Enhanced effects of co-administered dexamethasone and diclofenac on inflammatory pain processing and associated spinal c-Fos expression in the rat

Supramolecular Hydrogel Dexamethasone-Diclofenac for the Treatment of Rheumatoid Arthritis

Rheumatoid arthritis (RA) severely affects patients' quality of life and is commonly treated with glucocorticosteroids injections, like dexamethasone, which may have side effects. This study aimed to create a novel low dose of twin-drug hydrogel containing dexamethasone and diclofenac and explore its potential as a drug delivery system for an enhanced anti-inflammatory effect. Its characterization involved rheology, transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Furthermore, the hydrogel demonstrated thixotropic properties. The hydrogel exhibited no cytotoxicity against RAW 264.7 macrophages. Furthermore, the hydrogel demonstrated a significant anti-inflammatory efficacy by effectively downregulating the levels of NO, TNF-α, and IL-6 in lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. The co-delivery approach, when intra-articularly injected in adjuvant-induced arthritis (AIA) rats, significantly alleviated chronic inflammation leading to reduced synovitis, delayed bone erosion onset, and the downregulation of inflammatory cytokines. The biocompatibility and adverse effect evaluation indicated good biological safety. Furthermore, the hydrogel demonstrated efficacy in reducing NF-κB nuclear translocation in LPS-induced RAW 264.7 macrophages and inhibited p-NF-kB, COX-2, and iNOS expression both in RAW 264.7 macrophages and the joints of AIA rats. In conclusion, the findings indicate that the hydrogel possesses potent anti-inflammatory activity, which effectively addresses the limitations associated with free forms. It presents a promising therapeutic strategy for the management of RA.

Co-Administered Low Doses Of Ibuprofen And Dexamethasone Produce Synergistic Antinociceptive Effects On Neuropathic Mechanical Allodynia In Rats

Background

The traditional analgesics used to treat neuropathic pain such as anticonvulsants, opioids, and nonsteroidal anti-inflammatory drugs (NSAIDs) lack efficacy and/or carry unpleasant side effects. The present study aimed to investigate the synergistic antinociceptive effects of co-administered low doses of ibuprofen and dexamethasone in rats with trigeminal neuropathic pain.

Materials and methods

A Sprague-Dawley rat model for trigeminal neuropathic pain was produced using mal-positioned dental implants. The left mandibular second molar was extracted under anesthesia and replaced with a miniature dental implant to induce injury to the inferior alveolar nerve.

Results

Monotherapy with intraperitoneal injection of high-dose ibuprofen (30 mg/kg) or dexamethasone (10 mg/kg) but not low-dose ibuprofen (1, 5, 10 mg/kg) or dexamethasone (0.01, 1 mg/kg) attenuated the neuropathic mechanical allodynia in the rats with inferior alveolar nerve injury. We examined the synergistic antinociceptive effects of co-administered ibuprofen (5 mg/kg) and dexamethasone (0.01, 0.1, 1 mg/kg). The early co-administration of ibuprofen (5 mg/kg) with dexamethasone (0.1, 1 mg/kg) on postoperative days (POD) 1–3 significantly inhibited mechanical allodynia before the pain had been established. We also observed the synergistic antinociceptive effects of the same doses the combined treatment on mechanical allodynia on POD 7–9, when the pain had already been established. The attenuation of c-fos immuno-positive cells in the ipsilateral trigeminal subnucleus caudalis after the intraperitoneal co-administration of ibuprofen (5 mg/kg) with dexamethasone (1 mg/kg) confirmed these synergistic antinociceptive effects. Moreover, the magnitude of the effects of this co-administration was comparable with that of gabapentin both before and after the pain had been established.

Conclusion

These results suggest that a combination of ibuprofen and dexamethasone at low doses is an alternative therapeutic strategy for neuropathic pain and provide a rationale for the use of such drug combinations in patients who are unable to tolerate high-dose monotherapy.

A Lipid Micellar System Loaded with Dexamethasone Palmitate Alleviates Rheumatoid Arthritis

Glucocorticoids have been confirmed to be effective in the treatment of a variety of inflammatory diseases. However, their application encounters limitations in terms of tissue distribution and bioavailability in vivo. To address these key issues, we designed and developed a nanopreparation by using egg yolk lecithin/sodium glycocholate (EYL/SGC) and utilize such mixed micelles (MMs) to encapsulate dexamethasone palmitate (DMP) for the treatment of rheumatoid arthritis (RA). The prepared DMP-MMs had an average particle size of 49.18 ± 0.43 nm and were compared with an emulsion-based dexamethasone palmitate. Pharmacokinetic and in vivo fluorescence imaging showed that mixed micelles had higher bioavailability and targeting efficiency in inflammatory sites. An arthritis rat model was established via induction by Complete Freund's Adjuvant (CFA), followed by the efficacy studies by the observations of paw volume, histology, spleen index, pro-inflammatory cytokines, and CT images. It was confirmed that intravenous injection of DMP-MMs exhibited advantages in alleviating joint inflammation compared with the emulsion system. Composed of pharmaceutical adjuvants only, the nanoscale mixed micelles seem a promising carrier system for the RA treatment with lipophilic drugs.

Early life programming of pain: focus on neuroimmune to endocrine communication

Chronic pain constitutes a challenge for the scientific community and a significant economic and social cost for modern societies. Given the failure of current drugs to effectively treat chronic pain, which are based on suppressing aberrant neuronal excitability, we propose in this review an integrated approach that views pain not solely originating from neuronal activation but also the result of a complex interaction between the nervous, immune, and endocrine systems. Pain assessment must also extend beyond measures of behavioural responses to noxious stimuli to a more developmentally informed assessment given the significant plasticity of the nociceptive system during the neonatal period. Finally integrating the concept of perinatal programming into the pain management field is a necessary step to develop and target interventions to reduce the suffering associated with chronic pain. We present clinical and animal findings from our laboratory (and others) demonstrating the importance of the microbial and relational environment in programming pain responsiveness later in life via action on hypothalamo-pituitary adrenal (HPA) axis activity, peripheral and central immune system, spinal and supraspinal mechanisms, and the autonomic nervous system.

Dual encapsulation of hydrophobic and hydrophilic drugs in PLGA nanoparticles by a single-step method: drug delivery and cytotoxicity assays

Dual drug encapsulation in biodegradable nanoparticles is always challenging and often requires strenuous optimization of the synthesis–encapsulation processes.

Behavioral and molecular processing of visceral pain in the brain of mice: impact of colitis and psychological stress

Gastrointestinal disorders with abdominal pain are associated with central sensitization and psychopathologies that are often exacerbated by stress. Here we investigated the impact of colitis induced by dextran sulfate sodium (DSS) and repeated water avoidance stress (WAS) on spontaneous and nociception-related behavior and molecular signaling in the mouse brain. DSS increased the mechanical pain sensitivity of the abdominal skin while both WAS and DSS enhanced the mechanical and thermal pain sensitivity of the plantar skin. These manifestations of central sensitization were associated with augmented c-Fos expression in spinal cord, thalamus, hypothalamus, amygdala and prefrontal cortex. While WAS stimulated phosphorylation of mitogen-activated protein kinase (MAPK) p42/44, DSS activated another signaling pathway, both of which converged on c-Fos. The DSS- and WAS-induced hyperalgesia in the abdominal and plantar skin and c-Fos expression in the brain disappeared when the mice were subjected to WAS+DSS treatment. Intrarectal allyl isothiocyanate (AITC) evoked aversive behavior (freezing, reduction of locomotion and exploration) in association with p42/44 MAPK and c-Fos activation in spinal cord and brain. These effects were inhibited by morphine, which attests to their relationship with nociception. DSS and WAS exerted opposite effects on AITC-evoked p42/44 MAPK and c-Fos activation, which indicates that these transduction pathways subserve different aspects of visceral pain processing in the brain. In summary, behavioral perturbations caused by colitis and psychological stress are associated with distinct alterations in cerebral signaling. These findings provide novel perspectives on central sensitization and the sensory and emotional processing of visceral pain stimuli in the brain.

Assessment of the drug loading, in vitro and in vivo release behavior of novel pH-sensitive hydrogel

CONTEXT

As a glucocorticoid drug, dexamethasone has good therapeutic effects for ulcerative colitis. pH-sensitive hydrogels could make conventional changes of volume in response with different pH values. Meanwhile, they could load drugs depending on its internal three-dimensional network structure.

OBJECTIVE

Appropriate methods were used to improve the drug-loading capacity of hydrogel and exploring the colon-targeting character of dexamethasone hydrogel.

MATERIALS AND METHODS

Different solvents (ethanol and 1,2-propanediol) were employed to dissolve dexamethasone as well as hydrogel monomer materials (poly(ethylene glycol) methyl ether (MPEG)-poly(lactide acid)-acryloyl chloride macromonomer, itaconic acid (IA) and MPEG-methacrylate), then mixing them together to prepare hydrogel through the heat-initiated free radical polymerization method. Differential scanning calorimetry and X-ray diffraction methods were used to verify whether dexamethasone was loaded into hydrogels. In vitro drug release behavior and in vivo pharmacokinetic study were also investigated in detail.

RESULTS

Dexamethasone was successfully loaded into hydrogel, and its loading capacity was improved (5 mg/g). Both the in vitro release study and the in vivo pharmacokinetic study showed the good colon-targeting character of the pH-sensitive P(LE-IA-MEG) hydrogel (T max = 1.0 h, C max = 2.16 µg/ml of dexamethasone; T max = 3.9 h, C max = 0.43 µg/ml of dexamethasone hydrogel).

DISCUSSION

Dexamethasone could be targeted to the colon site by P(LE-IA-MEG) hydrogel, thereby improving its therapeutic effect and reduce its side effects.

CONCLUSION

P(LE-IA-MEG) hydrogel might have great potential application in colon-targeted drug delivery systems.

Potent anti-inflammatory/analgesic effects of lornoxicam in comparison to other nsaids: a c-fos study in the rat

This study evaluates the anti-inflammatory/analgesic effects of lornoxicam, a new non-steroidal anti-inflammatory drug, using the method of c-Fos protein immunoreactivity in the carrageenan model of inflammatory nociception in the rat. The immunohistochemical revelation of inflammatory/nociceptive stimulation evoked c-Fos expression in spinal neurons was used as an indirect marker of neurons involved in spinal nociceptive transmission. Lornoxicam (0.1, 0.3, 1, 3 and 9 mg/kg; n=10 rats for each group) was preadministered intravenously 25 min before an intraplantar injection of carrageenan (6 mg/150 ml of saline). Three hours after carrageenan, the peripheral oedema (paw and ankle diameters) and the number of c-Fos-protein-like immunoreactive (c-Fos-LI) neurons in the lumbar spinal cord, were assessed. Preadministered lornoxicam dose relatedly reduced the total number of c-Fos-LI neurons (regression coefficient r=0.79; p<0.001) with the strongest effect corresponding to the 75+/-2% reduction (p<0.001) for the highest dose of 9 mg/kg, and the 45+/-3% reduction (p<0.001) for the low dose of 0.3 mg/kg. Lornoxicam (0.1, 0.3, 1, 3 and 9 mg/kg iv) significantly reduced the number of c-Fos-LI neurons in both superficial (24+/-6, 33+/-5, 53+/-4, 54+/-4, and 63+/-4% reduction, respectively, p<0.001 for all doses) and deep (28+/-4, 48+/-4, 62+/-2, 69+/-3 and 79+/-2% reduction, respectively, p<0.001 for all doses) laminae of the dorsal horn of the spinal cord. These reducing effects were dose related in both superficial and deep laminae (regression coefficient r=0.66 and r=0.08, respectively; p<0.001 for both). The lowes dose of lornoxicam (0.1 mg/kg iv) had a similar effect in both superficial and deep laminae, whereas the four higher doses (0.3, 1, 3 and 9 mg/kg iv) had a significantly stronger effect on the number of c-Fos-LI neurons in deep laminae as compared to that in superficial laminae. Lornoxicam (0.1, 0.3, 1, 3 and 9 mg/kg iv) dose relatedly reduced the carrageenan induced oedema at both the paw and ankle levels (regression coefficient r=0.63 and r=0.53, respectively, p<0.001 for both), with a stronger effect on the ankle diameter (34+/-8, 61+/-9, 66+/-8, 80+/-6 and 83+/-5% reduction, respectively p<0.001 for all doses). Furthermore reductions of the carrageenan evoked peripheral oedema and spinal c-Fos expression were positively correlated (correlation coefficient r=0.74 and r=0.57 for the paw and ankle diameter respectively, p<0.001 for both). These correlations suggest a predominant peripheral site, without excluding central site of action of lornoxicam in the carrageenan-induced inflammation. Our results provide clear evidence for a potent anti-inflammatory/analgesic effects of low doses of lornoxicam which have a reduced risk of side effects. Taken together, the results of the present study revealed the effects of lornoxicam in the same range as those of other previously studied NSAIDs, more precisely, closely comparable to the effects of ketoprofen.

Activation of peroxisome proliferator-activated receptor gamma in brain inhibits inflammatory pain, dorsal horn expression of Fos, and local edema

Systemic administration of thiazolidinediones reduces peripheral inflammation in vivo, presumably by acting at peroxisome proliferator-activated receptor gamma (PPARgamma) in peripheral tissues. Based on a rapidly growing body of literature indicating the CNS as a functional target of PPARgamma actions, we postulated that brain PPARgamma modulates peripheral edema and the processing of inflammatory pain signals in the dorsal horn of the spinal cord. To test this in the plantar carrageenan model of inflammatory pain, we measured paw edema, heat hyperalgesia, and dorsal horn expression of the immediate-early gene c-fos after intracerebroventricular (ICV) administration of PPARgamma ligands or vehicle. We found that ICV rosiglitazone (0.5-50 microg) or 15d-PGJ(2) (50-200 microg), but not vehicle, dose-dependently reduced paw thickness, paw volume and behavioral withdrawal responses to noxious heat. These anti-inflammatory and anti-hyperalgesia effects result from direct actions in the brain and not diffusion to other sites, because intraperitoneal and intrathecal administration of rosiglitazone (50 microg) and 15d-PGJ(2) (200 microg) had no effect. PPARgamma agonists changed neither overt behavior nor motor coordination, indicating that non-specific behavioral effects do not contribute to PPAR ligand-induced anti-hyperalgesia. ICV administration of structurally dissimilar PPARgamma antagonists (either GW9662 or BADGE) reversed the anti-inflammatory and anti-hyperalgesic actions of both rosiglitazone and 15d-PGJ(2). To evaluate the effects of PPARgamma agonists on a classic marker of noxious stimulus-evoked gene expression, we quantified Fos protein expression in the dorsal horn. The number of carrageenan-induced Fos-like immunoreactive profiles was less in rosiglitazone-treated rats as compared to vehicle controls. We conclude that pharmacological activation of PPARgamma in the brain rapidly inhibits local edema and the spinal transmission of noxious inflammatory signals.

Subdiaphragmatic vagotomy promotes nociceptive sensitivity of deep tissue in rats

To verify whether vagal dysfunction is associated with chronic pain, we evaluated the effects of subdiaphragmatic vagotomy (vgx) on the sensitivity toward noxious stimuli in rats. Vgx rats showed sustained hyperalgesia in the gastrocnemius muscle without tissue damage (no increase in vgx-induced plasma creatine phosphokinase or lactose dehydrogenase levels) accompanied by hypersensitivity to colonic distension. We found a dramatic increase in the levels of metabotropic glutamate receptor 5, protein kinase C (PKC) gamma and phosphorylated-PKCgamma within the spinal cord dorsal horn in vgx rats, which suggests that vgx may evoke sensory nerve plasticity. Morphine produced a dose-dependent increase in the withdrawal threshold in both vgx and sham-operated rats, but the effect of a lower dose in vgx rats was weaker than that in sham-operated rats. Muscle hyperalgesia in vgx rats was also attenuated by gabapentin and amitriptyline, but was not affected by diclofenac, dexamethasone or diazepam. These findings indicate that subdiaphragmatic vagal dysfunction caused chronic muscle hyperalgesia accompanied by visceral pain and both gabapentin and amitriptyline were effective for subdiaphragmatic vagotomy-induced pain, which are partially similar to fibromyalgia syndrome. Furthermore, this chronic muscle pain may result from nociceptive neuroplasticity of the spinal cord dorsal horn.

Antinociceptive effect of amygdalin isolated from Prunus armeniaca on formalin-induced pain in rats

Amygdalin is a plant glucoside isolated from the stones of rosaceous fruits, such as apricots, peaches, almond, cherries, and plums. To investigate the pain-relieving activity of amygdalin, we induced pain in rats through intraplantar injection of formalin, and evaluated the antinociceptive effect of amygdalin at doses of 0.1, 0.5, 1.0, and 10.0 mg/kg-body weight by observing nociceptive behavior such as licking, biting and shaking, the number of Fos-immunoreactive neurons in the spinal cord, and the mRNA expression of inflammatory cytokines in the plantar skin. The intramuscular injection of amygdalin significantly reduced the formalin-induced tonic pain in both early (the initial 10 min after formalin injection) and late phases (10-30 min following the initial formalin injection). During the late phase, amygdalin did reduce the formalin-induced pain in a dose-dependent manner in a dose range less than 1 mg/kg. Molecular analysis targeting c-Fos and inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) also showed a significant effect of amygdalin, which matched the results of the behavioral pain analysis. These results suggest that amygdalin is effective at alleviating inflammatory pain and that it can be used as an analgesic with anti-nociceptive and anti-inflammatory activities.

Evaluation of fatty acid amides in the carrageenan-induced paw edema model

While it has long been recognized that Delta(9)-tetrahydrocannabinol (THC), the primary psychoactive constituent of cannabis, and other cannabinoid receptor agonists possess anti-inflammatory properties, their well known CNS effects have dampened enthusiasm for therapeutic development. On the other hand, genetic deletion of fatty acid amide hydrolase (FAAH), the enzyme responsible for degradation of fatty acid amides, including endogenous cannabinoid N-arachidonoyl ethanolamine (anandamide; AEA), N-palmitoyl ethanolamine (PEA), N-oleoyl ethanolamine (OEA), and oleamide, also elicits anti-edema, but does not produce any apparent cannabinoid effects. The purpose of the present study was to investigate whether exogenous administration of FAAs would augment the anti-inflammatory phenotype of FAAH (-/-) mice in the carrageenan model. Thus, we evaluated the effects of the FAAs AEA, PEA, OEA, and oleamide in wild-type and FAAH (-/-) mice. For comparison, we evaluated the anti-edema effects of THC, dexamethasone (DEX), a synthetic glucocorticoid, diclofenac (DIC), a nonselective cyclooxygenase (COX) inhibitor, in both genotypes. A final study determined if tolerance to the anti-edema effects of PEA occurs after repeated dosing. PEA, THC, DEX, DIC elicited significant decreases in carrageenan-induced paw edema in wild-type mice. In contrast OEA produced a less reliable anti-edema effect than these other drugs, and AEA and oleamide failed to produce any significant decreases in paw edema. Moreover, none of the agents evaluated augmented the anti-edema phenotype of FAAH (-/-) mice, suggesting that maximal anti-edema effects had already been established. PEA was the most effective FAA in preventing paw edema and its effects did not undergo tolerance. While the present findings do not support a role for AEA in preventing carrageenan-induced edema, PEA administration and FAAH blockade elicited anti-edema effects of an equivalent magnitude as produced by THC, DEX, and DIC in this assay.

Orofacial cold hyperalgesia due to infraorbital nerve constriction injury in rats: reversal by endothelin receptor antagonists but not non-steroidal anti-inflammatory drugs

The susceptibility of changes in responsiveness to noxious cold stimulation of rats submitted to chronic constriction of the infraorbital nerve (CION) or carrageenan to drug inhibition was compared. Nocifensive responses were measured as total time rats engaged in bilateral facial grooming with both forepaws over the first 2 min following tetrafluoroethane spray application to the snout. Carrageenan (50 microg, s.c. into upper lip) caused short-lived ipsilateral cold hyperalgesia (peak at 3 h: vehicle 8.4+/-1.3, carrageenan 21.2+/-3.0 s) which was markedly suppressed by i.p. indomethacin (4 mg/kg), celecoxib (10mg/kg) or s.c. dexamethasone (0.5 mg/kg), endothelin ET(A) or ET(B) receptor antagonists (BQ-123 and BQ-788, respectively; 10 nmol/lip). CION caused ipsilateral cold hyperalgesia between Days 2 and 12, which peaked on Days 4 (sham 15.3+/-1.8, CION 32.4+/-5.3s) to 6. Established peak CION-induced cold hyperalgesia was unaffected by indomethacin and celecoxib, whereas dexamethasone, BQ-123, BQ-788, and i.v. injections of selective antagonists of ET(A) (atrasentan, 3-10 mg/kg) or ET(B) (A-192621, 5-20 mg/kg) receptors caused significant inhibitions lasting 1-2.5h (peaks approximately 65-90%). Bosentan (dual ET(A)/ET(B) receptor antagonist, 10 mg/kg, i.v.) abolished CION-induced cold hyperalgesia for up to 6h. Thus, once established, CION-induced orofacial hyperalgesia to cold stimuli appears to lack an inflammatory component, but is alleviated by endothelin ET(A) and/or ET(B) receptor antagonists. If this CION injury model bears predictive value to trigeminal neuralgia (i.e., paroxysmal orofacial pain triggered by various stimuli), endothelin receptors might constitute new targets for treatment of this disorder.

Effect of etodolac, a COX-2 inhibitor, on neuropathic pain in a rat model

Etodolac, a cyclooxygenase-2 inhibitor, may alleviate nociceptive pain and inhibit the activation of osteoclasts. The aim of the present study was to determine whether etodolac can alleviate heat-evoked hyperalgesia and investigate its possible protective effects on osteoporosis induced by chronic constriction injury (CCI) in rats. A CCI to the sciatic nerve was performed, after which the rats received etodolac orally in a volume of 2 ml at 0, 1, and 10 mg/kg/day for 1 to 5 weeks following surgery (experiment 1); at 0 and 10 mg/kg/day for 1 day to 5 weeks following surgery (experiment 2); and at 0 mg/kg/day for 1 to 5 weeks, 10 mg/kg/day for 1 to 2 weeks after surgery, or 10 mg/kg/day for 1 to 3 weeks after surgery (experiment 3). Paw withdrawal latency after exposure to heat, bone mineral content (BMC) and bone mineral density (BMD) in the whole tibial bone, and the number of tartrate resistant acid phosphate (TRAP)-positive multinucleated osteoclasts were measured. Etodolac alleviated heat-evoked hyperalgesia in the CCI rats and the increase in number of TRAP-positive multinucleated osteoclasts on the CCI-side was abrogated, however, it did not inhibit the decrease of BMC and BMD on the CCI-side. Our results suggest that etodolac is useful for treatment of neuropathic pain.

Antinociception and the new COX inhibitors: research approaches and clinical perspectives

New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their traditional parent compounds. They are also safer than the classic non-steroidal anti-inflammatory drugs (NSAIDs) and are starting to be used not only for low to moderate intensity pain, but also for high intensity pain. Three different strategies have been followed to improve the pharmacological profile of COX inhibitors: 1. Development of COX-2 selective inhibitors. This is based on the initial hypothesis that considered COX-2 as the enzyme responsible for the generation of prostaglandins only in inflammation, and, therefore, uniquely responsible for inflammation, pain and fever. Initial expectations gave rise to controversial results, still under discussion. The second generation of these compounds is being developed and should contribute to clarifying both their efficacy and the specific functions of the COX enzymes. 2. Modified non-selective COX inhibitors. Molecules like nitro-NSAIDs or tromethamine salt derivatives have been synthesized considering that both COX-1 and COX-2 are responsible for the synthesis of prostaglandins involved either in homeostatic functions or inflammation. Nitroaspirin, nitroparacetamol or dexketoprofen trometamol are some examples of molecules that are already showing an important clinical efficacy. The modifications performed in their structures seem to lower the unwanted side effects as well as to enhance their analgesic efficacy. 3. Combined therapy of classic NSAIDs with other drugs. This strategy looks for improvements in the incidence of adverse effects or to take advantage of the synergistic enhancement of their therapeutic effects. Some of the molecules resulting from these strategies are very valuable as therapeutic agents and open a wide range of possibilities in the treatment of high intensity pain, including neuropathic pain, and opiate sparing therapy.

Antinociceptive effects of RB101(S), a complete inhibitor of enkephalin-catabolizing enzymes, are enhanced by (+)-HA966, a functional NMDA receptor antagonist: a c-Fos study in the rat spinal cord

The effects of the S enantiomer of RB101, a complete inhibitor of enkephalin-catabolizing enzymes, alone or in combination with a functional NMDA receptor antagonist, (+)-HA966 were studied on the spinal c-Fos protein expression in the carrageenan model of inflammatory nociception. One hour 30min after intraplantar carrageenan in awake rats, c-Fos immunoreactive (c-Fos-IR) nuclei were preferentially located in the laminae I-II and V-VI of the spinal dorsal horn, i.e., spinal areas containing numerous neurons responding exclusively, or not, to peripheral nociceptive stimuli. RB101(S) (5, 10, 20 and 40mg/kg i.v.) dose-dependently reduced the total number of carrageenan-evoked c-Fos-IR nuclei (r=0.63, P<0.01), with 49+/-3% reduction (P<0.001) for the highest dose. Two highest doses of RB101(S) (20 and 40mg/kg) significantly reduced the number of carrageenan-evoked c-Fos-IR nuclei in both superficial I-II (32+/-7% and 36+/-5% reduction, respectively, P<0.05 for both) and deep V-VI (42+/-6% and 61+/-2% reduction, respectively, P<0.001 for both) laminae. The effects of RB101(S) were naloxone-reversible. Combination of low doses of RB101(S) (2.5 or 10mg/kg i.v.) and an inactive dose of (+)-HA966 (2.5mg/kg s.c.) produced supra-additive effects (39+/-4% and 51+/-5% reduction of the total number of c-Fos-IR nuclei, respectively, P<0.001 for both). These effects were partially reversed by naloxone. These results provide evidence for the potent effects of combination of RB101(S) and (+)-HA966. Considering the absence of major opioid side effects of RB101(S) and the marked increase of its antinociceptive effects by NMDA receptor antagonist, this type of drug combination could have beneficial therapeutical application.

Further evidence for the interaction of mu- and delta-opioid receptors in the antinociceptive effects of the dual inhibitor of enkephalin catabolism, RB101(S). A spinal c-Fos protein study in the rat under carrageenin inflammation

We have previously shown that RB101, a dual inhibitor of enkephalin-degrading enzymes, decreased carrageenin-evoked c-Fos protein expression at the spinal cord level in awake rats. Moreover, we have also shown that c-Fos expression is a useful marker of the possible direct or indirect interactions between neural pathways, such as opioid and cholecystokinin systems. We now investigated the respective roles of the three main types of opioid receptors (mu, delta, or kappa) and their possible interactions, in the depressive effects of RB101 in inflammatory nociceptive conditions induced by intraplantar carrageenin (6 mg/150 microl of saline). We used beta-funaltrexamine (beta-FNA), naltrindole (NTI), and nor-binaltorphimine (BNI) as specific antagonists for mu, delta- and kappa-opioid receptors, respectively. c-Fos protein-immunoreactivity (c-Fos-IR) was evaluated as the number of c-Fos-IR nuclei in the lumbar spinal cord 90 min after carrageenin. c-Fos-IR nuclei were preferentially located in the superficial (I-II) and deep (V-VI) laminae of segments L4-L5 (areas containing numerous neurons responding exclusively, or not, to nociceptive stimuli). RB101(S) (30 mg/kg, i.v.) significantly reduced the total number of carrageenin-evoked c-Fos-IR nuclei (30% reduction, P<0.01). This effect was completely blocked by beta-FNA (10 mg/kg, i.v.), or NTI (1 mg/kg, i.v.). In contrast, BNI (2.5 mg/kg, i.v.) did not reverse the reducing effects of RB101(S) on carrageenin-evoked c-Fos protein expression. These results suggest that functional interactions occur between mu- and delta-opioid receptors in enkephalin-induced antinociceptive effects.

Acupoint stimulation using bee venom attenuates formalin-induced pain behavior and spinal cord fos expression in rats

In two previous reports, we have demonstrated that injection of bee venom (BV) into an acupoint produces a significant antinociceptive and anti-inflammatory effect in both a mouse model of visceral nociception and a rat model of chronic arthritis. The present study was designed to evaluate the potential antinociceptive effect of BV pretreatment on formalin-induced pain behavior and it associated spinal cord Fos expression in rats. Adult Sprague-Dawley rats were injected with BV directly into the Zusanli (ST36) acupoint or into an arbitrary non-acupoint located on the back. BV pretreatment into the Zusanli acupoint significantly decreased paw-licking time in the late phase of the formalin test. In contrast, BV injected into a non-acupoint in the back region did not suppress the paw-licking time. In addition, BV pretreatment into the Zusanli acupoint markedly inhibited spinal cord Fos expression induced by formalin injection. These findings indicate that BV pretreatment into the Zusanli acupoint has an antinociceptive effect on formalin-induced pain behavior.

RB101(S), a dual inhibitor of enkephalinases does not induce antinociceptive tolerance, or cross-tolerance with morphine: a c-Fos study at the spinal level

In behavioural tests, RB101 (N-[(S)-2-benzyl-3[(S)(2-amino-4-methyl-thio)butyldithio]-1-oxopropyl]-L-phenylalanine benzyl ester), a mixed inhibitor of enkephalin-degrading enzymes, induces antinociceptive effects without producing tolerance, or cross-tolerance with morphine. In the present experiments, the acute or chronic effects of enantiomer RB101(S) were examined on the response of spinal cord neurons to nociceptive inflammatory stimulation (intraplantar injection of carrageenin) using c-Fos studies in awake rats. The number of c-Fos immunoreactive nuclei was evaluated in the lumbar spinal cord 90 min after carrageenin. c-Fos-immunoreactive nuclei were preferentially located in the superficial (I-II) and deep (V-VI) laminae of segments L4-L5 (areas containing numerous neurones responding exclusively, or not, to nociceptive stimuli). In the first experimental series, acute RB101(S) (30 mg/kg, i.v.), morphine (3 mg/kg, i.v.), or respective vehicles were injected in rats chronically treated with RB101(S) (160 mg/kg/day for 4 days, s.c.). In chronically treated RB101(S) rats, both acute RB101(S) and morphine reduced the total number of carrageenin-evoked c-Fos-immunoreactive nuclei. In the second experimental series, acute RB101(S) (30 mg/kg, i.v.) reduced the total number of carrageenin-evoked c-Fos-immunoreactive nuclei with similar magnitude in naive and in morphine-tolerant (100 mg/kg/day for 3 days, s.c.) rats. These data provide further evidence that different cellular mechanisms occurred after chronic stimulation of opioid receptors by morphine or endogenous enkephalins.

Change in excitability and phenotype of substance P and its receptor in cat Abeta sensory neurons following peripheral inflammation

The effect of peripheral inflammation on spontaneous firing and level of substance P (SP) and its receptor in electrophysiologically identified cat Abeta neurons of dorsal root ganglion (DRG) was studied in vivo using a combination of intracellular recording, dye injection and immunohistochemical techniques. Following injection of carrageenan (Carg) into cat hindpaw, the number of Abeta neurons with spontaneous firing was enhanced significantly (42.9%, n=182) in comparison with control (16.8%, n=149, P<0.01). DRG Abeta neurons became less depolarized 2-4 h following Carg injection. After identifying the cell properties, Lucifer Yellow was injected and SP-like immunoreactivity (SP-LI) was then detected. A total of 17% of Abeta sensory neurons exhibited SP-LI in inflammatory cat. We also found in rat DRGs that the number of SP-LI positive large cells (>35 microm) was also significantly increased in Carg-treated DRG (11.8+/-1.2, n=8) compared with untreated DRG (1.8+/-0.8, n=8, P<0.01). In control cat, the topical use of SP in DRG did not induce any response of Abeta neurons. However, in Carg-treated cat, SP depolarized the membrane potential in most Abeta neurons (68.2%, n=22). L668,169, an antagonist of SP receptor, completely blocked the SP-induced responses. Furthermore, repeated application of SP did not induce obvious desensitization of Abeta neurons. These data suggest that peripheral inflammation increased the excitability, SP level and sensitivity of SP receptor of Abeta neurons. Therefore, we concluded that Abeta sensory neurons appear to contribute to inflammatory allodynia.

Glucocorticoid effects on Fos immunoreactivity and NADPH-diaphorase histochemical staining following spinal cord injury

Glucocorticoids (GC) provide neuroprotection and early recovery after spinal cord injury (SCI). While several mechanisms were proposed to account for these effects, limited information exists regarding GC actions in sensory areas of the spinal cord. Presently, we studied the time course of Fos expression, and reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical staining to monitor neuronal responses to SCI with or without GC treatment. Rats with sham-operation or transection at the thoracic level (T7-T8) received vehicle or 5 mg/kg of the GC dexamethasone (DEX) at 5 min post-lesion and were sacrificed 2 or 4 h after surgery. Another group of SCI rats received vehicle or intensive DEX treatment (5 min, 6 h, 18 h and 46 h post-lesion) and were sacrificed 48 h after surgery. The number of NADPH-d positive neurons or Fos immunoreactive nuclei was studied by computer-assisted image analysis in superficial dorsal horn (Laminae I-III) and central canal area (Lamina X) below the lesion. While constitutive Fos immunoreactive nuclei were sparse in controls, SCI increased Fos expression at 2 and 4 h after injury. DEX treatment significantly enhanced the number of Fos positive nuclei in Laminae I-III by 4 h after transection, although the response was not maintained by intensive steroid treatment when tested at 48 h after SCI. NADPH-d positive neurons in Laminae I-III increased at 2 and 4 h after SCI while a delayed increased was found in central canal area (Lamina X). DEX treatment decreased NADPH-d positive neurons to sham-operated levels at all time points examined. Thus, while GC stimulation of Fos suggests activation of neurons involved in sympathetic outflow and/or pain, down-regulation of NADPH-d indicates attenuation of nociceptive outflow, considering the role of enzyme-derived nitric oxide in pain-related mechanisms. Differential hormonal effects on these molecules agree with their localization in different cell populations.

Urethane anaesthesia could partly mask antinociceptive effects of non-steroidal anti-inflammatory drugs: a spinal c-Fos protein study

Urethane anaesthesia strongly reduced the peripheral edema (31+/-5 and 96+/-8% reduction of carrageenan-enhanced paw and ankle diameters, respectively; P<0.001 for both) and the spinal c-Fos protein expression (71+/-4% reduction of the number of c-Fos protein-labeled nuclei; P<0.001), 3 h after intraplantar injection of carrageenan in rats. In urethane anaesthetised rats, i.v. injection of racemic-flurbiprofen (0.3, 3 and 9 mg/kg) has weaker effects on carrageenan-evoked spinal c-Fos protein expression and peripheral edema than those previously described in the same inflammatory nociceptive model in awake rats.

Activation of silent mechanoreceptive cat C and Adelta sensory neurons and their substance P expression following peripheral inflammation

The effect of inflammation on the excitability and the level of substance P (SP) in cat mechanoreceptive C and Adelta dorsal root ganglion (DRG) neurons were studied in vivo using intracellular recording and immunocytochemical techniques. Following injections of carrageenan (Carg) into the cat hindpaw, the percentage of C neurons exhibiting spontaneous activity increased from 7.2 to 20.7% and the percentage of Adelta neurons increased from 6.9 to 18.6%. In contrast to most cells from normal cats, which fired regularly below 10 Hz, many cells from Carg-treated cats fired at higher frequencies or in bursts. Inflammation (Carg treatment) also depolarized membrane potentials, increased membrane input resistance, caused the disappearance of inward rectifying currents and lowered the mean current thresholds of tibial nerve-evoked responses in DRG neurons. With inflammation, the percentage of C or Adelta neurons responding to low threshold mechanoreceptive stimuli increased (C neurons: normal, 13%; inflamed, 41%; Adelta neurons: normal, 13 %; inflamed, 39 %), while the percentage of C or Adelta neurons responding to high threshold mechanoreceptive stimuli remained unchanged. Some receptive field (RF)-responsive cells were injected with Lucifer Yellow and their SP immunoreactivity was determined. Following Carg treatment, substantially higher percentages of RF-responsive cells were SP positive (C neurons: normal, 35.7%; inflamed, 60%; Adelta neurons: normal, 18.2%; inflamed, 66.7%). These combined increases in the excitability of DRG neurons and SP-containing RF-responsive neurons could lead to sensitization of sensory neurons, thus contributing to the development of hyperalgesia.

Effects of flurbiprofen and its enantiomers on the spinal c-Fos protein expression induced by noxious heat stimuli in the anaesthetized rat

We have evaluated the effects of either intravenous or intraplantar administration of racemic-, S(+)- and R(-)-flurbiprofen on the spinal c-Fos protein expression after a single noxious heat stimulation (52 degrees C for 15 s) of the rat hindpaw in urethane anaesthetized rats. Two hours after noxious heat, numerous c-Fos protein immunoreactive (c-Fos-IR) nuclei (>70 c-Fos-IR nuclei per section at the level of L4-L5 segments) were observed with essential localization in the superficial (I-II) laminae of the spinal dorsal horn, i.e. areas containing numerous neurons driven exclusively by noxious stimuli. Considering the number of c-Fos-IR nuclei in laminae I-II, the intravenous injection of racemic-flurbiprofen (0.3, 3 and 9 mg/kg) was inefficacious and S(+)-flurbiprofen had weak and non-dose-related effects. The same doses of R(-)-flurbiprofen produced dose-related effects (r=0.58, P<0.05) with weak, but significant, effects for doses of 3 and 9 mg/kg (18+/-6% and 26+/-5% reduction of the number of noxious heat-evoked c-Fos-IR nuclei in laminae I-II, P<0.05 and P<0.01, respectively). The weak effects of R(-)-flurbiprofen are probably due to the central site of action since the intraplantar injection of a relatively high dose of 30 microg is inefficacious. These results provide further evidence for weak effects of non-steroidal anti-inflammatory drugs and their enantiomers on the acute responses to nociceptive stimulus which are very efficacious upon inflammatory nociception, but not upon brief noxious heat-evoked nociception.

The effect of diclofenac on the expression of spinal cord c-fos-like immunoreactivity after ischemia-reperfusion-induced acute hyperalgesia in the rat tail

Ischemia-reperfusion of the rat tail for 20 min induces local acute hyperalgesia of approximately 1-h duration. We studied how this stimulus affected the expression of c-fos-like immunoreactivity (c-fos-LI) labeling of neurons of the sacral spinal cord, and how diclofenac pretreatment influenced the outcome. After ischemia, the number of c-fos-LI-labeled neurons was significantly increased when assessed at 60, 90, and 120 min after reperfusion (to 183%, 283%, and 164% of control, respectively; all P < 0.01). At 90 min, the number of regional c-fos-LI-labeled neurons was increased to 585% in laminae I-II, 183% in laminae III-IV, 270% in laminae V-X, and 286% in total, compared with respective control values (all P < 0.01). After diclofenac pretreatment (subcutaneous 40 mg/Kg, 30 min before insult) the number of c-fos-LI-labeled neurons at 90 min was increased to 424% in laminae I-II, 150% in laminae III-IV, 142% in laminae V-X, and 183% in total (all P < 0.01). Thus diclofenac pretreatment partially prevented the insult-induced increase in total and regional neuronal c-fos-LI. This acute nociceptive model involves only natural algogens. However, the results were similar to acute chemically induced or chronic adjuvant induced arthritic inflammatory pain models in which increases in c-Fos were partially inhibited by nonsteroidal antiinflammatory drugs.

Peripheral and/or central effects of racemic-, S(+)- and R(-)-flurbiprofen on inflammatory nociceptive processes: a c-Fos protein study in the rat spinal cord

1. We have evaluated the effects of intravenous or intraplantar racemic-, S(+)- and R(-)-flurbiprofen on both the carrageenan-evoked peripheral oedema and spinal c-Fos immunoreactivity, an indirect index of neurons involved in spinal nociceptive processes. 2. Three hours after intraplantar injection of carrageenan (6 mg in 150 microl of saline) in awake rats, a peripheral oedema and numerous c-Fos protein-like immunoreactive (c-Fos-LI) neurons in L4 L5 segments were observed. c-Fos-LI neurons were essentially located in the superficial (I-II) and deep (V-VI) laminae of the dorsal horn. 3. Intravenous racemic-flurbiprofen (0.3, 3 and 9 mg kg(-1)) dose-relatedly reduced the carrageenan-evoked oedema and spinal c-Fos expression (r=0.64, r=0.88 and r=0.84 for paw diameter, ankle diameter and number of c-Fos-LI neurons; P<0.05. P<0.001 and P<0.001 respectively). 4. Similar effects to those of intravenous racemic-flurbiprofen were obtained with intravenous S(+)-flurbiprofen (0.3, 3 and 9 mg kg(-1)) which dose-relatedly reduced the number of c-Fos-LI neurons (r=0.69, P<0.01) and diameters of paw and ankle (r=0.56 and r=0.52 respectively, P<0.05 for both). 5. For the dose of 0.3 mg kg(-1) i.v., R(-)-flurbiprofen did not modify the number of c-Fos-LI neurons and produced a weak reduction of oedema at only the ankle level (23+/-12% reduction, P<0.05). However, a ten times higher dose of R(-)-flurbiprofen (3 mg kg(-1) i.v.) was necessary to obtain effects comparable to those of S(+)- or racemic-flurbiprofen (0.3 mg kg(-1) i.v.). 6. Intraplantar racemic-flurbiprofen (1, 10 and 30 microg) dose-relatedly reduced the carrageenan-enhanced ankle diameter (r=0.81, P<0.001) and the number of c-Fos-LI neurons in L4-L5 segments (r=0.83, P<0.001). with a 60+/-3% reduction of the number of c-Fos-LI neurons (P<0.001), and 30+/-3 and 67+/-7% reduction of paw and ankle diameter respectively (P<0.001 for both) for the dose of 30 microg. 7. For intraplantar S(+)-flurbiprofen (1, 10 and 30 microg) the dose-related effects (r=0.77, r=0.60 and r=0.59 for c-Fos-LI neurons, paw and ankle diameters respectively, P<0.001, P<0.01 and P<0.01) were similar to those of racemic-flurbiprofen. In contrast, intraplantar R(-)-flurbiprofen (1, 10 and 30 microg) did not have detectable effects on all studied parameters. 8. The present study provides clear evidence for potent anti-inflammatory and antinociceptive effects of both intravenous or intraplantar racemic- and S(+)-flurbiprofen. These results further demonstrate marked anti-inflammatory and antinociceptive effects of intravenous, but not intraplantar, R(-)-flurbiprofen. These results suggest that the main site of action of racemic- and S(+ )-flurbiprofen is in the periphery and indicate that the site of action of R(-)-flurbiprofen is mainly of central origin.

Involvement of the spinoparabrachial pathway in inflammatory nociceptive processes: a c-Fos protein study in the awake rat

The effect of graded inflammatory stimuli (intraplantar-carrageenan, 0.2, 1, and 6 mg/150 microl) on paw edema and c-Fos protein expression at two levels of the spinoparabrachial pathway, the spinal cord and parabrachial area (PB), were studied. The present study, in awake rats, is an extension of previous study (Bester et al. [1997] J. Comp. Neurol. 383:439-458) which evaluated, in anesthetized rats, the effect of graded cutaneous heat stimulation on c-Fos-expression at the same levels. At the spinal level, the c-Fos-protein-like-immunoreactive (c-Fos-LI) neurons were located primarily in superficial laminae ipsilateral to intraplantar carrageenan. The number of c-Fos-LI neurons increased dose dependently (r = 0.973, n = 24) for carrageenan, from a number close to zero for the saline injection. At the PB level, c-Fos was predominantly expressed contralateral to intraplantar carrageenan. c-Fos-LI neurons were located primarily around the pontomesencephalic junction in (i) a restricted pontine area, centered in the lateral crescent, and including an adjacent part of the outer portion of the external lateral subnucleus, and (ii) the mesencephalic superior lateral subnuclei. The number of c-Fos-LI neurons in the PB area was correlated with that in the superficial laminae (r = 0.935, n = 24) and with the paw edema (r = 0.931, n = 24). No significant changes in c-Fos expression were observed in the nucleus of the solitary tract and ventrolateral medulla. The close correlation between c-Fos expression at both the spinal and PB levels and inflammatory edema provides further evidence for the involvement of spinoparabrachial pathway in inflammatory nociceptive processes. The present results are congruent with the existence of electrophysiologically demonstrated spinoparabrachio-amygdaloid and -hypothalamic nociceptive pathways.

Pituitary-adrenocortical responses to persistent noxious stimuli in the awake rat: endogenous corticosterone does not reduce nociception in the formalin test

Although glucocorticoids inhibit inflammation and are used to treat painful inflammatory rheumatic diseases, the contribution, if any, of endogenous pituitary-adrenocortical activity to the control of pain remains unclear. We report that injection of dilute formalin into the hindpaw not only evokes inflammation and pain-related behavior, but it also increases ACTH and corticosterone to a greater extent than restraint and saline injection alone. This difference was particularly robust during the final periods of pain-related behavior in the formalin test, when the ACTH and corticosterone (B) levels in the restraint/saline control group had returned to normal. These results indicate that formalin-evoked increases in ACTH and B reflect nociceptive input, rather than the stress associated with handling. To test the hypothesis that the formalin-induced increase in corticosterone reduces pain and inflammation, we next evaluated the effect of adrenalectomy (to prevent activation of glucocorticoid receptors) or high-dose dexamethasone (to saturate glucocorticoid receptors) on nociceptive processing in the formalin test. Neither adrenalectomy nor dexamethasone changed behavioral or cardiovascular nociceptive responses. Furthermore, the increases in blood pressure and heart rate produced by formalin may not be mediated by adrenomedullary catecholamine release. In addition, we conclude that the nociceptive component of the formalin stimulus is sufficient to activate the pituitary-adrenocortical system in the awake rat, but that the resulting release of corticosterone does not feed back and reduce nociceptive processing.

The contribution of peripheral bradykinin B2 receptors to carrageenan-evoked oedema and spinal c-Fos expression in rats

Intraplantar co-injection of HOE140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]bradykinin), a selective bradykinin B2 receptor antagonist (0.1, 1 and 10 micrograms), with carrageenan dose-dependently (r = 0.66, P < 0.01) reduced the carrageenan-evoked total number of c-Fos protein-like immunoreactive (c-Fos-LI) neurones (23 +/- 5%, 35 +/- 6% and 50 +/- 5% reduction; P < 0.01, P < 0.001 and P < 0.001, respectively). These reducing effects were dose-dependent for the number of c-Fos-LI neurones in both superficial (r = 0.70, P < 0.01) and deep (r = 0.53, P < 0.05) laminae. Intraplantar co-injection of HOE140 (0.1, 1 and 10 micrograms) with carrageenan significantly reduced the carrageenan-evoked paw (25 +/- 7%, 41 +/- 6% and 41 +/- 3% reduction; P < 0.001 for all) and ankle (46 +/- 6%, 61 +/- 5% and 61 +/- 5% reduction; P < 0.001 for all) oedema. Our results provide further evidence for the involvement of peripheral bradykinin B2 receptors in carrageenan-induced inflammatory nociceptive transmission.

Ketoprofen produces profound inhibition of spinal c-Fos protein expression resulting from an inflammatory stimulus but not from noxious heat

This study assesses the anti-inflammatory/analgesic effects of ketoprofen a non-steroidal anti-inflammatory drug, using the method of c-Fos immunoreactivity at the spinal cord level in two models of noxious stimulation: carrageenan-induced inflammatory pain or acute noxious heat. Ketoprofen was pre-administered intravenously or orally 25 min before an intraplantar injection of carrageenan (6 mg in 150 microliters of saline) in hindpaw of the non-anaesthetised rat or before a single noxious heat (52 degrees C, 15 sec) stimulation of hindpaw of the anaesthetised rat. Three hours after carrageenan or 2 h after noxious heat, the number of spinal c-Fos protein-like immunoreactive (c-Fos-LI) neurons in L4-L5 segments and both the ankle and paw diameter, the indicator of peripheral oedema, were assessed. Pre-administered ketoprofen (1, 3 and 10 mg/kg i.v.) dose-dependently blocks the development of the carrageenan-induced spinal c-Fos protein expression and peripheral oedema, with the highest dose influencing in parallel both parameters (75 +/- 2% diminution of total number of c-Fos-LI neurons per L4-L5 section; 64 +/- 4% and 82 +/- 6% diminution of paw and ankle oedema, respectively). The effect of ketoprofen was significantly greater on the number of c-Fos-LI neurons in deep, as compared to superficial, laminae. Furthermore, the dose-dependent effects of ketoprofen on the carrageenan-induced spinal c-Fos protein expression and both the paw and ankle oedema were correlated. Oral pre-administration of ketoprofen (20 mg/kg) produced the blockage of development of the carrageenan-induced spinal c-Fos protein expression (65 +/- 3% diminution of total number of c-Fos-LI neurons per L4-L5 section) and peripheral oedema (20 +/- 3% and 59 +/- 10% diminution of paw and ankle oedema, respectively). In contrast, the same doses of both the intravenous and oral pre-administration of ketoprofen did not influence either the spinal c-Fos protein expression nor slightly enhanced paw diameter induced by a single noxious heat stimulation. This study suggests a predominant peripheral site, without excluding a central site of action of ketoprofen in the carrageenan-induced inflammation. The method of c-Fos protein-like immunoreactivity revealed ketoprofen to be more potent in comparison to members of other families of non-steroidal anti-inflammatory drugs, previously studied in the same experimental conditions of carrageenan-induced inflammatory pain.

The contribution of GABAB receptor-mediated events to inflammatory pain processing: carrageenan oedema and associated spinal c-Fos expression in the rat

In this pharmacological study we have assessed the effect of baclofen, a selective GABAB receptor agonist, on spinal expression of the immediate early gene c-Fos and the peripheral oedema evoked by a prolonged peripheral inflammation due to intraplantar carrageenan. Baclofen was administered intravenously 30 min before intraplantar injection of carrageenan in freely moving rats. Three hours after carrageenan the number of spinal c-Fos protein-like immunoreactive neurons and peripheral (ankle and paw) oedema were assessed. For the two series of experiments the total number of control carrageenan-evoked c-Fos protein-like immunoreactive neurons in segments L4-L5 of the spinal cord was 176 +/- 6 and 177 +/- 9 c-Fos protein-like immunoreactive neurons per section, for carrageenan control with intravenous and intraplantar saline, respectively. c-Fos protein-like immunoreactive neurons were predominantly located in laminae I-II and V-VI of the dorsal horn of the spinal cord in carrageenan controls receiving intravenous (68 +/- 3 and 69 +/- 2 c-Fos protein-like immunoreactive neurons, respectively) and intraplantar (62 +/- 4 and 71 +/- 5 c-Fos protein-like immunoreactive neurons, respectively) saline. Pre-administered systemic baclofen (0.05, 1.5 and 3 mg/kg i.v.) dose dependently reduced the total number of c-Fos protein-like immunoreactive neurons (81 +/- 3, 66 +/- 4 and 49 +/- 4% of control total number of c-Fos protein-like immunoreactive neurons, respectively), with strongest effects on the number of deep (74 +/- 3, 60 +/- 3 and 43 +/- 4% of control, respectively) as compared with superficial (90 +/- 4, 77 +/- 5 and 59 +/- 5% of control, respectively) c-Fos protein-like immunoreactive neurons. The effects of systemic baclofen on the carrageenan-induced spinal c-Fos expression and both the paw and ankle oedema were positively correlated (r = 0.479, P < 0.05 and r = 0.733, P < 0.001, respectively). Intraplantar baclofen (50 and 100 micrograms in 50 microliters of saline), simultaneously injected with intraplantar carrageenan, did not significantly influence carrageenan-evoked spinal c-Fos expression or ankle oedema. Despite the fact that the highest dose of intraplantar baclofen significantly reduced paw oedema (23 +/- 3% reduction of control paw oedema), our results are clearly in favour of a spinal site of action of systemic baclofen.