Role of CRF1 receptor in post-incisional plasma extravasation and nociceptive responses in mice.

The corticotropin-releasing factor (CRF) is involved in a number of physiological functions including pain perception. The purpose of this study was to evaluate the role of CRF1 receptor in the long-lasting post-surgical changes in somatic nociceptive thresholds and in local inflammatory responses, using genetically engineered mice lacking functional CRF1 receptor. Animals underwent a plantar incision under anaesthesia with remifentanil (80µg/kg s.c.) and sevoflurane. Mechanical thresholds (von Frey) and plasma extravasation (Evan's blue) were evaluated at different time points. On postoperative day 20, mechanical thresholds had returned to baseline in CD1 mice (3.07±6.21%), while B6,129CRHtklee mice presented significant hyperalgesia, which was similar in wild-type (WT) (-29.81±8.89%) and CRF1 receptor knockout (KO) (-37.10±10.75%) mice, showing strain differences. The administration of naloxone (1mg/kg, s.c.) on postoperative day 21 produced hyperalgesia revealing surgery-induced latent pain sensitization. The extent of hyperalgesia was greater in KO versus WT mice, suggesting a role of CRF1 receptors in the upward modulation of endogenous opioid release. Furthermore, two days after surgery, plasma extravasation returned to baseline in WT mice but remained elevated in KO mice. In non-manipulated B6,129CRHtklee KO mice we observed an increase in the number of writhes (41.25±11.36) versus WT (23.80±4.71), while in the tail immersion test no differences could be detected. Our results show that CRF/CRF1 receptors seem to be a protective role in latent pain sensitization induced by surgery and in the local inflammatory response to injury.

Almitrine fails to improve oxygenation during one-lung ventilation with sevoflurane anesthesia.

OBJECTIVE: Almitrine enhances hypoxic pulmonary vasoconstriction (HPV) and can improve hypoxemia related to one-lung ventilation (OLV). Studies using almitrine have been conducted without inhaled anesthetics because they could inhibit HPV, counteracting the effect of almitrine. This hypothesis, however, has not been confirmed. This study's aim was to evaluate whether almitrine could improve oxygenation when administered during OLV with sevoflurane anesthesia. DESIGN: A prospective, randomized, double-blind, placebo-controlled trial. SETTING: A tertiary care, university teaching hospital. PARTICIPANTS: Thirty adult patients undergoing open-chest thoracic surgery. INTERVENTIONS: Patients were assigned randomly to receive almitrine or placebo during OLV. Respiratory and hemodynamic variables were recorded continuously. Anesthesia was maintained with sevoflurane and remifentanil. Intraoperative techniques and medical teams were the same all over the study. MEASUREMENTS AND MAIN RESULTS: Respiratory and hemodynamic variables were measured during two-lung ventilation and during open-chest OLV. Two-way repeated-measures analysis of variance was used to compare the effects of almitrine and placebo. During OLV, PaO2 and shunt fraction worsened in all patients without significant differences between groups. At 30-minutes of OLV, PaO2 was 184±67 mmHg in the almitrine group and 145±56 mmHg in the placebo group, while shunt fraction were 31%±6% and 36%±13%, respectively. Mean pulmonary artery pressure was higher in the almitrine group (31±5 v 24±5 mmHg, p<0.001). CONCLUSIONS: During anesthesia with sevoflurane for open-chest OLV, almitrine failed to improve oxygenation and increased pulmonary artery pressure. The combination of sevoflurane and almitrine should, therefore, be avoided.

A ¹8F-fluorodeoxyglucose MicroPET imaging study to assess changes in brain glucose metabolism in a rat model of surgery-induced latent pain sensitization.

BACKGROUND: Neuroplastic changes involved in latent pain sensitization after surgery are poorly defined. We assessed temporal changes in glucose brain metabolism in a postoperative rat model using positron emission tomography. We also investigated brain metabolism after naloxone administration. METHODS: Rats were given remifentanil anesthetic and underwent a plantar incision, with 1 mg/kg of (-)-naloxone subcutaneously administered on postoperative days 20 and 21. Using the von Frey test, mechanical thresholds were measured pre- and postoperatively at different time points in awake animals during F-fluorodeoxyglucose (F-FDG) uptake. Brain images were also obtained the day before mechanical testing, using a positron emission tomography R4 scanner (Concorde Microsystems, Siemens, Knoxville, TN). Differences in brain activity were assessed utilizing a statistical parametric mapping. RESULTS: Surgery induced minor changes in F-FDG uptake in the cerebellum, hippocampus, and posterior cortex, which extended to the thalamus, hypothalamus, and brainstem on days 6 and 7. Changes were still present on day 21. Maximal postoperative hypersensitivity was observed on day 2. The administration of (-)-naloxone on day 21 induced significant hypersensitivity, greatly enhancing the effect on F-FDG uptake. In sham-operated rats, naloxone induced changes limited to the striatum and the cerebellum. Nonnociceptive stimulation with von Frey filaments had no effect on F-FDG uptake. CONCLUSIONS: Surgery, remifentanil, and their combination induced long-lasting and significant metabolic changes in the pain brain matrix, with a positive correlation with hypersensitivity after naloxone. Changes in brain F-FDG precipitated by naloxone suggest that surgery under remifentanil anesthetic induces the greatest neuroplastic brain adaptations in opioid-related pathways involved in nociceptive processing and long-lasting pain sensitization.

Increased spinal dynorphin levels and phospho-extracellular signal-regulated kinases 1 and 2 and c-Fos immunoreactivity after surgery under remifentanil anesthesia in mice.

In humans, remifentanil anesthesia enhances nociceptive sensitization in the postoperative period. We hypothesized that activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and the expression of c-Fos, prodynorphin (mRNA), and dynorphin in the spinal cord could participate in the molecular mechanisms underlying postoperative opioid-induced sensitization. In a mouse model of incisional pain, we evaluated thermal (Hargreaves test) and mechanical (von Frey) hyperalgesia during the first 21 postoperative days. Moreover, prodynorphin (mRNA, real-time polymerase chain reaction), dynorphin (enzymatic immunoassay), c-Fos expression, and ERK1/2 phosphorylation (both by immunohistochemistry) in the lumbar spinal cord were assessed. Surgery performed under remifentanil anesthesia induced a maximal decrease in nociceptive thresholds between 4 h and 2 days postoperatively (p < 0.001) that lasted 10 to 14 days compared with noninjured animals. In the same experimental conditions, a significant increase in prodynorphin mRNA expression (at 2 and 4 days) followed by a sustained increase of dynorphin (days 2 to 10) in the spinal cord was observed. We also identified an early expression of c-Fos immunoreactivity in the superficial laminae of the dorsal horn of the spinal cord (peak at 4 h; p < 0.001), together with a partial activation of ERK1/2 (4 h; p < 0.001). These findings suggest that activated ERK1/2 could induce c-Fos expression and trigger the transcription of prodynorphin in the spinal cord. This in turn would result in long-lasting increased levels of dynorphin that, in our model, could participate in the persistence of pain but not in the manifestation of first pain.

Analysis of the opioid-opioid combinations according to the nociceptive stimulus in mice.

The purpose of the present study was to characterize the antinociceptive effects of tramadol, fentanyl and morphine, when two of them were systemically combined in a 1:1 potency ratio, in the hot plate, the acetic acid writhing, and the formalin tests in mice. Interaction indexes and isobolographic analysis were used to assess the type of interaction. Fentanyl was the most potent drug, followed by morphine and tramadol, with the exception in the phase I of formalin test. Synergistic interactions were obtained when tramadol was combined with fentanyl or with morphine in the writhing and formalin tests. But, in the hot plate only additive interactions were obtained. Changes were induced on the type of interaction depending on the level of effect of opioid-opioid combinations. Moreover, co-administration of fentanyl with morphine showed additivity, regardless of the type of stimulus. Standard rotarod test analysis confirmed intact motor coordination. The present findings suggest that the type of interaction between opioids is not only related to the nature of nociceptive stimulus but also to non-opioid analgesic pathways.

Pronociceptive effects of remifentanil in a mouse model of postsurgical pain: effect of a second surgery.

BACKGROUND: Remifentanil anesthesia enhances postoperative pain in animals and humans. The authors evaluated the impact of the dose (microg x kg(-1) x min(-1)) and duration of remifentanil infusion, and the effects of a second surgery on postoperative pain sensitization. METHODS: Mice received different doses of remifentanil over 30 or 60 min. The authors assessed thermal (Hargreaves) and mechanical hyperalgesia (von Frey) at 2, 4, 7, and 10 days. In other experiments, mice had a plantar incision during sevoflurane with or without remifentanil anesthesia that was repeated 27 days later, when nociceptive thresholds returned to baseline. Linear mixed models were used for statistical analysis. RESULTS: Remifentanil induced dose-dependent pronociceptive effects with calculated ED(50)s of 1.7 (95% confidence interval, 1.3-2.1) and 1.26 (1.0-1.6) microg x kg(-1) x min(-1) for thermal and mechanical hyperalgesia, respectively, which lasted longer with higher doses (P < 0.001). The duration of infusion did not alter the pronociceptive effects of remifentanil when administered at a constant dose of infusion. When given during surgery, high (2.66 microg x kg(-1) x min(-1)) or low (0.66 microg x kg(-1) x min(-1)) remifentanil increased the extent (P < 0.05) and duration (P < 0.01) of thermal and mechanical hyperalgesia. The latter was further enhanced after a second surgery performed in the same experimental conditions (P < 0.05). Surgery or remifentanil infusion, each one individually, induced significant mechanical hyperalgesia, which was greater when repeated (P < 0.05). CONCLUSIONS: In this model of incisional pain, remifentanil induces pronociceptive effects, which are dose dependent but unaltered by the duration of administration. A second surgery performed on the same site and experimental conditions induces greater postoperative hyperalgesia that is enhanced when remifentanil is used as an anesthetic.

Isobolographic analysis of multimodal analgesia in an animal model of visceral acute pain.

Multiple analgesic-drug combinations are commonly used in the management of acute and chronic pain in humans during multimodal or balanced analgesia. At present, these combinations are used empirically in clinical practice and are considered to be beneficial for the patient. Interactions between two antinociceptive drugs have been thoroughly examined, but the nature of interactions between three analgesics has not been studied. The antinociceptive interaction of ketoprofen (K) with a mixture of morphine (M) and paracetamol (P) was evaluated using a model of visceral acute tonic pain, the acetic-acid writhing test in mice. The i.p. administration of the combination M/P+K resulted in a significant potentiation of the antinociception induced either by K or by the synergic two-drug mixtures M/K, P/K and M/P. The effect of opioid, cholinergic, adrenergic and serotonergic antagonists on the analgesic interaction was assessed. The pretreatment of mice with atropine (1 mg/kg) did not produce any change in the synergistic interaction of the triple combination. The pretreatment with naltrexone (1 mg/kg) or tropisetron (1 mg/kg) reduced the intensity of M/P+K synergic interaction, while prazosin (0.1 mg/kg) significantly potentiated the synergy. The findings of this work suggest that the two major pathways of descending inhibitory systems, noradrenergic and serotonergic are significantly involved in the mechanism of the antinociceptive synergy induced by the triple combination. On the other hand, opioid pathways also seem to participate, since pretreatment with naltrexone reduced the synergy. In conclusion, the triple combination M/P+K induced a strong synergistic antinociceptive effect, which could be of interest for optimal multimodal clinical analgesia.

Dexketoprofen-induced antinociception in animal models of acute pain: synergy with morphine and paracetamol.

The antinociceptive activity of dexketoprofen was studied in mice using the acetic acid writhing test (acute tonic pain), the tail flick test (acute phasic pain) and the formalin assay (inflammatory pain). Isobolographic analysis was used to study the antinociceptive interactions between morphine and paracetamol co-administered with dexketoprofen. In the writhing test, the intraperitoneal administration of dexketoprofen or ketoprofen resulted in parallel dose-response curves with equal efficacy, but higher relative potency for dexketoprofen. In the tail flick test, the curves were parallel with similar efficacy and potency. The administration of morphine or paracetamol in both tests resulted in dose-response curves not parallel with that of dexketoprofen, which showed a potency between morphine and paracetamol. In the formalin assay, the antinociceptive activity of morphine during phase I was 122, 295 and 1695 times higher than dexketoprofen, ketoprofen and paracetamol, respectively. Isobolographic analysis demonstrated that the combination of sub-analgesic doses of dexketoprofen with morphine or with paracetamol was strongly synergic in all three tests. Synergistic drug combinations should improve effective pharmacological treatment of pain, minimizing drug specific adverse effects. These findings are undoubtedly worthy of additional controlled clinical trials in severe pain syndromes.

Synergistic interaction between dexamethasone and tramadol in a murine model of acute visceral pain.

Tramadol is effective in the management of mild to moderate postoperative pain, but its administration is associated with nausea and vomiting. Patients treated with tramadol, often receive dexamethasone as antiemetic. The aim of our investigation was to assess if the two drugs interact in a murine model of acute visceral pain. Using the acetic acid writhing test in mice, we assessed the antinociceptive effects of tramadol and dexamethasone (a glucocorticoid with antiemetic effect) administrated individually and in a 1 : 1 fixed ratio combination. Tramadol and dexamethasone induced a dose-dependent inhibition of the writhing response when administered individually, with ED(50) values of 2.9 [2.09-4.31, 95% confidence limit (CL)] mg/kg, and 0.13 (0.05-0.29, 95% CL) mg/kg, respectively. The ED(50) of the combination was 0.13 (0.01-0.29, 95% CL) mg/kg; the isobolographic and interaction index analysis revealed a synergistic interaction. The results suggest that the combination of tramadol and dexamethasone could be beneficial in the management of postoperative pain in humans.

Postoperative Pain Management in Spanish Hospitals: A Cohort Study Using the PAIN-OUT Registry.

Pain after surgery remains a problem worldwide, although there are no published data on postoperative outcomes in Spain. We evaluated 2,922 patients on the first day after surgery in 13 tertiary care Spanish hospitals, using the PAIN-OUT questionnaire. The aims were to: assess postoperative outcomes and anesthetic/analgesic management in Orthopedics (ORT) and General Surgery (GEN) patients; explore the influence of the analgesic therapy on outcomes and opioid requirements; evaluate and compare outcomes and analgesic management according to surgical procedure. Mean worst pain and percentage of patients in severe pain were 5.6 (on a numeric rating scale of 0-10) and 39.4%, respectively, slightly lower than those reported in Western countries (range, 5.0-8.4 and 33-55%). Patients' pain assessment (83.1%) and information were high (63.3%), but participation in decision-making (4.8) was lower than in the United States (7.0) and Europe (Germany, France, Norway, and Denmark; mean, 5.9). Patients after orthopedic surgery had the worst outcomes. General anesthesia was more frequent in GEN patients, whereas regional (central and peripheral) was more frequent in ORT surgery patients. Mean opioid consumption (20.2 mg per patient per 24 hours, oral morphine equivalents), was lower than reported and decreased >50% after regional analgesia. Intravenous morphine patient-controlled analgesia was seldom used (6.2%). Acute opioid treatments were associated with worsened outcomes whereas multimodal analgesia (mainly antipyretic analgesics-nonsteroidal anti-inflammatory drugs-opioids) were associated with improved results. Epidurals in abdominal surgery (16.7%) were also associated with better outcomes. Presurgical chronic pain (>7) and/or chronic opioid consumption, were associated with worsened pain outcomes; the latter with a 50% increase in postoperative opioid requirements. Tibia/fibula and foot surgeries (ORT), and gastric, small intestine, and anterior abdominal wall procedures (GEN) were the most painful. Rigorous control of chronic pain before surgery, and combining opioids with adjuvants and other analgesics perioperatively, might improve postoperative outcomes. PERSPECTIVE: We analyzed postoperative outcomes and analgesic management in patients from tertiary care Spanish hospitals. The study serves as a point of comparison with other Western countries and shows that pain intensity outcomes and opioid consumption were slightly better in the Spanish population. Chronic pain before surgery (numeric rating scale score >7) and/or chronic opioid consumption, were associated with worsened pain outcomes, suggesting that rigorous control of chronic pain before surgery, and combining opioids with adjuvants and other analgesics perioperatively, might improve outcomes. Patients' pain participation in decision-making was inadequate and should be improved in Spanish hospitals.

Synergism between paracetamol and nonsteroidal anti-inflammatory drugs in experimental acute pain.

The antinociception induced by the intraperitoneal coadministration of combinations of paracetamol with the nonsteroidal anti-inflammatory drugs (NSAIDs) diclofenac, ibuprofen, ketoprofen, meloxicam, metamizol, naproxen, nimesulide, parecoxib and piroxicam was studied by isobolographic analysis in the acetic acid abdominal constriction test of mice (writhing test). The effective dose that produced 50% antinociception (ED50) was calculated from the log dose-response curves of fixed ratio combinations of paracetamol with each NSAID. By isobolographic analysis, this ED50 was compared to the theoretical additive ED50 calculated from the ED(50) of paracetamol and of each NSAID alone obtained from ED50 dose-response curves. As shown by isobolographic analysis, all the combinations were synergistic, the experimental ED50s being significantly smaller than the theoretically calculated ED50s. The results of this study demonstrate potent interactions between paracetamol and NSAIDs and validate the clinical use of combinations of these drugs in the treatment of pain conditions.

Expression of opioid receptors and c-fos in CB1 knockout mice exposed to neuropathic pain.

The development of neuropathic pain is associated with multiple changes in gene expression occurring in the dorsal root ganglia (DRG) and spinal cord. The goal of this study was to evaluate whether the disruption of CB1 cannabinoid receptor gene modulates the changes induced by neuropathic pain in the expression of mu- (MOR), delta- (DOR) and kappa-opioid receptors (KOR) mRNA levels in the DRG and spinal cord. The induction of c-fos expression in the lumbar and sacral regions of the spinal cord was also evaluated in these animals. Opioid receptors mRNA levels were determined by using real-time PCR and Fos protein levels by immunohistochemistry. Nerve injury significantly reduced the expression of MOR in the DRG and the lumbar section of the spinal cord from CB1 cannabinoid knockout (KO) mice and wild-type littermates (WT). In contrast, mRNA levels of DOR and KOR were not significantly changed in any of the different sections analysed. Furthermore, sciatic nerve injury evoked a similar increase of c-fos expression in lumbar and sacral regions of the spinal cord of both KO and WT. In all instances, no significant differences were observed between WT and KO mice. These data revealed specific changes induced by neuropathic pain in MOR expression and c-fos levels in the DRG and/or spinal cord that were not modified by the genetic disruption of CB1 cannabinoid receptors.

Synergistic interaction between fentanyl and the histamine H3 receptor agonist R-(alpha)-methylhistamine, on the inhibition of nociception and plasma extravasation in mice.

Here we report a synergistic interaction between fentanyl and the histamine H(3) receptor agonist R-(alpha)-methylhistamine on the inhibition of nociception and plasma extravasation in mice. Chronic inflammation was induced by subplantar injection of Complete Freund's Adjuvant into the right hind paw, and the effect of the drugs was evaluated 7 days later. Nociception and plasma extravasation were assessed by hot-plate and Evans blue tests respectively. Subcutaneous administration of fentanyl (0.01-0.1 mg/kg) induced dose-related anti-nociceptive and anti-extravasation effects (E(max)=100% and 62%, respectively). R-(alpha)-methylhistamine administration (0.3-3 mg/kg) showed a dose-related inhibitory effect on extravasation (E(max)=65%) but not on nociception. To analyze possible interaction between these two drugs, a dose-response curve to fentanyl plus a fixed dose of R-(alpha)-methylhistamine (0.5 mg/kg) was obtained. The dose-response curve for the combined treatment showed a shift to the left compared with that for fentanyl alone. Our results confirm that fentanyl and R-(alpha)-methylhistamine interact in a synergic way, inhibiting nociception and plasma extravasation.

Interaction between tramadol and two anti-emetics on nociception and gastrointestinal transit in mice.

BACKGROUND: Clinical studies suggest that tramadol-induced analgesia is partially antagonized by ondansetron. AIMS: To investigate the type of interaction between tramadol and two anti-emetics on antinociception and gastrointestinal transit in mice. METHODS: We assessed the antinociceptive (acetic acid writhing test, plantar test) and antitransit (charcoal meal) effects of tramadol individually, and combined with ondansetron or droperidol in female Swiss CD-1 mice. Isobolograms and analysis of variance were used to determine the type of interaction. RESULTS: In the writhing test, tramadol, ondansetron and droperidol, each induced dose-related inhibition of nociception. The ED(50)'s were: tramadol 4.2+/-0.33 mg kg(-1); ondansetron 1.03+/-0.05 mg kg(-1), and droperidol 1.00+/-0.14 mg kg(-1). Dose-response curves were also obtained with tramadol combined with ondansetron or droperidol at 1:1 fixed ratios. The isobolographic analysis demonstrated antagonism for both combinations. In the plantar test, the ED(50) for tramadol was 51.4+/-2.3 mg kg(-1), but no dose-response curves could be obtained with ondansetron or droperidol individually. The interaction was assessed from dose-response curves to tramadol in the presence of a fixed dose of ondansetron (0.1 mg kg(-1)) or droperidol (0.05 mg kg(-1)). The results show antagonism between tramadol-ondansetron (p<0.05) and no interaction for the tramadol-droperidol combination. Both anti-emetics antagonized the antitransit effects of tramadol. CONCLUSIONS: The interaction of tramadol with ondansetron or droperidol on antinociception can be antagonistic or additive, depending on the type of stimuli. Both anti-emetics antagonize the anti-transit effects of tramadol. The results demonstrate antagonism between tramadol and the two anti-emetics for analgesia and inhibition of gastrointestinal transit, supporting previous clinical studies.

Antihyperalgesic effects of dexketoprofen and tramadol in a model of postoperative pain in mice - effects on glial cell activation.

OBJECTIVES: To define likely targets (i.e. glia) and protocols (analgesic combinations) to improve postoperative pain outcomes and reduce chronic pain after surgery. Specifically, to assess the antihyperalgesic effects of the dexketoprofen : tramadol (DEX : TRM) combination, exploring the implication of glial activation. METHODS: In a mouse model of postincisional pain, we evaluated mechanical nociceptive thresholds (Von Frey) for 21 days postoperatively. We assessed DEX and TRM alone and combined (1 : 1 ratio) on postoperative hyperalgesia (POH, day 1) and delayed latent pain sensitisation (substantiated by a naloxone challenge; PS, day 21). The interactions were analysed using isobolograms, and concomitant changes in spinal glial cell activation were measured. KEY FINDINGS: On day 1, DEX completely blocked POH, whereas TRM induced 32% inhibition. TRM, but not DEX, partially (47%) protected against PS, at 21 days. Co-administration of DEX : TRM (1 : 1 ratio) showed additivity for antihyperalgesia. Both drugs and their combination totally inhibited surgery-induced microglia activation on day 1, but had no effect on surgery-induced astrocyte activation (1 day) or re-activation after naloxone (21 days). CONCLUSIONS: The DEX : TRM combination could have clinical advantages: a complete prevention of POH after surgery, together with a substantial (48%) inhibition of the development of PS by TRM. Microglia, but not astrocyte activation, could play a relevant role in the development of postoperative pain hypersensitivity.

The involvement of nitric oxide in the enhanced expression of mu-opioid receptors during intestinal inflammation in mice.

Intestinal inflammation enhances the potency of mu-opioid receptor (MOR) agonists inhibiting gastrointestinal transit and increases the expression of MOR in mice intestine. The precise mechanisms implicated in the increased expression of MOR during intestinal inflammation are not known. The aim of the study is to evaluate if nitric oxide released during intestinal inflammation could modulate MOR gene expression and affect gastrointestinal transit. Intestinal inflammation was induced by the intragastric administration of croton oil. In CD-1 mice, with and without inflammation, we evaluated the anti-transit effects of morphine in animals treated with NOS inhibitors (L-NAME and L-NIL) and the intestinal levels of iNOS enzyme mRNA. The anti-transit effects of morphine and the expression of MOR mRNA in the gut of wild-type (WT) and iNOS-/- mice were also assessed. Gastrointestinal transit was measured with charcoal meal and mRNA levels determined by real-time PCR. In CD-1 mice, inflammation induced a 10-fold increase (P<0.0001) in iNOS mRNA levels in the gut. The absence of iNOS gene and treatment of CD-1 mice with L-NAME or L-NIL abolished the increased antitransit effects of morphine observed during inflammation. Moreover, although the basal levels of MOR mRNA were similar in WT and iNOS animals (-/-), intestinal inflammation only increased the MOR expression in the gut of WT (P<0.01) but not in iNOS-/- mice. The results suggest that nitric oxide derived from the increased expression of iNOS is implicated in the enhanced effects of morphine and in the upregulation of MOR gene transcription observed during intestinal inflammation.

Anti-exudative effects of opioid receptor agonists in a rat model of carrageenan-induced acute inflammation of the paw.

We evaluated the anti-exudative effects (Evan's blue) of mu-, delta- and kappa-opioid receptor agonists in a rat model of carrageenan-induced acute inflammation. The contribution of different components was assessed after the administration of: cyclosporine A, capsaicin, 6-hydroxydopamine, compound 48/80, and specific histamine-receptor antagonists. The results show that the mu-opioid receptor agonists morphine and fentanyl and the delta-opioid receptor agonists DPDPE (enkephalin, [D-Pen(2,5)]) and SNC 80 ((+)-4-[(alpha R)-alpha((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N diethylbenzamide) decrease plasma extravasation in a dose-dependent manner, with a biphasic response. The effects were reversed by specific antagonists, and are predominantly mediated by peripheral opioid receptors. The integrity of sensory and sympathetic fibres is essential for the anti-exudative effects of fentanyl and DPDPE. Histamine and functional histamine H(2) and H(3) receptors are required for morphine and fentanyl (but not DPDPE) inhibition of plasma extravasation, suggesting different mechanism for mu- and delta-opioid receptor agonists. The present findings implicate multiple sites and mechanisms in the anti-exudative effects of exogenous opioids.

Current pain education within undergraduate medical studies across Europe: Advancing the Provision of Pain Education and Learning (APPEAL) study.

OBJECTIVES: Unrelieved pain is a substantial public health concern necessitating improvements in medical education. The Advancing the Provision of Pain Education and Learning (APPEAL) study aimed to determine current levels and methods of undergraduate pain medicine education in Europe. DESIGN AND METHODS: Using a cross-sectional design, publicly available curriculum information was sought from all medical schools in 15 representative European countries in 2012-2013. Descriptive analyses were performed on: the provision of pain teaching in dedicated pain modules, other modules or within the broader curriculum; whether pain teaching was compulsory or elective; the number of hours/credits spent teaching pain; pain topics; and teaching and assessment methods. RESULTS: Curriculum elements were publicly available from 242 of 249 identified schools (97%). In 55% (133/242) of schools, pain was taught only within compulsory non-pain-specific modules. The next most common approaches were for pain teaching to be provided wholly or in part via a dedicated pain module (74/242; 31%) or via a vertical or integrated approach to teaching through the broader curriculum, rather than within any specific module (17/242; 7%). The curricula of 17/242 schools (7%) showed no evidence of any pain teaching. Dedicated pain modules were most common in France (27/31 schools; 87%). Excluding France, only 22% (47/211 schools) provided a dedicated pain module and in only 9% (18/211) was this compulsory. Overall, the median number of hours spent teaching pain was 12.0 (range 4-56.0 h; IQR: 12.0) for compulsory dedicated pain modules and 9.0 (range 1.0-60.0 h; IQR: 10.5) for other compulsory (non-pain specific) modules. Pain medicine was principally taught in classrooms and assessed by conventional examinations. There was substantial international variation throughout. CONCLUSIONS: Documented pain teaching in many European medical schools falls far short of what might be expected given the prevalence and public health burden of pain.

Expression of opioid receptors during peripheral inflammation.

Opioid receptors (OR) and their mRNA are present in the central and peripheral nervous system of mammals. In this review we examine the behavioral effects of opioids and the expression of their receptors during peripheral inflammation in two experimental models: the rat paw and the mouse intestine. Inflammation increased the antinociceptive (paw) and the inhibitory effects of opioids in the gut (transit, permeability and plasma extravasation) by interaction with OR located at peripheral sites. Based on agonist efficacy, micro > delta >> kappa-OR mediate the antinociceptive and antitransit effects of opioids during inflammation. Intestinal permeability is modulated by delta = micro >> kappa-OR, while kappa > delta >> micro-OR are involved in the inhibition of plasma extravasation. Intestinal inflammation increased the transcription of micro and delta-OR (but not kappa) genes in the gut, thus explaining the enhanced antitransit and antisecretory effects of micro and delta-OR agonists; however, the increased inhibitory effects of kappa-OR agonists on plasma extravasation could result from post-transcriptional regulation of the receptor. Similarly, the increased expression of peripheral micro-OR observed in the rat paw during inflammation, occurs at post-transcriptional levels and is related to an increased axonal transport from the dorsal root ganglia to peripheral terminals. The sites and mechanisms implicated in the increased transcription of micro and delta-OR during intestinal inflammation are under investigation.