and cytochrome oxidase (CO) in the spinal cord of the agouti, a medium-sized diurnal rodent, together with the distribution pattern and morphometrical characteristics of NADPH-d reactive neurons across different spinal segments. Neuropil labeling pattern was remarkably similar for both enzymes in coronal sections: reactivity was higher in regions involved with pain processing. We found two distinct types of NADPH-d reactive neurons in the agouti's spinal cord: type I neurons had large, heavily stained cell bodies while type II neurons displayed relatively small and poorly stained somata. We concentrated our analysis on type I neurons. These were found mainly in the dorsal horn and around the central canal of every spinal segment, with a few scattered neurons located in the ventral horn of both cervical and lumbar regions. Overall, type I neurons were more numerous in the cervical region. Type I neurons were also found in the white matter, particularly in the ventral funiculum. Morphometrical analysis revealed that type I neurons located in the cervical region have dendritic trees that are more complex than those located in both lumbar and thoracic regions. In addition, NADPH-d cells located in the ventral horn had a larger cell body, especially in lumbar segments. The resulting pattern of cell body and neuropil distribution is in accordance with proposed schemes of segregation of function in the mammalian spinal cord.

Sensory nerves have altered function contralateral to a monoarthritis and may contribute to the symmetrical spread of inflammation

Rheumatoid arthritis (RA) and rat models of RA exhibit symmetrical mirror-image spread. Many studies have sought to understand the underlying mechanisms and have reported contralateral effects that are manifested in many different forms. It is now well accepted that neurogenic mechanisms contribute to the symmetrical spread of inflammation. However, very few investigators have directly assessed changes in contralateral nerve function and there is a paucity of data. In the present study our aim was to investigate whether there are changes, in particular in the nervous system but also in the vascular system contralateral to an inflamed rat knee joint, that might precede overt inflammation and symmetrical spread. Three to five days following Complete Freund's Adjuvant (CFA) injection we found spontaneous antidromic (away from the CNS) activity in the homologous sensory nerve contralateral to the inflamed joint. Antidromic activity of this nature is known to result in the peripheral release of pro-inflammatory and vasoactive neuropeptides. Importantly, this activity was modulated by systemic analgesic treatment. Furthermore, levels of Evans blue dye extravasation were significantly increased in the joint contralateral to inflammation, indicating altered vascular function. These data suggest that contralateral increases in sensory neural activity and vascular function may account for the symmetrical spread of RA, and that early analgesic treatment may prevent or delay the spread of this debilitating disease.

Acute intracerebroventricular administration of palmitoylethanolamide, an endogenous peroxisome proliferator-activated receptor-alpha agonist, modulates carrageenan-induced paw edema in mice

Peroxisome proliferator-activated receptor (PPAR)-alpha is a nuclear transcription factor. Although the presence of this receptor in different areas of central nervous system (CNS) has been reported, its role remains unclear. Palmitoylethanolamide (PEA), a member of the fatty-acid ethanolamide family, acts peripherally as an endogenous PPAR-alpha ligand, exerting analgesic and anti-inflammatory effects. High levels of PEA in the CNS have been found, but the specific function of this lipid remains to be clarified. Using carrageenan-induced paw edema in mice, we show that i.c.v. administration of PEA may control peripheral inflammation through central PPAR-alpha activation. A single i.c.v. administration of 0.01 to 1 microg of PEA, 30 min before carrageenan injection, reduced edema formation in the mouse carrageenan test. This effect was mimicked by 0.01 to 1 microg of GW7647 [2-[[4-[2-[[(cyclohexylamino)carbonyl](4-cyclohexylbutyl)amino]ethyl]phenyl]thio]-2-methylpropanoic acid], a synthetic PPAR-alpha agonist. Moreover, central PEA administration significantly reduced the expression of the proinflammatory enzymes cyclooxygenase-2 and inducible nitric-oxide synthase, and it significantly restored carrageenan-induced PPAR-alpha reduction in the spinal cord. To investigate the mechanism by which i.c.v. PEA attenuated the development of carrageenan-induced paw edema, we evaluated inhibitor kappaB-alpha (I kappa B-alpha) degradation and nuclear factor-kappaB (NF-kappaB) p65 activation in the cytosolic or nuclear extracts from spinal cord tissue. PEA prevented IkB-alpha degradation and NF-kappaB nuclear translocation, confirming the involvement of this transcriptional factor in the control of peripheral inflammation. The obligatory role of PPAR-alpha in mediating the effects of PEA was confirmed by the lack of the compounds anti-inflammatory effects in mutant mice lacking PPAR-alpha. In conclusion, our data show for the first time that PPAR-alpha activation in the CNS can control peripheral inflammation.

Prostaglandins, glutamate and nitric oxide synthase mediate nitroglycerin-induced hyperalgesia in the formalin test

Increasing evidence supports a possible role for nitric oxide (NO) in the transmission of pain signals and in the development of central mechanisms of hyperalgesia. Previously, we have shown that nitroglycerin, an NO donor, is able to induce a long-lasting hyperalgesic state in rats. Nitroglycerin-induced hyperalgesia can be detected as an increase in the nociceptive behavior evoked by the formalin test. In the present study we investigated the possible mediators in the nitroglycerin-induced hyperalgesic state. Male Sprague-Dawley rats were injected with nitroglycerin and pretreated with indomethacin, 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate (MK-801) or N(omega)-nitro-L-arginine methyl ester (L-NAME). The results obtained showed that inhibition of prostaglandins or NO synthesis prevents nitroglycerin-induced hyperalgesia in Phase II of the formalin test. A similar inhibitory effect was also observed following pretreatment with the glutamate antagonist MK801. The present findings point to the role of prostaglandins, NO synthesis and glutamate activity in the induction of nitroglycerin-induced hyperalgesia.

GW274150, a novel and highly selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), shows analgesic effects in rat models of inflammatory and neuropathic pain

Nitric oxide (NO), synthesised by different isoforms of nitric oxide synthase (NOS), has been linked with the development and maintenance of nociception. We studied the role of the inducible isoform, iNOS, in two different rat pain models with an inflammatory component. iNOS was immunohistochemically detected locally in the paw 6h after Freund's Complete Adjuvant (FCA) injection, showing a plateau at 24-72 h and falling slowly in the following weeks. This correlated with the late phase of the hypersensitivity to pain revealed in the behavioural tests. A highly selective iNOS inhibitor GW274150 (1-30 mg/kg orally, 24h after FCA) suppressed the accumulation of nitrite in the inflamed paw indicating substantial iNOS inhibition. At the same time it partially reversed FCA-induced hypersensitivity to pain and edema in a dose-dependent manner. After Chronic Constriction Injury (CCI) surgery to the sciatic nerve, iNOS presence was only detected locally in the region of the nerve (inflammatory cells). GW274150 (3-30 mg/kg orally, 21 days after surgery) also reversed significantly the CCI-associated hypersensitivity to pain. No iNOS was detectable in dorsal root ganglia, spinal cord or brain in either model. This study demonstrates a role for peripherally-expressed iNOS in pain conditions with an inflammatory component and the potential value of iNOS inhibitors in such conditions.

Preemptive effects of intrathecal cyclooxygenase inhibitor or nitric oxide synthase inhibitor on thermal hypersensitivity following peripheral nerve injury

The present study provides an important implication for the management of chronic neuropathic pain, focusing on prostaglandin (PG) and nitric oxide (NO) in the spinal cord. To determine if spinally administered cyclooxygenase (COX) inhibitor or nitric oxide synthase (NOS) inhibitor had preemptive analgesia on thermal hypersensitivity induced by chronic constrictive nerve injury, Sprague-Dawley rats were chronically implanted with an intrathecal (i.t.) catheter. The left sciatic nerve was loosely ligated with 2-mm polyethylene tubing to produce painful mononeuropathy. Animals received tenoxicam (7.5, 15 or 30 micromol/10 microl, i.t.), NS-398 (15 or 30 micromol), or L-NAME (30, 150 or 300 micromol) immediately before the nerve injury, followed by daily injection extending into the four postoperative days. The hindpaw was immersed into a hot (42 degrees C, 44 degrees C and 46 degrees C) or cold (10 degrees C) water bath. The paw immersion test revealed significant thermal hyperalgesia and allodynia 5 day after nerve injury in vehicle control animals. Tenoxicam (7.5, 15 or 30 micromol) or L-NAME (30, 150 or 300 micromol) dose-dependently attenuated hyperalgesia and allodynia. Equimolar dose of NS-398 (15 or 30 micromol) also diminished these nociceptive behaviors. Higher dose of either drug primarily produced longer duration of inhibition. The inhibitory effect of tenoxicam (30 micromol) on hyperalgesia was more effective than that of an equimolar dose of NS-398 or L-NAME. These results demonstrated that intrathecally administered COX inhibitor or NOS inhibitor provides preemptive analgesia on thermal hypersensitivity following chronic constrictive nerve injury in rats.

Expression of gonadotropin-releasing hormone and gonadotropin-releasing hormone receptor in sheep spinal cord

Consistent with its neuroendocrine role, gonadotropin-releasing hormone (GnRH) is located principally within the hypothalamus, although extra-hypothalamic expression has been reported. The present study characterized the expression of GnRH and GnRH receptor (GnRH-R) in sheep spinal cord using real-time PCR and immunocytochemistry. Both GnRH and GnRH-R mRNA were detected in sheep spinal cord. Expression of GnRH peptide was localized to discrete locations in the spinal cord, including lamina X (the area surrounding the central canal) and motoneurons in the ventral horn. Although there is no known functional role for GnRH in spinal cord, a role as a potential neurotransmitter/neuromodulator is supported by the expression of both GnRH and GnRH-R in this tissue.

Differential salutary effects of nonselective and selective COX-2 inhibitors in postoperative ileus in rats

BACKGROUND

Postoperative ileus (PI) is a common surgical complication, the treatment of which consists of supportive measures.

AIM

The effects of several cyclooxygenase (COX) inhibitors and their interaction with L-arginine/nitric oxide synthase (NOS) pathway were tested in a rat PI model.

METHODS

Intestinal transit was measured as Evans blue migration after skin incision, laparotomy, or laparotomy followed by evisceration and gut handling.

RESULTS

In contrast to a selective inducible NOS (iNOS) blocker, L-N(6)-(1-iminoethyl)lysine hydrochloride (L-NIL), N(omega)-nitro-L-arginine methyl ester (L-NAME) reversed the additional inhibitory effects of gut manipulation after laparotomy on the gastrointestinal transit (GI) in a dose-dependent, L-arginine-sensitive manner. Laparotomy and manipulations of small intestine increased blood plasma nitrites and nitrates level (NOx), an effect preventable by L-NAME. Indomethacin, resveratrol (selective COX-1 blocker), and COX-2 antagonists, nimesulide, NS-398, DuP-697, and L-752860, attenuated the additional inhibitory effects of gut manipulation following laparotomy in a dose-dependent manner. In contrast, only nimesulide, NS-398, DuP-697, and L-752860 partly, but significantly, reversed the effects of laparotomy on the intestinal transit. Administration of L-NAME subsequent to COX inhibitors abolished the salutary effects of the latter, implying that at least the synthesis of either NO or prostanoids must remain unaffected to enable a return of GI transit during the postoperative period.

CONCLUSION

In addition to NO synthesized by constitutive NOS (cNOS), prostaglandins produced by both COX-1 and COX-2 participate in the pathogenesis of PI, albeit in different pathological mechanisms. Thus laparotomy stimulated COX-2 activity, whereas gut manipulation led to an excessive cNOS activity and prostaglandin synthesis by COX-1.

Pharmacodynamics and enantioselective pharmacokinetics of racemic carprofen in the horse

Carprofen is a nonsteroidal anti-inflammatory drug of the 2-arylpropionate subclass. It contains a single chiral centre and exists in two enantiomeric forms. In this study rac-carprofen, at two dosages, 0.7 and 4.0 mg/kg, and placebo were administered i.v. to six New Forest horses in a three period cross-over study. The concentration-time profiles were established for R(-) and S(+)-carprofen for plasma and both inflamed (exudate) and noninflamed (transudate) tissue cage fluids. R(-)-carprofen was the predominant enantiomer in all three fluids, as indicated by plasma area under the curve (AUC) values for R(-) and S(+)-carprofen of 117.4 and 22.6 microg h/mL (low dose carprofen) and 557.5 and 138.1 microg h/mL (high dose carprofen) respectively. Penetration of both enantiomers into exudate was slow and limited and passage into transudate was even lower. The pharmacodynamics of rac-carprofen was investigated at both the molecular level and in terms of the ability to suppress components of the tissue cage inflammatory response. Low dose carprofen produced only moderate and transient inhibition of serum thromboxane (Tx)B2 but failed to affect exudate prostaglandin (PG)E2 concentrations, whilst suppression of exudate leukotriene (LT)B4 and beta-glucuronidase was not significant. High dose carprofen produced greater and more persistent inhibition of serum TxB2 and virtually abolished exudate PGE2 synthesis. Some inhibition of LTB4 and beta-glucuronidase in exudate was also obtained. At both dosages rac-carprofen reduced the swelling produced by intradermal bradykinin injection but only high dose carprofen was anti-inflammatory as indicated by suppression of temperature rise over exudate tissue cages and neither dose affected leucocyte numbers in exudate. When considered in conjunction with previous data on carprofen, the present findings indicate that carprofen is not a selective inhibitor of cyclooxygenase (COX) isoenzymes, COX-1 and COX-2 in the horse, although it may show some preference for COX-2 inhibition. Because low dose carprofen, which is the clinically recommended dosage, produces minimal inhibition of COX, it is likely to achieve its therapeutic effects at least partially through other pathways, possibly including weak to moderate inhibition of 5-lipoxygenase and of enzyme release. The good safety margin of carprofen in clinical use might also be explained by weak COX inhibition and by other actions at the molecular level.

Effects of nimesulide on nitric oxide-induced hyperalgesia in humans--a neurophysiological study

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to induce analgesia mainly via the inhibition of cyclo-oxygenase. Several reports suggest that chronic pain is mediated by central sensitization, an N-methyl-D-aspartate (NMDA)-mediated phenomenon influenced by cyclo-oxygenase activity and nitric oxide (NO). In this double-blind study, we evaluated the effects of a preferential inhibitor of the inducible isoform of cyclo-oxygenase-2, nimesulide, on the spinal nociceptive flexion reflex (RIII reflex) before and after administration of an NO donor in healthy volunteers. Nimesulide caused a reduction of the RIII reflex area, which persisted after NO donor administration. Conversely, in the placebo group the RIII reflex area significantly increased following the administration of the NO donor. These data suggest a central effect for nimesulide, possibly related to a reduction of nociceptive activity at spinal level.

Nitric oxide synthase/PGE(2) cross-talk in rat submandibular gland

It is known that nitric oxide modulates the prostaglandin generation. However, little is known about the regulatory action of prostaglandin on nitric oxide production. There is a molecular cross-talk between nitric oxide and prostaglandin. Here, we examined biochemical signalling pathways coupled to the prostaglandin E(2) (PGE(2)) receptor related to nitric oxide synthase stimulation in rat submandibular gland. PGE(2) through the stimulation of its own receptor, triggered activation of phosphoinositide turnover (IPs), translocation of protein kinase C (PKC), stimulation of nitric oxide synthase activity (NOS) and increased production of cyclic GMP (cGMP). PGE(2) stimulation of NOS and cGMP production was blunted by agents interfering with calcium influx, calcium/calmodulin and phospholipase C (PLC) activities; while PKC inhibitor was able to stimulate PGE(2) effects. PGE(2) did not evoke amylase release, indicating that NOS/ cGMP pathway were not associated with this enzyme secretion. Our results suggest that this prostanoid could act as vasoactive chemical mediator through its ability to activate NOS-cGMP pathway via own gland membrane receptor.

Twenty-four hour exposure to prostaglandin downregulates prostanoid receptor binding but does not alter PGE(2)-mediated sensitization of rat sensory neurons

Although the tissue levels of prostaglandins are elevated for a relatively long period during injury or inflammation, few studies have been performed to assess the effects of prolonged prostaglandin exposure on receptor binding and activity in sensory neurons. Consequently, we examined whether unilateral inflammation or a 24 h exposure to prostaglandin E2 (PGE2) altered binding of this prostanoid in spinal cord tissue or in isolated sensory neurons, respectively. To assess functional changes in EP receptors, we also examined PGE2-induced cAMP production and the prostanoid-mediated augmentation of substance P release from isolated sensory neurons after acute and 24 h pretreatment with PGE2. Injection of complete Freund's adjuvant into the hindpaw decreased binding of PGE2 in ipsilateral, but not contralateral dorsal spinal cord 24 h after injection. This decrease in Bmax was blocked by administration of intrathecal ketorolac (10 nmol/microl/h) for 24 h prior to and throughout the period of inflammation, suggesting that the inflammation-induced decrease in binding is dependent on prostaglandin synthesis. In an analogous manner, treating sensory neurons grown in culture with 1 microM PGE2 for 24 h decreased [3H]-PGE2 binding by approximately 50% without altering binding affinity. Exposing neuronal cultures to 1 microM PGE2 for 24 h also reduced, but did not abolish the ability of the prostanoid to increase the production of cAMP. This treatment, however, did not significantly alter the ability of PGE2 to augment the evoked release of immunoreactive substance P from sensory neurons. These results demonstrate that under conditions that significantly downregulate PGE2 binding, sensory neurons are still capable of maintaining PGE2-mediated sensitization.

Therapeutic administration of nitric oxide synthase inhibitors reverses hyperalgesia but not inflammation in a rat model of polyarthritis

Nitric oxide (NO) has been postulated to play a role in pain as well as in inflammation. In the present studies, the effects of NO synthase (NOS) inhibitors on both pain and inflammation were examined in a rat model of polyarthritis. Female Lewis rats were injected intraperitoneally (i.p.) with peptidoglycan/polysaccharide (PG/PS) or saline to induce arthritis. Hind paw volume, response latency to thermal nociceptive stimulus and mechanical threshold were measured daily for the next 35 days. Paw inflammation, thermal hyperalgesia and mechanical allodynia developed in all rats that received PG/PS compared to saline. On day 19 (chronic inflammation phase), rats were given either N(G)-nitro-L-arginine methyl ester (L-NAME, non-selective NOS inhibitor, 100 mg/l), L-N (6)-(1-iminoethyl) lysine (L-NIL, selective inducible NOS inhibitor, 10 mg/l) or no drug in drinking water. By day 21, L-NAME treatment reversed the thermal hyperalgesia completely and this effect remained until day 35. Similarly, L-NIL treatment reversed thermal hyperalgesia from days 24 to 34. Neither treatment affected mechanical allodynia. Paw volume was not different between PG/PS treated and PG/PS plus L-NAME treated rats. However, the PG/PS plus L-NIL treatment produced an increase in paw volume greater than did PG/PS alone. Other rats were treated with PG/PS plus the antiinflammatory agent indomethacin (days 19-35). Indomethacin treatment reversed all the measured parameters, although the reversal of mechanical allodynia was only partial. These results suggest that NO is involved in thermal, but not mechanical sensory pathways and that the selective inhibition of inducible NOS activity exacerbates established inflammation.

The role of nitric oxide in nociception

Pharmacologic, electrophysiologic, and immunohistochemical studies have suggested a role of nitric oxide (NO) in nociception processing. Recent studies have indicated that NO may modulate spinal and sensory neuron excitability through multiple mechanisms that may underlie its distinctive roles in different pain states. Differential regulation of a family of NO-producing enzymes, NO synthases, contributes mainly to the complexity underlying the role of NO in nociception. This review summarizes the latest advances in our understanding of the contribution of NO to pain transduction. Possible cellular mechanisms regarding the connection between NO production and the abnormal sensation derived from different stimuli and pathologic conditions are discussed.

Overview of pain in the lame patient

Pain is often the limiting factor associated with joint disease. Pain results from the stimulation of nociceptors by excessive mechanical stimulation, chemical stimulation associated with the inflammatory process, or a combination of both. Even though OA is considered to be a noninflammatory disease, the mild degree of inflammation frequently associated with this condition can result in peripheral sensitization. This results in increased spontaneous activity and decreased activation threshold of nociceptive fibers. Activity of the primary joint afferents also leads to changes within the dorsal spinal horn, resulting in central sensitization and changes in the neural structures of the dorsal horn that facilitate and amplify the nociceptive response. Changes in the periarticular tissues correspond to the neurobiologic changes, resulting in increased stimulation of nociceptors caused by mechanical and chemical alterations resulting from tissue damage. Similar pathophysiologic events occur regardless of whether the initiating event is an acute joint injury or a chronic condition such as OA. The combination of these events results in the complex dynamic of joint pain. Because of this complex interaction of the musculoskeletal and nervous systems, it is difficult to imagine a single treatment that is effective for the alleviation of pain, because that agent would require inhibition of a number of stimulatory pathways. Instead, restoration of mechanical integrity, relief of peripheral inflammation, and blockage of central neurotransmission are all likely to have a role in the relief of joint pain and resolution of lameness.