Remifentanil-induced Hyperalgesia Research Articles

Role of spinal kinesin superfamily motor protein 17 in remifentanil-induced hyperalgesia in rats with incisional pain

Objective To evaluate the role of spinal kinesin superfamily motor protein 17(KIF17)in remifentanil-induced hyperalgesia in rats with incisional pain. Methods Forty male Sprague-Dawley rats, aged 2-3 months, weighing 240-260 g, were divided into 5 groups(n=8 each)using a random number table: control group(group C), remifentanil group(group R), incisional pain group(group I), remifentanil plus incisional pain group(group R+ I)and remifentanil plus incisional pain plus KIF17 inhibitor group(group R+ I+ M). Normal saline 1.5 ml was intravenously infused for 60 min in group C. Remifentanil 1 μg·kg-1·min-1 was intravenously infused for 60 min in group R. In group I, incisional pain model was established, and normal saline 1.5 ml was intravenously infused for 60 min at the same time.In group R+ I, incisional pain model was established, and remifentanil 1.5 ml was intravenously infused for 60 min at the same time.In group R+ I+ M, KIF17 inhibitor Myr-Rc-13 10 μg(in 10 μl dimethyl sulfoxide)was injected intrathecally, and remifentanil 1 μg·kg-1·min-1 was intravenously infused for 60 min while incisional pain model was established.The mechanical paw withdrawal threshold(MWT)and thermal paw withdrawal latency(TWL)were measured at 24 h before remifentanil or normal saline infusion and at 2, 6, 24 and 48 h after the end of infusion.The rats were sacrificed after the last measurement of pain threshold, and the lumbar segment of the spinal cord was removed for determination of the expression of KIF17 and phosphorylated KIF17(pKIF17)by Western blot. Results Compared with group C, MWT was significantly decreased, TWL was shortened, and the expression of KIF17 and pKIF17 was up-regulated in R, I and R+ I groups(P<0.05). Compared with R and I groups, MWT was significantly decreased, TWL was shortened, and the expression of KIF17 and pKIF17 was up-regulated in group R+ I(P<0.05). Compared with group I+ R, MWT was significantly increased, TWL was prolonged, and the expression of KIF17 and pKIF17 was down-regulated in group R+ I+ M(P<0.05). Conclusion Increased activity of KIF17 is involved in the development and maintenance of remifentanil-induced hyperalgesia in rats with incisional pain. Key words: Piperidines; Pain, postoperative; Hyperalgesia; Kinesin; Spinal cord

Efficacy of different low-doses of nalmefene in preventing remifentanil-induced postoperative hyperalgesia

Objective To evaluate the efficacy of different low-doses of nalmefene in preventing remifentanil-induced postoperative hyperalgesia. Methods One hundred American Society of Anesthesiologist physical status Ⅰor Ⅱpatients, aged 20-64 yr, wih body mass index of 18-25 kg/m2, scheduled for elective gynecological laparoscopic surgery under general anesthesia, were divided into 4 groups(n=25 each)using a random number table: control group(group C)and different doses of nalmefene groups(N1, N2 and N3 groups). In N1, N2 and N3 groups, nalmefene 0.2, 0.3 and 0.5 μg/kg(diluted to 5 ml in normal saline)were intravenously injected, respectively, at 5 min before anesthesia induction, while the equal volume of normal saline was given in group C. Anesthesia was induced with midazolam 0.05 mg/kg, sufentanil 0.3 μg/kg, etomidate 0.3 mg/kg and rocuronium 0.6 mg/kg.The patients were mechanically ventilated after tracheal intubation.Anesthesia was maintained by IV infusion of remifentanil 0.3 μg·kg-1·min-1 and inhalation of 4%-6% desflurane, bispectral index value was maintained at 45-60, and muscle relaxation was maintained with intermittent IV boluses of rocuronium.After admission to postanesthesia care unit, patient-controlled analgesia(PCA)was performed, and PCA solution contained sufentanil 1 μg/ml in 100 ml of normal saline.PCA pump was programmed to deliver a 0.5 ml bolus dose with a lockout interval of 15 min and background infusion at 2 ml/h.Numeric rating scale score was maintained <4.The time for remifentanil infusion was recorded.The consumption of sufentanil was recorded in 0-1, 1-3, 3-6, 6-12 and 12-24 h periods after surgery, and the occurrence of nausea, vomiting, tachycardia, hypertension and shivering was also recorded within 24 h after surgery. Results Compared with group C, the postoperative consumption of sufentanil was significantly reduced in 0-1 h and 1-3 h periods after surgery in group N1 and in 0-1, 1-3, 3-6 and 6-12 h periods after surgery in group N2, and the incidence of postoperative nausea was significantly decreased in N1, N2 and N3 groups(P<0.05). The consumption of sufentanil in 3-6 h period after surgery was significantly lower in group N2 than in group N1(P<0.05). Conclusion The optimal dose of nalmefene is 0.3 μg/kg when used to prevent remifentanil-induced postoperative hyperalgesia. Key words: Morphinane; Piperidines; Hyperalgesia

The influence of ketamine on KCC2 in spinal cord of rat in remifentanil-induced hyperalgesia

Objective To explore the effect of pre-treatment of subcutaneous injection of ketamine on remifentanil induced hyperalgesia and K+ /Cl-cotransporter 2, KCC2) expression on spinal cord of rats. Methods 60 male adult SD rats were randomly divided into five groups(n=12 in each group): control group (group C), the incision group(group I), the incision plus remifentanil group(group I+ R), the incision plus ketamine group(group I+ K) and the incision plus remifentanil and ketamine group(group I+ R+ K). Mechanical withdrawal threshold (MWT) was evaluated at 24 hours before incision(T0), 2 hours, 6 hours, 24 hours and 48 hours after incision(T1~T4). The lumbar spinal cords of rats were taken out at T4 time point and the KCC2 detected was detected by immunofluorescence analysis and western blot analysis. Results Compared with group C(T1(14.5±1.7)g, T2(14.2±1.1)g, T3(13.9±1.8)g, T4(14.2±1.1)g), MWT of other groups at T1 (I(5.6±0.8)g, I+ R(3.2±1.0)g, I+ K(6.8±1.7)g, I+ R+ K(5.1±1.6)g), T2 (I(6.9±1.0)g, I+ R(4.3±1.2)g, I+ K(8.0±1.4)g, I+ R+ K(6.2±1.5)g), T3 (I(7.6±0.9)g, I+ R(5.4±1.1)g, I+ K(10.3±1.2)g, I+ R+ K(7.1±1.1)g), T4 (I(8.9±1.1)g, I+ R(7.5±1.4)g, I+ K(11.3±1.2)g, I+ R+ K(8.3±1.2)g)and the expression of KCC2 at T4 decreased (P<0.05). Compared with group I(T1(5.6±0.8)g, T2(6.9±1.0)g, T3(7.6±0.9)g, T4(8.9±1.1)g), MWT of group I+ R (T1(3.2±1.0)g, T2(4.3±1.2)g, T3(5.4±1.1)g, T4(7.5±1.4)g) decreased at all time points after incision (T1~T4)(P<0.05) and the expression of KCC2 at T4 decreased significantly (P<0.05). Compared with group I(T1(5.6±0.8)g, T2(6.9±1.0)g, T3(7.6±0.9)g, T4(8.9±1.1)g), MWT of group I+ K (T1(6.8±1.7)g, T2(8.0±1.4)g, T3(10.3±1.2)g, T4(11.3±1.2)g) increased at all time points after incision (T1~T4)(P<0.05) and the expression of KCC2 at T4 increased (P<0.05). Compared with group I+ R(T1(3.2±1.0)g, T2(4.3±1.2)g, T3(5.4±1.1)g, T4(7.5±1.4)g), MWT of group I+ R+ K (T1(5.1±1.6)g, T2(6.2±1.5)g, T3(7.1±1.1)g, T4(8.3±1.2)g) increased at all time points after incision (T1~T4)(P<0.05) and the expression of KCC2 at T4 increased (P<0.05). Conclusion Pre-treatment of subcutaneous injection of ketamine can reduce the hyperalgesia of rats induced by remifentanil and reduce the inhibition of KCC2 expression on dorsal horn of spinal cord. Key words: Remifentanil; Hyperalgesia; Ketamine; KCC2

CXCL13 regulates the trafficking of GluN2B-containing NMDA receptor via IL-17 in the development of remifentanil-induced hyperalgesia in rats

BackgroundThis study aimed to investigate whether CXCL13 modulated the trafficking of NMDA receptor via interleukin (IL)-17 in a rat model of remifentanil-induced hyperalgesia (RIH).Although chemokines are crucial regulators of neuroinflammation, spinal N-methyl-d-aspartate (NMDA) receptor activation, and development of hypernociceptive process, little is known about specific pathogenesis and effective treatment. Inflammatory mediators are required for excitatory synaptic transmission in pathologic pain. MethodsA neutralizing antibody against CXCL13 (anti-CXCL13), antiserum against IL-17 (anti-IL-17), and recombinant CXCL13 and IL-17 were administered intrathecally to explore the roles of CXCL13, IL-17, and NMDA receptor, as well as the prevention of hyperalgesia. Paw withdrawal threshold and paw withdrawal latency were employed to record mechanical allodynia and thermal hyperalgesia. Reverse transcriptase quantitative polymerase chain reaction was used to evaluate the levels of CXCL13/CXCR5 and IL-17/IL-17RA in the spinal dorsal horn. The trafficking of spinal GluN2B-containing NMDA receptor was assessed by Western blot after nociceptive testing. ResultsThis study found mechanical allodynia and thermal hyperalgesia with a remarkable increase in the expression of spinal CXCL13/CXCR5 and IL-17/IL-17RA and trafficking of GluN2B-containing NMDA receptor after remifentanil exposure. Behavioral RIH and elevated GluN2B trafficking were dampened by intrathecal anti-CXCL13 and anti-IL-17, respectively. The delivery of exogenous CXCL13 dose-dependently generated a rapid nociceptive hypersensitivity in naïve rats, which was prevented by coadministering anti-IL-17. CXCL13-induced IL-17RA overproduction and GluN2B trafficking were reversed by anti-IL-17 treatment. GluN2B antagonist also blocked CXCL13, and IL-17 directly induced hyperalgesia. ConclusionThis study highlighted the contribution of IL-17 pathway in the trafficking of CXCL13-induced GluN2B-containing NMDA receptor in the pathogenesis of RIH.

Magnesium sulphate attenuate remifentanil-induced postoperative hyperalgesia via regulating tyrosine phosphorylation of the NR2B subunit of the NMDA receptor in the spinal cord

BackgroundRemifentanil induced hyperalgesia (RIH) is characterized by stimulation evoked pain including allodynia and thermal hyperalgesia after remifentanil infusion. N-methyl-D-aspartate (NMDA) receptor was reported to be involved in the progress of RIH. We hypothesized that intrathecal MgSO4 could relieve hyperalgesia after remifentanil infusion via regulating phosphorylation of NMDA receptor NR2B subunit activity in this study.MethodsThirty two rats were randomly allocated into control group, model of RIH group, RIH plus 100ug MgSO4 group, RIH plus 300ug MgSO4 group. Mechanical and thermal hyperalgesia were tested at -24th h, 2nd h, 6th h, 24th h, 48th h after remifentanil infusion. Following sacrifice of rats after the last behavioral test, we performed the western blot to detect the expression of spinal phosphorylated NMDA receptor NR2B subunit (pNR2B) in the L4-L5 segments.ResultsIntrathecal MgSO4 (100, 300 μg) dose-dependently reduced thermal and mechanical hyperalgesia from 2 h to 48 h after remifentanil infusion. Remifentanil infusion remarkably stimulated the expression of pNR2B. Nevertheless, the increased amount of pNR2B by RIH was dose-dependently suppressed by intrathecal infusion of MgSO4 in rats.ConclusionsRemifentanil induced hyperalgesia/allodynia could be ameliorated by Mg-mediated blockade targeting the NR2B subunit in NMDA receptors.

Changes in expression of TRPV1 in dorsal root ganglions during remifentanil-induced hyperalgesia in rats with incisional pain

Objective To evaluate the changes in the expression of transient receptor potential vanilloid l (TRPV1) in dorsal root ganglions (DRGs) during remifentanil-induced hyperalgesia in the rats with incisional pain. Methods Thirty-two SPF healthy male Sprague-Dawley rats, weighing 240-260 g, aged 2-3 months, in which caudal catheters were successfully implanted, were divided into 4 groups (n=8 each) using a random number table: control group (group C), incisional pain group (group I), remifentanil group (group R), and incisional pain + remifentanil group (group I+ R). A 1 cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the left hindpaw to establish the model of incisional pain.In group R, remifentanil was intravenously infused for 60 min at a rate of 1.2 μg·kg-1·min-1.In group I, the model of incisional pain was established, and the equal volume of normal saline was intravenously infused for 60 min at the same time.In group I+ R, the model of incisional pain was established, and remifentanil was intravenously infused for 60 min at a rate of 1.2 μg·kg-1·min-1 at the same time.In group C, the equal volume of normal saline was intravenously infused for 60 min.The mechanical paw withdrawal threshold (MWT) and thermal paw withdrawl latency (TWL) were measured at 24 h before normal saline or remifentanil infusion (T0) and 2, 6, 24 and 48 h after the end of infusion (T1-4). The rats were sacrificed after the last measurement of pain threshold, and the DRGs of the lumbar segment (L4-6) were removed for determination of the expression of TRPV1 protein and mRNA by Western blot and real-time polymerase chain reaction, respectively. Results Compared with group C, the MWT was significantly decreased, and the TWL was shortened at T1-4, and the expression of TRPV1 protein and mRNA was up-regulated in R, I and I+ R groups (P<0.05). Compared with group R or group I, the MWT was significantly decreased, and the TWL was shortened at T1-4, and the expression of TRPV1 protein and mRNA was up-regulated in group I+ R (P<0.05) Conclusion Up-regulated expression of TRPV1 in DRGs may be involved in the mechanism underlying remifentanil-induced hyperalgesia in the rats with incisional pain. Key words: TRPV cation channels; Piperidines; Hyperalgesia; Ganglia, spinal

Prevention of Remifentanil Induced Postoperative Hyperalgesia by Dexmedetomidine via Regulating the Trafficking and Function of Spinal NMDA Receptors as well as PKC and CaMKII Level In Vivo and In Vitro

Remifentanil-induced secondary hyperalgesia has been demonstrated in both animal experiments and clinical trials. Enhancement of N-methyl-D-aspartate (NMDA) receptor trafficking as well as protein kinase C (PKC) and calmodulin-dependent protein kinase II (CaMKII) have been reported to be involved in the induction and maintenance of central sensitization. In the current study, it was demonstrated that dexmedetomidine could prevent remifentanil-induced hyperalgesia (RIH) via regulating spinal NMDAR-PKC-Ca2+/ CaMKII pathway in vivo and in vitro. We firstly investigated the effect of dexmedetomidine, a highly selective α2-adrenergic receptor agonist, on mechanical and thermal hyperalgesia using a rat model of RIH. NMDA receptor subunits (NR1, NR2A and NR2B) expression and membrane trafficking as well as PKC and CaMKII expression in spinal cord L4–L5 segments were measured by Western blot analysis. The expression of NMDA receptor subunits (NR1, NR2A and NR2B) were also detected by immunohistochemistry. Further more, the effect of dexmedetomidine on NMDA receptor current amplitude and frequency in spinal cord slices were investigated by whole-cell patch-clamp recording. We found that remifentail infusion at 1.2 μg.kg−1.min−1 for 90 min caused mechanical and thermal hyperalgesia, up-regulated NMDA receptor subunits NR1 and NR2B expression in both membrane fraction and total lysate as well as increased PKC and CaMKII expression in spinal cord dorsal horn. Subcutaneously injection of dexmedetomidine at the dose of 50 μg/kg at 30 min before plantar incision significantly attenuated remifentanil-induced mechanical and thermal hyperalgesia from 2 h to 48 h after infusion, and this was associated with reversal of up-regulated NR1 and NR2B subunits in both membrane fraction and total lysate as well as increased PKC and CaMKII expression in spinal cord dorsal horn. Furthermore, remifentanil incubation increased amplitude and frequency of NMDA receptor-induced current in dorsal horn neurons, which was dose-dependently attenuated by dexmedetomidine. These results suggest that dexmedetomidine can significantly ameliorate RIH via modulating the expression, membrane trafficking and function of NMDA receptors as well as PKC and CaMKII level in spinal dorsal horn, which present useful insights into the mechanistic action of dexmedetomidine as a potential anti-hyperalgesic agents for treating RIH.

Enhancement of spinal dorsal horn neuron NMDA receptor phosphorylation as the mechanism of remifentanil induced hyperalgesia: Roles of PKC and CaMKII.

BackgroundModulation of N-methyl-D-aspartate receptor subunits NR1 and NR2 through phosphorylation mediates opioid-induced hyperalgesia, and activations of protein kinase C and extracellular signal-regulated kinase 1/2 potentiate while activation of calcium/calmodulin-dependent protein kinase II inhibits opioid-induced hyperalgesia. However, the mechanism of opioid-induced hyperalgesia development and in particular the potential interplay between N-methyl-D-aspartate receptors and protein kinase C or calcium/calmodulin-dependent protein kinase II or extracellular signal-regulated kinase 1/2 in the development of remifentanil-induced hyperalgesia is unclear.MethodsRemifentanil (1 µg ċ kg−1 ċ min−1) was given intravenously over 60 min in rats, followed by the infusion of either vehicle solution or the respective inhibitors of protein kinase C (chelerythrine), extracellular signal-regulated kinase II (KN93), or extracellular signal-regulated kinase 1/2 (PD98059). Thereafter, the pain behaviors were evaluated by the paw withdrawal mechanical threshold and paw withdrawal thermal latency. In in vitro studies, fetal spinal cord dorsal horn neurons were primary cultured in the presence of 4 nM remifentanil for 60 min, and then the remifentanil was washed out and replaced immediately by culturing in the absence or presence of chelerythrine, KN93 or PD98059, respectively for up to 8 h. The expressions of N-methyl-D-aspartate receptors subunits and their phosphorylation (NR1, NR2B, p-NR1, p-NR2B) were analyzed by Western blotting after the completion of treatments. Functional changes of N-methyl-D-aspartate receptors were evaluated by electrophysiologic recordings of N-methyl-D-aspartate currents.ResultsRemifentanil induced significant thermal and mechanical hyperalgesia, which were significantly attenuated by Chelerythrine or KN93 but not PD98059. The expressions of NR1, NR2B, p-NR1, and p-NR2B were increased significantly and progressively over time after remifentanil administration, and these increases were all significantly attenuated by either chelerythrine or KN93 but not PD98059. Intriguingly, N-methyl-D-aspartate receptor functional enhancement induced by remifentanil was attenuated by Chelerythrine, KN93, and PD98059.ConclusionsIt is concluded that the enhancements in function and quantity of N-methyl-D-aspartate receptor via phosphorylation of its subunits through protein kinase C and calcium/calmodulin-dependent protein kinase II activation may represent the major mechanism whereby remifentanil induced hyperalgesia.

Intraoperative electroacupuncture relieves remifentanil-induced postoperative hyperalgesia via inhibiting spinal glial activation in rats.

BackgroundAccumulating studies have suggested that remifentanil, the widely-used opioid analgesic in clinical anesthesia, can activate the pronociceptive systems and enhance postoperative pain. Glial cells are thought to be implicated in remifentanil-induced hyperalgesia. Electroacupuncture is a complementary therapy to relieve various pain conditions with few side effects, and glial cells may be involved in its antinociceptive effect. In this study, we investigated whether intraoperative electroacupuncture could relieve remifentanil-induced postoperative hyperalgesia by inhibiting the activation of spinal glial cells, the production of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.MethodsA rat model of remifentanil-induced postoperative hyperalgesia was used in this study. Electroacupuncture during surgery was conducted at bilateral Zusanli (ST36) acupoints. Behavior tests, including mechanical allodynia and thermal hyperalgesia, were performed at different time points. Astrocytic marker glial fibrillary acidic protein, microglial marker Iba1, proinflammatory cytokines, and phosphorylated mitogen-activated protein kinases in the spinal cord were detected by Western blot and/or immunofluorescence.ResultsMechanical allodynia and thermal hyperalgesia were induced by both surgical incision and remifentanil infusion, and remifentanil infusion significantly exaggerated and prolonged incision-induced pronociceptive effects. Glial fibrillary acidic protein, Iba1, proinflammatory cytokines (interleukin-1β and tumor necrosis factor-α), and phosphorylated mitogen-activated protein kinases (p-p38, p-JNK, and p-ERK1/2) were upregulated after surgical incision, remifentanil infusion, and especially after their combination. Intraoperative electroacupuncture significantly attenuated incision- and/or remifentanil-induced pronociceptive effects, spinal glial activation, proinflammatory cytokine upregulation, and phosphorylated mitogen-activated protein kinase upregulation.ConclusionsOur study suggests that remifentanil-induced postoperative hyperalgesia can be relieved by intraoperative electroacupuncture via inhibiting the activation of spinal glial cells, the upregulation of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.

Cathepsin S in the spinal microglia contributes to remifentanil-induced hyperalgesia in rats

Cysteine protease Cathepsin S (CatS) expressed by spinal microglia has been shown to play a critical role in nerve injury and inflammation-induced chronic pain. However, whether microglial CatS contributes to remifentanil-induced acute hyperalgesia remains unstudied. In the present study, intravenous remifentanil infusion induced a significant increase in the expression of premature and mature form of CatS in the activated microglia in the spinal cord. Spinal delivery of irreversible CatS inhibitor LHVS reduced hyperalgesia, attenuated activation of spinal microglia and blocked phosphorylation of NMDA receptor NR1 subunit induced by remifentanil. Furthermore, inhibition of microglia by minocycline effectively suppressed remifentanil-induced hyperalgesia, as well as CatS upregulation. In addition, remifentanil infusion also induced an increase in reactive oxygen species (ROS) levels in spinal neurons. Systemic administration of ROS scavenger PBN was sufficient to suppress remifentanil-induced painful hypersensitivity. Removal of ROS by PBN prevented upregulation of mature CatS in spinal microglia. However, increased protein level of premature form of CatS was not affected by PBN. Altogether, our findings demonstrate that neuronal ROS promote maturation of microglial CatS which facilitates activation of NMDA in the spinal dorsal horn. Therefore, such mechanism is involved in neuron-microglia positive feedback and contributes to remifentanil-induced hyperalgesia.

Protective effects of dexmedetomidine combined with flurbiprofen axetil on remifentanil-induced hyperalgesia: A randomized controlled trial.

High dosages of intra-operative remifentanil are associated with opioid-induced hyperalgesia (OIH). The aim of the present study was to investigate the effect of combined dexmedetomidine and flurbiprofen axetil treatment on remifentanil-induced hyperalgesia. Patients with an American Society of Anesthesiologists physical status of I–II who were diagnosed with hysteromyoma and scheduled for laparoscopic assisted vaginal hysterectomy (LAVH) were randomly divided into three groups. Group hyperalgesia (Group H, n=29) received intra-operative remifentanil, Group hyperalgesia and dexmedetomidine (Group HD, n=28) received remifentanil and a continuous infusion of dexmedetomidine, and Group hyperalgesia, dexmedetomidine and flurbiprofen axetil (Group HDF, n=29) received remifentanil, flurbiprofen axetil and dexmedetomidine. Mechanical pain thresholds were measured during the preoperative visit and postoperatively at 1, 6 and 24-h time points. Visual analog scale (VAS) scores, time to analgesic requirement, total sufentanil consumption and side effects were assessed postoperatively. Mechanical pain threshold at the incision site was significantly lower in Group H compared with Groups HD and HDF (both P<0.05), and significantly higher in Group HDF than in Group HD (P<0.05). The area of secondary hyperalgesia at the incision site was greater in Group H than in the other two groups (both P<0.05), and significantly smaller in Group HDF compared with Group HD (P<0.05). VAS scores and total sufentanil consumption were significantly higher in Group H compared with the other two groups (both P<0.05), and were significantly lower in Group HDF compared with Group HD (P<0.05). Dexmedetomidine combined with flurbiprofen axetil exhibits synergetic effects in the prevention of remifentanil-induced hyperalgesia in patients undergoing LAVH.

PICK1 Regulates the Expression and Trafficking of AMPA Receptors in Remifentanil-Induced Hyperalgesia.

Remifentanil is used widely in clinical anesthesia because it induces more rapid and more common hyperalgesia than other opioid analgesics. Activation of N-methyl-D-aspartate (NMDA) receptors takes a pivotal part in remifentanil-induced hyperalgesia. Like NMDA receptors, the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are excitatory ion glutamate receptors in postsynaptic membrane, which are involved in the transmission of both acute and chronic pain. Protein interacting with C kinase 1 (PICK1) plays an important role in NMDA receptor-mediated internalization of glutamate receptor 2 (GluR2)-containing AMPARs and contributes to the induction and maintenance of inflammation-induced pain. This study aimed to test the hypothesis that PICK1 contributes to remifentanil-induced hyperalgesia by regulating AMPAR expression and trafficking in the spinal cord. Using a rat model of remifentanil-induced hyperalgesia by intravenous infusion of remifentanil, we first measured changes in mechanical and thermal hyperalgesia at 24 hours before remifentanil infusion and 2, 6, 24, and 48 hours after infusion. PICK1 mRNA and protein expression and AMPAR subunit expression and trafficking in the spinal cord were then detected by reverse transcription-qualitative polymerase chain reaction, immunohistochemistry, and Western blot. In addition, we knocked down PICK1 expression by intrathecal administration of PICK1 antisense oligodeoxynucleotide to investigate the effects of PICK1 deficiency on remifentanil-induced hyperalgesia and the expression and trafficking of AMPARs. A significant time-group interaction was found for nociceptive thresholds (paw withdrawal threshold and paw withdrawal latency; all P < .0001). Remifentanil infusion induced distinct hyperalgesia at different time points (P < .0001), which was partly reversed by PICK1 knockdown (P < .007). Besides, remifentanil infusion increased the expression of PICK1 mRNA and protein (P < .0001) and the membrane GluR1 and GluR2 internalization in spinal dorsal horn neurons (P < .0011). More importantly, PICK1 deficiency could attenuate remifentanil-induced GluR2 internalization in the spinal cord dorsal horn (P < .01) but had no effect on remifentanil-induced membrane GluR1 expression (P ≥ .985). These results indicate that PICK1 deficiency might reverse remifentanil-induced hyperalgesia through regulating GluR2-containing AMPAR expression and trafficking in the spinal cord dorsal horn.

Effect of dexmedetomidine on trafficking of N-methyl-D-aspartate receptors in spinal dorsal horn neurons during remifentanil-induced hyperalgesia in rats with incisional pain

Objective To investigate the effect of dexmedetomidine on trafficking of N-methyl-D-aspartate(NMDA)receptors in spinal dorsal horn neurons during remifentanil-induced hyperalgesia in the rats with incisional pain. Methods Twenty-four male Sprague-Dawley rats, aged 2-3 months, weighing 240-260 g, were randomly divided into 3 groups(n=8 each)using a random number table: control group(group C), remifentanil + incisional pain group(group R+ I), and dexmedetomidine + remifentanil + incisional pain group(group D+ R+ I). A 1 cm longitudinal incision was made in the plantar surface of the left hindpaw to establish the model of incisional pain in anesthetized rats.In group D+ R+ I, dexmedetomidine 50 μg/kg was injected subcutaneously at 30 min before establishment of the model.In R+ I and D+ R+ I groups, remifentanil was infused for 90 min at a rate of 1.2 μg·kg-1·min-1 at the same time as the model was established.In group C, normal saline was infused for 90 min at a rate of 0.12 ml·kg-1·min-1.The thermal paw withdrawal latency(TWL)and mechanical paw withdrawal threshold(MWT)were measured before administration of dexmedetomidine(T0), and at 2, 6, 24 and 48 h after stopping infusion of remifentanil(T1-4). The rats were sacrificed after the last behavioral testing, and the L4-6 segments of the spinal cord were removed for determination of the expression of NMDA receptor NR1, NR2A and NR2B subunits in membrane(m)and total(t)proteins in the spinal dorsal horn by Western blot analysis.The ratios of mNR1/tNR1, mNR2A/tNR2A and mNR2B/tNR2B were calculated. Results Compared with group C, the TWL was significantly shortened, the MWT was significantly decreased, the expression of mNR1, tNR1, mNR2B and tNR2B was significantly up-regulated, the ratios of mNR1/tNR1 and mNR2B/tNR2B were significantly increased(P 0.05). Compared with group R+ I, the TWL was significantly prolonged, the MWT was significantly increased, the expression of mNR1, tNR1, mNR2B and tNR2B was significantly down-regulated, the ratios of mNR1/tNR1 and mNR2B/tNR2B were significantly decreased(P 0.05). Conclusion The mechanism by which dexmedetomidine prevents remifentanil-induced hyperalgesia is related to reduction of trafficking of NR1 and NR2B subunits-containing NMDA receptors in spinal dorsal horn neurons of the rats with incisional pain. Key words: Dexmedetomidine; Piperidines; Receptors, N-methyl-D-aspartate; Pain; Postoperative complications; Hyperalgesia; Spinal cord

The role of p38MAPK activation in spinal dorsal horn in remifentanil-induced postoperative hyperalgesia in rats

Objectives: Remifentanil may induce hyperalgesia. Recent studies implicate a close relationship between post-surgical hyperalgesia and phosphorylation and activation of p38 mitogen-activated protein kinase (p38MAPK) in the spinal microglia. This study aimed to investigate whether the combination of post-surgical and remifentanil-induced hyperalgesia worsens post-operative pain and whether phosphorylated p38MAPK (phospho-p38MAPK) in the spinal dorsal horn in rats is involved in remifentanil-induced postoperative hyperalgesia.Methods: Sprague-Dawley rats were randomly divided into six groups: control, incision only, remifentanil only, remifentanil + incision, remifentanil + incision + SB203580, and remifentanil + incision + DMSO. The p38MAPK inhibitor SB203580 and DMSO were injected intrathecally. A right plantar surgical incision was performed in the incision groups, and remifentanil was infused for 60 min in the remifentanil groups. Mechanical paw withdrawal threshold (PWT) and thermal paw withdrawal latency (PWL) of the bilateral hind paws were measured and the number of phospho-p38MAPK-positive cells in rat spinal dorsal horn sections was counted.Results: Intravenous remifentanil infusion decreased bilateral plantar PWL values from 1 h to 3 days after surgery, however there was no additive effect with incision-induced values. There was a significant increase in the number of dorsal horn phospho-p38MAPK-positive cells in the remifentanil + incision group compared to the incision group, but no increase in the number of these cells when remifentanil was given alone. Intrathecal pretreatment with SB203580 attenuated remifentanil + incision–induced postoperative hyperalgesia and significantly reduced activation of phospho-p38MAPK in spinal dorsal horn.Conclusions: Incision-induced and remifentanil-induced increases in hyperalgesia were not additive when incision and remifentanil were used together. Data on phospho-38MAPK activation in remifenanil-induced hyperalgesia were contradictory and need further clarification.

Involvement of CCL3/CCR5 Signaling in Dorsal Root Ganglion in Remifentanil-induced Hyperalgesia in Rats.

Several mechanisms of remifentanil-induced hyperalgesia in spinal cord mainly have been explained such as N-methyl-D-aspartate receptors activation, but the mechanism in dorsal root ganglion (DRG) is poorly understood. It has been reported that CCL3 may be a regulator in both inflammatory pain and hyperalgesia. In this paper we explored whether CCL3 and CCR5, the mainly receptor of CCL3, play a role in the remifentanil-induced hyperalgesia in DRG by using a rat model with remifentanil administration. The von Frey test and hot plate test were performed to measure the different threshold to evaluate mechanical and thermal hyperalgesia. Real-time polymerase chain reaction and Western blot analysis were used to evaluate time course of CCL3 and CCR5 expression in DRG after remifentanil infusion. The changes of glial cells and the expression of CCL3 and CCR5 were detected by immunofluorescence assay. Finally, intrathecal injection of CCL3-neutralizing antibody and maraviroc, the CCR5 antagonists, were used sevoflurane to confirm the role of CCL3/CCR5 signaling in the rat model of remifentanil-induced hyperalgesia. Remifentanil infusion profoundly increased thermal and mechanical hyperalgesia from 2 to 48 hours according to paw withdrawal latency (PWL) and paw withdrawal thresholds (PWT) (mean±SD, hyperalgesia vs. control, 17.4±0.91 vs. 8.5±1.46 s; 20.1±0.32 vs. 9.6±0.5 g, n=8). Moreover, the expression of mRNAs and proteins of CCL3 and its receptor CCR5 in DRG were dramatically increased after remifentanil infusion as compared with the normal saline group. We also found that CCL3 and CCR5 were colocalized with glial cells or neurons. Furthermore, intrathecal injection of CCL3-neutralizing antibody (mean±SD, hyperalgesia vs. control, 17.4±0.91 vs. 8.5±1.46 s; 20.1±0.32 vs. 9.6±0.5 g, n=5) and maraviroc(mean±SD, hyperalgesia vs. control, 17.4±0.91 vs. 8.5±1.46 s; 20.1±0.32 vs. 9.6±0.5 g, n=5) were able to suppress remifentanil-related thermal and mechanical hyperalgesia according to behavioral test. The results highlighted the fact that CCL3 and its receptor CCR5 in DRG might contribute to remifentanil-induced hyperalgesia. Thus CCL3/CCR5 signaling may be further considered in the development of new therapeutic strategies.

Involvement of Spinal PKMζ Expression and Phosphorylation in Remifentanil-Induced Long-Term Hyperalgesia in Rats.

Up-regulation of GluN2B-containing N-methyl-D-aspartate receptors (NMDARs) expression and trafficking is the key mechanism for remifentanil-induced hyperalgesia (RIH), nevertheless, the signaling pathway and pivotal proteins involved in RIH remain equivocal. PKMζ, an isoform of protein kinase C (PKC), maintains pain memory storage in neuropathic pain and inflammatory pain, which plays a parallel role regulated by NMDARs in long-term memory trace. In the present study, ZetaInhibitory Peptide (ZIP), a PKMζ inhibitor, and a selective GluN2B antagonist Ro-256981 are injected intrathecally before remifentanil infusion (1μgkg-1min-1 for 1h, iv) in order to detect whether GluN2B contributes to RIH through affecting synthesis and activity of PKMζ in spinal dorsal horn. Nociceptive tests are measured by Paw withdrawal mechanical threshold (PWT) and paw withdrawal thermal latency (PWL). The L4-L6 segments of dorsal horn taken from rats with RIH are for determining expression of PKMζ and pPKMζ by Western blot and immunohistochemistry. Our data suggest that remifentanil infusion causes an increase of PKMζ in expression and phosphorylation in rats with nociceptive sensitization, beginning at 2h, peaked at 2days, and returned to basal level at 7days. ZIP (10ng) could block behavioral sensitization induced by remifentanil. Ro25-6981 dosage-dependently attenuated mechanical and thermal hyperalgesia and reversed expression of PKMζ and pPKMζ, indicating that GluN2B-containing NMDA receptor facilitates development of RIH through mediating expression and activity of spinal PKMζ in rats. Although detailed mechanisms require further comprehensive study, the preventive role of Ro25-6981 and ZIP provide novel options for the effective precaution of RIH in clinics.

Changes in spinal iron content during remifentanil-induced hyperalgesia in a rat model of incisional pain

Objective To evaluate the changes in the spinal iron content during remifentanil-induced hyperalgesia in a rat model of incisional pain. Methods Thirty-two pathogen-free adult male Sprague-Dawley rats, weighing 240-260 g, were randomly divided into 4 groups (n=8 each)using a random number table: control group (group C), incisional pain group (group I), remifentanil group (group R), and incisional pain + remifentanil group (group I+ R). In I and I+ R groups, a 1 cm longitudinal incision was made in the plantar surface of left hindpaw in sevoflurane-anesthetized rats.Normal saline was infused at a rate of 0.1 ml·kg-1·min-1 for 60 min via the caudal vein in C and I groups.Remifentanil was infused at a rate of 1.0 μg·kg-1·min-1 for 60 min via the caudal vein in R and I+ R groups.At 24 h before intravenous infusion and 6, 24 and 48 h after the end of infusion (T0-3), the mechanical paw withdrawal threshold (MWT)and thermal paw withdrawal latency (TWL)were measured.All the rats were sacrificed after the last measurement of pain thresholds, and the L4-6 segments of the spinal cord were removed for determination of iron content using the Perl′s iron staining and atomic absorption spectrophotometer. Results Compared with group C, the MWT was significantly decreased, and the TWL was significantly shortened at T1-3, and the iron content was significantly increased in I, R and I+ R groups (P<0.05). Compared with I and R groups, the MWT was significantly decreased, and the TWL was significantly shortened at T1-3, and the iron content was significantly increased in group I+ R (P<0.05). Conclusion The development of remifentanil-induced hyperalgesia is probably related to increased spinal iron content in a rat model of incisional pain. Key words: Piperidines; Hyperalgesia; Iron; Spinal cord

The Effects of the Toll-Like Receptor 4 Antagonist, Ibudilast, on Sevoflurane's Minimum Alveolar Concentration and the Delayed Remifentanil-Induced Increase in the Minimum Alveolar Concentration in Rats.

Ultralow doses of naloxone, an opioid and toll-like receptor 4 antagonist, blocked remifentanil-induced hyperalgesia and the associated increase in the minimum alveolar concentration (MAC), but not tolerance. The aim was to determine the effects of the toll-like receptor 4 antagonist, ibudilast, on the MAC in the rat and how it might prevent the effects of remifentanil. Male Wistar rats were randomly allocated to 5 treatment groups (n = 7 per group): 10 mg/kg ibudilast intraperitoneally, 240 µg/kg/h remifentanil IV, ibudilast plus remifentanil, remifentanil plus naloxone IV, or saline. The sevoflurane MAC was determined 3 times in every rat and every day (days 0, 2, and 4): baseline (MAC-A) and 2 further determinations were made after treatments, 1.5 hours apart (MAC-B and MAC-C). A reduction in baseline MAC was produced on day 0 by ibudilast, remifentanil, remifentanil plus ibudilast, remifentanil plus naloxone (P < 0.01), but not saline. Similar effects were found on days 2 and 4. A tolerance to remifentanil was found on days 0, 2, and 4, which neither ibudilast nor naloxone prevented. The MAC increase produced by remifentanil on day 4 (P = 0.001) was prevented by either ibudilast or naloxone. Ibudilast, besides reducing the MAC, prevented the delayed increase in baseline MAC produced by remifentanil but not the increase in MAC caused by tolerance to remifentanil.

Changes in expression of spinal divalent metal transporter 1 during remifentanil-induced hyperalgesia in a rat model of incisional pain

Objective To evaluate the changes in the expression of spinal divalent metal transporter 1 (DMT1) during remifentanil-induced hyperalgesia in a rat model of incisional pain. Methods Thirty-two male Sprague-Dawley rats, weighing 240-260 g, aged 2-3 months, were randomly divided into 4 groups (n=8 each) using a random number table: control group (group C), incisional pain group (group I), remifentanil group (group R), and incisional pain+ remifentanil group (group I+ R). In group C, normal saline was infused for 60 min at a rate of 0.1 ml·kg-1·min-1.A 1-cm longitudinal incision was made through skin, fascia and muscle of the plantar aspect of the left hindpaw in sevoflurane-anesthetized rats, and normal saline was infused intravenously for 60 min at a rate of 1.0 μg·kg-1·min-1 at the same time in group I. In group R, remifentanil was infused for 60 min at a rate of 1.0 μg·kg-1·min-1.In group I+ R, the model of incisional pain was established, and remifentanil was simultaneously infused for 60 min at a rate of 1.0 μg·kg-1·min-1.At 24 h before normal saline or remifentanil infusion and 6, 24 and 48 h after the end of infusion (T0-3), the mechanical paw withdrawal threshold (MWT) and thermal paw withdrawal latency (TWL) were measured.All the rats were sacrificed after the last measurement of pain thresholds, and the spinal cord was removed for determination of DMT1 with/without iron-responsive element [DMT1(+ )IRE and DMT1(-)IRE] expression (by Western blot analysis and immunohistochemistry). Results Compared with group C, the MWT was significantly decreased, and the TWL was significantly shortened at T1-3, and the expression of spinal DMT1(-)IRE was significantly up-regulated in I, R and I+ R groups (P 0.05). Conclusion Spinal DMT1(-)IRE activation may be involved in the mechanism underlying remifentanil-induced hyperalgesia in a rat model of incisional pain. Key words: Piperidines; Pain, postoperative; Hyperalgesia; Cation transport proteins; Spinal cord

Remifentanil and worse patient-reported outcomes regarding postoperative pain management after thyroidectomy

BackgroundIntraoperative remifentanil has been associated with postoperative hyperalgesia, higher visual analogic pain scores, and increased postoperative morphine consumption. However, this has not been investigated from patient’s perspective by using a patient-reported outcomes (PROs) approach with a validated questionnaire. MethodsWe joined the largest prospective observational study on postoperative pain, PAIN OUT Project (NCT02083835), and collected data for 2 years. We studied the effects of remifentanil (R+) vs nonremifentanil (R−) anesthesia on PROs regarding their pain management after elective thyroidectomy. We selected 5 primary PROs (worst pain experienced, time spent in severe pain, relief received by treatment, satisfaction about pain management, wish for more pain treatment) and five secondary PROs (drowsiness, itching, nausea, dizziness, waking up due to pain) from the validated International Pain Outcomes questionnaire. ResultsThe analysis included 317 patients, 208 in the R+ group (65.6%) and 109 in the R− group (34.4%), the latter receiving fentanyl as intraoperative opioid. Although the R+ group received more frequently intraoperative nonopioids (202/208, 97.1% vs 86/109, 78.9%; P < .0001) and opioids (184/208, 88.5% vs 38/109, 34.9%; P < .001), it reported higher worst pain (5.1±2.1 vs 4.3±2.1, P < .005), lower satisfaction (7.4±2.0 vs 8.1±2.1, P < .001), and worse results in 4 secondary PROs. A sensitivity analysis performed matching 67 couples of patients yielded similar results in primary PROs. ConclusionsOur study suggests that remifentanil-based anesthesia is associated with worse pain-related PROs in patients undergoing thyroidectomy despite more frequent intraoperative analgesic administration. This study adds further evidence to the growing literature about opioid- and remifentanil-induced hyperalgesia.