The spinal phospholipase-cyclooxygenase-prostanoid cascade in nociceptive processing

Intravenous acetaminophen is superior to ketamine for postoperative pain after abdominal hysterectomy: results of a prospective, randomized, double-blind, multicenter clinical trial

BACKGROUND

In recent years, intravenously (IV) administered acetaminophen has become one of the most common perioperative analgesics. Despite its now-routine use, IV acetaminophen's analgesic comparative efficacy has never been compared with that of ketamine, a decades-old analgesic familiar to obstetricians, gynecologists, and anesthesiologists alike. This doubleblind clinical trial aimed to evaluate the analgesic effects of ketamine and IV acetaminophen on postoperative pain after abdominal hysterectomy.

METHODS

Eighty women aged 25-70 years old and meeting inclusion and exclusion criteria were randomly allocated into two groups of 40 to receive either IV acetaminophen or ketamine intraoperatively. Postoperatively, each patient had patient-controlled analgesia. Pain and sedation (Ramsay Sedation Scale) were documented based on the visual analog scale in the recovery room and at 4 hours, 6 hours, 12 hours, and 24 hours after the surgery. Hemodynamic changes, adverse medication effects, and the need for breakthrough meperidine were also recorded for both groups. Data were analyzed by repeated-measures analysis of variance.

RESULTS

Visual analog scale scores were significantly lower in the IV acetaminophen group at each time point (P<0.05), and this group required significantly fewer doses of breakthrough analgesics compared with the ketamine group (P=0.039). The two groups had no significant differences in terms of adverse effects.

CONCLUSION

Compared with ketamine, IV acetaminophen significantly improved postoperative pain after abdominal hysterectomy.

Animal models of diabetes-induced neuropathic pain

Neuropathy will afflict over half of the approximately 350 million people worldwide who currently suffer from diabetes and around one-third of diabetic patients with neuropathy will suffer from painful symptoms that may be spontaneous or stimulus evoked. Diabetes can be induced in rats or mice by genetic, dietary, or chemical means, and there are a variety of well-characterized models of diabetic neuropathy that replicate either type 1 or type 2 diabetes. Diabetic rodents display aspects of sensorimotor dysfunction such as stimulus-evoked allodynia and hyperalgesia that are widely used to model painful neuropathy. This allows investigation of pathogenic mechanisms and development of potential therapeutic interventions that may alleviate established pain or prevent onset of pain.

Neurogenic neuroinflammation: inflammatory CNS reactions in response to neuronal activity

The CNS is endowed with an elaborated response repertoire termed 'neuroinflammation', which enables it to cope with pathogens, toxins, traumata and degeneration. On the basis of recent publications, we deduce that orchestrated actions of immune cells, vascular cells and neurons that constitute neuroinflammation are not only provoked by pathological conditions but can also be induced by increased neuronal activity. We suggest that the technical term 'neurogenic neuroinflammation' should be used for inflammatory reactions in the CNS in response to neuronal activity. We believe that neurogenic neuro-inflammation maintains homeostasis to enable the CNS to cope with enhanced metabolic demands and increases the computational power and plasticity of CNS neuronal networks. However, neurogenic neuroinflammation may also become maladaptive and aggravate the outcomes of pain, stress and epilepsy.

Piroxicam-β-cyclodextrin: a GI safer piroxicam

Although NSAIDs are very effective drugs, their use is associated with a broad spectrum of adverse reactions in the liver, kidney, cardiovascular (CV) system, skin and gut. Gastrointestinal (GI) side effects are the most common and constitute a wide clinical spectrum ranging from dyspepsia, heartburn and abdominal discomfort to more serious events such as peptic ulcer with life-threatening complications of bleeding and perforation. The appreciation that CV risk is also increased further complicates the choices of physicians prescribing anti-inflammatory therapy. Despite prevention strategies should be implemented in patients at risk, gastroprotection is often underused and adherence to treatment is generally poor. A more appealing approach would be therefore to develop drugs that are devoid of or have reduced GI toxicity. Gastro-duodenal mucosa possesses many defensive mechanisms and NSAIDs have a deleterious effect on most of them. This results in a mucosa less able to cope with even a reduced acid load. NSAIDs cause gastro-duodenal damage, by two main mechanisms: a physiochemical disruption of the gastric mucosal barrier and systemic inhibition of gastric mucosal protection, through inhibition of cyclooxygenase (COX, PG endoperoxide G/H synthase) activity of the GI mucosa. However, against a background of COX inhibition by anti-inflammatory doses of NSAIDs, their physicochemical properties, in particular their acidity, underlie the topical effect leading to short-term damage. It has been shown that esterification of acidic NSAIDs suppresses their gastrotoxicity without adversely affecting anti-inflammatory activity. Another way to develop NSAIDs with better GI tolerability is to complex these molecules with cyclodextrins (CDs), giving rise to so-called “inclusion complexes” that can have physical, chemical and biological properties very different from either those of the drug or the cyclodextrin. Complexation of NSAIDs with β-cyclodextrin potentially leads to a more rapid onset of action after oral administration and improved GI tolerability because of minimization of the drug gastric effects. One such drug, piroxicam-β-cyclodextrin (PBC), has been used in Europe for 25 years. Preclinical and clinical pharmacology of PBC do show that the β-cyclodextrin inclusion complex of piroxicam is better tolerated from the upper GI tract than free piroxicam, while retaining all the analgesic and anti-inflammatory properties of the parent compound. In addition, the drug is endowed with a quick absorption rate, which translates into a faster onset of analgesic activity, an effect confirmed in several clinical studies. An analysis of the available trials show that PBC has a GI safety profile, which is better than that displayed by uncomplexed piroxicam. Being an inclusion complex of piroxicam, whose CV safety has been pointed out by several observational studies, PBC should be viewed as a CV safe anti-inflmmatory compound and a GI safer alternative to piroxicam. As a consequence, it should be considered as a useful addition to our therapeutic armamentarium.

Neuronal prostaglandin E2 receptor subtype EP3 mediates antinociception during inflammation

The pain mediator prostaglandin E2 (PGE2) sensitizes nociceptive pathways through EP2 and EP4 receptors, which are coupled to Gs proteins and increase cAMP. However, PGE2 also activates EP3 receptors, and the major signaling pathway of the EP3 receptor splice variants uses inhibition of cAMP synthesis via Gi proteins. This opposite effect raises the intriguing question of whether the Gi-protein-coupled EP3 receptor may counteract the EP2 and EP4 receptor-mediated pronociceptive effects of PGE2. We found extensive localization of the EP3 receptor in primary sensory neurons and the spinal cord. The selective activation of the EP3 receptor at these sites did not sensitize nociceptive neurons in healthy animals. In contrast, it produced profound analgesia and reduced responses of peripheral and spinal nociceptive neurons to noxious stimuli but only when the joint was inflamed. In isolated dorsal root ganglion neurons, EP3 receptor activation counteracted the sensitizing effect of PGE2, and stimulation of excitatory EP receptors promoted the expression of membrane-associated inhibitory EP3 receptor. We propose, therefore, that the EP3 receptor provides endogenous pain control and that selective activation of EP3 receptors may be a unique approach to reverse inflammatory pain. Importantly, we identified the EP3 receptor in the joint nerves of patients with painful osteoarthritis.

Parecoxib added to ropivacaine prolongs duration of axillary brachial plexus blockade and relieves postoperative pain

BACKGROUND

Cyclooxygenase (COX)-2 antagonist is widely used for intravenous postoperative pain relief. Recent studies reported COX-2 in the spinal dorsal horn could modulate spinal nociceptive processes. Epidural parecoxib in rats showed no neurotoxicity. These findings suggested applying a COX-2 antagonist directly to the central or peripheral nerve might provide better analgesia.

QUESTIONS/PURPOSES

We therefore determined: (1) whether the addition of parecoxib to ropivacaine injected locally on the nerve block affected the sensory and motor block times of the brachial plexus nerve block; and (2) whether parecoxib injected locally on the nerve or intravenously had a similar analgesic adjuvant effect.

METHODS

We conducted a randomized controlled trial from January 2009 to November 2010 with 150 patients scheduled for elective forearm surgery, using a multiple-nerve stimulation technique. Patients were randomly allocated into one of three groups: Group A (n = 50) received ropivacaine 0.25% alone on the brachial plexus nerve; Group B (n = 50) received ropivacaine together with 20 mg parecoxib locally on the nerve block; and Group C (n = 50) received 20 mg parecoxib intravenously. We recorded the duration of the sensory and motor blocks, and the most severe pain score during a 24-hour postoperative period.

RESULTS

Parecoxib added locally on the nerve block prolonged the motor and sensory block times compared with Group A. However, parecoxib injected intravenously had no such effect. Pain intensity scores in Group B were lower than those in Groups A and C.

CONCLUSIONS

Parecoxib added to ropivacaine locally on the nerve block prolonged the duration of the axillary brachial plexus blockade and relieved postoperative pain for patients having forearm orthopaedic surgery.

LEVEL OF EVIDENCE

Level I, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Polyanalgesic Consensus Conference 2012: recommendations for the management of pain by intrathecal (intraspinal) drug delivery: report of an interdisciplinary expert panel

INTRODUCTION

The use of intrathecal (IT) infusion of analgesic medications to treat patients with chronic refractory pain has increased since its inception in the 1980s, and the need for clinical research in IT therapy is ongoing. The Polyanalgesic Consensus Conference (PACC) panel of experts convened in 2000, 2003, and 2007 to make recommendations on the rational use of IT analgesics based on preclinical and clinical literature and clinical experiences.

METHODS

The PACC panel convened again in 2011 to update the standard of care for IT therapies to reflect current knowledge gleaned from literature and clinical experience. A thorough literature search was performed, and information from this search was provided to panel members. Analysis of published literature was coupled with the clinical experience of panel members to form recommendations regarding the use of IT analgesics to treat chronic pain.

RESULTS

After a review of literature published from 2007 to 2011 and discussions of clinical experience, the panel created updated algorithms for the rational use of IT medications for the treatment of neuropathic pain and nociceptive pain.

CONCLUSIONS

The advent of new algorithmic tracks for neuropathic and nociceptive pain is an important step in improving patient care. The panel encourages continued research and development, including the development of new drugs, devices, and safety recommendations to improve the care of patients with chronic pain.

Perioperative pain management in the neurosurgical patient

Perioperative pain management in neurosurgical patients has been inadequately recognized and treated. An increased awareness of pain management and advances in understanding of pain modulation and pathophysiology have led to improved perioperative care of patients. There is a need to assess neurologic function while providing superior analgesia with minimal side effects. Several classes of drugs are currently available or under investigation for use as adjuvants or alternative therapies. There remains a need to determine the best treatment of perioperative pain in this patient population. Improved awareness, assessment, and treatment of pain result in better care and overall patient outcome.

Spinal astrocytes contribute to the circadian oscillation of glutamine synthase, cyclooxygenase-1 and clock genes in the lumbar spinal cord of mice

Spinal astrocytes have key roles in the regulation of pain transmission. However, the relationship between astrocytes and the circadian system in the spinal cord remains poorly defined. In the current study, the circadian variations in the expression of several clock genes in the lumbar spinal cord of mice were examined by using real-time PCR. The expression of Period1, Period2 and Cryptochrome1 showed significant circadian oscillations, each gene peaking in the early evening. The expression of Bmal1 mRNA also exhibited a circadian pattern, peaking from around midnight to early morning. The mRNA levels of Cryptochrome2 were slightly, but not significantly altered. Molecules related to pain transmission were also investigated. The mRNA expression of glutamine synthase (GS), and cyclooxygenases (COXs), known to be involved in various spinal sensory functions, showed rhythmicity with a peak in the early evening, although the expression of the neurokinin-1 receptor, subunits of the N-methyl-d-aspartate receptor, and glutamate transporters did not change. In addition, we found that protein levels of GS and COX-1 were also high at midnight compared with midday. Furthermore, we examined the effect of intrathecal fluorocitrate (100pmol), an inhibitor of astrocytic metabolism, on the expression of oscillating genes in lumbar spinal cord. Fluorocitrate significantly suppressed astrocyte function. Furthermore, the circadian oscillation of clock gene expression and GS and COX-1 expression were suppressed. Together, these results suggest that a significant circadian rhythmicity of the expression of clock genes is present in the spinal cord and that the components of the circadian clock timed by astrocytes might contribute to spinal functions, including nociceptive processes.

Neuronal hyperexcitability: a substrate for central neuropathic pain after spinal cord injury

Neuronal hyperexcitability produces enhanced pain transmission in the spinal dorsal horn after spinal cord injury (SCI). Spontaneous and evoked neuronal excitability normally are well controlled by neural circuits. However, SCI produces maladaptive synaptic circuits in the spinal dorsal horn that result in neuronal hyperexcitability. After SCI, activated primary afferent neurons produce enhanced release of glutamate, neuropeptides, adenosine triphosphate, and proinflammatory cytokines, which are known to be major components for pain transmission in the spinal dorsal horn. Enhanced neurochemical events contribute to neuronal hyperexcitability, and neuroanatomical changes also contribute to maladaptive synaptic circuits and neuronal hyperexcitability. These neurochemical and neuroanatomical changes produce enhanced cellular signaling cascades that ensure persistently enhanced pain transmission. This review describes altered neurochemical and neuroanatomical contributions on neuronal hyperexcitability in the spinal dorsal horn, which serve as substrates for central neuropathic pain after SCI.

Constitutive cyclo-oxygenase-2 does not contribute to the development of human visceral pain hypersensitivity

BACKGROUND AND AIMS

Central sensitisation (CS), contributes to the development and maintenance of gastrointestinal pain hypersensitivity. Constitutive cyclo-oxygenase-2 (COX-2) contributes to central sensitisation in somatic pain hypersensitivity but its role in mediating visceral pain hypersensitivity is unknown. We therefore conducted a study to determine if COX-2 inhibition with Valdecoxib attenuates the development or early maintenance of CS in a validated human oesophageal pain hypersensitivity model.

METHODS

Healthy volunteers were studied in two randomised, double blind, crossover studies in which pain thresholds (PT) to electrical stimulation were assessed in the proximal oesophagus, chest wall and foot, prior to and following a distal oesophageal acid infusion. Protocol 1: Valdecoxib, (40 mg) or matching placebo was given orally for 4 days prior to oesophageal acid infusion. Protocol 2: IV Parecoxib (40 mg) or saline was given 120 min after oesophageal acid infusion.

RESULTS

Valdecoxib did not prevent the induction of secondary allodynia in the proximal oesophagus nor did it attenuate it following its establishment. Chest wall PT fell following oesophageal acid but foot PT remained unchanged; highlighting the development viscero-somatic convergence due to CS. Valdecoxib had no analgesic or anti-hyperalgesic effect on chest wall or foot PT.

CONCLUSIONS

Neither the induction nor initial maintenance of acid induced oesophageal pain hypersensitivity is prevented by Valdecoxib, suggesting that constitutive spinal COX-2 does not contribute to the development or early maintenance of acute visceral central sensitisation.

Health-related quality of life in child patients with temporomandibular disorder pain

Temporomandibular disorders (TMDs) occurs frequently in children and measuring health-related quality of life (HRQL) can complement efficacy measures, offering a complete picture of the impact of disease and treatment on overall well-being.

AIM

To compare HRQL, pain threshold (PT) and range of motion (ROM) in child patients with temporomandibular disorder (TMD) pain and an age and gender matched control group.

METHODS

The study design was a controlled cross-sectional study. Forty-two children participated in the study. Twenty-one child patients referred to a dental pediatric clinic for specialist treatment because of TMD pain and an age and gender matched control group completed the Child health questionnaire-child form 87 (CHQ-CF87). PT was measured with Pain matcher and ROM in terms of maximum unassisted mandibular opening was measured with a ruler.

RESULTS

The child patients with pain more than once a week had a pain duration ranging from 3 months to almost 6 years. The median for pain intensity measured with visual analogue scale (VAS) was 47 ranging from 5 to 80 and the median for behavioral rating scale (BRS) was 3 ranging from 1 to 4. Child patients with TMD pain more than once a week reported significantly lower scores in CHQ-CF87 when compared with a control group. The results for PT and ROM were non-significant.

CONCLUSION

CHQ-CF87 could be used for measuring health and to evaluate the efficacy of treatment in child patients with TMD pain.

A comparison of ketamine and paracetamol for preventing remifentanil induced hyperalgesia in patients undergoing total abdominal hysterectomy

BACKGROUND

The aim of this prospective, randomized, placebo-controlled study was to compare the effects of ketamine and paracetamol on preventing remifentanil induced hyperalgesia.

METHODS

Ninety patients undergoing total abdominal hysterectomy were randomly assigned to one of three groups to receive (I) either saline infusion; (II) 0.5 mg/kg ketamine iv bolus or (III) 1000 mg iv paracetamol infusion before induction of anesthesia. Until the skin closure, anesthesia was maintained with 0.4 µg/kg/min remifentanil infusion in all groups, additionally Group II received 5 µg/kg/min ketamine infusion. Pressure pain thresholds were measured the day before surgery during the preoperative visit for baseline measurements and repeated postoperatively at 24 and 48 hours (hrs). Pressure pain thresholds were established by digital algometer on three different peri- incisional regions for calculating mean pressure pain threshold values. The visual analogue scale (VAS), sedation scores, total morphine consumption and side effects were assessed postoperatively.

RESULTS

Demographic characteristics, duration of surgery and anesthesia were similar in the three groups. Pain thresholds at the incision region were significantly lower at 24 and 48 hrs postoperatively in Group I than the other Groups (p<0.05). In Group І, pain thresholds were lower compared with preoperative baseline values. Thresholds in Group ІІ and Group ІІІ were higher compared with preoperative baseline values (p<0.05) The VAS scores at all evaluation times were significantly higher in Group І when compared to Group ІІ and at 2, 4, 6 ,12 hrs were higher in Group I than Group ІІІ (p<0.05). The morphine consumption was higher in Group ІІІ at 24 and 48 hrs postoperatively (p<0.05).

CONCLUSION

It was shown that ketamine and paracetamol were both effective in preventing remifentanil induced hyperalgesia.

EP1 receptor within the ventrolateral periaqueductal grey controls thermonociception and rostral ventromedial medulla cell activity in healthy and neuropathic rat

The aim of this study was to investigate the expression of prostaglandin EP1 receptor within the ventrolateral periaqueductal grey (VL PAG). The role of VL PAG EP1 receptor in controlling thermonociception and rostral ventromedial medulla (RVM) activity in healthy and neuropathic rats was also examined. EP1 receptor was indeed found to be expressed within the VL PAG and co-localized with vesicular GABA transporter. Intra-VL PAG microinjection of ONO-DI-004, a selective EP1 receptor agonist, dose-dependently reduced tail flick latency as well as respectively increasing and decreasing the spontaneous activity of ON and OFF cells. Furthermore, it increased the ON cell burst and OFF cell pause. Intra-VL PAG prostaglandin E2 (PGE2) behaved similarly to ONO-DI-004. The effects of ONO-DI-004 and PGE2 were antagonized by intra-VL PAG L335677, a selective EP1 receptor antagonist. L335677 dose-dependently increased the tail flick latency and ongoing activity of the OFF cells, while reducing the ongoing ON cell activity. It also decreased the ON cell burst and OFF cell pause. In neuropathic rats using spare nerve injury (SNI) of the sciatic nerve model, EP1 receptor expression decreased in the VL PAG. However, ONO-DI-004 and L335677 were able to alter pain responses and ON and OFF cell activity, as they did in healthy animals. Collectively, these data show that within the VL PAG, EP1 receptor has a facilitatory effect on the nociceptive response and consistently affects RVM neuron activity. Thus, the blockade of EP1 receptor in the VL PAG leads to antinociception in neuropathic pain conditions, despite its down-regulation. The expression of EP1 receptor on GABAergic neurons is consistent with an EP1 receptor blockade-induced disinhibition of the antinociceptive descending pathway at VL PAG level.

Effect of perzinfotel and a proprietary phospholipase A(2) inhibitor on kinetic gait and subjective lameness scores in dogs with sodium urate-induced synovitis

OBJECTIVE

To investigate the ability of perzinfotel (an N-methyl-d-aspartate receptor antagonist) and a proprietary phospholipase A(2) (PLA(2)) inhibitor to attenuate lameness in dogs with sodium urate (SU)-induced synovitis.

ANIMALS

8 adult dogs.

PROCEDURES

A blinded 4-way crossover study was performed. Dogs received perzinfotel (10 mg/kg), a proprietary PLA(2) inhibitor (10 mg/kg), carprofen (4.4 mg/kg; positive control treatment), or no treatment (negative control treatment). On the fourth day after initiation of treatment, synovitis was induced via intra-articular injection of SU 1 hour before administration of the last treatment dose. Ground reaction forces were measured and clinical lameness evaluations were performed before (baseline [time 0]) and 2, 4, 6, 8, 12, and 25 hours after SU injection. There was a 21-day washout period between subsequent treatments. Data were analyzed via repeated-measures ANOVAs.

RESULTS

Peak vertical force (PVF) and vertical impulse (VI) values for negative control and perzinfotel treatments were significantly lower at 2 and 4 hours, compared with baseline values. Values for PVF and VI for the PLA(2) inhibitor and positive control treatments did not differ from baseline values at any time points. Between-treatment comparisons revealed significantly higher PVF and VI values for the positive control treatment than for the negative control and perzinfotel treatments at 2 and 4 hours. Values for VI were higher for PLA(2) inhibitor treatment than for negative control treatment at 2 hours.

CONCLUSIONS AND CLINICAL RELEVANCE

Perzinfotel did not significantly alter SU-induced lameness. The proprietary PLA(2) inhibitor attenuated lameness but not as completely as did carprofen.

Gene therapy for chronic neuropathic pain: how does it work and where do we stand today?

OBJECTIVES

Chronic neuropathic pain has been an enigma to physicians and researchers for decades. A better understanding of its pathophysiology has given us more insight into its various mechanisms and possible treatment options. We now have an understanding of the role of various ionic channels, biologically active molecules involved in pain, and also the intricate pain pathways where possible interventions might lead to substantial pain relief. The recent research on laboratory animals using virus-based vectors for gene transfer at targeted sites is very promising and may lead to additional human clinical trials. However, one needs to be aware that this "novel" approach is still in its infancy and that many of its details need to be further elucidated. The purpose of this article is to thoroughly review the current available literature and analyze the deficiencies in our current knowledge.

DESIGN

Literature review.

METHODS

After an extensive online literature search, a total of 133 articles were selected to synthesize a comprehensive review about chronic neuropathic pain and gene therapy in order to understand the concepts and mechanisms.

RESULTS

Most of the studies have shown benefits of gene therapy in animal models, and recently, phase 1 human trials using herpes simplex virus vector have started for intractable cancer pain.

CONCLUSION

Although animal data have shown safety and efficacy, and initial human trials have been promising, additional studies in humans are required to more completely understand the actual benefits and risks of using gene therapy for the treatment of chronic neuropathic pain.

Acetylcholine and norepinephrine mediate GABAergic but not glycinergic transmission enhancement by melittin in adult rat substantia gelatinosa neurons

GABAergic and glycinergic inhibitory synaptic transmissions in substantia gelatinosa (SG; lamina II of Rexed) neurons of the spinal dorsal horn play an important role in regulating nociceptive transmission from the periphery. It has not yet been well known whether each of the inhibitory transmissions plays a distinct role in the regulation. We report an involvement of neurotransmitters in GABAergic but not glycinergic transmission enhancement produced by the PLA2 activator melittin, where the whole-cell patch-clamp technique is applied to the SG neurons of adult rat spinal cord slices. Glycinergic but not GABAergic spontaneous inhibitory postsynaptic current (sIPSC) was increased in frequency and amplitude by melittin in the presence of nicotinic, muscarinic acetylcholine, and α1-adrenergic receptor antagonists (mecamylamine, atropine, and WB-4101, respectively). GABAergic transmission enhancement produced by melittin was unaffected by the 5-hydroxytryptamine 3 receptor and P2X receptor antagonists (ICS-205,930 and pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid, respectively). Nicotinic and muscarinic acetylcholine receptor agonists [(−)-nicotine and carbamoylcholine, respectively] and norepinephrine, as well as melittin, increased GABAergic sIPSC frequency and amplitude. A repeated application of (−)-nicotine, carbamoylcholine, and norepinephrine, but not melittin, at an interval of 30 min produced a similar transmission enhancement. These results indicate that melittin produces the release of acetylcholine and norepinephrine, which activate (nicotinic and muscarinic) acetylcholine and α1-adrenergic receptors, respectively, resulting in GABAergic but not glycinergic transmission enhancement in SG neurons. The desensitization of a system leading to the acetylcholine and norepinephrine release is slow in recovery. This distinction in modulation between GABAergic and glycinergic transmissions may play a role in regulating nociceptive transmission.

Number of synapses increased in the rat spinal dorsal horn after sciatic nerve transection: a stereological study

We recently found that the number of synapses in the spinal dorsal horn, as estimated by stereological techniques, increased by 86% after chronic constriction injury of sciatic nerve in rats. In this study, we aimed to reveal whether transection of sciatic nerve was also associated with a plasticity change in the number of synapses. 18 adult SD rats were randomly divided into 3 groups undergoing (i) unilateral sham operation, (ii) unilateral sciatic nerve transection, and (iii) unilateral sciatic nerve transection with postoperative medication (parecoxib) for 3 days, respectively. 28 days postoperation, the L4-6 segment of the spinal cord was removed; paraffin-embedded sections were prepared and stained with Nissl's method and synaptophysin immunohistochemistry. The optical disector (a contemporary stereological technique) was used to estimate the numbers of neurons and synapses in the spinal dorsal horn. Compared to the non-operated side, the axotomy induced a 74.3% increase in the number of synapses per unit length of spinal cord or a 67.4% increase in the ratio between the numbers of synapses and neurons in the middle tissue block from the L4-6 segment on the operated side but not in either the rostral or caudal tissue block. Parecoxib had no effect on the parameters. In conclusion, peripheral nerve injury, model for neuropathic pain, is associated with a synaptic plasticity (numerical increase) in the spinal dorsal horn.

Analgesic effects of the ethanolic extract from Magnolia ovata (Magnoliaceae) trunk bark and of N-acetylxylopine, a semi-synthetic analogue of xylopine

This study investigated the antinociceptive effects of the ethanolic extract (EEMO) obtained from Magnolia ovata (A.St.-Hil.) Spreng and N-acetylxylopine (AXyl), a stable derivative of xylopine in different models of nociception. The EEMO and AXyl inhibited the nociception induced by acetic acid in mice, in a dose-dependent manner with a maximal inhibition of 91 ± 9% and 50 ± 11%, respectively. Oral administration of EEMO or AXyl also significantly inhibited the inflammatory phase of formalin-induced nociception with maximal reduction of 87 ± 3.9% and 71 ± 10%, respectively. Confirming the effectiveness of the extract and the isolated compound in inflammatory responses, EEMO or AXyl inhibited carrageenan-induced mechanical allodynia with percentage of inhibition of 40 ± 6% for EEMO and 82 ± 8% for AXyl. Intraplantar injection of AXyl in the ipsilateral paw, but not in the contralateral paw, also reduced carrageenan-induced mechanical allodynia in mice. The response of the animals for maximal doses tested of EEMO and AXyl in the hot-plate or rota-rod models were not altered. These results show that the extract from M. ovata and the stable derivative AXyl possess analgesic properties towards inflammatory pain acting on peripheral sites.

Indirect role of beta2-adrenergic receptors in the mechanism of analgesic action of nonsteroidal antiinflammatory drugs

OBJECTIVE

Adrenal gland hormones have been shown to have a role in the antiinflammatory effect mechanism of nonsteroidal antiinflammatory drugs. This study investigates whether the analgesic effects of indomethacin, diclofenac sodium, aspirin, and nimesulide (IDAN; upper case letters of the four drugs we used) are also related to adrenal gland hormones.

DESIGN

The analgesic effects of IDAN were studied in the carrageenan-induced inflammatory pain model using both intact and adrenalectomized rats. Paw withdrawal tests were performed in adrenalectomized rats that had been pretreated with phenoxybenzamine, propranolol, and metoprolol.

SETTING

This study was performed in Pharmacology and Biochemistry Laboratories of Faculty of Medicine.

PATIENTS/SUBJECTS

A total of 306 (114 intact and 192 adrenalectomized) male Albino Wistar rats were used.

INTERVENTIONS

Adrernalectomy, drug administrations, pain model induction and pain threshold measurements were performed during the study.

MEASUREMENTS AND MAIN RESULTS

Although the analgesic effects of nonsteroidal antiinflammatory drugs were lost in adrenalectomized rats, they exerted significant analgesia in adrenalectomized rats that had been pretreated with prednisolone and adrenalin. All these drugs were found to decrease serum adrenalin concentration but did not change serum cortisole (corticosterone in rats) concentration. Prednisolone and adrenalin inhibited carrageenan-induced hyperalgesia in adrenalectomized rat groups pretreated with metoprolol or phenoxybenzamine, but not in rats given propranolol. Propranolol also negated the analgesic effects of IDAN in intact rats. The analgesic effects provided by either prednisolone or adrenalin could not be inhibited by the alpha1, alpha2, or beta1 blockers but disappeared when beta2 receptors were blocked.

CONCLUSIONS

The analgesic effects of nonsteroidal antiinflammatory drugs appear to be related to endogenous adrenalin and cortisole. We have demonstrated that adrenalin and prednisolone play important roles in the analgesic effect mechanism of IDAN. Prednisolone and adrenalin produce analgesic effects through beta2-adrenergic receptors, suggesting an indirect role for beta2-adrenergic receptors in the analgesic effect mechanism of the nonsteroidal antiinflammatory drugs mentioned.

[Sedation and analgesia in intensive care: physiology and application]

Many therapeutic and diagnostic procedures in intensive care medicine are perceived as painful by most patients. As a consequence analgesia and sedation represent two of the main pillars in the treatment of the critically ill. Adaptation to the individual needs of the patients poses one of the biggest challenges that we are confronted with. Both morbidity and mortality can be positively influenced by adequate treatment. In the first part of this review we will discuss the physiology of sleep patterns and pain. Furthermore modes of action and side effects of the most common anesthetics and analgetics will be presented. Finally, the last part of the manuscript deals with the practical application of these therapeutics and their monitoring in intensive care medicine.

Release of prostaglandin E(2) and nitric oxide from spinal microglia is dependent on activation of p38 mitogen-activated protein kinase

BACKGROUND

The spinal release of prostaglandins (PGs), nitric oxide (NO), and cytokines has been implicated in spinal nociceptive processing. Microglia represent a possible cell of origin for these proexcitatory mediators. Spinal microglia possess Toll-like receptor 4 (TLR4) and neurokinin 1 (NK1) receptors, and both receptors play a significant role in peripheral nerve injury- and inflammation-induced spinal sensitization. Accordingly, we examined the properties of the cascades activated by the respective targets, which led to the release of PGE(2) and an increase in nitrite (NO(2)(-)) (a marker of NO) from cultured rat spinal microglia.

METHODS

Spinal microglia isolated from Sprague-Dawley neonatal rats were cultured with lipopolysaccharide (LPS) or substance P (SP) alone, with LPS in combination with SP, and with LPS in the presence of each inhibitor of cyclooxygenase (COX), NO synthase 2 (NOS2) or p38 mitogen-activated protein kinase (p38), or minocycline for 24 hours and 48 hours. Concentrations of PGE(2) and NO(2)(-) in culture supernatants were measured using an enzyme immunoassay and a colorimetric assay, respectively.

RESULTS

Application of LPS (a TLR4 ligand, 0.1 to 10 ng/mL) to cultured microglia produced a dose- and time-dependent increase in PGE(2) and NO(2)(-) production, whereas no effects were observed after incubation with SP (an NK1 agonist, up to 10(-5) M) alone or in combination with LPS. Antagonist studies with SC-560 (COX-1 inhibitor) and SC-236 (COX-2 inhibitor) showed that LPS-induced PGE(2) release was generated from both COX-1 and COX-2. LPS-induced NO release was suppressed by 1400W, an inhibitor of NOS2. Minocycline, an agent blocking microglial activation, and SB203580, an inhibitor of p38, both attenuated the LPS-induced PGE(2) and NO release. The 1400W, at the doses that suppressed NO release, also blocked increased PGE(2) release.

CONCLUSIONS

Our findings suggest that (a) activation of spinal microglia via TLR4 but not NK1 receptors produces PGE(2) and NO release from these cells; (b) the evoked PGE(2) release is generated by both COX-1 and COX-2, and (c) the COX-PGE(2) pathway is regulated by p38 and NOS2. Taken together with our previous in vivo work, the current findings emphasize that p38 in spinal microglia is a key player in regulating production of pronociceptive molecules, such as PGE(2) and NO.

Phospholipase A2 and its molecular mechanism after spinal cord injury

Phospholipases A(2) (PLA(2)s) are a diverse family of lipolytic enzymes which hydrolyze the acyl bond at the sn-2 position of glycerophospholipids to produce free fatty acids and lysophospholipids. These products are precursors of bioactive eicosanoids and platelet-activating factor which have been implicated in pathological states of numerous acute and chronic neurological disorders. To date, more than 27 isoforms of PLA(2) have been found in the mammalian system which can be classified into four major categories: secretory PLA(2), cytosolic PLA(2), Ca(2+)-independent PLA(2), and platelet-activating factor acetylhydrolases. Multiple isoforms of PLA(2) are found in the mammalian spinal cord. Under physiological conditions, PLA(2)s are involved in diverse cellular responses, including phospholipid digestion and metabolism, host defense, and signal transduction. However, under pathological situations, increased PLA(2) activity, excessive production of free fatty acids and their metabolites may lead to the loss of membrane integrity, inflammation, oxidative stress, and subsequent neuronal injury. There is emerging evidence that PLA(2) plays a key role in the secondary injury process after traumatic spinal cord injury. This review outlines the current knowledge of the PLA(2) in the spinal cord with an emphasis being placed on the possible roles of PLA(2) in mediating the secondary SCI.

Inflammatory hyperalgesia induces essential bioactive lipid production in the spinal cord

Lipid molecules play an important role in regulating the sensitivity of sensory neurons and enhancing pain perception, and growing evidence indicates that the effect occurs both at the site of injury and in the spinal cord. Using high-throughput mass spectrometry methodology, we sought to determine the contribution of spinal bioactive lipid species to inflammation-induced hyperalgesia in rats. Quantitative analysis of CSF and spinal cord tissue for eicosanoids, ethanolamides and fatty acids revealed the presence of 102 distinct lipid species. After induction of peripheral inflammation by intra-plantar injection of carrageenan to the ipsilateral hind paw, lipid changes in cyclooxygenase (COX) and 12-lipoxygenase (12-LOX) signaling pathways peaked at 4 h in the CSF. In contrast, changes occurred in a temporally disparate manner in the spinal cord with LOX-derived hepoxilins followed by COX-derived prostaglandin E(2), and subsequently the ethanolamine anandamide. Systemic treatment with the mu opioid agonist morphine, the COX inhibitor ketorolac, or the LOX inhibitor nordihydroguaiaretic acid significantly reduced tactile allodynia, while their effects on the lipid metabolites were different. Morphine did not alter the lipid profile in the presence or absence of carrageenan inflammation. Ketorolac caused a global reduction in eicosanoid metabolism in naïve animals that remained suppressed following injection of carrageenan. Nordihydroguaiaretic acid-treated animals also displayed reduced basal levels of COX and 12-LOX metabolites, but only 12-LOX metabolites remained decreased after carrageenan treatment. These findings suggest that both COX and 12-LOX play an important role in the induction of carrageenan-mediated hyperalgesia through these pathways.

Role of spinal p38alpha and beta MAPK in inflammatory hyperalgesia and spinal COX-2 expression

Pharmacological studies indicate that spinal p38 mitogen-activated protein kinase plays a role in the development of hyperalgesia. We investigated whether either the spinal isoform p38alpha or p38beta is involved in peripheral inflammation evoked pain state and increased expression of spinal COX-2. Using intrathecal antisense oligonucleotides, we show that hyperalgesia is prevented by downregulation of p38beta but not p38alpha, whereas increases in spinal COX-2 protein expression at 8 hours are mediated by both p38alpha and beta isoforms. These data suggest that early activation of spinal p38beta isoform may affect acute facilitatory processing, and both p38beta and alpha isoforms mediate temporally delayed upregulation of spinal COX-2.

Ketoprofen produces modality-specific inhibition of pain behaviors in rats after plantar incision

BACKGROUND

Postoperative pain remains a significant problem despite optimal treatment with current drugs. Nonsteroidal antiinflammatory drugs reduce inflammation and provide analgesia but are associated with adverse side effects.

METHODS

We tested low doses (0.5-5 mg/kg) of parenteral ketoprofen against pain-related behaviors after plantar incision in rats. To further evaluate the potential sites of action of ketoprofen in our model, a novel, sustained-release microparticle formulation of ketoprofen was placed into the wound, and tested for its effects on pain behaviors. Intrathecal ketoprofen (150 microg) was also studied. Plasma samples were assayed for drug concentrations.

RESULTS

We found that low doses of parenterally administered ketoprofen produced a modality-specific effect on pain behaviors; guarding after incision was decreased, whereas no inhibition of exaggerated responses to heat or mechanical stimuli was evident. Very low doses, 0.5 mg/kg, could produce inhibition of guarding. The locally applied sustained-release ketoprofen-eluting microparticles and intrathecally administered ketoprofen also produced a modality-specific effect on pain behaviors after incision, inhibiting only guarding. Plasma levels of ketoprofen after parenteral or local administration were in the range of therapeutic blood levels in postoperative patients.

CONCLUSIONS

This study demonstrates that ketoprofen is an effective analgesic for nonevoked guarding in rats after plantar incision. There was no effect on mechanical or heat responses, which highlights the importance of multiple-modality testing of pain behaviors for drug evaluation. We found efficacy at doses used clinically in postoperative patients.

Postoperative analgesic effect of preoperative intravenous flurbiprofen in arthroscopic rotator cuff repair

PURPOSE

This study was carried out to evaluate the postoperative analgesic effects of preoperative intravenous flurbiprofen in patients undergoing arthroscopic rotator cuff repair under general anesthesia.

METHODS

We studied 44 patients who underwent an elective arthroscopic rotator cuff repair in a prospective, randomized, and double-blind fashion. The patients were divided into two groups. Group A (n = 22) received lipid emulsion 0.1 ml kg(-1) as a placebo, and group B (n = 22) received flurbiprofen 1 mg kg(-1) before the surgery. Intralipid or flurbiprofen was given intravenously 5 min before the surgery. General anesthesia was maintained with sevoflurane and nitrous oxide, and 10 ml of 0.75% ropivacaine was administered intraarticularly at the end of the surgery. Postoperative analgesia was supplied with intravenous 0.1 mg buprenorphine according to the patient's demand. The effectiveness of flurbiprofen's analgesic effect was measured by a visual analog scale (VAS) and by the amount of buprenorphine consumption at 0.5, 1, 2, 4, 6, 12, and 24 h after the surgery. Time to the first analgesic was also recorded.

RESULTS

VAS in group B was significantly (P < 0.01) lower than that in group A during the first 6 h postoperatively. The amount of buprenorphine consumption in group B was also significantly (P < 0.01) less than that in group A within the first 2 h postoperatively. The time to first analgesic request in group B was significantly (P < 0.01) longer than that in group A.

CONCLUSION

These results show that preoperative intravenous flurbiprofen facilitates the analgesic effect in the early postoperative period after arthroscopic rotator cuff repair.

Spinal antinociceptive effects of cyclooxygenase inhibition during inflammation: Involvement of prostaglandins and endocannabinoids

Both cyclooxygenase-1 and -2 are expressed in the spinal cord, and the spinal COX product prostaglandin E(2) (PGE(2)) contributes to the generation of central sensitization upon peripheral inflammation. Vice versa spinal COX inhibition is considered an important mechanism of antihyperalgesic pain treatment. Recently, however, COX-2 was shown to be also involved in the metabolism of endocannabinoids. Because endocannabinoids can have analgesic actions it is conceivable that inhibition of spinal COX produces analgesia not only by inhibition of PG synthesis but also by inhibition of endocannabinoid breakdown. In the present study, we recorded from spinal cord neurons with input from the inflamed knee joint and we measured the spinal release of PGE(2) and the endocannabinoid 2-arachidonoyl glycerol (2-AG) in vivo, using the same stimulation procedures. COX inhibitors were applied spinally. Selective COX-1, selective COX-2 and non-selective COX inhibitors attenuated the generation of spinal hyperexcitability when applied before and during development of inflammation but, when inflammation and spinal hyperexcitability were established, only selective COX-2 inhibitors reversed spinal hyperexcitability. During established inflammation all COX inhibitors reduced release of spinal PGE(2) almost equally but only the COX-2 inhibitor prevented breakdown of 2-AG. The reversal of spinal hyperexcitability by COX-2 inhibitors was prevented or partially reversed by AM-251, an antagonist at the cannabinoid-1 receptor. We conclude that inhibition of spinal COX-2 not only reduces PG production but also endocannabinoid breakdown and provide evidence that reversal of inflammation-evoked spinal hyperexcitability by COX-2 inhibitors is more related to endocannabinoidergic mechanisms than to inhibition of spinal PG synthesis.

Mitochondrial Ca2+ cycling facilitates activation of the transcription factor NFAT in sensory neurons

Ca(2+)-dependent gene regulation controls many aspects of neuronal plasticity. Significant progress has been made toward understanding the roles of voltage- and ligand-gated Ca(2+) channels in triggering specific transcriptional responses. In contrast, the functional importance of Ca(2+) buffers and Ca(2+) transporters in neuronal gene regulation is less clear despite their critical contribution to the spatiotemporal control of Ca(2+) signals. Here we examined the role of mitochondrial Ca(2+) uptake and release in regulating the Ca(2+)-dependent transcription factor NFAT (nuclear factor of activated T-cells), which has been implicated in synaptic plasticity, axonal growth, and neuronal survival. Intense stimulation of sensory neurons by action potentials or TRPV1 agonists induced rapid activation and nuclear import of NFAT. Nuclear translocation of NFAT was associated with a characteristic prolonged [Ca(2+)](i) elevation (plateau) that resulted from Ca(2+) uptake by, and its subsequent release from, mitochondria. Measurements using a mitochondrial Ca(2+) indicator, mtPericam, showed that this process recruited mitochondria throughout the cell body, including the perinuclear region. [Ca(2+)](i) levels attained during the plateau phase were similar to or higher than those required for NFAT activation (200-300 nm). The elimination of the [Ca(2+)](i) plateau by blocking either mitochondrial Ca(2+) uptake via the uniporter or Ca(2+) release via the mitochondrial Na(+)/Ca(2+) exchanger strongly reduced nuclear import of NFAT. Furthermore, preventing Ca(2+) mobilization via the mitochondrial Na(+)/Ca(2+) exchanger diminished NFAT-mediated transcription. Collectively, these data implicate activity-induced Ca(2+) uptake and prolonged release from mitochondria as a novel regulatory mechanism in neuronal excitation-transcription coupling.

Prostanoid receptor antagonists: development strategies and therapeutic applications

Identification of the primary products of cyclo-oxygenase (COX)/prostaglandin synthase(s), which occurred between 1958 and 1976, was followed by a classification system for prostanoid receptors (DP, EP(1), EP(2) ...) based mainly on the pharmacological actions of natural and synthetic agonists and a few antagonists. The design of potent selective antagonists was rapid for certain prostanoid receptors (EP(1), TP), slow for others (FP, IP) and has yet to be achieved in certain cases (EP(2)). While some antagonists are structurally related to the natural agonist, most recent compounds are 'non-prostanoid' (often acyl-sulphonamides) and have emerged from high-throughput screening of compound libraries, made possible by the development of (functional) assays involving single recombinant prostanoid receptors. Selective antagonists have been crucial to defining the roles of PGD(2) (acting on DP(1) and DP(2) receptors) and PGE(2) (on EP(1) and EP(4) receptors) in various inflammatory conditions; there are clear opportunities for therapeutic intervention. The vast endeavour on TP (thromboxane) antagonists is considered in relation to their limited pharmaceutical success in the cardiovascular area. Correspondingly, the clinical utility of IP (prostacyclin) antagonists is assessed in relation to the cloud hanging over the long-term safety of selective COX-2 inhibitors. Aspirin apart, COX inhibitors broadly suppress all prostanoid pathways, while high selectivity has been a major goal in receptor antagonist development; more targeted therapy may require an intermediate position with defined antagonist selectivity profiles. This review is intended to provide overviews of each antagonist class (including prostamide antagonists), covering major development strategies and current and potential clinical usage.

NCX 2057, a novel NO-releasing derivative of ferulic acid, suppresses inflammatory and nociceptive responses in in vitro and in vivo models

BACKGROUND AND PURPOSE

We previously reported that NCX 2057, a compound comprising a nitric oxide (NO)-releasing moiety and the natural antioxidant, ferulic acid (FA), inhibits pro-inflammatory mediators through NO-mediated gene regulation. Here, we have assessed the activities of NCX 2057 in models of inflammatory and neuropathic pain, and characterized its effects on cyclooxygenase (COX)-1 and COX-2.

EXPERIMENTAL APPROACH

Anti-nociceptive and anti-inflammatory activities of NCX 2057 were measured in vitro and in vivo in models of inflammatory (carrageenan) and neuropathic (chronic constriction injury; CCI) pain. Effects of NCX 2057 were measured on COX-1 and COX-2 activities in RAW 264.7 macrophages.

KEY RESULTS

NCX 2057 dose-dependently inhibited single motor unit responses to noxious mechanical stimulation (ID(50)= 100 micromol kg(-1)) and wind-up responses in rats with paw inflammation induced by carrageenan. Moreover, NCX 2057 inhibited allodynic responses following CCI of the sciatic nerve [ipsilateral Paw Withdrawal Threshold (g): vehicle: 41.4 +/- 3.3; NCX 2057: 76.3 +/- 4.8 FA: 37.9 +/- 15.5 at 175 micromol kg(-1)]. NCX 2057 reversed carrageenan-induced hyperalgesic responses in mice and inhibited prostaglandin E(2) formation in paw exudates. Finally, NCX 2057 competitively inhibited COX-1 and COX-2 activities in whole RAW macophages (IC(50)= 14.7 +/- 7.4 and 21.6 +/- 7.5 microM, respectively). None of these properties were exhibited by equivalent treatments with FA or standard NO donor compounds.

CONCLUSIONS AND IMPLICATIONS

These studies indicate that NCX 2057 is effective in chronic inflammatory and neuropathic pain models, probably because of its particular combination of anti-COX, antioxidant and NO-releasing properties.