Glycogen Synthase Kinase-3β Inhibition Prevents Remifentanil-Induced Postoperative Hyperalgesia via Regulating the Expression and Function of AMPA Receptors

Pharmacological interventions for remifentanil-induced hyperalgesia: A systematic review and network meta-analysis of preclinical trials

BACKGROUND

To improve perioperative pain management, several interventions have been suggested for the prevention of increased pain sensitivity caused by opioids (called opioid-induced hyperalgesia). It is currently unclear which intervention is the most effective or appropriate in preventing opioid-induced hyperalgesia. Remifentanil is the most investigated opioid causing opioid-induced hyperalgesia. Thus, to guide future research, we conducted a systematic review and a network meta-analysis of preclinical trials investigating pharmacological interventions for remifentanil-induced hyperalgesia.

METHODS

To identify relevant articles, electronic database searches were conducted in Embase, PubMed, Web of Science, and Google Scholar. Study characteristics were extracted, and the risk of bias was evaluated. Studies were included in the network meta-analysis if they shared similar characteristics with at least one other study. The interventions were ranked based on P-scores.

RESULTS

Overall, the 62 eligible trials tested 86 individual interventions and 6 combination interventions. Thirty-five studies eligible in the network meta-analysis formed five groups which were further divided into subgroups based on the quantitative sensory tests used. The best-ranked interventions within the subgroups were Anxa12-26, MRS2179, salicylaldehyde isonicotinoyl hydrazone (SIH), ANA-12, TDZD-8, ketamine, dexmedetomidine, JWH015, and the combination of KN93 and ketamine.

DISCUSSION

The current literature is too heterogeneous to produce a clear answer on which intervention is the most effective in preventing remifentanil-induced hyperalgesia. Future research in this field should prioritise finding the most effective intervention over testing the efficacy of new options. The results of our work can be used in planning which comparisons should be included in new trials.

Euchromatin histone-lysine N-methyltransferase 2 regulates the expression of potassium-sodium-activated channel subfamily T member 1 in primary sensory neurons and contributes to remifentanil-induced pain sensitivity

Intraoperative remifentanil administration has been linked to increased postoperative pain sensitivity. Recent studies have identified the involvement of euchromatic histone-lysine N-methyltransferase 2 (Ehmt2/G9a) in neuropathic pain associated with the transcriptional silencing of many potassium ion channel genes. This study investigates whether G9a regulates the potassium sodium-activated channel subfamily T member 1 (Slo2.2) in remifentanil-induced post-incisional hyperalgesia (RIH) in rodents. We performed remifentanil infusion (1 μg·kg-1·min-1 for 60 min) followed by plantar incision to induce RIH in rodents. Our results showed that RIH was accompanied by increased G9a and H3K9me2 production and decreased Slo2.2 expression 48 h postoperatively. Deletion of G9a rescued Slo2.2 expression in DRG and reduced RIH intensity. Slo2.2 overexpression also reversed this hyperalgesia phenotype. G9a overexpression decreased Slo2.2-mediated leak current and increased excitability in the small-diameter DRG neurons and laminal II small-diameter neurons in the spinal dorsal horn, which was implicated in peripheral and central sensitization. These results suggest that G9a contributes to the development of RIH by epigenetically silencing Slo2.2 in DRG neurons, leading to decreased central sensitization in the spinal cord. The findings may have implications for the development of novel therapeutic targets for the treatment of postoperative pain.

Glycogen Synthase Kinase 3β Is a Key Regulator in the Inhibitory Effects of Accumbal Cocaine- and Amphetamine-Regulated Transcript Peptide 55-102 on Amphetamine-Induced Locomotor Activity

Microinjection of cocaine- and amphetamine-regulated transcript (CART) peptide 55-102 into the nucleus accumbens (NAcc) core significantly attenuates psychostimulant-induced locomotor activity. However, the molecular mechanism remains poorly understood. We examined the phosphorylation levels of Akt, glycogen synthase kinase 3β (GSK3β), and glutamate receptor 1 (GluA1) in NAcc core tissues obtained 60 min after microinjection of CART peptide 55-102 into this site, followed by systemic injection of amphetamine (AMPH). Phosphorylation levels of Akt at Thr308 and GSK3β at Ser9 were decreased, while those of GluA1 at Ser845 were increased, by AMPH treatment. These effects returned to basal levels following treatment with CART peptide 55-102. Furthermore, the negative regulatory effects of the CART peptide on AMPH-induced changes in phosphorylation levels and locomotor activity were all abolished by pretreatment with the S9 peptide, an artificially synthesized indirect GSK3β activator. These results suggest that the CART peptide 55-102 in the NAcc core plays a negative regulatory role in AMPH-induced locomotor activity by normalizing the changes in phosphorylation levels of Akt-GSK3β, and subsequently GluA1 modified by AMPH at this site. The present findings are the first to reveal GSK3β as a key regulator of the inhibitory role of the CART peptide in psychomotor stimulant-induced locomotor activity.

Pharmacological Interventions for Opioid-Induced Hyperalgesia: A Scoping Review of Preclinical Trials

BACKGROUND

Opioid analgesics are the most effective pharmacological agents for moderate and severe pain. However, opioid use has several limitations such as opioid-induced hyperalgesia (OIH), which refers to the increased pain sensitivity that occurs once analgesia wears off after opioid administration. Several pharmacological interventions have been suggested for OIH, but the current literature does not provide guidelines on which interventions are the most effective and whether they differ depending on the opioid that induces hyperalgesia. This scoping review aimed to identify and describe all the preclinical trials investigating pharmacological interventions for OIH caused by remifentanil, fentanyl, or morphine as the first step towards evaluating whether the most effective OIH interventions are different for different opioids.

METHODS

Electronic database searches were carried out in Embase, PubMed, and Web of Science. Detailed data extraction was conducted on the eligible trials.

RESULTS

72 trials were eligible for the review. Of these, 27 trials investigated remifentanil, 14 trials investigated fentanyl, and 31 trials investigated morphine. A total of 82 interventions were identified. The most studied interventions were ketamine (eight trials) and gabapentin (four trials). The majority of the interventions were studied in only one trial. The most common mechanism suggested for the interventions was inhibition of N-methyl-D-aspartate (NMDA) receptors.

CONCLUSION

This scoping review identified plenty of preclinical trials investigating pharmacological interventions for OIH. Using the current literature, it is not possible to directly compare the effectiveness of the interventions. Hence, to identify the most effective interventions for each opioid, the interventions must be indirectly compared in a meta-analysis.

Sciatic nerve block downregulates the BDNF pathway to alleviate the neonatal incision-induced exaggeration of incisional pain via decreasing microglial activation

Sciatic nerve block is under investigation as a possible therapeutic strategy for neonatal injury-induced exaggeration of pain responses to reinjury. Spinal microglial priming, brain-derived neurotrophic factor (BDNF) and Src homology-2 domain-containing protein tyrosine phosphatase-2 (SHP2) participate in exaggerated incisional pain induced by neonatal incision. However, effects of sciatic nerve block on exacerbated incisional pain and underlying mechanisms remain unclear. Here, we demonstrated that sciatic nerve block alleviates pain hypersensitivity and microglial activation in rats subjected to neonatal incision and adult incision (nIN-IN). Chemogenetic activation or inhibition of spinal microglia attenuates or mimics effects of sciatic nerve block on pain hypersensitivity, respectively. Moreover, α-amino-3-hydroxy- 5-methy- 4-isoxazole propionate (AMPA) receptor subunit GluA1 contributes to the exaggeration of incisional pain. The inhibition of BDNF or SHP2 blocks upregulations of downstream molecules in nIN-IN rats. Knockdown of SHP2 attenuates the increase of GluA1 induced by injection of BDNF in adult rats with only neonatal incision. The inhibition of microglia or ablation of microglial BDNF attenuates upregulations of SHP2 and GluA1. Additionally, sciatic nerve block downregulates the expression of these three molecules. Upregulation of BDNF, SHP2 or AMPA receptor attenuates sciatic nerve block-induced reductions of downstream molecules and pain hypersensitivity. Microglial activation abrogates reductions of these three molecules induced by sciatic nerve block. These results suggest that decreased activation of spinal microglia contributes to beneficial effects of sciatic nerve block on the neonatal incision-induced exaggeration of incisional pain via downregulating BDNF/SHP2/GluA1-containing AMPA receptor signaling. Thus, sciatic nerve block may be a promising therapy.

Dezocine relieves the postoperative hyperalgesia in rats through suppressing the hyper-action of Akt1/GSK-3β pathway

The relieving role of dezocine in pain after surgery was previously reported, while the potential mechanism was not completely clear. Therefore, the current research probed into the regulatory mechanism of dezocine in pain after surgery. A postoperative pain model was established by performing plantar incision surgery on the juvenile Sprague-Dawley rats. After the rats were treated with dezocine or SC79 (Akt1 activator), the paw withdrawal threshold and paw withdrawal latency of rats were detected to evaluate the mechanical allodynia and thermal hyperalgesia. After the plantar tissue, dorsal root ganglions, and spinal cord of rats were collected, the expressions of Akt1, p-Akt1, GSK-3β, and p-GSK-3β in the tissues were determined by western blot to evaluate the activation state of the Akt1/GSK-3β pathway. After surgery, the paw withdrawal threshold and paw withdrawal latency of rats were lessened, whereas the ratios of p-Akt1/Akt1 and p-GSK-3β/GSK-3β were augmented in rat plantar tissue, dorsal root ganglions, and spinal cord. After treatment with dezocine alone, the paw withdrawal threshold and paw withdrawal latency of postoperative rats were elevated, but ratios of p-Akt1/Akt1 and p-GSK-3β/GSK-3β were reduced. After co-treatment with dezocine and SC79, SC79 reversed the effects of dezocine on elevating the paw withdrawal threshold and paw withdrawal latency, and reducing the ratios of p-Akt1/Akt1 and p-GSK-3β/GSK-3β in postoperative rats. Dezocine ameliorated the postoperative hyperalgesia in rats via repressing the hyper-action of Akt1/GSK-3β pathway.

A Role for Transmembrane Protein 16C/Slack Impairment in Excitatory Nociceptive Synaptic Plasticity in the Pathogenesis of Remifentanil-induced Hyperalgesia in Rats

Remifentanil is widely used to control intraoperative pain. However, its analgesic effect is limited by the generation of postoperative hyperalgesia. In this study, we investigated whether the impairment of transmembrane protein 16C (TMEM16C)/Slack is required for α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) activation in remifentanil-induced postoperative hyperalgesia. Remifentanil anesthesia reduced the paw withdrawal threshold from 2 h to 48 h postoperatively, with a decrease in the expression of TMEM16C and Slack in the dorsal root ganglia (DRG) and spinal cord. Knockdown of TMEM16C in the DRG reduced the expression of Slack and elevated the basal peripheral sensitivity and AMPAR expression and function. Overexpression of TMEM16C in the DRG impaired remifentanil-induced ERK1/2 phosphorylation and behavioral hyperalgesia. AMPAR-mediated current and neuronal excitability were downregulated by TMEM16C overexpression in the spinal cord. Taken together, these findings suggest that TMEM16C/Slack regulation of excitatory synaptic plasticity via GluA1-containing AMPARs is critical in the pathogenesis of remifentanil-induced postoperative hyperalgesia in rats.

P2X4 receptor in the dorsal horn contributes to BDNF/TrkB and AMPA receptor activation in the pathogenesis of remifentanil-induced postoperative hyperalgesia in rats

The mechanism underlying the high incidence of remifentanil-induced postoperative hyperalgesia is unclear. Also, no effective prevention method exists. Inflammatory pain-related studies showed that P2X4 purinergic receptors (P2X4Rs) in the dorsal horn of the spinal cord and dorsal root ganglia are essential for maintaining allodynia caused by inflammation. However, little is known about its role in opioid-induced hyperalgesia. This study aimed to determine the role of P2X4R and related signaling pathways in the remifentanil-induced postoperative hyperalgesia (RIH) model. The study simulated the remifentanil infusion and surgical incision during general anesthesia. The mRNA and protein expression level of P2X4R in rats with RIH model increased from 2 h to 48 h after the surgery. The administration of P2X4R inhibitors prevented the occurrence of RIH, resulting in a reduction in mechanical and thermal pain. Moreover, P2X4R was involved in RIH in male and female rats, indicating no sex-specific difference. P2X4R also increased the expression of AMPA receptor subunit GluA1 in a brain-derived neurotrophic factor (BDNF) / tyrosine receptor kinase B (TrkB) dependent manner. The results from whole-cell patch-clamp recording suggested that P2X4R also regulated AMPA receptor-mediated miniature excitatory postsynaptic currents and participated in the synaptic plasticity of spinal dorsal horn neurons. In summary, P2X4R was involved in AMPAR expression, electrophysiological function, and synaptic plasticity of spinal dorsal horn neurons through BDNF/TrkB signaling. This might be the mechanism underlying RIH, and hence inhibition of P2X4R might be a potential treatment strategy.

Involvement of 5-Hydroxytryptamine Receptor 2A in the Pathophysiology of Medication-Overuse Headache

Background

Recent studies indicated that analgesic overuse upregulated 5-hydroxytryptamine receptor 2A (5-HT_2AR) and subsequently activated nitric oxide synthase (NOS) and thus induced latent sensitization, which provided a mechanistic basis for medication-overuse headache (MOH). Moreover, glycogen synthase kinase-3β (GSK-3β) was regulated by serotonin receptors and the phosphorylation of GSK-3β affected NOS activity, indicating that GSK-3β could be involved in the regulation of NOS activity by 5-HT_2AR in MOH pathophysiology. Herein, we performed this study to investigate the role of 5-HT_2AR in MOH pathophysiology and the role of GSK-3β in the regulation of NOS activity by 5-HT_2AR.

Materials and Methods

Wistar rats were daily administered with paracetamol (200 mg/kg) for 30 days to set animal models for pre-clinical MOH research. After the rat MOH models were successfully established, the expression of 5-HT_2AR and NOS, GSK-3β activity in trigeminal nucleus caudalis (TNC) were assayed. Then, 5-HT_2AR antagonist ketanserin and agonist DOI were applied to investigate the effect of 5-HT_2AR on NOS activity in TNC of MOH rats, and GSK-3β antagonist LiCl and agonist perifosine were applied to explore the role of GSK-3β in the activation of NOS by 5-HT_2AR.

Results

We found that the expression of 5-HT_2AR and NOS, GSK-3β activity were enhanced in TNC of MOH rats. 5-HT_2AR modulator regulated the activity of NOS and GSK-3β in TNC of MOH rats, and drugs acting on GSK-3β affected NOS activity.

Conclusion

These data suggest that GSK-3β may mediate the activation of NOS by 5-HT_2AR and underline the role of 5-HT_2AR in MOH pathophysiology.

Association Between Intraoperative Remifentanil Dosage and Postoperative Opioid Consumption in Adolescent Idiopathic Spine Surgery: A Retrospective Cohort Study

BACKGROUND

Adolescent idiopathic scoliosis (AIS) surgery is associated with significant postoperative pain. Remifentanil is a short-acting opioid that is often used as a component of total intravenous anesthesia. Remifentanil has been implicated in acute opioid tolerance and opioid-induced hyperalgesia, resulting in increased postoperative pain and opioid consumption. This retrospective study sought to investigate the relationship between the dose of intraoperative remifentanil and cumulative postoperative opioid consumption through 72 hours following surgery for pediatric AIS patients.

METHODS

We performed a retrospective chart review of adolescent patients undergoing posterior spine instrumentation under total intravenous general anesthesia at a single major pediatric center between January 2015 and October 2017. The relationship between intraoperative cumulative weight-adjusted remifentanil dose and logarithmic transformation of cumulative weight-adjusted opioid consumption through 72 hours following surgery was examined by regression analysis. A priori determined potential confounding variables were collected, including demographic data, perioperative analgesic agents (ie, ketamine, dexmedetomidine, and acetaminophen), surgical duration, vertebrae instrumented, and blood transfusion. Multivariable linear regression analysis was used to adjust for these possible confounding variables.

RESULTS

Eighty-nine patients met inclusion criteria, of which 78 had complete data for analysis. Univariable linear regression analysis revealed no association between remifentanil dose and opioid consumption through 72 hours following surgery (slope = 0.79 [95% confidence interval [CI], 0.61-0.98; R2 = 0.0039; P = .588]). After adjustment for possible confounding factors, no relationship between remifentanil dose (regression coefficient (coeff.) -0.08; 95% CI, -1.59 to 1.43; P = .912) and opioid consumption through 72 hours was found (slope =0.90 [95% CI, -0.65 to 2.46]; R2 = 0.1634). Similar results were obtained when the model was repeated for opioid consumption in postanesthesia care unit (PACU).

CONCLUSIONS

In this study examining adolescent patients undergoing surgery for idiopathic scoliosis, no association was found between the dose of intraoperative remifentanil and postoperative opioid consumption in the context of a propofol-based total intravenous anesthetic and multimodal analgesia. These results provide direction for future prospective controlled studies to further evaluate this relationship.

Spinal and Peripheral Mechanisms Individually Lead to the Development of Remifentanil-induced Hyperalgesia

The present study was performed to determine neuronal loci and individual molecular mechanisms responsible for remifentanil-induced hyperalgesia. The effect of methylnaltrexone (MNX) on remifentanil-induced behavioral hyperalgesia was assessed to distinguish contributions of the peripheral and/or central nervous system to remifentanil-induced hyperalgesia. Phosphorylation of p38 mitogen-activated protein kinase (p38MAPK) in the dorsal root ganglion (DRG) neurons after remifentanil infusion, and the effect of a p38MAPK inhibitor on remifentanil-induced hyperalgesia were analyzed to investigate involvement of p38MAPK in the peripheral mechanisms of remifentanil-induced hyperalgesia. Spinal levels of prodynorphin mRNA after remifentanil infusion, and the effect of the BK2 bradykinin receptor antagonist on remifentanil-induced hyperalgesia were investigated to assess potential spinal mechanisms. The effects of MNX and BK2 antagonists on remifentanil-induced exacerbation of post-incisional hyperalgesia were also investigated using behavioral analysis. Remifentanil infusion induced hyperalgesia in the early (4 h to 2 days) and late (8-14 days) post-infusion periods. MNX inhibited hyperalgesia only during the early post-infusion period. p38MAPK phosphorylation was observed in the DRG neuron, and the p38MAPK inhibitor inhibited hyperalgesia during the early post-infusion period. Prodynorphin expression increased in the spinal cord, and a BK2 antagonist inhibited hyperalgesia during the late post-infusion period. Remifentanil-induced exacerbation of incisional hyperalgesia was inhibited by MNX and the BK2 antagonist. The present study demonstrated that remifentanil activates peripheral and spinal neurons to promote chronologically distinctive hyperalgesia. p38MAPK phosphorylation in the DRG neuron leads to peripherally-driven hyperalgesia during the early post-infusion period, while spinal dynorphin-bradykinin signaling promotes hyperalgesia during the late post-infusion period.

Inhibition Of Glycogen Synthase Kinase 3 Beta Suppresses The Growth And Survival Of Skull Base Chordoma Cells By Downregulating Brachyury Expression

Purpose

Chordomas are locally aggressive tumors arising from notochordal remnants. Brachyury, a protein coded by T-gene, is crucial for chordoma cell proliferation. The aim of this study was to evaluate the effects of glycogen synthase kinase 3 beta (GSK3β) activity on brachyury expression and on the growth and survival of skull base chordoma cells.

Patients and methods

In this study, 16 paraffin-embedded specimens of primary skull base chordomas were analyzed for the expression of phosphorylated GSK3β and brachyury using immunohistochemistry. The UM-Chor1 cell line derived from a clival chordoma was treated with AR-A014418 (AR), an inhibitor of GSK3β, and brachyury expression was analyzed by qRT-PCR and Western blotting. The possible mechanism by which brachyury regulates the Wnt/β-catenin signaling pathway was investigated by immunocytochemistry. The effects of AR on cell proliferation as well as sensitivity to chemotherapeutic drugs were also examined.

Results

The results suggested that phosphorylated GSK3β and brachyury were upregulated in chordoma tissues. The GSK3β inhibitor (AR) decreased brachyury expression and suppressed the growth and survival of the chordoma cells, possibly via regulation of the Wnt/β-catenin signaling pathway. Moreover, AR increased the sensitivity of chordoma cells to chemotherapeutic drugs in vitro.

Conclusion

This study provides evidence for the clinical development of the GSK3β inhibitor (AR-A014418) as a potential chemotherapeutic adjuvant for the treatment of chordoma.

Supraphysiologic-dose anabolic-androgenic steroid use: A risk factor for dementia?

Supraphysiologic-dose anabolic-androgenic steroid (AAS) use is associated with physiologic, cognitive, and brain abnormalities similar to those found in people at risk for developing Alzheimer's Disease and its related dementias (AD/ADRD), which are associated with high brain β-amyloid (Aβ) and hyperphosphorylated tau (tau-P) protein levels. Supraphysiologic-dose AAS induces androgen abnormalities and excess oxidative stress, which have been linked to increased and decreased expression or activity of proteins that synthesize and eliminate, respectively, Aβ and tau-P. Aβ and tau-P accumulation may begin soon after initiating supraphysiologic-dose AAS use, which typically occurs in the early 20s, and their accumulation may be accelerated by other psychoactive substance use, which is common among non-medical AAS users. Accordingly, the widespread use of supraphysiologic-dose AAS may increase the numbers of people who develop dementia. Early diagnosis and correction of sex-steroid level abnormalities and excess oxidative stress could attenuate risk for developing AD/ADRD in supraphysiologic-dose AAS users, in people with other substance use disorders, and in people with low sex-steroid levels or excess oxidative stress associated with aging.

Sevoflurane-induced learning deficits and spine loss via nectin-1/corticotrophin-releasing hormone receptor type 1 signaling

In recent years, the neurotoxicity of general anesthetics in the developing brain has been studied and raised great concern as a major health issue to the public and physicians. Sevoflurane inhalation may induce neurotoxicity expressed as memory and learning impairment in young animals. In the current study, we investigated the role of nectin-1 and corticotrophin-releasing hormone receptor type 1 (CRHR1) in sevoflurane-induced learning deficits and dendritic spines loss in neonatal mice. Neonatal mice (P7) were treated with 3% sevoflurane with 60% O₂ or 60% O₂ for 6 h. Cognitive function was evaluated by Y Maze, Object recognition test, and Morris Water Maze. Hippocampal nectin-1 and L-afadin expression assessed using western blot analysis. The dendritic spines morphology of the hippocampus was determined using Golgi impregnation on 7 d and 2 months old. Sevoflurane exposed to neonatal mice decreased hippocampal nectin-1 levels from 1 h to 2 months after sevoflurane inhalation and attenuated working and spatial memory and spinal number in adulthood, which could be reversed by nectin-1 overexpression and CRHR1 antagonist Antalarmin. Nectin-1 knockdown caused spatial learning deficits and dendritic spine loss and lower L-afadin protein expression. Sevoflurane-induced nectin-1 and L-afadin expression decrease was mediated by CRHR1 signaling in the hippocampus. This information can be used to develop targeted intervention aimed at decreasing the neurotoxicity of sevoflurane inhalation.

Electroacupuncture Treatment Alleviates the Remifentanil-Induced Hyperalgesia by Regulating the Activities of the Ventral Posterior Lateral Nucleus of the Thalamus Neurons in Rats

Mechanisms underlying remifentanil- (RF-) induced hyperalgesia, a phenomenon that is generally named as opioid-induced hyperalgesia (OIH), still remain elusive. The ventral posterior lateral nucleus (VPL) of the thalamus, a key relay station for the transmission of nociceptive information to the cerebral cortex, is activated by RF infusion. Electroacupuncture (EA) is an effective method for the treatment of pain. This study aimed to explore the role of VPL in the development of OIH and the effect of EA treatment on OIH in rats. RF was administered to rats via the tail vein for OIH induction. Paw withdrawal threshold (PWT) in response to mechanical stimuli and paw withdrawal latency (PWL) to thermal stimulation were tested in rats for the assessment of mechanical allodynia and thermal hyperalgesia, respectively. Spontaneous neuronal activity and local field potential (LFP) in VPL were recorded in freely moving rats using the in vivo multichannel recording technique. EA at 2 Hz frequency (pulse width 0.6 ms, 1-3 mA) was applied to the bilateral acupoints "Zusanli" (ST.36) and "Sanyinjiao" (SP.6) in rats. The results showed that both the PWT and PWL were significantly decreased after RF infusion to rats. Meanwhile, both the spontaneous neuronal firing rate and the theta band oscillation in VPL LFP were increased on day 3 post-RF infusion, indicating that the VPL may promote the development of RF-induced hyperalgesia by regulating the pain-related cortical activity. Moreover, 2 Hz-EA reversed the RF-induced decrease both in PWT and PWL of rats and also abrogated the RF-induced augmentation of the spontaneous neuronal activity and the power spectral density (PSD) of the theta band oscillation in VPL LFP. These results suggested that 2 Hz-EA attenuates the remifentanil-induced hyperalgesia via reducing the excitability of VPL neurons and the low-frequency (theta band) oscillation in VPL LFP.

Spinal Protein Kinase Mζ Regulates α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid Receptor Trafficking and Dendritic Spine Plasticity via Kalirin-7 in the Pathogenesis of Remifentanil-induced Postincisional Hyperalgesia in Rats

Background

Intraoperative remifentanil anesthesia exaggerates postoperative pain sensitivity. Recent studies recapitulate the significance of protein kinase Mζ in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor–mediated pathologic pain. Kalirin-7, a Rho guanine nucleotide exchange factor, coordinates AMPA receptor trafficking and dendritic spine plasticity. This study examines whether protein kinase Mζ and Kalirin-7 contribute to remifentanil-induced postincisional hyperalgesia via AMPA receptor.

Methods

Plantar incision was performed 10 min after the start of remifentanil infusion (1 µg · kg−1 · min−1 for 60 min). Paw withdrawal threshold (primary outcome), spinal protein kinase Mζ activity, Kalirin-7 expression, AMPA receptor trafficking, and spine morphology were assessed. Protein kinase Mζ inhibitor and Kalirin-7 knockdown by short hairpin RNA elucidated the mechanism and prevention of hyperalgesia. Whole-cell patch-clamp recording analyzed the role of protein kinase Mζ in spinal AMPA receptor–induced current.

Results

Remifentanil reduced postincisional paw withdrawal threshold (mean ± SD, control vs. hyperalgesia, 18.9 ± 1.6 vs. 5.3 ± 1.2 g, n = 7) at postoperative 48 h, which was accompanied by an increase in spinal protein kinase Mζ phosphorylation (97.8 ± 25.1 vs. 181.5 ± 18.3%, n = 4), Kalirin-7 production (101.9 ± 29.1 vs. 371.2 ± 59.1%, n = 4), and number of spines/10 µm (2.0 ± 0.3 vs. 13.0 ± 1.6, n = 4). Protein kinase Mζ inhibitor reduced remifentanil-induced hyperalgesia, Kalirin-7 expression, and GluA1 trafficking. Incubation with protein kinase Mζ inhibitor reversed remifentanil-enhanced AMPA receptor-induced current in dorsal horn neurons. Kalirin-7 deficiency impaired remifentanil-caused hyperalgesia, postsynaptic GluA1 insertion, and spine plasticity. Selective GluA2-lacking AMPA receptor antagonist prevented hyperalgesia in a dose-dependent manner.

Conclusions

Spinal protein kinase Mζ regulation of GluA1-containing AMPA receptor trafficking and spine morphology via Kalirin-7 overexpression is a fundamental pathogenesis of remifentanil-induced hyperalgesia in rats.

Withdrawal from spinal application of remifentanil induces long-term potentiation of c-fiber-evoked field potentials by activation of Src family kinases in spinal microglia

It is well known that remifentanil, a widely used intravenous anesthesia drug, can paradoxically induce hyperalgesia. The underlying mechanisms are still not clear despite the wide investigations. The present study demonstrated that withdrawal from spinal application of remifentanil could dose-dependently induce long term potentiation (LTP) of C-fiber evoked field potentials. Remifentanil withdrawal could activate Src family kinases (SFKs) in microglia, and upregulate the expression of tumor necrosis factor alpha (TNFα) in spinal dorsal horn. Furthermore, pretreatment with either microglia inhibitor Minocycline, SFKs inhibitor PP2 or TNF αneutralization antibody could block remifentanil withdrawal induced spinal LTP, whereas supplement of recombinant rat TNFα to the spinal cord could reverse the inhibitory effect of Minocycline or PP2 on remifentanil withdrawal induced LTP. Our results suggested that TNFαrelease following SFKs activation in microglia is involved in the induction of LTP induced by remifentanil withdrawal.

Δ-opioid receptor inhibition prevents remifentanil-induced post-operative hyperalgesia via regulating GluR1 trafficking and AMPA receptor function

The interaction of remifentanil with glutamate systems has an important role in remifentanil-induced thermal and mechanical hyperalgesia. A previous study by our group suggested that the trafficking and function of glutamate receptor 1 (GluR1) subunits contributes to remifentanil-induced hyperalgesia by regulating the phosphorylation of GluR1 in dorsal horn neurons. The present study demonstrated that δ opioid receptor (DOR) inhibition prevented thermal and mechanical hyperalgesia, which was induced by remifentanil infusion via attenuating GluR1 subunit trafficking and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function in dorsal horn neurons. Sprague Dawley rats received a plantar incision and remifentanil infusion to induce a model of postoperative hyperalgesia. Thermal and mechanical pain was tested at 8 different time-points. Expression of AMPAR subunits GluR1 and DOR, as well as the phosphorylation status of GluR1 were evaluated by western blot analysis. Furthermore, the function of AMPAR in the spinal dorsal horn was measured by whole-cell patch-clamp recording. Remifentanil-induced thermal and mechanical hyperalgesia appeared after the 60-min infusions, reaching a peak level on day 2 and persisting for 5 days. Remifentanil infusion led to upregulation of membrane expression of the AMPAR subunit GluR1 and DOR (P=0.003 and 0.001, respectively) no change in total GluR1 and DOR expression levels (P=0.244 and 0.531, respectively). Selective DOR inhibitor naltrindole caused a reduction of remifentanil-induced hyperalgesia, which was accompanied by downregulation of membrane levels of GluR1 in the spinal cord (P=0.0013). In addition, DOR inhibition led to downregulation of GluR1 phosphorylated at Ser845. Furthermore, the AMPAR-mediated miniature excitatory post-synaptic current was increased in frequency and in amplitude in dorsal horn neurons (P=0.002 and 0.0011, respectively), which was decreased by incubation with naltrindole. Combined behavioral, western blot and electrophysiological evidence indicated that remifentanil-induced hyperalgesia was mediated by DOR activation, followed by phosphorylation-dependent GluR1 trafficking and AMPAR function enhancement in the spinal cord. DOR appears to be required for remifentanil and incision-induced hyperalgesia development and to be a potential biochemical target for treating opioid-induced postoperative hyperalgesia.

Casein kinase 1-epsilon deletion increases mu opioid receptor-dependent behaviors and binge eating1

Genetic and pharmacological studies indicate that casein kinase 1 epsilon (Csnk1e) contributes to psychostimulant, opioid, and ethanol motivated behaviors. We previously used pharmacological inhibition to demonstrate that Csnk1e negatively regulates the locomotor stimulant properties of opioids and psychostimulants. Here, we tested the hypothesis that Csnk1e negatively regulates opioid and psychostimulant reward using genetic inhibition and the conditioned place preference assay in Csnk1e knockout mice. Similar to pharmacological inhibition, Csnk1e knockout mice showed enhanced opioid-induced locomotor activity with the mu opioid receptor agonist fentanyl (0.2 mg/kg i.p.) as well as enhanced sensitivity to low-dose fentanyl reward (0.05 mg/kg). Interestingly, female knockout mice also showed a markedly greater escalation in consumption of sweetened palatable food - a behavioral pattern consistent with binge eating that also depends on mu opioid receptor activation. No difference was observed in fentanyl analgesia in the 52.5°C hot plate assay (0-0.4 mg/kg), naloxone conditioned place aversion (4 mg/kg), or methamphetamine conditioned place preference (0-4 mg/kg). To identify molecular adaptations associated with increased drug and food behaviors in knockout mice, we completed transcriptome analysis via mRNA sequencing of the striatum. Enrichment analysis identified terms associated with myelination and axon guidance and pathway analysis identified a differentially expressed gene set predicted to be regulated by the Wnt signaling transcription factor, Tcf7l2. To summarize, Csnk1e deletion increased mu opioid receptor-dependent behaviors, supporting previous studies indicating an endogenous negative regulatory role of Csnk1e in opioid behavior.