NT-3 contributes to chemotherapy-induced neuropathic pain through TrkC-mediated CCL2 elevation in DRG neurons.

Cancer patients undergoing treatment with antineoplastic drugs often experience chemotherapy-induced neuropathic pain (CINP), and the therapeutic options for managing CINP are limited. Here, we show that systemic paclitaxel administration upregulates the expression of neurotrophin-3 (Nt3) mRNA and NT3 protein in the neurons of dorsal root ganglia (DRG), but not in the spinal cord. Blocking NT3 upregulation attenuates paclitaxel-induced mechanical, heat, and cold nociceptive hypersensitivities and spontaneous pain without altering acute pain and locomotor activity in male and female mice. Conversely, mimicking this increase produces enhanced responses to mechanical, heat, and cold stimuli and spontaneous pain in naive male and female mice. Mechanistically, NT3 triggers tropomyosin receptor kinase C (TrkC) activation and participates in the paclitaxel-induced increases of C-C chemokine ligand 2 (Ccl2) mRNA and CCL2 protein in the DRG. Given that CCL2 is an endogenous initiator of CINP and that Nt3 mRNA co-expresses with TrkC and Ccl2 mRNAs in DRG neurons, NT3 likely contributes to CINP through TrkC-mediated activation of the Ccl2 gene in DRG neurons. NT3 may be thus a potential target for CINP treatment.

FUS Contributes to Nerve Injury-Induced Nociceptive Hypersensitivity by Activating NF-κB Pathway in Primary Sensory Neurons.

Dysregulation of pain-associated genes in the dorsal root ganglion (DRG) is considered to be a molecular basis of neuropathic pain genesis. Fused in sarcoma (FUS), a DNA/RNA-binding protein, is a critical regulator of gene expression. However, whether it contributes to neuropathic pain is unknown. This study showed that peripheral nerve injury caused by the fourth lumbar (L4) spinal nerve ligation (SNL) or chronic constriction injury (CCI) of the sciatic nerve produced a marked increase in the expression of FUS protein in injured DRG neurons. Blocking this increase through microinjection of the adeno-associated virus (AAV) 5-expressing Fus shRNA into the ipsilateral L4 DRG mitigated the SNL-induced nociceptive hypersensitivities in both male and female mice. This microinjection also alleviated the SNL-induced increases in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) and glial fibrillary acidic protein (GFAP) in the ipsilateral L4 dorsal horn. Furthermore, mimicking this increase through microinjection of AAV5 expressing full-length Fus mRNA into unilateral L3/4 DRGs produced the elevations in the levels of p-ERK1/2 and GFAP in the dorsal horn, enhanced responses to mechanical, heat and cold stimuli, and induced the spontaneous pain on the ipsilateral side of both male and female mice in the absence of SNL. Mechanistically, the increased FUS activated the NF-κB signaling pathway by promoting the translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Our results indicate that DRG FUS contributes to neuropathic pain likely through the activation of NF-κB in primary sensory neurons.SIGNIFICANCE STATEMENT In the present study, we reported that fused in sarcoma (FUS), a DNA/RNA-binding protein, is upregulated in injured dorsal root ganglion (DRG) following peripheral nerve injury. This upregulation is responsible for nerve injury-induced translocation of p65 into the nucleus and phosphorylation of p65 in the nucleus from injured DRG neurons. Because blocking this upregulation alleviates nerve injury-induced nociceptive hypersensitivity, DRG FUS participates in neuropathic pain likely through the activation of NF-κB in primary sensory neurons. FUS may be a potential target for neuropathic pain management.

A sensory neuron-specific long non-coding RNA reduces neuropathic pain by rescuing KCNN1 expression.

Nerve injury to peripheral somatosensory system causes refractory neuropathic pain. Maladaptive changes of gene expression in primary sensory neurons are considered molecular basis of this disorder. Long non-coding RNAs (lncRNAs) are key regulators of gene transcription; however, their significance in neuropathic pain remains largely elusive.Here, we reported a novel lncRNA, named sensory neuron-specific lncRNA (SS-lncRNA), for its expression exclusively in dorsal root ganglion (DRG) and trigeminal ganglion. SS-lncRNA was predominantly expressed in small DRG neurons and significantly downregulated due to a reduction of early B cell transcription factor 1 in injured DRG after nerve injury. Rescuing this downregulation reversed a decrease of the calcium-activated potassium channel subfamily N member 1 (KCNN1) in injured DRG and alleviated nerve injury-induced nociceptive hypersensitivity. Conversely, DRG downregulation of SS-lncRNA reduced the expression of KCNN1, decreased total potassium currents and afterhyperpolarization currents and increased excitability in DRG neurons and produced neuropathic pain symptoms.Mechanistically, downregulated SS-lncRNA resulted in the reductions of its binding to Kcnn1 promoter and heterogeneous nuclear ribonucleoprotein M (hnRNPM), consequent recruitment of less hnRNPM to the Kcnn1 promoter and silence of Kcnn1 gene transcription in injured DRG.These findings indicate that SS-lncRNA may relieve neuropathic pain through hnRNPM-mediated KCNN1 rescue in injured DRG and offer a novel therapeutic strategy specific for this disorder.

Effect of intrathecal NIS-lncRNA antisense oligonucleotides on neuropathic pain caused by nerve trauma, chemotherapy, or diabetes mellitus.

BACKGROUND: Blocking increased expression of nerve injury-specific long non-coding RNA (NIS-lncRNA) in injured dorsal root ganglia (DRG) through DRG microinjection of NIS-lncRNA small hairpin interfering RNA or generation of NIS-lncRNA knockdown mice mitigates neuropathic pain. However, these strategies are impractical in the clinic. This study employed a Food and Drug Administration (FDA)-approved antisense oligonucleotides strategy to examine the effect of NIS-lncRNA ASOs on neuropathic pain. METHODS: Effects of intrathecal injection of NIS-lncRNA antisense oligonucleotides on day 7 or 14 after chronic constriction injury (CCI) of the sciatic nerve, fourth lumbar (L4) spinal nerve ligation, or intraperitoneal injection of paclitaxel or streptozotocin on the expression of DRG NIS-lncRNA and C-C chemokine ligand 2 (CCL2, an NIS-lncRNA downstream target) and nociceptive hypersensitivity were examined. We also assessed whether NIS-lncRNA antisense oligonucleotides produced cellular toxicity. RESULTS: Intrathecal NIS-lncRNA antisense oligonucleotides attenuated CCI-induced mechanical allodynia, heat hyperalgesia, cold hyperalgesia, and ongoing nociceptive responses, without changing basal or acute nociceptive responses and locomotor function. Intrathecal NIS-lncRNA antisense oligonucleotides also blocked CCI-induced increases in NIS-lncRNA and CCL2 in the ipsilateral L3 and L4 DRG and hyperactivities of neurones and astrocytes in the ipsilateral L3 and L4 spinal cord dorsal horn. Similar results were found in antisense oligonucleotides-treated mice after spinal nerve ligation or intraperitoneal injection of paclitaxel or streptozotocin. Normal morphologic structure and no cell loss were observed in the DRG and spinal cord of antisense oligonucleotides-treated mice. CONCLUSION: These findings further validate the role of NIS-lncRNA in trauma-, chemotherapy-, or diabetes-induced neuropathic pain and demonstrate potential clinical application of NIS-lncRNA antisense oligonucleotides for neuropathic pain management.

FTO (Fat-Mass and Obesity-Associated Protein) Participates in Hemorrhage-Induced Thalamic Pain by Stabilizing Toll-Like Receptor 4 Expression in Thalamic Neurons.

Background and Purpose: Hemorrhage-caused gene changes in the thalamus likely contribute to thalamic pain genesis. RNA N6-methyladenosine modification is an additional layer of gene regulation. Whether FTO (fat-mass and obesity-associated protein), an N6-methyladenosine demethylase, participates in hemorrhage-induced thalamic pain is unknown. Methods: Expression of Fto mRNA and protein was assessed in mouse thalamus after hemorrhage caused by microinjection of Coll IV (type IV collagenase) into unilateral thalamus. Effect of intraperitoneal administration of meclofenamic acid (a FTO inhibitor) or microinjection of adeno-associated virus 5 (AAV5) expressing Cre into the thalamus of Ftofl/fl mice on the Coll IV microinjection­induced TLR4 (Toll-like receptor 4) upregulation and nociceptive hypersensitivity was examined. Effect of thalamic microinjection of AAV5 expressing Fto (AAV5-Fto) on basal thalamic TLR4 expression and nociceptive thresholds was also analyzed. Additionally, level of N6-methyladenosine in Tlr4 mRNA and its binding to FTO or YTHDF2 (YTH N6-methyladenosine RNA binding protein 2) were observed. Results: FTO was detected in neuronal nuclei of thalamus. Level of FTO protein, but not mRNA, was time-dependently increased in the ipsilateral thalamus on days 1 to 14 after Coll IV microinjection. Intraperitoneal injection of meclofenamic acid or adeno-associated virus-5 expressing Cre microinjection into Ftofl/fl mouse thalamus attenuated the Coll IV microinjection­induced TLR4 upregulation and tissue damage in the ipsilateral thalamus and development and maintenance of nociceptive hypersensitivities on the contralateral side. Thalamic microinjection of AAV5-Fto increased TLR4 expression and elicited hypersensitivities to mechanical, heat and cold stimuli. Mechanistically, Coll IV microinjection produced an increase in FTO binding to Tlr4 mRNA, an FTO-dependent loss of N6-methyladenosine sites in Tlr4 mRNA and a reduction in the binding of YTHDF2 to Tlr4 mRNA in the ipsilateral thalamus. Conclusions: Our findings suggest that FTO participates in hemorrhage-induced thalamic pain by stabilizing TLR4 upregulation in thalamic neurons. FTO may be a potential target for the treatment of this disorder.

Eukaryotic initiation factor 4 gamma 2 contributes to neuropathic pain through down-regulation of Kv1.2 and the mu opioid receptor in mouse primary sensory neurones.

BACKGROUND: Nerve injury-induced changes in gene expression in the dorsal root ganglion (DRG) contribute to neuropathic pain genesis. Eukaryotic initiation factor 4 gamma 2 (eIF4G2) is a general repressor of cap-dependent mRNA translation. Whether DRG eIF4G2 participates in nerve injury-induced alternations in gene expression and nociceptive hypersensitivity is unknown. METHODS: The expression and distribution of eIF4G2 mRNA and protein in mouse DRG after spinal nerve ligation (SNL) were assessed. Effects of eIF4G2 siRNA microinjected through a glass micropipette into the injured DRG on the SNL-induced DRG mu opioid receptor (MOR) and Kv1.2 downregulation and nociceptive hypersensitivity were examined. In addition, effects of DRG microinjection of adeno-associated virus 5-expressing eIF4G2 (AAV5-eIF4G2) on basal DRG MOR and Kv1.2 expression and nociceptive thresholds were analysed. RESULTS: eIF4G2 protein co-expressed with Kv1.2 and MOR in DRG neurones. Levels of eIF4G2 mRNA (1.7 [0.24] to 2.3 [0.14]-fold of sham, P<0.01) and protein (1.6 [0.14] to 2.5 [0.22]-fold of sham, P<0.01) in injured DRG were time-dependently increased on days 3-14 after SNL. Blocking increased eIF4G2 through microinjection of eIF4G2 siRNA into the injured DRG attenuated SNL-induced downregulation of DRG MOR and Kv1.2 and development and maintenance of nociceptive hypersensitivities. DRG microinjection of AAV5-eIF4G2 reduced DRG MOR and Kv1.2 expression and elicited hypersensitivities to mechanical, heat and cold stimuli in naïve mice. CONCLUSIONS: eIF4G2 contributes to neuropathic pain through participation in downregulation of Kv1.2 and MOR in injured DRG and is a potential target for treatment of this disorder.

Contribution of DNMT1 to Neuropathic Pain Genesis Partially through Epigenetically Repressing Kcna2 in Primary Afferent Neurons.

Expressional changes of pain-associated genes in primary sensory neurons of DRG are critical for neuropathic pain genesis. DNA methyltransferase (DNMT)-triggered DNA methylation silences gene expression. We show here that DNMT1, a canonical maintenance methyltransferase, acts as the de novo DNMT and is required for neuropathic pain genesis likely through repressing at least DRG Kcna2 gene expression in male mice. Peripheral nerve injury upregulated DNMT1 expression in the injured DRG through the transcription factor cAMP response element binding protein-triggered transcriptional activation of Dnmt1 gene. Blocking this upregulation prevented nerve injury-induced DNA methylation within the promoter and 5'-untranslated region of Kcna2 gene, rescued Kcna2 expression and total Kv current, attenuated hyperexcitability in the injured DRG neurons, and alleviated nerve injury-induced pain hypersensitivities. Given that Kcna2 is a key player in neuropathic pain, our findings suggest that DRG DNMT1 may be a potential target for neuropathic pain management.SIGNIFICANCE STATEMENT In the present study, we reported that DNMT1, a canonical DNA maintenance methyltransferase, is upregulated via the activation of the transcription factor CREB in the injured DRG after peripheral nerve injury. This upregulation was responsible for nerve injury-induced de novo DNA methylation within the promoter and 5'-untranslated region of the Kcna2 gene, reductions in Kcna2 expression and Kv current and increases in neuronal excitability in the injured DRG. Since pharmacological inhibition or genetic knockdown of DRG DNMT1 alleviated nerve injury-induced pain hypersensitivities, DRG DNMT1 contributes to neuropathic pain genesis partially through repression of DRG Kcna2 gene expression.

DNMT3a-triggered downregulation of K2p 1.1 gene in primary sensory neurons contributes to paclitaxel-induced neuropathic pain.

Antineoplastic drugs induce dramatic transcriptional changes in dorsal root ganglion (DRG) neurons, which may contribute to chemotherapy-induced neuropathic pain. K2p 1.1 controls neuronal excitability by setting the resting membrane potential. Here, we report that systemic injection of the chemotherapy agent paclitaxel time-dependently downregulates the expression of K 2p 1.1 mRNA and its coding K2p 1.1 protein in the DRG neurons. Rescuing this downregulation mitigates the development and maintenance of paclitaxel-induced mechanical allodynia and heat hyperalgesia. Conversely, in the absence of paclitaxel administration, mimicking this downregulation decreases outward potassium current and increases excitability in the DRG neurons, leading to the enhanced responses to mechanical and heat stimuli. Mechanically, the downregulation of DRG K 2p 1.1 mRNA is attributed to paclitaxel-induced increase in DRG DNMT3a, as blocking this increase reverses the paclitaxel-induced the decrease of DRG K2p 1.1 and mimicking this increase reduces DRG K2p 1.1 expression. In addition, paclitaxel injection increases the binding of DNMT3a to the K 2p 1.1 gene promoter region and elevates the level of DNA methylation within this region in the DRG. These findings suggest that DNMT3a-triggered downregulation of DRG K2p 1.1 may contribute to chemotherapy-induced neuropathic pain.

Elevation of Transient Receptor Potential Vanilloid 1 Function in the Lateral Habenula Mediates Aversive Behaviors in Alcohol-withdrawn Rats.

WHAT WE ALREADY KNOW ABOUT THIS TOPIC: Chronic alcohol use and withdrawal leads to increased pain perception, anxiety, and depression. These aberrant behaviors are accompanied by increased excitatory glutamatergic transmission to, and activity of, the lateral habenula neurons.Vanilloid type 1, or TRPV1, channels are expressed in the habenula and they facilitate glutamatergic transmission. Whether TRPV1 channel plays a role in habenula hyperactivity is not clear. WHAT THIS ARTICLE TELLS US THAT IS NEW: Glutamatergic transmission in the lateral habenula was inhibited by TRPV1 channel antagonists. In vivo, local administration of TRPV1 antagonists into the lateral habenula attenuated hyperalgesia, anxiety, and relapse-like drinking in rats who chronically consumed alcohol.The data suggest that enhanced TRPV1 channel function during withdrawal may contribute to aberrant behavior that promotes relapse alcohol consumption. BACKGROUND: Recent rat studies indicate that alcohol withdrawal can trigger a negative emotional state including anxiety- and depression-like behaviors and hyperalgesia, as well as elevated glutamatergic transmission and activity in lateral habenula neurons. TRPV1, a vanilloid receptor expressed in the habenula, is involved in pain, alcohol dependence, and glutamatergic transmission. The authors therefore hypothesized that TRPV1 contributes to the changes in both the behavioral phenotypes and the habenula activity in alcohol-withdrawn rats. METHODS: Adult male Long-Evans rats (n = 110 and 280 for electrophysiology and behaviors, respectively), randomly assigned into the alcohol and water (Naïve) groups, were trained to consume either alcohol or water-only using an intermittent-access procedure. Slice electrophysiology was used to measure spontaneous excitatory postsynaptic currents and firing of lateral habenula neurons. The primary outcome was the change in alcohol-related behaviors and lateral habenula activity induced by pharmacologic manipulation of TRPV1 activity. RESULTS: The basal frequency of spontaneous excitatory postsynaptic currents and firing of lateral habenula neurons in alcohol-withdrawn rats was significantly increased. The TRPV1 antagonist capsazepine (10 µM) induced a stronger inhibition on spontaneous excitatory postsynaptic currents (mean ± SD; by 26.1 ± 27.9% [n = 11] vs. 6.7 ± 18.6% [n = 17], P = 0.027) and firing (by 23.4 ± 17.6% [n = 9] vs. 11.9 ± 16.3% [n = 12], P = 0.025) in Withdrawn rats than Naive rats. By contrast, the TRPV1 agonist capsaicin (3 µM) produced a weaker potentiation in Withdrawn than Naïve rats (spontaneous excitatory postsynaptic currents: by 203.6 ± 124.7% [n = 20] vs. 415.2 ± 424.3% [n = 15], P < 0.001; firing: 38.1 ± 14.7% [n = 11] vs. 73.9 ± 41.9% [n = 11], P < 0.001). Conversely, capsaicin's actions in Naïve but not in Withdrawn rats were significantly attenuated by the pretreatment of TRPV1 endogenous agonist N-Oleoyldopamine. In Withdrawn rats, intra-habenula infusion of TRPV1 antagonists attenuated hyperalgesia and anxiety-like behaviors, decreased alcohol consumption upon resuming drinking, and elicited a conditioned place preference. CONCLUSIONS: Enhanced TRPV1 function may contribute to increased glutamatergic transmission and activity of lateral habenula neurons, resulting in the aberrant behaviors during ethanol withdrawal.

Best Practices for Postoperative Brain Health: Recommendations From the Fifth International Perioperative Neurotoxicity Working Group.

As part of the American Society of Anesthesiology Brain Health Initiative goal of improving perioperative brain health for older patients, over 30 experts met at the fifth International Perioperative Neurotoxicity Workshop in San Francisco, CA, in May 2016, to discuss best practices for optimizing perioperative brain health in older adults (ie, >65 years of age). The objective of this workshop was to discuss and develop consensus solutions to improve patient management and outcomes and to discuss what older adults should be told (and by whom) about postoperative brain health risks. Thus, the workshop was provider and patient oriented as well as solution focused rather than etiology focused. For those areas in which we determined that there were limited evidence-based recommendations, we identified knowledge gaps and the types of scientific knowledge and investigations needed to direct future best practice. Because concerns about perioperative neurocognitive injury in pediatric patients are already being addressed by the SmartTots initiative, our workshop discussion (and thus this article) focuses specifically on perioperative cognition in older adults. The 2 main perioperative cognitive disorders that have been studied to date are postoperative delirium and cognitive dysfunction. Postoperative delirium is a syndrome of fluctuating changes in attention and level of consciousness that occurs in 20%-40% of patients >60 years of age after major surgery and inpatient hospitalization. Many older surgical patients also develop postoperative cognitive deficits that typically last for weeks to months, thus referred to as postoperative cognitive dysfunction. Because of the heterogeneity of different tools and thresholds used to assess and define these disorders at varying points in time after anesthesia and surgery, a recent article has proposed a new recommended nomenclature for these perioperative neurocognitive disorders. Our discussion about this topic was organized around 4 key issues: preprocedure consent, preoperative cognitive assessment, intraoperative management, and postoperative follow-up. These 4 issues also form the structure of this document. Multiple viewpoints were presented by participants and discussed at this in-person meeting, and the overall group consensus from these discussions was then drafted by a smaller writing group (the 6 primary authors of this article) into this manuscript. Of course, further studies have appeared since the workshop, which the writing group has incorporated where appropriate. All participants from this in-person meeting then had the opportunity to review, edit, and approve this final manuscript; 1 participant did not approve the final manuscript and asked for his/her name to be removed.

Meloxicam in the management of post-operative pain: Narrative review.

Oral formulations of meloxicam, a preferential cyclooxygenase-2 (COX-2) inhibitor, have long been used to treat osteoarthritis, rheumatoid arthritis, ankylosing spondylitis, as well as various pain syndromes of skeletomuscular origin (e.g., low back pain). However, these preparations are rarely indicated for the treatment of acute pain due to a poor dissolution rate and consequently a slow onset of action. The recent introduction of an intravenous (IV) NanoCrystal Colloidal Dispersion formulation opens up the possibility of using this drug during the perioperative period. The present review summarizes the pharmacologic properties of meloxicam, including its pharmacokinetics, adverse effects, and tolerability. In addition, we critically examined a number of recently completed clinical trials that evaluated the efficacy and safety of meloxicam IV in the treatment of post-operative pain. Literature retrieval was performed through PubMed and Medline (through March 2018) using combinations of the terms meloxicam, acute pain, and pharmacology. In addition, bibliographical information, including contributory unpublished data, was requested from the company developing the drug. Clinical trials suggest that single IV doses of 30 mg meloxicam significantly reduce post-operative pain as well as opioid requirements. We conclude that meloxicam IV is an effective and well-tolerated analgesic agent for the management of moderate to severe post-operative pain.

Role of dorsal root ganglion K2p1.1 in peripheral nerve injury-induced neuropathic pain.

Abstract: Peripheral nerve injury-caused hyperexcitability and abnormal ectopic discharges in the primary sensory neurons of dorsal root ganglion (DRG) play a key role in neuropathic pain development and maintenance. The two-pore domain background potassium (K2P) channels have been identified as key determinants of the resting membrane potential and neuronal excitability. However, whether K2P channels contribute to neuropathic pain is still elusive. We reported here that K2P1.1, the first identified mammalian K2P channel, was highly expressed in mouse DRG and distributed in small-, medium-, and large-sized DRG neurons. Unilateral lumbar (L) 4 spinal nerve ligation led to a significant and time-dependent reduction of K2P1.1 mRNA and protein in the ipsilateral L4 DRG, but not in the contralateral L4 or ipsilateral L3 DRG. Rescuing this reduction through microinjection of adeno-associated virus-DJ expressing full-length K2P1.1 mRNA into the ipsilateral L4 DRG blocked spinal nerve ligation-induced mechanical, thermal, and cold pain hypersensitivities during the development and maintenance periods. This DRG viral microinjection did not affect acute pain and locomotor function. Our findings suggest that K2P1.1 participates in neuropathic pain development and maintenance and may be a potential target in the management of this disorder.

Electroacupuncture Attenuates Hyperalgesia in Rats Withdrawn from Chronic Alcohol Drinking via Habenular Mu Opioid Receptors.

BACKGROUND: Hyperalgesia or increased sensitivity to pain is often found in alcoholics during alcohol withdrawal and may contribute to relapse drinking. Alternative therapies such as acupuncture and electroacupuncture (EA), through mechanisms involving opioid receptors, may reduce pain and substance dependence and withdrawal syndromes. The lateral habenula (LHb), an epithalamic structure rich in mu opioid receptors (MORs), is a critical target for both drugs of abuse and pain. We previously observed hyperalgesia in rats withdrawn from chronic ethanol (EtOH) drinking and found that EA at the acupoint Zusanli (ST36) reduced EtOH intake. This raised question of whether EA can alleviate hyperalgesia during alcohol withdrawal and, if so, whether the mechanism involves MORs in the LHb. METHODS: We trained male rats to drink EtOH using the intermittent access 20% EtOH 2-bottle free-choice drinking paradigm for 8 weeks, after which the alcohol supply was discontinued. We measured pain sensitivity using radiant heat (a light beam directed at the hind paw of rats) and compared the paw withdrawal latencies (PWLs) with and without EA at ST36. RESULTS: The PWLs were significantly shorter in rats at 24, 48, and 72 hours and 7 days after the discontinuation of EtOH when compared to EtOH-naïve rats. After a single administration of 2-Hz EA for 20 minutes at ST36, the PWLs at 24 hours after the withdrawal of EtOH were significantly greater than those of the sham group (2-Hz EA at the tail). Furthermore, the effect of EA on PWLs was significantly attenuated by bilateral intrahabenula infusion of the MOR antagonist naltrexone. CONCLUSIONS: These results suggest that EA can alleviate hyperalgesia during EtOH withdrawal through a mechanism involving MORs in the habenula. Based on this, EA could be of potential value as a therapy for hyperalgesia in alcohol dependence.

G9a inhibits CREB-triggered expression of mu opioid receptor in primary sensory neurons following peripheral nerve injury.

Neuropathic pain, a distressing and debilitating disorder, is still poorly managed in clinic. Opioids, like morphine, remain the mainstay of prescribed medications in the treatment of this disorder, but their analgesic effects are highly unsatisfactory in part due to nerve injury-induced reduction of opioid receptors in the first-order sensory neurons of dorsal root ganglia. G9a is a repressor of gene expression. We found that nerve injury-induced increases in G9a and its catalyzed repressive marker H3K9m2 are responsible for epigenetic silencing of Oprm1, Oprk1, and Oprd1 genes in the injured dorsal root ganglia. Blocking these increases rescued dorsal root ganglia Oprm1, Oprk1, and Oprd1 gene expression and morphine or loperamide analgesia and prevented the development of morphine or loperamide-induced analgesic tolerance under neuropathic pain conditions. Conversely, mimicking these increases reduced the expression of three opioid receptors and promoted the mu opioid receptor-gated release of primary afferent neurotransmitters. Mechanistically, nerve injury-induced increases in the binding activity of G9a and H3K9me2 to the Oprm1 gene were associated with the reduced binding of cyclic AMP response element binding protein to the Oprm1 gene. These findings suggest that G9a participates in the nerve injury-induced reduction of the Oprm1 gene likely through G9a-triggered blockage in the access of cyclic AMP response element binding protein to this gene.

Dorsal root ganglion transcriptome analysis following peripheral nerve injury in mice.

BACKGROUND: Peripheral nerve injury leads to changes in gene expression in primary sensory neurons of the injured dorsal root ganglia. These changes are believed to be involved in neuropathic pain genesis. Previously, these changes have been identified using gene microarrays or next generation RNA sequencing with poly-A tail selection, but these approaches cannot provide a more thorough analysis of gene expression alterations after nerve injury. METHODS: The present study chose to eliminate mRNA poly-A tail selection and perform strand-specific next generation RNA sequencing to analyze whole transcriptomes in the injured dorsal root ganglia following spinal nerve ligation. Quantitative real-time reverse transcriptase polymerase chain reaction assay was carried out to verify the changes of some differentially expressed RNAs in the injured dorsal root ganglia after spinal nerve ligation. RESULTS: Our results showed that more than 50 million (M) paired mapped sequences with strand information were yielded in each group (51.87 M-56.12 M in sham vs. 51.08 M-57.99 M in spinal nerve ligation). Six days after spinal nerve ligation, expression levels of 11,163 out of a total of 27,463 identified genes in the injured dorsal root ganglia significantly changed, of which 52.14% were upregulated and 47.86% downregulated. The largest transcriptional changes were observed in protein-coding genes (91.5%) followed by noncoding RNAs. Within 944 differentially expressed noncoding RNAs, the most significant changes were seen in long interspersed noncoding RNAs followed by antisense RNAs, processed transcripts, and pseudogenes. We observed a notable proportion of reads aligning to intronic regions in both groups (44.0% in sham vs. 49.6% in spinal nerve ligation). Using quantitative real-time polymerase chain reaction, we confirmed consistent differential expression of selected genes including Kcna2, Oprm1 as well as lncRNAs Gm21781 and 4732491K20Rik following spinal nerve ligation. CONCLUSION: Our findings suggest that next generation RNA sequencing can be used as a promising approach to analyze the changes of whole transcriptomes in dorsal root ganglia following nerve injury and to possibly identify new targets for prevention and treatment of neuropathic pain.

High Frequency Electrical Stimulation of Lateral Habenula Reduces Voluntary Ethanol Consumption in Rats.

BACKGROUND: Development of new strategies that can effectively prevent and/or treat alcohol use disorders is of paramount importance, because the currently available treatments are inadequate. Increasing evidence indicates that the lateral habenula (LHb) plays an important role in aversion, drug abuse, and depression. In light of the success of high-frequency stimulation (HFS) of the LHb in improving helplessness behavior in rodents, we assessed the effects of LHb HFS on ethanol-drinking behavior in rats. METHODS: We trained rats to drink ethanol under an intermittent access two-bottle choice procedure. We used c-Fos immunohistochemistry and electrophysiological approaches to examine LHb activity. We applied a HFS protocol that has proven effective for reducing helplessness behavior in rats via a bipolar electrode implanted into the LHb. RESULTS: c-Fos protein expression and the frequency of both spontaneous action potential firings and spontaneous excitatory postsynaptic currents were higher in LHb neurons of ethanol-withdrawn rats compared to their ethanol-naïve counterparts. HFS to the LHb produced long-term reduction of intake and preference for ethanol, without altering locomotor activity. Conversely, low-frequency electrical stimulation to the LHb or HFS applied to the nearby nucleus did not affect drinking behavior. CONCLUSIONS: Our results suggest that withdrawal from chronic ethanol exposure increases glutamate release and the activity of LHb neurons, and that functional inhibition of the LHb via HFS reduces ethanol consumption. Thus, LHb HFS could be a potential new therapeutic option for alcoholics.

Contribution of the Suppressor of Variegation 3-9 Homolog 1 in Dorsal Root Ganglia and Spinal Cord Dorsal Horn to Nerve Injury-induced Nociceptive Hypersensitivity.

BACKGROUND: Peripheral nerve injury-induced gene alterations in the dorsal root ganglion (DRG) and spinal cord likely participate in neuropathic pain genesis. Histone methylation gates gene expression. Whether the suppressor of variegation 3-9 homolog 1 (SUV39H1), a histone methyltransferase, contributes to nerve injury-induced nociceptive hypersensitivity is unknown. METHODS: Quantitative real-time reverse transcription polymerase chain reaction analysis, Western blot analysis, or immunohistochemistry were carried out to examine the expression of SUV39H1 mRNA and protein in rat DRG and dorsal horn and its colocalization with DRG µ-opioid receptor (MOR). The effects of a SUV39H1 inhibitor (chaetocin) or SUV39H1 siRNA on fifth lumbar spinal nerve ligation (SNL)-induced DRG MOR down-regulation and nociceptive hypersensitivity were examined. RESULTS: SUV39H1 was detected in neuronal nuclei of the DRG and dorsal horn. It was distributed predominantly in small DRG neurons, in which it coexpressed with MOR. The level of SUV39H1 protein in both injured DRG and ipsilateral fifth lumbar dorsal horn was time dependently increased after SNL. SNL also produced an increase in the amount of SUV39H1 mRNA in the injured DRG (n = 6/time point). Intrathecal chaetocin or SUV39H1 siRNA as well as DRG or intraspinal microinjection of SUV39H1 siRNA impaired SNL-induced allodynia and hyperalgesia (n = 5/group/treatment). DRG microinjection of SUV39H1 siRNA also restored SNL-induced DRG MOR down-regulation (n = 6/group). CONCLUSIONS: The findings of this study suggest that SUV39H1 contributes to nerve injury-induced allodynia and hyperalgesia through gating MOR expression in the injured DRG. SUV39H1 may be a potential target for the therapeutic treatment of nerve injury-induced nociceptive hypersensitivity.

Premedication with Intravenous Ibuprofen Improves Recovery Characteristics and Stress Response in Adults Undergoing Laparoscopic Cholecystectomy: A Randomized Controlled Trial.

OBJECTIVES: Examine the effect of preoperative dose of IV ibuprofen on stress response and postoperative recovery in laparoscopic cholecystectomy patients. DESIGN: Prospective, randomized, controlled, double-blind, multicenter trial. SETTING: Three university-based, tertiary care hospitals. SUBJECTS: Fifty-five adults, ASA 1, 2, or 3 scheduled for laparoscopic cholecystectomy were given a single preoperative dose of placebo or IV ibuprofen 800 mg. METHODS: Neurobehavioral assessments were evaluated preoperatively, in PACU, POD 1, and POD 3, using the 40-item Quality of Recovery questionnaire (QoR40), 9-item Modified Fatigue Severity Scale (MFSS), and 15-item Geriatric Depression scale (GDS). Blood samples were taken for cytokines (TNF-alpha, IL-1ß, IL-2, IL-6, IL-10, IFNγ), cortisol, CRP, epinephrine, and norepinephrine prior to the administration of study drug/placebo, intraoperatively, and after surgery. RESULTS: Global QoR40 scores remained at baseline for ibuprofen patients but significantly decreased in the placebo group. Severity of fatigue increased in patients receiving placebo but had no change with ibuprofen. The placebo group had lower GDS scores on POD 3. Epinephrine and norepinephrine were significantly lower intraoperatively for the ibuprofen group. Cortisol decreased postoperatively in the ibuprofen group. There was an impact of drug treatment on the immune response, as seen by an increase in TNFα and an increase in IL-10 when compared with placebo. CONCLUSIONS: Our results suggest the addition of NSAIDs may improve the overall quality of recovery, postsurgical fatigue, and early postoperative outcomes. Preoperative administration of IV ibuprofen modulates the stress and inflammatory response, as demonstrated by a decrease in the level of catecholamines, cortisol, and cytokines. TRIAL REGISTRATION: Clinicaltrials.gov identifier: 01938040.

mTOR, a new potential target for chronic pain and opioid-induced tolerance and hyperalgesia.

Chronic pain is a major public health problem with limited treatment options. Opioids remain a routine treatment for chronic pain, but extended exposure to opioid therapy can produce opioid tolerance and hyperalgesia. Although the mechanisms underlying chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia remain to be uncovered, mammalian target of rapamycin (mTOR) is involved in these disorders. The mTOR complex 1 and its triggered protein translation are required for the initiation and maintenance of chronic pain (including cancer pain) and opioid-induced tolerance/hyperalgesia. Given that mTOR inhibitors are FDA-approved drugs and an mTOR inhibitor is approved for the treatment of several cancers, these findings suggest that mTOR inhibitors will likely have multiple clinical benefits, including anticancer, antinociception/anti-cancer pain, and antitolerance/hyperalgesia. This paper compares the role of mTOR complex 1 in chronic pain, opioid-induced tolerance, and opioid-induced hyperalgesia.

Short-term pre- and post-operative stress prolongs incision-induced pain hypersensitivity without changing basal pain perception.

BACKGROUND: Chronic stress has been reported to increase basal pain sensitivity and/or exacerbate existing persistent pain. However, most surgical patients have normal physiological and psychological health status such as normal pain perception before surgery although they do experience short-term stress during pre- and post-operative periods. Whether or not this short-term stress affects persistent postsurgical pain is unclear. RESULTS: In this study, we showed that pre- or post-surgical exposure to immobilization 6 h daily for three consecutive days did not change basal responses to mechanical, thermal, or cold stimuli or peak levels of incision-induced hypersensitivity to these stimuli; however, immobilization did prolong the duration of incision-induced hypersensitivity in both male and female rats. These phenomena were also observed in post-surgical exposure to forced swimming 25 min daily for 3 consecutive days. Short-term stress induced by immobilization was demonstrated by an elevation in the level of serum corticosterone, an increase in swim immobility, and a decrease in sucrose consumption. Blocking this short-term stress via intrathecal administration of a selective glucocorticoid receptor antagonist, RU38486, or bilateral adrenalectomy significantly attenuated the prolongation of incision-induced hypersensitivity to mechanical, thermal, and cold stimuli. CONCLUSION: Our results indicate that short-term stress during the pre- or post-operative period delays postoperative pain recovery although it does not affect basal pain perception. Prevention of short-term stress may facilitate patients' recovery from postoperative pain.