The spinal phospholipase-cyclooxygenase-prostanoid cascade in nociceptive processing

The increased trafficking of the calcium channel subunit alpha2delta-1 to presynaptic terminals in neuropathic pain is inhibited by the alpha2delta ligand pregabalin

Neuropathic pain results from damage to the peripheral sensory nervous system, which may have a number of causes. The calcium channel subunit alpha(2)delta-1 is upregulated in dorsal root ganglion (DRG) neurons in several animal models of neuropathic pain, and this is causally related to the onset of allodynia, in which a non-noxious stimulus becomes painful. The therapeutic drugs gabapentin and pregabalin (PGB), which are both alpha(2)delta ligands, have antiallodynic effects, but their mechanism of action has remained elusive. To investigate this, we used an in vivo rat model of neuropathy, unilateral lumbar spinal nerve ligation (SNL), to characterize the distribution of alpha(2)delta-1 in DRG neurons, both at the light- and electron-microscopic level. We found that, on the side of the ligation, alpha(2)delta-1 was increased in the endoplasmic reticulum of DRG somata, in intracellular vesicular structures within their axons, and in the plasma membrane of their presynaptic terminals in superficial layers of the dorsal horn. Chronic PGB treatment of SNL animals, at a dose that alleviated allodynia, markedly reduced the elevation of alpha(2)delta-1 in the spinal cord and ascending axon tracts. In contrast, it had no effect on the upregulation of alpha(2)delta-1 mRNA and protein in DRGs. In vitro, PGB reduced plasma membrane expression of alpha(2)delta-1 without affecting endocytosis. We conclude that the antiallodynic effect of PGB in vivo is associated with impaired anterograde trafficking of alpha(2)delta-1, resulting in its decrease in presynaptic terminals, which would reduce neurotransmitter release and spinal sensitization, an important factor in the maintenance of neuropathic pain.

Activation of NMDA receptor is associated with up-regulation of COX-2 expression in the spinal dorsal horn during nociceptive inputs in rats

Cyclooxygenases-2 (COX-2) in the spinal dorsal horn is up-regulated and plays an important role in pain and hyperalgesia induced by nociceptive stimulation. The mechanisms involved in the up-regulation of spinal COX-2 during nociceptive stimulation are yet not well understood. Because the important role of NMDA and its receptor in transmission of nociceptive information in the spinal cord, activation of the spinal NMDA receptor might contribute to the up-regulation of spinal COX-2 expression. The present study was undertaken to demonstrate the above hypothesis by observing changes of COX-2 expression in the spinal dorsal horn in rats subjected to formalin test and intrathecal administration of NMDA, a selective NMDA receptor agonist, in conditions with or without presence of MK-801, an antagonist of NMDA receptor, using methods of Western blotting, reverse transcription polymerase chain reaction and immunohistochemistry. The results showed that intrathecal injection of MK-801, a noncompetitive antagonist of NMDA receptor, significantly suppressed the up-regulation of the COX-2 expression and characteristic pain behavior responses evoked in formalin test. Whereas, intrathecal injection of NMDA significantly up-regulated the expression of COX-2 in the spinal dorsal horn in a time course corresponding to that of nociceptive behavioral responses elicited by the intrathecal NMDA administration. In addition, the up-regulation of the COX-2 expression induced by the intrathecal NMDA was dose-dependent and blocked by prior administration of MK-801. These findings proved that activation of NMDA receptor is associated with the up-regulation of COX-2 expression in the spinal dorsal horn during nociceptive stimulation in rats.

A randomized, double-blind, placebo-controlled study of preemptively administered intravenous parecoxib: effect on anxiety levels and procedural pain during epidural catheter placement for surgical operations or for chronic pain therapy

BACKGROUND

The effect of parecoxib, when used perioperatively or during interventional techniques, is well demonstrated in the literature. Little is known about its effects on anxiety levels before the analgesic technique application. The aim of this prospective, randomized, double-blind, placebo-controlled, clinical study is to investigate whether parecoxib, preemptively administrated, has an effect on anxiety levels reported prior to an epidural puncture, and if it influences the reported pain of the interventional technique itself.

MATERIAL AND METHODS

The study protocol involved 110 patients, scheduled for epidural catheter placement for chronic pain therapy--Group I, as well as 112 patients scheduled for orthopedic operations under epidural anesthesia--Group II. Patients in each group were randomly allocated into two subgroups in relation to parecoxib/placebo administration before epidural catheter placement: Group Ia, parecoxib 40 mg i.v. (n = 54), Group Ib, placebo (n = 56), Group IIa, parecoxib 40 mg i.v. (n = 57), Group IIb, placebo (n = 55). Patients were given a self-administered inventory to measure the anxiety level of the presurgical/preprocedural state (State-Trait Spielberger Anxiety Inventory) and anxiety levels were recorded 1 hour before epidural puncture, 20 minutes postdosing, and 1 hour after epidural catheter placement. Anxiety levels were also measured and recorded using visual analog scale (VAS). One hour after epidural puncture, reported procedural pain was recorded (VAS). One hour and 6 hours postepidural, patients' satisfaction was also recorded, on a 4-point scale.

RESULTS

All four subgroups were similar regarding demographic, operative/procedural data, and coexisting diseases. Preprocedural anxiety levels were significantly decreased with parecoxib administration in comparison with placebo in both groups (P < 0.05). Reported VAS regarding pain from epidural puncture was lower in Groups IA and Ib. Patients' satisfaction was greater with parecoxib in comparison with placebo.

CONCLUSION

The levels of anxiety have been investigated in several medical procedures and early, in the study of pain. The higher the expectation of pain and the anxiety are, the higher the intensity of the pain. Parecoxib seems to exert positive influence on pain and anxiety levels of interventional procedure. Further studies are needed to elucidate the actual mechanisms that are involved.

The COX-2/PGE2 pathway: key roles in the hallmarks of cancer and adaptation to the tumour microenvironment

It is widely accepted that alterations to cyclooxygenase-2 (COX-2) expression and the abundance of its enzymatic product prostaglandin E(2) (PGE(2)) have key roles in influencing the development of colorectal cancer. Deregulation of the COX-2/PGE(2) pathway appears to affect colorectal tumorigenesis via a number of distinct mechanisms: promoting tumour maintenance and progression, encouraging metastatic spread, and perhaps even participating in tumour initiation. Here, we review the role of COX-2/PGE(2) signalling in colorectal tumorigenesis and highlight its ability to influence the hallmarks of cancer--attributes defined by Hanahan and Weinberg as being requisite for tumorigenesis. In addition, we consider components of the COX-prostaglandin pathway emerging as important regulators of tumorigenesis; namely, the prostanoid (EP) receptors, 15-hydroxyprostaglandin dehydrogenase and the prostaglandin transporter. Finally, based on recent findings, we propose a model for the cellular adaptation to the hypoxic tumour microenvironment that encompasses the interplay between COX-2, hypoxia-inducible factor 1 and dynamic switches in beta-catenin function that fine-tune signalling networks to meet the ever-changing demands of a tumour.

Functional tetrodotoxin-resistant Na(+) channels are expressed presynaptically in rat dorsal root ganglia neurons

The tetrodotoxin-resistant (TTX-R) voltage-gated Na(+) channels Na(v)1.8 and Na(v)1.9 are expressed by a subset of primary sensory neurons and have been implicated in various pain states. Although recent studies suggest involvement of TTX-R Na(+) channels in sensory synaptic transmission and spinal pain processing, it remains unknown whether TTX-R Na(+) channels are expressed and function presynaptically. We examined expression of TTX-R channels at sensory synapses formed between rat dorsal root ganglion (DRG) and spinal cord (SC) neurons in a DRG/SC co-culture system. Immunostaining showed extensive labeling of presynaptic axonal boutons with Na(v)1.8- and Na(v)1.9-specific antibodies. Measurements using the fluorescent Na(+) indicator SBFI demonstrated action potential-induced presynaptic Na(+) entry that was resistant to tetrodotoxin (TTX) but was blocked by lidocaine. Furthermore, presynaptic [Ca(2+)](i) elevation in response to a single action potential was not affected by TTX in TTX-resistant DRG neurons. Finally, glutamatergic synaptic transmission was not inhibited by TTX in more than 50% of synaptic pairs examined; subsequent treatment with lidocaine completely blocked these TTX-resistant excitatory postsynaptic currents. Taken together, these results provide evidence for presynaptic expression of functional TTX-R Na(+) channels that may be important for shaping presynaptic action potentials and regulating transmitter release at the first sensory synapse.

Consequences of altered eicosanoid patterns for nociceptive processing in mPGES-1-deficient mice

Cyclooxygenase-2 (COX-2)-dependent prostaglandin (PG) E₂ synthesis in the spinal cord plays a major role in the development of inflammatory hyperalgesia and allodynia. Microsomal PGE₂ synthase-1 (mPGES-1) isomerizes COX-2-derived PGH₂ to PGE₂. Here, we evaluated the effect of mPGES-1-deficiency on the noci-ceptive behavior in various models of nociception that depend on PGE₂ synthesis. Surprisingly, in the COX-2-dependent zymosan-evoked hyperalgesia model, the nociceptive behavior was not reduced in mPGES-1-deficient mice despite a marked decrease of the spinal PGE₂ synthesis. Similarly, the nociceptive behavior was unaltered in mPGES-1-deficient mice in the formalin test. Importantly, spinal cords and primary spinal cord cells derived from mPGES-1-deficient mice showed a redirection of the PGE₂ synthesis to PGD₂, PGF_2α and 6-keto-PGF_1α (stable metabolite of PGI₂). Since the latter prostaglandins serve also as mediators of noci-ception they may compensate the loss of PGE₂ synthesis in mPGES-1-deficient mice.

Acetaminophen prevents hyperalgesia in central pain cascade

Acetaminophen is an analgesic and antipyretic drug believed to exert its effect through interruption of nociceptive processing. In order to determine whether this effect is due to peripheral or central activity, we studied the efficacy of systemic (oral) and intrathecal (IT) application of acetaminophen in preventing the development of hyperalgesia induced through the direct activation of pro-algogenic spinal receptors. Spinal administration of substance P (SP, 30 nmol, IT) in rats produced a decreased thermal threshold, indicating centrally mediated hyperalgesia. Pretreatment of rats with oral acetaminophen (300 mg/kg), but not vehicle, significantly attenuated IT SP-induced hyperalgesia. Acetaminophen given IT also produced a dose-dependent (10-200 microg) antinociceptive effect. In addition, oral acetaminophen suppressed spinal PGE(2) release evoked by IT SP in an in vivo IT dialysis model. The ability of IT as well as oral acetaminophen to reverse this spinally initiated hyperalgesia emphasizes the likely central action and bioavailability of the systemically delivered drug. Jointly, these data argue for an important central antihyperalgesic action of acetaminophen.

Inhibition of spinal cytosolic phospholipase A(2) expression by an antisense oligonucleotide attenuates tissue injury-induced hyperalgesia

Activation of the spinal phospholipase A(2) (PLA(2)) -cyclooxygenase (COX) -prostaglandin signaling pathway is widely implicated in nociceptive processing. Although the role of spinal COX isoforms in pain signal transmission has been extensively characterized, our knowledge of PLA(2) enzymes in this cascade is limited. Among all PLA(2) groups, cytosolic calcium-dependent PLA(2) group IVA (cPLA(2)IVA) appears to be the predominant PLA(2) enzyme in the spinal cord. In the present study we sought to (i) characterize anatomical and cellular distribution and localization of cPLA(2)IVA in dorsal horn of rat spinal cord, (ii) verify efficacy and selectivity of intrathecal (IT) delivery of an antisense oligonucleotide (AS) targeting rat cPLA(2)IVA mRNA on spinal expression of this enzyme, and (iii) examine the effect of down-regulation of spinal cPLA(2)IVA on peripheral tissue injury-induced pain behavior. Here we demonstrate that cPLA(2)IVA is constitutively expressed in rat spinal cord, predominantly in dorsal horn neurons and oligodendrocytes but not in astrocytes or microglia. Intrathecal injection of AS significantly down-regulated both protein and gene expression of cPLA(2)IVA in rat spinal cord, while control missense oligonucleotide (MS) had no effect. Immunocytochemistry confirmed that the reduction occurred in neurons and oligodendrocytes. cPLA(2)IVA AS did not alter expression of several other PLA(2) isoforms, such as secretory PLA(2) (groups IIA and V) and calcium-independent PLA(2) (group VI), indicating that the AS was specific for cPLA(2)IVA. This selective knockdown of spinal cPLA(2)IVA did not change acute nociception (i.e. paw withdrawal thresholds to acute thermal stimuli and intradermal formalin-induced first phase flinching), however, it significantly attenuated formalin-induced hyperalgesia (i.e. second phase flinching behavior), which reflects spinal sensitization. Thus the present findings suggest that cPLA(2)IVA may specifically participate in spinal nociceptive processing.

Mechanisms of prolonged presynaptic Ca2+ signaling and glutamate release induced by TRPV1 activation in rat sensory neurons

Transient receptor potential vanilloid receptor 1 (TRPV1)-mediated release of neuroactive peptides and neurotransmitters from the peripheral and central terminals of primary sensory neurons can critically contribute to nociceptive processing at the periphery and in the CNS. However, the mechanisms that link TRPV1 activation with Ca2+ signaling at the release sites and neurosecretion are poorly understood. Here we demonstrate that a brief stimulation of the receptor using either capsaicin or the endogenous TRPV1 agonist N-arachidonoyl-dopamine induces a prolonged elevation of presynaptic [Ca2+](i) and a concomitant enhancement of glutamate release at sensory synapses. Initiation of this response required Ca2+ entry, primarily via TRPV1. The sustained phase of the response was independent of extracellular Ca2+ and was prevented by inhibitors of mitochondrial Ca2+ uptake and release mechanisms. Measurements using a mitochondria-targeted Ca2+ indicator, mtPericam, revealed that TRPV1 activation elicits a long-lasting Ca2+ elevation in presynaptic mitochondria. The concentration of TRPV1 agonist determined the duration of mitochondrial and cytosolic Ca2+ signals in presynaptic boutons and, consequently, the period of enhanced glutamate release and action potential firing by postsynaptic neurons. These data suggest that mitochondria control vanilloid-induced neurotransmission by translating the strength of presynaptic TRPV1 stimulation into duration of the postsynaptic response.

Protein kinase A anchoring via AKAP150 is essential for TRPV1 modulation by forskolin and prostaglandin E2 in mouse sensory neurons

Phosphorylation-dependent modulation of the vanilloid receptor TRPV1 is one of the key mechanisms mediating the hyperalgesic effects of inflammatory mediators, such as prostaglandin E(2) (PGE(2)). However, little is known about the molecular organization of the TRPV1 phosphorylation complex and specifically about scaffolding proteins that position the protein kinase A (PKA) holoenzyme proximal to TRPV1 for effective and selective regulation of the receptor. Here, we demonstrate the critical role of the A-kinase anchoring protein AKAP150 in PKA-dependent modulation of TRPV1 function in adult mouse dorsal root ganglion (DRG) neurons. We found that AKAP150 is expressed in approximately 80% of TRPV1-positive DRG neurons and is coimmunoprecipitated with the capsaicin receptor. In functional studies, PKA stimulation with forskolin markedly reduced desensitization of TRPV1. This effect was blocked by the PKA selective inhibitors KT5720 [(9S,10R,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]benzodiazocine-10-carboxylicacid hexyl ester] and H89 (N-[2-(p-bromo-cinnamylamino)-ethyl]-5-isoquinoline-sulfon-amide 2HCl), as well as by the AKAP inhibitory peptide Ht31. Similarly, PGE(2) decreased TRPV1 desensitization in a manner sensitive to the PKA inhibitor KT5720. Both the forskolin and PGE(2) effects were strongly impaired in DRG neurons from knock-in mice that express a mutant AKAP150 lacking the PKA-binding domain (Delta36 mice). Protein kinase C-dependent sensitization of TRPV1 remained intact in Delta36 mice. The PGE(2)/PKA signaling defect in DRG neurons from Delta36 mice was rescued by overexpressing the full-length human ortholog of AKAP150 in these cells. In behavioral testing, PGE(2)-induced thermal hyperalgesia was significantly diminished in Delta36 mice. Together, these data suggest that PKA anchoring by AKAP150 is essential for the enhancement of TRPV1 function by activation of the PGE(2)/PKA signaling pathway.

Inhibition of fatty acid amide hydrolase and cyclooxygenase-2 increases levels of endocannabinoid related molecules and produces analgesia via peroxisome proliferator-activated receptor-alpha in a model of inflammatory pain

The antinociceptive effects of the endocannabinoids (ECs) are enhanced by inhibiting catabolic enzymes such as fatty acid amide hydrolase (FAAH). The physiological relevance of the metabolism of ECs by other pathways, such as cyclooxygenase-2 (COX2) is less clear. To address this question we compared the effects of local inhibition of FAAH versus COX2 (URB597 and nimesulide, respectively) on inflammatory hyperalgesia and levels of endocannabinoids and related molecules in the hindpaw. Inflammatory hyperalgesia was measured following intraplantar injection of carrageenan. Effects of intraplantar injection of URB597 (25 microg and 100 microg) or nimesulide (50 microg) on hyperalgesia and hindpaw levels of anandamide (AEA), 2-arachidonoylglycerol (2AG) and N-palmitoylethanolamine (PEA) were determined. Although both doses of URB597 increased levels of AEA and 2AG in the carrageenan inflamed hindpaw, only the lower dose of URB597 attenuated hyperalgesia (P<0.05). Nimesulide attenuated both hyperalgesia and hindpaw oedema (P<0.001, P<0.01, respectively) and increased levels of PEA (P<0.05) in the hindpaw. Since both AEA and PEA are ligands for peroxisome proliferator-activated receptor-alpha (PPARalpha), the effects of the PPARalpha antagonist GW6471 on nimesulide- and URB597-mediated effects were studied. GW6471, but not a PPARgamma antagonist, blocked the inhibitory effects of nimesulide and URB597 on hyperalgesia. Our data suggest that both COX2 and FAAH play a role in the metabolism of endocannabinoids and related molecules. The finding that PPARalpha antagonism blocked the inhibitory effects of nimesulide and URB597 suggests that PPARalpha contributes to their antinociceptive effects in the carrageenan model of inflammatory hyperalgesia.

Phospholipase A2 Activation Enhances Inhibitory Synaptic Transmission in Rat Substantia Gelatinosa Neurons

Phospholipase A2 (PLA2) activation enhances glutamatergic excitatory synaptic transmission in substantia gelatinosa (SG) neurons, which play a pivotal role in regulating nociceptive transmission in the spinal cord. By using melittin as a tool to activate PLA2, we examined the effect of PLA2 activation on spontaneous inhibitory postsynaptic currents (sIPSCs) recorded at 0 mV in SG neurons of adult rat spinal cord slices by use of the whole cell patch-clamp technique. Melittin enhanced the frequency and amplitude of GABAergic and glycinergic sIPSCs. The enhancement of GABAergic but not glycinergic transmission was largely depressed by Na+ channel blocker tetrodotoxin or glutamate-receptor antagonists (6-cyano-7-nitroquinoxaline-2,3-dione and/or dl-2-amino-5-phosphonovaleric acid) and also in a Ca2+-free Krebs solution. The effects of melittin on glycinergic sIPSC frequency and amplitude were dose-dependent with an effective concentration of ∼0.7 μM for half-maximal effect and were depressed by PLA2 inhibitor 4-bromophenacyl bromide or aristolochic acid. The melittin-induced enhancement of glycinergic transmission was depressed by lipoxygenase inhibitor nordihydroguaiaretic acid but not cyclooxygenase inhibitor indomethacin. These results indicate that the activation of PLA2 in the SG enhances GABAergic and glycinergic inhibitory transmission in SG neurons. The former action is mediated by glutamate-receptor activation and neuronal activity increase, possibly the facilitatory effect of PLA2 activation on excitatory transmission, whereas the latter action is due to PLA2 and subsequent lipoxygenase activation and is independent of extracellular Ca2+. It is suggested that PLA2 activation in the SG could enhance not only excitatory but also inhibitory transmission, resulting in the modulation of nociception.

How readily does ketorolac penetrate cerebrospinal fluid in children?

Ketorolac is a potent nonsteroidal anti-inflammatory analgesic used in postoperative pain management. Ketorolac elicits its analgesic action by inhibiting the cyclo-oxygenase enzyme in peripheral tissues and in the spinal cord. Central nervous system penetration of parenteral ketorolac has been evaluated in adults but not in children. In the present study we investigated ketorolac cerebrospinal fluid penetration via spinal anesthesia in 30 healthy children undergoing surgery in the lower part of the body. A single cerebrospinal fluid and blood sample was obtained between 11 minutes and 6 hours after receiving ketorolac 0.5 mg x kg(-1) IV. Ketorolac concentrations were determined by gas chromatography with mass spectrometric detection. Ketorolac was detected from 22 of the 30 cerebrospinal fluid samples, and the concentrations ranged between 0.2 and 7.6 microg x L(-1) (median, 0.6 microg x L(-1)). The cerebrospinal fluid to unbound plasma concentration-ratio ranged between 0.01 and 0.69 (median, 0.08). These low concentrations indicate that ketorolac does not readily penetrate cerebrospinal fluid in children.

Preventive effects of perioperative parecoxib on post-discectomy pain

BACKGROUND

Cyclooxygenase inhibitor treatment is viewed increasingly critical because of safety considerations, and there are several open questions on their optimal use.

METHODS

In a randomized placebo-controlled study in 320 patients undergoing discectomy, we administered parecoxib 40 mg either perioperatively (before operation and after operation), after operation (first dose given in the evening after surgery), or before operation (single parecoxib dose given 45 min before surgery). We measured the main outcome variables: average pain score, morphine consumption, and opioid-related symptom distress at 25, 49, and 73 h after surgery.

RESULTS

Perioperative parecoxib significantly (i) improved the pain score compared with both placebo and postoperative parecoxib, (ii) decreased morphine consumption, and (iii) reduced the opioid-related symptom distress score. Neither a single preoperative dose nor postoperative parecoxib (first dose given in the evening after surgery) significantly improved morphine's analgesic effectiveness.

CONCLUSIONS

Perioperative parecoxib compared with postoperative parecoxib improves post-discectomy pain and results in a reduction in adverse effects associated with opioid therapy. Postoperative parecoxib, or a single pre-incisional parecoxib dose, does not significantly improve post-discectomy pain or opioid side-effects up to 3 days after surgery.

Localization of S100A8 and S100A9 expressing neutrophils to spinal cord during peripheral tissue inflammation

Investigation of hyperalgesia at the spinal transcriptome level indicated that carrageenan-induced inflammation of rat hind paws leads to a rapid but sustained increase in S100A8 and S100A9 expression, two genes implicated in the pathology of numerous inflammatory diseases including rheumatoid arthritis and gout. In situ hybridization revealed that the elevation occurred in neutrophils that migrate to the spinal cord vasculature during peripheral inflammation, not in spinal neurons or glial cells. Immunohistochemical analysis suggests, but does not prove, that these neutrophils abundantly release S100A8 and S100A9. Consistent with this, we detected an increase in ICAM and VCAM, both indicators of endothelial activation, a known trigger for secretion of S100A8 and S100A9. Migration of S100A8- and S100A9-expressing neutrophils to spinal cord is selective, since MCP-1- and CD68-expressing leukocytes do not increase in spinal cord vasculature during hind paw inflammation. Examination of many neutrophil granule mediators in spinal cord indicated that they are not regulated to the same degree as S100A8 and S100A9. Neutrophil migration also occurs in the vasculature of brain and pituitary gland during peripheral inflammation. Together, these findings suggest an interaction between a subpopulation of leukocytes and the CNS during peripheral tissue inflammation, as implied by an apparent release and possible diffusion of S100A8 and S100A9 through the endothelial blood-brain barrier. Although the present findings do not establish the neurophysiological or behavioral relevance of these observations to nociceptive processing, the data raise the possibility that selective populations of leukocytes may communicate the presence of disease or tissue damage from the periphery to cells in the central nervous system.

Endocannabinoid metabolism and uptake: novel targets for neuropathic and inflammatory pain

Cannabinoid CB1 and CB2 receptors are located at key sites involved in the relaying and processing of noxious inputs. Both CB1 and CB2 receptor agonists have analgesic effects in a range of models of inflammatory and neuropathic pain. Importantly, clinical trials of cannabis-based medicines indicate that the pre-clinical effects of cannabinoid agonists may translate into therapeutic potential in humans. One of the areas of concern with this pharmacological approach is that CB1 receptors have a widespread distribution in the brain and that global activation of CB1 receptors is associated with adverse side effects. Studies of the endogenous cannabinoids (endocannabinoids) have demonstrated that they are present in most tissues and that in some pain states, such as neuropathic pain, levels of endocannabinoids are elevated at key sites involved in pain processing. An alternative approach that can be used to harness the potential therapeutic effects of cannabinoids is to maximise the effects of the endocannabinoids, the actions of which are terminated by re-uptake and metabolism by various enzymes, including fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL) and cyclooxygenase type 2 (COX2). Preventing the metabolism, or uptake, of endocannabinoids elevates levels of these lipid compounds in tissue and produces behavioural analgesia in models of acute pain. Herein we review recent studies of the effects of inhibition of metabolism of endocannabinoids versus uptake of endocannabinoids on nociceptive processing in models of inflammatory and neuropathic pain.

COX-2 inhibitor celecoxib prevents chronic morphine-induced promotion of angiogenesis, tumour growth, metastasis and mortality, without compromising analgesia

Morphine and its congener opioids are the main therapy for severe pain in cancer. However, chronic morphine treatment stimulates angiogenesis and tumour growth in mice. We examined if celecoxib (a cyclooxygenase-2 (COX-2) inhibitor) prevents morphine-induced tumour growth without compromising analgesia. The effect of chronic treatment with celecoxib (by gavage) and/or morphine (subcutaneously), or PBS on tumour prostaglandin E₂ (PGE₂), COX-2, angiogenesis, tumour growth, metastasis, pain behaviour and survival was determined in a highly invasive SCK breast cancer model in A/J mice. Two weeks of chronic morphine treatment at clinically relevant doses stimulates COX-2 and PGE₂ (4.5-fold compared to vehicle alone) and angiogenesis in breast tumours in mice. This is accompanied by increased tumour weight (∼35%) and increased metastasis and reduced survival. Co-administration of celecoxib prevents these morphine-induced effects. In addition, morphine and celecoxib together provided better analgesia than either agent alone. Celecoxib prevents morphine-induced stimulation of COX-2, PGE₂, angiogenesis, tumour growth, metastasis and mortality without compromising analgesia in a murine breast cancer model. In fact, the combination provided significantly better analgesia than with morphine or celecoxib alone. Clinical trials of this combination for analgesia in chronic and severe pain in cancer are warranted.

Cerebrospinal fluid distribution of ibuprofen after intravenous administration in children

BACKGROUND

Ibuprofen is the most commonly used nonsteroidal, antipyretic, antiinflammatory analgesic in children. Nonsteroidal, antipyretic, antiinflammatory analgesics act in both the peripheral tissues and the central nervous system. The central nervous system penetration of ibuprofen has been described in adults but not in children.

OBJECTIVES

Our goals were to investigate the cerebrospinal fluid penetration of ibuprofen in children and evaluate the analgesic plasma concentration of ibuprofen after inguinal surgery in children.

MATERIALS AND METHODS

A total 36 healthy children (25 boys) aged 3 months to 12 years received a single intravenous injection of ibuprofen (10 mg/kg). A paired cerebrospinal fluid and blood sample was obtained 10 minutes to 8 hours after the injection. In children having inguinal surgery, a second blood sample was obtained at the time that the child first had wound pain.

RESULTS

The ibuprofen level was determined in all cerebrospinal fluid and plasma samples. Cerebrospinal fluid concentrations ranged between 15 and 541 microg/L, and the highest concentrations were measured 30 to 38 minutes after dosing. In all cerebrospinal fluid samples collected after 30 minutes, ibuprofen concentration exceeded that of unbound plasma. The plasma analgesic concentrations after inguinal surgery ranged between 10 and 25 mg/L.

CONCLUSIONS

Ibuprofen penetrates the cerebrospinal fluid readily, with peak concentrations attained 30 to 40 minutes after intravenous injection of a 10 mg/kg dose. The plasma analgesic concentration after inguinal surgery with spinal anesthesia is 10 to 25 mg/L.

Methylprednisolone and ketorolac rapidly reduce hyperalgesia around a skin burn injury and increase pressure pain thresholds

BACKGROUND

Glucocorticoids and non-steroidal anti-inflammatory drugs (NSAIDs) decrease acute postoperative pain and hyperalgesia. The objectives of this study were to investigate the effects of methylprednisolone and ketorolac on hyperalgesia around a skin burn injury and on pressure pain thresholds.

METHODS

In a double-blind, placebo-controlled, randomized trial with cross-over design, methylprednisolone 125 mg, ketorolac 60 mg or placebo was administered intravenously in 12 male volunteers on three separate days at least 4 days apart. Primary and secondary hyperalgesia were produced by a first-degree burn injury on abdominal skin 45 min before injection of the test medicines. The area of secondary mechanical hyperalgesia outside the site of injury was measured. Pressure pain stimuli were applied on the base of a fingernail, increasing until the pressure pain detection threshold (PPDT) and pressure pain tolerance threshold (PPTT) were reached.

RESULTS

Compared with placebo, the active drugs reduced the area of secondary hyperalgesia (methylprednisolone, P < 0.001; ketorolac, P < 0.01). Ketorolac but not methylprednisolone increased PPDT compared with placebo (P < 0.05). Both active drugs increased PPTT compared with placebo (methylprednisolone, P < 0.01; ketorolac, P < 0.001). Ketorolac increased PPTT more than methylprednisolone (P < 0.05).

CONCLUSIONS

Methylprednisolone and ketorolac increased PPTT attenuated secondary hyperalgesia around a skin burn injury. PPTT increased after both methylprednisolone and ketorolac. The present study demonstrates analgesic and anti-hyperalgesic properties of a glucocorticoid and a non-selective NSAID that have not been demonstrated previously in human subjects.

Perioperative pain management in the neurosurgical patient

The perioperative management of pain in neurosurgical patients is a controversial topic with management decisions based mainly on reports of anecdotal experiences. There is no consensus regarding the standardization of pain control in this patient population. In the last decade, improved awareness and advances in the practice of pain management have resulted in the implementation of diverse techniques to achieve adequate analgesia in this undertreated group of patients. This article provides information about the various techniques and approaches, based on the latest research and clinical trials conducted in this patient population. Specifically, the physiology of pain in patients undergoing brain or spine surgery, the different modalities for pain control, and the diverse choice of drugs, with their associated risks and benefits, are reviewed.

Bradykinin-induced nuclear factor of activated T-cells-dependent transcription in rat dorsal root ganglion neurons

Bradykinin produced at sites of tissue injury and inflammation elicits acute pain and alters the sensitivity of nociceptive neurons to subsequent stimuli. We tested the hypothesis that bradykinin could elicit long-lasting changes in nociceptor function by activating members of the nuclear factor of activated T-cells (NFAT) family of transcription factors. Bradykinin activation of B2 receptors evoked concentration-dependent (EC50 = 6.0 +/- 0.3 nM) increases in intracellular Ca2+ concentration ([Ca2+]i) in a proportion of dorsal root ganglion neurons in primary culture. These [Ca2+] increases were sensitive to inhibition of phospholipase C (PLC) and depletion of Ca2+ stores. In neurons expressing a green fluorescent protein (GFP)-NFAT4 fusion protein, a 2-min exposure to bradykinin induced the translocation of GFP-NFAT4 from the cytoplasm to the nucleus. Translocation was partially inhibited by the removal of extracellular Ca2+ and was blocked by inhibition of calcineurin. Furthermore, bradykinin triggered a concentration-dependent increase in NFAT-mediated transcription of a luciferase gene reporter (EC50 = 24.2 +/- 0.1 nM). This depended on the B2 receptor, PLC activation, and inositol triphosphate-mediated Ca2+ release. Transcription was not inhibited by capsazepine. Finally, as indicated by quantitative reverse transcription-polymerase chain reaction, bradykinin elicited an increase in cyclooxygenase mRNA. This increase was sensitive to calcineurin and B2 receptor inhibition. These findings suggest a mechanism by which short-lived bradykinin-mediated stimuli can enact lasting changes in nociceptor function and sensitivity.

Pro-algesic versus analgesic actions of immune cells

PURPOSE OF REVIEW

When tissue is destroyed, pain arises. Tissue destruction is associated with an inflammatory reaction. This leads to activation of nociceptors. The following review will concentrate on pro-algesic and analgesic mediators, which arise from immune cells or resident cells in the periphery or the circulation during inflammation.

RECENT FINDINGS

In early inflammation endogenous hyperalgesic mediators are produced, including cytokines, chemokines, nerve growth factor as well as bradykinin, prostaglandins and ATP. Simultaneously, analgesic mediators are secreted: opioid peptides, somatostatin, endocannabinoids and certain cytokines. Inflammation increases the expression of peripheral opioid receptors on sensory nerve terminals and enhances their signal transduction, as well as the amount of opioid peptides in infiltrating immune cells. Interference with the recruitment of opioid-containing immune cells into inflamed tissue by blockade of adhesion molecules or by intrathecal morphine injection reduces endogenous analgesia.

SUMMARY

Inflammatory pain is the result of the interplay between pro-algesic and analgesic mediators. To avoid central side effects, future analgesic therapy should be targeted at either selectively blocking novel pro-algesic mediators or at enhancing endogenous peripheral analgesic effects.

Heat injury-induced drop of the noxious heat threshold measured with an increasing-temperature water bath: A novel rat thermal hyperalgesia model

Conventional thermonociceptive tests are based on measurement of the latency of nocifensive reactions evoked by constant, suprathreshold heat stimuli. In the present study, a novel, increasing-temperature water bath was developed for determination of the noxious heat threshold temperature of lightly restrained conscious rats. One of the hindpaws of a rat was immersed into the water bath whose temperature was increased from 30 degrees C at a rate of 24 degrees C/min until the animal withdrew its hindpaw from the water. The corresponding bath temperature was considered as behavioural noxious heat threshold. The heat threshold of untreated rats was 43.5+/-0.4 degrees C (n=10) and was reproducible upon repeated measurements at intervals of 10 min for 60 min. Thermal hyperalgesia was induced by mild heat injury (51 degrees C water for 20 s) which led to a 7-8 degrees C decrease of the noxious heat threshold. Thermal hyperalgesia was detected at least for 60 min after heat injury. Morphine, diclofenac, ibuprofen and paracetamol administered intraperitoneally 20 min after heat injury dose-dependently inhibited the drop of heat threshold with minimum effective doses of 0.3, 0.3, 10 and 30 mg/kg, and ED(50) values of 0.5, 3, 18 and 100 mg/kg, respectively. Thermal hyperalgesia was also decreased by intraplantar treatment with morphine (10 microg), diclofenac (10 microg) or ibuprofen (100 microg). In conclusion, the mild heat injury-induced drop of the noxious heat threshold measured with the increasing-temperature water bath is a novel thermal hyperalgesia model highly sensitive to both opioid and non-opioid analgesics upon systemic or local administration.

Barriers to rehabilitation following surgery for primary breast cancer

Surgery is a mainstay of primary breast cancer therapy. Alterations in surgical technique have reduced normal tissue injury, yet pain and functional compromise continue to occur following treatment. A tenuous evidence base bolstered by considerable expert opinion suggests that early intervention with conventional rehabilitative modalities can reduce surgery-associated pain and dysfunction. Barriers to the timely rehabilitation of functionally morbid sequelae are discussed at length in this article. Barriers arise from a wide range of academic, human, logistic, and financial sources. Despite obstacles, expeditious and effective post-surgical rehabilitation is being regularly delivered to breast cancer patients at many institutions. This experience has given rise to anecdotal information on the management of common sequelae that may undermine function. The epidemiology, pathophysiology, and management of these sequelae are outlined in this article with an emphasis on the caliber of supporting evidence. Myofascial dysfunction, axillary web syndrome, frozen shoulder, lymphostasis, post-mastectomy syndrome, and donor site morbidity following breast reconstruction are addressed. A critical need for more definitive evidence to guide patient management characterizes the current treatment algorithms for surgical sequelae.

Perioperative pain management

The under-treatment of postoperative pain has been recognised to delay patient recovery and discharge from hospital. Despite recognition of the importance of effective pain control, up to 70% of patients still complain of moderate to severe pain postoperatively. The mechanistic approach to pain management, based on current understanding of the peripheral and central mechanisms involved in nociceptive transmission, provides newer options for clinicians to manage pain effectively. In this article we review the rationale for a multimodal approach with combinations of analgesics from different classes and different sites of analgesic administration. The pharmacological options of commonly used analgesics, such as opioids, NSAIDs, paracetamol, tramadol and other non-opioid analgesics, and their combinations is discussed. These analgesics have been shown to provide effective pain relief and their combinations demonstrate a reduction in opioid consumption. The basis for using non-opioid analgesic adjuvants is to reduce opioid consumption and consequently alleviate opioid-related adverse effects. We review the evidence on the opioid-sparing effect of ketamine, clonidine, gabapentin and other novel analgesics in perioperative pain management. Most available data support the addition of these adjuvants to routine analgesic techniques to reduce the need for opioids and improve quality of analgesia by their synergistic effect. Local anaesthetic infiltration, epidural and other regional techniques are also used successfully to enhance perioperative analgesia after a variety of surgical procedures. The use of continuous perineural techniques that offer prolonged analgesia with local anaesthetic infusion has been extended to the care of patients beyond hospital discharge. The use of nonpharmacological options such as acupuncture, relaxation, music therapy, hypnosis and transcutaneous nerve stimulation as adjuvants to conventional analgesia should be considered and incorporated to achieve an effective and successful perioperative pain management regimen.

Expression of COX-1 and COX-2 in a clinical model of acute inflammation

Cyclooxygenase (COX) plays an important role in the induction of pain and inflammation as well as the analgesic actions of NSAIDs and coxibs. This study evaluates the expression of the two isoforms COX-1 and COX-2 in a clinical model in which the surgical removal of impacted third molars is used to evaluate the analgesic activity of anti-inflammatory drugs. A 3-mm punch biopsy was performed on the oral mucosa overlying 1 impacted third molar immediately before extraction of 2 impacted lower third molars. After the second tooth was extracted, a second biopsy was performed adjacent to the surgical site either immediately after surgery or 30, 60, or 120 minutes after surgery. RNA was extracted from the biopsy specimens, and RT-PCR was performed to assess mRNA levels of COX-1, COX-2, and glyceraldehyde-3-phosphate dehydrogenase (G3PDH). The RT-PCR products in the biopsy specimens were normalized to G3PDH and compared with baseline. COX-2 mRNA was progressively increased at 30, 60, and 120 minutes after surgery (P<.05); COX-1 mRNA was transiently decreased at 60 minutes during the postsurgical period (P<.05). The results demonstrate peripheral elevation of COX-2 after tissue injury, which may contribute to increased prostaglandin E(2) at the site of injury, pain onset, and the analgesic activity of both nonselective NSAIDs and selective COX-2 inhibitors.

PERSPECTIVE

This clinical study uses a physiologically relevant model to determine the time course of expression of COX-1 and COX-2 in acute inflammation of the human oral mucosa. This study furthers our understanding of the contribution of the COX isoforms to acute pain.

Increased Tumor Necrosis Factor-α and Prostaglandin E2 Concentrations in the Cerebrospinal Fluid of Rats with Inflammatory Hyperalgesia: The Effects of Analgesic Drugs

BACKGROUND

We examined the changes in cerebrospinal fluid (CSF) concentrations of prostaglandin E2 (PGE2) and tumor necrosis factor-alpha (TNF-alpha) after intraplantar administration of complete Freund's adjuvant (CFA) in rats. In addition, we investigated whether different analgesic drugs orally administered at antihyperalgesic doses were able to prevent the changes in PGE2 and TNF-alpha spinal levels associated with hindpaw inflammation.

METHODS

The Randall-Selitto paw-withdrawal test was used to measure inflammatory hyperalgesia. Tramadol (7.5 mg/kg), paracetamol (65 mg/kg), tramadol plus paracetamol and nimesulide (5 mg/kg) were administered orally twice a day, starting from the first day after the CFA injection. PGE2 in the CSF was measured by enzyme immunoassay, and TNF-alpha by ELISA. Behavioral and biochemical parameters were measured on Day 7 after intraplantar injection of CFA or saline.

RESULTS

Withdrawal thresholds to mechanical stimuli decreased markedly in the CFA-treated paw. In these animals the quantification of proinflammatory mediators in the CSF revealed a significant increase in both PGE2 and TNF-alpha concentrations. All the pharmacological treatments prevented the development of the hyperalgesia as well as the PGE2 increase in the CSF. Conversely, a prevention of the increase in TNF-alpha levels was observed only in rats treated with nimesulide or tramadol and paracetamol in combination.

CONCLUSIONS

Our results demonstrate that peripheral inflammatory hyperalgesia is associated with significant changes of proinflammatory mediators in the CSF. It is important to note, however, that spinal PGE2 and TNF-alpha proved to be differently affected by pharmacological treatments able to fully abolish the hyperalgesia.

Plasma and cerebrospinal fluid concentrations of indomethacin in children after intravenous administration

The objective of this study was to evaluate the cerebrospinal fluid (CSF) permeation of indomethacin in healthy children. The participants (n = 31, aged 4-144 months) received indomethacin (0.35 mg/kg) as a 10-minute intravenous infusion prior to surgery under spinal anaesthesia. A single CSF and plasma sample from each individual was collected 14 to 225 minutes after the infusion. Indomethacin concentrations were determined from the CSF, plasma, and protein-free plasma. Total plasma, protein-free plasma, and CSF concentrations of indomethacin ranged between 90 and 2200 ng/mL (median, 780 ng/mL), 0.3 and 0.8 ng/mL (median, 0.5 ng/mL), and 0.2 and 5.0 ng/mL (median, 1.4 ng/mL), respectively. The CSF to plasma concentration ratio remained less than 0.01. There was no correlation between the administration time and CSF concentrations. Eleven children developed 12 nonserious adverse effects, from which 5 were central nervous system (CNS) effects (agitation). In conclusion, indomethacin permeated into the CSF of children, which enables both desired and adverse CNS effects of indomethacin.

Preadministration of flurbiprofen suppresses prostaglandin production and postoperative pain in orthopedic patients undergoing tourniquet inflation

STUDY OBJECTIVES

To evaluate the effect of preadministration of flurbiprofen on the plasma concentrations of prostaglandin E2 (PGE2) and postoperative pain.

DESIGN

Prospective, randomized, controlled and double-blind study.

SETTING

Inpatient surgery at Nagasaki Rosai Hospital.

PATIENTS

32 ASA physical status I to II patients scheduled for total knee arthroplasty or open anterior cruciate ligament reconstruction.

INTERVENTIONS

Patients were randomly assigned to two groups. Five minutes before tourniquet inflation (350 mmHg), group A (n = 16) received placebo (intralipid, one mL . kg(-1)), and group B (n = 16) received flurbiprofen one mg . kg(-1) IV. Catheters were placed in the ipsilateral femoral vein for collection of local blood and in a cubital vein for sampling of systemic blood.

MEASUREMENTS

Prostaglandin E2 (femoral vein and cubital vein) was measured before tourniquet inflation (T1), before tourniquet deflation (T2), and immediately after tourniquet deflation (T3). Postoperative analgesia was provided with intravenous buprenorphine, 0.1 mg, on patient demand. Pain (Visual Analog Scale) was assessed at 0.5, one, two, 4, 6, 12 and 24 hours after surgery.

MAIN RESULTS

Visual Analog Scale and buprenorphine consumptions in group B were significantly lower than those in group A during the first 4 postoperative hours. In group A, PGE2 in femoral vein increased significantly at T2 (359 +/- 105 pg mL(-1), P < 0.0001), compared with T1 (211 +/- 61 pg mL(-1)) and returned to control values at T3 (252 +/- 77 pg mL(-1)), whereas PGE2 in the cubital vein showed no change. In group B, PGE2 in either the femoral vein or cubital vein showed no change throughout the time course.

CONCLUSIONS

Preadministration of flurbiprofen suppresses the local production of PGE2 during tourniquet ischemia, resulting in reduced early postoperative pain in patients undergoing knee surgery.

Peripheral and central mechanisms of visceral sensitization in man

Visceral hypersensitivity (perception of gastrointestinal sensory events at a lower-than-normal threshold) is considered to be an important pathophysiological mechanism in the development of functional gastrointestinal disorders (FGIDs), such as irritable bowel syndrome, non-cardiac chest pain and functional dyspepsia. These disorders are associated with significant health care and socioeconomic costs due to factors such as repeated visits to consultants, hospitalizations and work absenteeism. Despite the presence of extensive evidence linking visceral hypersensitivity and FGIDs, the mechanism(s) underlying visceral hypersensitivity has not been fully elucidated. Suggested hypotheses include sensitization of afferent neurones, both at the level of the enteric and the (afferent) autonomic nervous system (peripheral sensitization), sensitization of spinal cord dorsal horn neurones (central sensitization) and psychosocial factors/psychiatric comorbidity influencing the processing of afferent signals at the level of the brain. Importantly, these hypotheses may be complementary rather than mutually exclusive. However, the degree to which each of these mechanisms contributes to the overall perception of visceral pain, and therefore the generation of symptoms, still remains unclear. This article discusses the mechanisms that may underlie visceral hypersensitivity, with reference to FGIDs. Understanding these mechanisms is essential in order to improve the diagnosis and treatment of patients with these disorders.

Update in Cancer Pain Syndromes

Cancer pain assessment and management are integral to palliative medicine. This paper reviews recent publications in the period 1999-2004 in the broad categories of epidemiology, pain assessment, nonpharmacologic approaches to cancer pain (radiation therapy, anesthetic blocks, palliative surgery and chemotherapy, complementary and alternative medicine), and in nociceptive pain, neuropathic pain, visceral pain, and bone pain.

Contributions of cyclooxygenase-2 to neuroplasticity and neuropathology of the central nervous system

Cyclooxygenase (COX) enzymes, or prostaglandin-endoperoxide synthases (PTGS), are heme-containing bis-oxygenases that catalyze the first committed reaction in metabolism of arachidonic acid (AA) to the potent lipid mediators, prostanoids and thromboxanes. Two isozymes of COX enzymes (COX-1 and COX-2) have been identified to date. This review will focus specifically on the neurobiological and neuropathological consequences of AA metabolism via the COX-2 pathway and discuss the potential therapeutic benefit of COX-2 inhibition in the setting of neurological disease. However, given the controversy surrounding the use of COX-2 selective inhibitors with respect to cardiovascular health, it will be important to move beyond COX to identify which down-stream effectors are responsible for the deleterious and/or potentially protective effects of COX-2 activation in the setting of neurological disease. Important advances toward this goal are highlighted herein. Identification of unique effectors in AA metabolism could direct the development of new therapeutics holding significant promise for the prevention and treatment of neurological disorders.

Preoperative administration of intravenous flurbiprofen axetil reduces postoperative pain for spinal fusion surgery

PURPOSE

The aim of the study was to investigate postoperative analgesia and the opioid-sparing effect of the preoperative administration of intravenous flurbiprofen axetil in patients undergoing spinal fusion surgery.

METHODS

Thirty-six patients were randomly allocated into one of three groups. Group A received preoperative flurbiprofen axetil, 1 mg x kg(-1). Group B received postoperative flurbiprofen axetil, 1 mg x kg(-1). Group C received a placebo. All groups were given a standardized anesthesia and intravenous morphine via a patient-controlled analgesia device for postoperative analgesia. The pain score was evaluated by a visual analog scale (VAS) at 0 (T(0)), 1 (T(1)), 2 (T(2)), 6 (T(3)), 12 (T(4)), and 24 (T(5)) h after surgery, and the morphine requirement was recorded during the study period.

RESULTS

VAS in group A was significantly lower than that in group B at T(0) and T(1). VAS in group A was significantly lower than that in group C throughout the time course after surgery. Postoperative morphine consumption in group A was significantly lower than that in groups B and C at T(0) to T(3).

CONCLUSION

As compared with postoperative administration, preoperative administration of intravenous flurbiprofen axetil provides better postoperative analgesia and an opioid-sparing effect in patients undergoing spinal fusion surgery under general anesthesia.

Intrathecal Administration of a Cylcooxygenase-1, but Not a Cyclooxygenase-2 Inhibitor, Reverses the Effects of Laparotomy on Exploratory Activity in Rats

Studies of hypersensitivity to mechanical stimuli after incisional surgery suggest that cyclooxygenase (COX)-1, but not COX-2, in the spinal cord participates in postoperative pain. In the current study, we sought to determine the role of COX isoenzymes after laparotomy, examining spontaneous exploratory behavior rather than withdrawal reflexes. Adult male Sprague-Dawley rats underwent subcostal laparotomy surgery under isoflurane anesthesia or received anesthesia without surgery. Exploratory locomotor activity was measured on the first postoperative day after intrathecal injection of dimethyl sulfoxide (vehicle) or COX-1 (SC-560) or COX-2 (NS-398) inhibitors. Laparotomy reduced ambulation, rearing, and rapid small movements (stereotypy) similarly in animals without intrathecal catheters and those receiving intrathecal vehicle control. SC-560 produced a dose-related return to normal exploratory behavior with complete return at doses of 20 mug and larger. In contrast, NS-398 in doses up to 50 mug failed to increase exploratory behavior. These data with exploratory behavior and laparotomy agree with studies with reflexive withdrawal responses after incisional surgery and indicate that COX-1 inhibition reduces pain responses after surgery. Spinal COX-1 inhibition completely restores exploratory activity, including rearing behavior that stretches the abdominal muscles. These data suggest that targeting COX-1 in the spinal cord may produce postoperative analgesia.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Depression of NMDA-receptor-mediated segmental transmission by ketamine and ketoprofen, but not L-NAME, on the in vitro neonatal rat spinal cord preparation

Activation of spinal N-methyl-D-aspartate (NMDA) receptors and then the nitric oxide and the arachidonic acid pathways is important in pain transmission. This study assessed the effects of the NMDA receptor channel blocker ketamine, the nitric oxide synthase inhibitor L-NAME, and the cyclooxygenase inhibitor ketoprofen in nociceptive transmission using an in vitro neonatal rat spinal cord preparation. Supramaximal electrical stimulation of the dorsal root evoked the A-fibre- and C-fibre-mediated high intensity excitatory postsynaptic potential (EPSP) in the ipsilateral ventral root. Low intensity stimulation evoked the A-fibre-mediated monosynaptic compound action potential (MSR) superimposed on the low intensity EPSP. Both the low intensity EPSP and the high intensity EPSP contain NMDA-receptor-mediated components. Only ketamine and ketoprofen depressed the synaptic responses. Ketamine depressed all three spinal reflexes with IC(50) values (with 95% CI) of 10.80 microM (5.97 to 19.54 microM) for the MSR, 8.29 microM (4.53 to 14.17 microM) for the low intensity EPSP, and 5.35 microM (3.05 to 9.40 microM) for the high intensity EPSP. Ketoprofen depressed the low intensity EPSP and the high intensity EPSP only; IC(50) values (with 95% CI) were 354.5 microM (217.5 to 576.8 microM) and 302.7 microM (174.0 to 526.7 microM), respectively. Reflexes recovered after drug washout. These data demonstrated that ketamine and ketoprofen, but not L-NAME, depressed NMDA-mediated nociceptive transmission in spinal cord preparations from neonatal rats.

Signalling networks regulating cyclooxygenase-2

Cyclooxygenease-2 (COX-2) is the key enzyme regulating the production of prostaglandins, central mediators of inflammation. The expression of cyclooxygenease-2 is induced by several extra cellular signals including pro-inflammatory and growth-promoting stimuli. All signals converge to the activation of mitogen-activated protein kinases (MAPK) that regulate cyclooxygenease-2 mRNA levels both at the transcriptional and post-transcriptional level. The machinery appears to be highly specialized involving activation of distinct signalling molecules depending on the type of extracellular stimulus. Expression of cyclooxygenease-2 mRNA is regulated by several transcription factors including the cyclic-AMP response element binding protein (CREB), nuclear factor kappa B (NFkB) and the CCAAT-enhancer binding protein (C/EBP). Cyclooxygenease-2 is also affected post-transcriptionaly, at the level of mRNA stability. Finally, cyclooxygenease-2 can be affected directly at its enzymatic activity by nitric oxide and nitric oxide synthase (iNOS). Each step of cyclooxygenease-2 regulation can be used as potential therapeutic target.

Cancer-related bone pain is attenuated by a systemically available delta-opioid receptor agonist

Patients with bone cancer report severe pain and receive mu-opioids. We developed a family of peptidomimetic delta-agonists, one of which H2N-Tyr-dVal-Gly-Phe-Ala-OH ([dVal(L)2,Ala(L)5]E) binds with a 1700x affinity at the delta versus mu receptor. To examine the systemic analgesic efficacy of this delta-agonist versus morphine in osteosarcoma pain, osteosarcoma cells are injected into one femur of the anesthetized mouse. After 10-18 days, a decalcification of the injected femur occurs along with a pronounced tactile allodynia. IP morphine and [dVal(L)2,Ala(L)5]E produced a dose-dependent reversal of allodynia with the respective ED50 values being 5.3+/-1.9 mg/kg for morphine and 1.3+/-0.3 mg/kg for [dVal(L)2,Ala(L)5]E. Plotting peak effect versus area under the analgesic curve for doses of morphine and [dVal(L)2,Ala(L)5]E revealed overlapping curves suggesting that for a given effect, [dVal(L)2,Ala(L)5]E produced a similar duration of action as morphine. These effects were reversed by IP naloxone (3 mg/kg). IP naltrindole (1 mg/kg) preferentially reversed [dVal(L)2,Ala(L)5]E. The upper dose effects of morphine but not [dVal(L)2,Ala(L)5]E were limited by pronounced hyperactivity. No other effects were noted. These results show that IP [dVal(L)2,Ala(L)5]E through a delta receptor produces analgesia equal in efficacy to that of morphine but with a 4.5-fold greater potency. Over the doses examined, morphine actions were side effect limited. The delta side effects were not so limited, suggesting a favorable therapeutic ratio for delta-agonists in this pain model. These studies suggest that a systemically delivered delta-opioid agonist has pronounced analgesic properties on a preclinical cancer pain model.

Lack of interaction between prostaglandin E2 receptor subtypes in regulating adenylyl cyclase activity in cultured rat dorsal root ganglion cells

The hyperalgesic response to prostaglandin E2 (PGE2) is thought to be mediated by activation of the cAMP/protein kinase A pathway in primary sensory neurones. The aim of this study was to investigate the relative contribution of different PGE2 (EP) receptor subtypes to the overall activity of adenylyl cyclase in adult rat isolated dorsal root ganglion (DRG) cells, in vitro. PGE2 and the prostanoid EP4 receptor agonist ONO-AE1-329 increased [3H]cAMP production with EC50 values of 500 nM and 70 nM, respectively, and showed similar efficacies. No combination of prostanoid EP1, EP2, EP3 or EP4 receptor selective agonists produced synergistic increases in [3H]cAMP. The prostacyclin mimetic cicaprost increased [3H]cAMP production with an EC50 value of 42 nM and produced a significantly greater maximal response compared with PGE2. No evidence for prostanoid EP3 receptor-dependent inhibition of adenylyl cyclase activity could be obtained to account for the relatively weak effect of PGE2 compared with prostacyclin receptor agonists. Interestingly, sulprostone (prostanoid EP3/EP1 receptor agonist) caused a Rho-kinase-dependent retraction of neurites, suggesting an alternative role for prostanoid EP3 receptors in DRG cells. In conclusion, PGE2 mediated increases in adenylyl cyclase activity in primary sensory neurones is likely to be mediated by activation of prostanoid EP4 receptors, and is not under inhibitory control by prostanoid EP3 receptors.