Activation of CXCL10/CXCR3 Signaling Attenuates Morphine Analgesia: Involvement of Gi Protein

Based on Virtual Screening and Simulation Exploring the Mechanism of Plant-Derived Compounds with PINK1 to Postherpetic Neuralgia

Accumulating evidence strongly supports that PINK1 mutation can mediate mitochondrial autophagy dysfunction in dopaminergic neurons. This study was conducted to determine the role of PINK1 in the pathogenesis of postherpetic neuralgia (PHN) and find new targets for its treatment. A rigorous literature review was conducted to identify 2801 compounds from more than 200 plants in Asia. Virtual screening was used to shortlist the compounds into 20 groups based on their binding energies. MM/PBSA was used to further screen the compound dataset, and vitexin, luteoloside, and 2'-deoxyadenosine-5'-monophosphate were found to have a score of - 59.439, - 52.421, and - 47.544 kcal/mol, respectively. Pain behavioral quantification, enzyme-linked immunosorbent assay, quantitative polymerase chain reaction, western blotting, and transmission electron microscopy were used to confirm the effective mechanism. Vitexin had the most significant therapeutic effect on rats with PHN followed by luteoloside; 2'-deoxyadenosine-5'-monophosphate had no significant effect. Our findings suggested that vitexin could alleviate PHN by regulating mitochondrial autophagy through PINK1.

Pharmacological Modulation of the MIP-1 Family and Their Receptors Reduces Neuropathic Pain Symptoms and Influences Morphine Analgesia: Evidence from a Mouse Model

Neuropathic pain pathophysiology is not fully understood, but it was recently shown that MIP-1 family members (CCL3, CCL4, and CCL9) have strong pronociceptive properties. Our goal was to examine how pharmacological modulation of these chemokines and their receptors (CCR1 and CCR5) influence hypersensitivity after nerve injury in Albino Swiss male mice. The spinal changes in the mRNA/protein levels of the abovementioned chemokines and their receptors were measured using RT-qPCR and ELISA/Western blot techniques in a mouse model of chronic constriction injury of the sciatic nerve. Behavioral studies were performed using the von Frey and cold plate tests after pharmacological treatment with neutralizing antibodies (nAbs) against chemokines or antagonists (CCR1-J113863, CCR5-TAK-220/AZD-5672) alone and in coadministration with morphine on Day 7, when the hypersensitivity was fully developed. Our results showed enhanced protein levels of CCL3 and CCL9 1 and 7 days after nerve injury. The single intrathecal administration of CCL3 or CCL9 nAb, J113863, TAK-220, or AZD-5672 diminished neuropathic pain symptoms and enhanced morphine analgesia. These findings highlight the important roles of CCL3 and CCL9 in neuropathic pain and additionally indicate that these chemokines play essential roles in opioid analgesia. The obtained results suggest CCR1 and CCR5 as new, interesting targets in neuropathy treatment.

New insights into the analgesic properties of the XCL1/XCR1 and XCL1/ITGA9 axes modulation under neuropathic pain conditions - evidence from animal studies

Recent studies have indicated the involvement of chemokine-C-motif ligand 1 (XCL1) in nociceptive transmission; however, the participation of its two receptors, canonical chemokine-C-motif receptor 1 (XCR1) and integrin alpha-9 (ITGA9), recently recognized as a second receptor, has not been clarified to date. The aim was to explore by which of these receptors XCL1 reveals its pronociceptive properties and how the XCL1-XCR1 and XCL1-ITGA9 axes blockade/neutralization influence on pain-related behavior and opioid analgesia in the model of neuropathic pain. In our studies we used Albino Swiss mice which were exposed to the unilateral sciatic nerve chronic constriction injury (CCI) as a neuropathic pain model. Animals received single intrathecal (i.t.) injection of XCL1, XCL1 neutralizing antibodies, antagonist of XCR1 (vMIP-II) and neutralizing antibodies of ITGA9 (YA4), using lumbar puncture technique. Additionally we performed i.t. co-administration of abovementioned neutralizing antibodies and antagonists with single dose of morphine/buprenorphine. To assess pain-related behavior the von Frey and cold plate tests were used. To measure mRNA and protein level the RT-qPCR and Western Blot/Elisa/immunofluorescence techniques were performed, respectively. Statistical analysis was conducted using ANOVA with a Bonferroni correction. Presented studies have shown time-dependent upregulation of the mRNA and/or protein expression of XCL1 in the spinal cord after nerve injury as measured on day 1, 4, 7, 14, and 35. Our immunofluorescence study showed that XCL1 is released by astroglial cells located in the spinal cord, despite the neural localization of its receptors. Our results also provided the first evidence that the blockade/neutralization of both receptors, XCR1 and ITGA9, reversed hypersensitivity after intrathecal XCL1 administration in naive mice; however, neutralization of ITGA9 was more effective. In addition, the results proved that the XCL1 neutralizing antibody and, similarly, the blockade of XCR1 and neutralization of ITGA9 diminished thermal and mechanical hypersensitivity in nerve injury-exposed mice after 7 days. Additionally, neutralization of XCL1 improves morphine analgesia. Moreover, blockade of XCR1 positively influences buprenorphine effectiveness, and neutralization of ITGA9 enhances not only buprenorphine but also morphine analgesia. Therefore, blockade of the XCL1-ITGA9 interaction may serve as an innovative strategy for the polypharmacotherapy of neuropathic pain in combination with opioids.

Chemokine CXCL10 regulates pain behaviors via PI3K-AKT signaling pathway in mice

The analgesic efficacy of morphine can be affected by a variety of factors. Our previous studies demonstrated that chemokine (CXC motif) ligand 10 (CXCL10) could induce algesia directly and attenuate the analgesic effect produced by a single dose of morphine. However, the underlying mechanism remains unclear. In the present study, we aimed to further investigate the mechanism of CXCL10-mediated inhibition on morphine analgesic effect. According to our findings, recombinant CXCL10 protein (rmCXCL10) could increase the phosphorylation of serine-threonine kinase AKT reduced by morphine in spinal cord. Blocking AKT activation by phosphoinositide 3-kinase (PI3K) inhibitor could effectively attenuate CXCL10-induced algesia, and reverse the decrease of paw withdrawal thresholds caused by the co-administration of morphine and rmCXCL10. Furthermore, rmCXCL10 could enhance the spinal expression of pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β, which could be blocked by PI3K inhibitor. In summary, these findings suggest that PI3K-AKT signaling pathway mediates the effect of CXCL10 on the regulation of morphine analgesia and the release of cytokines in spinal cord. Our study provides a new insight into the mechanism of chemokine-relative pain regulation.

Targeting Chemokines and Chemokine GPCRs to Enhance Strong Opioid Efficacy in Neuropathic Pain

Neuropathic pain (NP) originates from an injury or disease of the somatosensory nervous system. This heterogeneous origin and the possible association with other pathologies make the management of NP a real challenge. To date, there are no satisfactory treatments for this type of chronic pain. Even strong opioids, the gold-standard analgesics for nociceptive and cancer pain, display low efficacy and the paradoxical ability to exacerbate pain sensitivity in NP patients. Mounting evidence suggests that chemokine upregulation may be a common mechanism driving NP pathophysiology and chronic opioid use-related consequences (analgesic tolerance and hyperalgesia). Here, we first review preclinical studies on the role of chemokines and chemokine receptors in the development and maintenance of NP. Second, we examine the change in chemokine expression following chronic opioid use and the crosstalk between chemokine and opioid receptors. Then, we examine the effects of inhibiting specific chemokines or chemokine receptors as a strategy to increase opioid efficacy in NP. We conclude that strong opioids, along with drugs that block specific chemokine/chemokine receptor axis, might be the right compromise for a favorable risk/benefit ratio in NP management.

Chemokine receptor antagonists enhance morphine's antinociceptive effect but not respiratory depression

AIMS

We have shown that chemokines injected into the periaqueductal gray region of the brain blocks opioid-induced analgesia in the rat cold-water tail flick test (CWTF). The present experiments tested whether chemokine receptor antagonists (CRAs), in combination with sub-analgesic doses of morphine, would provide maximal analgesia in the CWTF test and the mouse formalin pain assay. The effect of CRAs on respiratory depression was also evaluated.

MAIN METHODS

One, two or four CRAs (AMD3100/CXCR4, maraviroc/CCR5, RS504393/CCR2 orAZD8797/CX3CR1) were used in combination with sub-analgesic doses of morphine, all given systemically. Pain was assessed using the rat CWTF test or formalin injection into the paw of mice scored by licking. Respiration and oxygen saturation were measured in rats using a MouseOX® Plus - pulse oximeter.

KEY FINDINGS

In the CWTF test, a sub-maximal dose of morphine in combination with maraviroc alone, maraviroc plus AMD3100, or with the four chemokine receptor antagonists, produced synergistic increases in antinociception. In the formalin test, the combination of four CRAs plus a sub-maximal dose of morphine resulted in increased antinociception in both male and female mice. AMD3100 had an additive effect with morphine in both sexes. Coadministration of CRAs with morphine did not potentiate the opioid respiratory depressive effect.

SIGNIFICANCE

These results support the conclusion that combinations of CRAs can increase the potency of sub-analgesic doses of morphine analgesia without increasing respiratory depression. The results support an "opioid sparing" strategy for alleviation of pain using reduced doses of opioids in combination with CRAs to achieve maximal analgesia.

Spinal Ninjurin2 contributes to the neuropathic pain via NF-κB-mediated neuroinflammation in the spared sciatic nerve injury rats

OBJECT

Ninjurin2 (nerve injury induced protein 2, NINJ2) is a molecule which mediates cell-to-cell and cell-to-extracellular matrix interactions in the nervous system. Clinical study shows NINJ2 is associated with the development of postherpetic neuralgia. However, it is lack of direct evidence that NINJ2 participated in neuropathic pain. In this study, we aim to investigate the role of NINJ2 in the development of neuropathic pain in spared sciatic nerve injury rats and the underlying mechanism.

METHOD

Spared sciatic nerve injury (SNI) models were established. The level of NINJ2 and p-p65 (a NF-κB family member) were measured in SNI rats by western blots and immunofluorescent staining. Lentivirus encoding small interfering RNA targeting NINJ2 (RNAi) was intrathecally injected into rats. Then the change of pain behavior of rats induced by NINJ2 RNAi was tested by Von-Frey hairs. The change of p-p65 in the spinal cord in rats after NINJ2 RNAi treatment was also measured by western blots. inhibitor of p-p65-induced change of TNF-α, IL-1β, and IL-6 levels were measured by ELISA.

RESULTS

NINJ2 and p-p65 were increased in the spinal cord of SNI rats on the 3, 7, 14th days after modeling. NINJ2 were mainly expressed in neurons, and co-located with p-p65 in the spinal dorsal horn. When down regulating the level of NINJ2 by RNAi, the development of pain in SNI rats was partially blocked. Phosphorylation of p65 was also inhibited by NINJ2 RNAi. Blocking the phosphorylation of NF-κB pathway could inhibit the increase of TNF-α, IL-1β, and IL-6 in the spinal cord of SNI rats.

CONCLUSION

NINJ2 protein was increased in the spinal cord of SNI rats. It participated in the development of nerve injury-induced neuropathic pain by activating neuroinflammation in the spinal cord via NF-κB pathway. This study provides a new target to investigate the mechanism of neuropathic pain.

CXCR3 signalling partially contributes to the pathogenesis of neuropathic pain in male rodents

BACKGROUND

Currently, there is a lack of effective therapy for chronic pain. Increasing evidence has shown that chemokines and their correlative receptors involved in the neuron-glial cell cross-talk could contribute to the pathogenesis of neuropathic pain. Our previous studies suggested that CXCR3 expression was elevated in the spinal dorsal horn after nerve injury.

OBJECTIVES

In this study, we aimed to explore the role of CXCR3 signalling in chronic pain modulation.

METHODS

Reverse transcription quantitative PCR and Western blotting were used to measure the expression of CXCR3 and its ligands in the spinal cord following chronic constriction injury (CCI) of the sciatic nerve. Cxcr3 -knockout mice were used to observe the effect of the receptor on pain-related behaviour and microglial activation. Immunohistochemistry was used to investigate the expression of two activation markers for spinal microglia, Iba-1 and phosphorylated-p38 (p-p38) in these mice.

RESULTS

The expression of CXCR3 and its ligand CXCL11 was upregulated in the lumbar dorsal horn of the spinal cord in CCI models. In Cxcr3 -knockout mice, CCI-induced tactile allodynia and thermal hyperalgesia were observed to be alleviated during the early stage of pain processing. Meanwhile, the expression of the glial activation markers, namely, Iba-1 and p-p38, was decreased.

CONCLUSION

Our results demonstrate that CXCR3 could be a key modulator involved in pain modulation of the spinal cord; therefore, CXCR3-related signalling pathways could be potential targets for the treatment of intractable pathological pain.

Natural Compounds as Medical Strategies in the Prevention and Treatment of Psychiatric Disorders Seen in Neurological Diseases

Psychiatric disorders are frequently encountered in many neurological disorders, such as Alzheimer’s and Parkinson diseases along with epilepsy, migraine, essential tremors, and stroke. The most common comorbid diagnoses in neurological diseases are depression and anxiety disorders along with cognitive impairment. Whether the underlying reason is due to common neurochemical mechanisms or loss of previous functioning level, comorbidities are often overlooked. Various treatment options are available, such as pharmacological treatments, cognitive-behavioral therapy, somatic interventions, or electroconvulsive therapy. However oral antidepressant therapy may have some disadvantages, such as interaction with other medications, low tolerability due to side effects, and low efficiency. Natural compounds of plant origin are extensively researched to find a better and safer alternative treatment. Experimental studies have shown that phytochemicals such as alkaloids, terpenes, flavonoids, phenolic acids as well as lipids have significant potential in in vitro and in vivo models of psychiatric disorders. In this review, various efficacy of natural products in in vitro and in vivo studies on neuroprotective and their roles in psychiatric disorders are examined and their neuro-therapeutic potentials are shed light.

Distinct Gene Expression Patterns of Ion Channels and Cytokines in Rat Primary Sensory Neurons During Development of Bone Cancer and Cancer Pain

Cancer and cancer pain processes a major clinical challenge and the underlined mechanisms of pathogenesis remain elusive. We examined the specific changes in the transcriptomic profiles in the dorsal root ganglion (DRG) neurons of rats with bone cancer and bone cancer pain (BCP) using RNA sequencing technology. The bone cancer and BCP was induced by tumor cells implantation (TCI) into the tibia bone cavity in adult female rats. One week after treatment, TCI caused up- and down-regulation of thousands of genes in DRG. These genes were mainly involved in the immune process, inflammatory response, and intracellular signaling transduction of carbohydrate and cytokine. The cAMP and calcium signaling pathways were the major processes in the initial responses. Differentially expressed gene (DEG) analysis further showed that the genes for ion channels increased during day 1-7, while the genes for cytokine signaling pathways sustainedly increased during day 7-14 after TCI. The time courses of gene expression for ion channels and cytokines support their distinct roles in the early induction and late maintenance of BCP development. In addition, among the top 500 up- and down-regulated genes, 80-90% were unique for bone cancer pain as well as neuropathic and inflammatory pain, while less than 2% were shared among the three different forms of pain. This study reveals the uniqueness of mechanisms underlying bone cancer with pain, which is, to a large extent, differently from pain after acute inflammatory and nerve injury and provides novel potential targets of DEGs for bone cancer with pain.

Selective Ablation of Descending Serotonin from the Rostral Ventromedial Medulla Unmasks Its Pro-Nociceptive Role in Chemotherapy-Induced Painful Neuropathy

Purpose

Chemotherapy-induced painful neuropathy (CIPN) is a severe adverse effect of many anti-neoplastic drugs that is difficult to manage. Serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter in the rostral ventromedial medulla (RVM), which modulates descending spinal nociceptive transmission. However, the influence of the descending 5-HT from the RVM on CIPN is poorly understood. We investigated the role of 5-HT released from descending RVM neurons in a paclitaxel-induced CIPN rat model.

Methods

CIPN rat model was produced by intraperitoneally injecting of paclitaxel. Pain behavioral assessments included mechanical allodynia and heat hyperalgesia. 5-HT content was analyzed by high-performance liquid chromatography (HPLC). Western blot and immunohistochemistry were used to determine tryptophan hydroxylase (Tph) and c-Fos expression. The inhibitors p-chlorophenylalanine (PCPA) and SB203580 were administrated by stereotaxical RVM microinjection. Ondansetron was injected through intrathecal catheterization.

Results

The results demonstrated that Tph, the rate-limiting enzyme in 5-HT synthesis, was significantly upregulated in the RVM, and that spinal 5-HT release was increased in CIPN rats. Intra-RVM microinjection of Tph inhibitor PCPA significantly attenuated mechanical and thermal pain behavior through Tph downregulation and decreased spinal 5-HT. Intra-RVM administration of p38 mitogen-activated protein kinase (p38 MAPK) inhibitor SB203580 alleviated paclitaxel-induced pain in a similar manner to PCPA. Intrathecal injection of ondansetron, a 5-HT3 receptor antagonist, partially reversed paclitaxel-induced pain, indicating that 5-HT3 receptors were involved in descending serotoninergic modulation of spinal pain processing.

Conclusion

The results suggest that activation of the p38 MAPK pathway in the RVM leads to increased RVM Tph expression and descending serotoninergic projection to the spinal dorsal horn and contributes to the persistence of CIPN via spinal 5-HT3 receptors.

Blockade of CCR4 Diminishes Hypersensitivity and Enhances Opioid Analgesia - Evidence from a Mouse Model of Diabetic Neuropathy

Chemokine signaling has been implicated in the pathogenesis of diabetic neuropathy; however, the role of chemokine CC motif receptor 4 (CCR4) remains unknown. The goal was to examine the function of CCR4 in hypersensitivity development and opioid effectiveness in diabetic neuropathy. Streptozotocin (STZ; 200 mg/kg, intraperitoneally administered)-induced mouse model of diabetic neuropathy were used. An analysis of the mRNA/protein expression of CCR4 and its ligands was performed by qRT-PCR, microarray and/or Western blot methods. C021 (CCR4 antagonist), morphine and buprenorphine were injected intrathecally or intraperitoneally, and pain-related behavior was evaluated by the von Frey, cold plate and rotarod tests. We observed that on day 7 after STZ administration, the blood glucose level was increased, and as a consequence, hypersensitivity to tactile and thermal stimuli developed. In addition, we observed an increase in the mRNA level of CCL2 but not CCL17/CCL22. The microarray technique showed that the CCL2 protein level was also upregulated. In naive mice, the pronociceptive effect of intrathecally injected CCL2 was blocked by C021, suggesting that this chemokine acts through CCR4. Importantly, our results provide the first evidence that in a mouse model of diabetic neuropathy, single intrathecal and intraperitoneal injections of C021 diminished neuropathic pain-related behavior in a dose-dependent manner and improved motor functions. Moreover, both single intrathecal and intraperitoneal injections of C021 enhanced morphine and buprenorphine effectiveness. These results reveal that pharmacological modulation of CCR4 may be a good potential therapeutic target for the treatment of diabetic neuropathy and may enhance the effectiveness of opioids.

Evaluating the Role of CXCR3 in Pain Modulation: A Literature Review

CXCR3 is a well-known receptor involved in immune cell recruitment and inflammation. Pathological inflammation leads to pain stimulation and hence nociception. Therefore, we decided to review the recent research on CXCR3 to identify its precise role in the modulation of pain in a variety of clinical conditions targeting various regions of the body. Studies were selected from PubMed Medline, which relate CXCR3 to the progression of diseases with either bone cancer pain, neuropathic pain, cystitis pain, osteoarthritis and rheumatoid arthritis pain, dental pain, in particular, periodontitis and pulpitis. In all the diseases studied, a high prevalence of CXCR3 and/or its ligand were identified where CXCR3 is a key player in the pathophysiological process of many inflammatory conditions. CXCR3 and its ligands, particularly CXCL10, modulate nociception via actions in the dorsal root ganglia and dorsal horn of the spinal cord, in cases of bone cancer pain, neuropathic, and joint pain. However, with the other studied disease, no direct link to pain has been made, although it contributes to the pathological progression of the diseases and hence would be a causal factor for the pain. Furthermore, CXCR3 appears to play a role in desensitizing the opioid receptor in the descending modulatory pathway within the brain stem as well as modulating opioid-induced hyperalgesia in the dorsal horn of the spinal cord. Further research is required for understanding the exact mechanisms of CXCR3 in pain modulation centrally and peripherally. A greater understanding of the immunological activities and pharmacological consequence of CXCR3 and its ligands could help in the discovery of newer drugs for modulating pain arising from pathogenic or inflammatory sources. Given the significance of the CXCR3 for nociception, its utilization may prove to be beneficial as a target for analgesia.

The endocannabinoid system: Novel targets for treating cancer induced bone pain

Treating Cancer-induced bone pain (CIBP) continues to be a major clinical challenge and underlying mechanisms of CIBP remain unclear. Recently, emerging body of evidence suggested the endocannabinoid system (ECS) may play essential roles in CIBP. Here, we summarized the current understanding of the antinociceptive mechanisms of endocannabinoids in CIBP and discussed the beneficial effects of endocannabinoid for CIBP treatment. Targeting non-selective cannabinoid 1 receptors or selective cannabinoid 2 receptors, and modulation of peripheral AEA and 2-AG, as well as the inhibition the function of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have produced analgesic effects in animal models of CIBP. Management of ECS therefore appears to be a promising way for the treatment of CIBP in terms of efficacy and safety. Further clinical studies are encouraged to confirm the possible translation to humans of the very promising results already obtained in the preclinical studies.

Effect of interscalene nerve block on the inflammatory response in shoulder surgery: a randomized trial

BACKGROUND

Comparing techniques of general anesthesia and regional anesthesia in arthroscopic shoulder surgery, some studies have shown differences in the intensity of immediate postoperative pain and neuroendocrine response, but the inflammatory response when using balanced general anesthesia (BGA) vs. an ultrasound-guided (USG) single-dose interscalene block (SDIB) has not been compared.

MATERIALS AND METHODS

In a single-center, prospective, randomized clinical trial, the inflammatory response of 2 groups of 10 patients scheduled to undergo arthroscopic shoulder surgery was evaluated through measurement of a panel of cytokines that act on cells of the adaptive immune response to promote or inhibit inflammation, chemokines involved in chemotaxis, the erythrocyte sedimentation rate (ESR), the high-sensitivity C-reactive protein (CRP) level, and the white blood cell (WBC) count in 3 blood samples (before anesthesia, immediately postoperatively, and 24 hours postoperatively) with 2 types of anesthesia (BGA vs. USG SDIB). Postoperative pain intensity (immediately, at 12 hours, and at 24 hours) was also assessed.

RESULTS

The ESR and CRP level increased significantly at 24 hours after surgery; however, the increase in ESR (P < .0001) and CRP level (P < .0001) was lower in the USG SDIB group. Significant increases in the levels of soluble interleukin 2 receptor α (P = .022) and interleukin 12p40 (P = .016) occurred in the immediate postoperative period in the USG SDIB group. Immediate postoperative pain showed a significant increase (P < .001) in the BGA group.

CONCLUSIONS

In arthroscopic shoulder surgery, the use of a USG SDIB compared with the use of BGA is possibly associated with improved pain control in the immediate postoperative period and lower immunosuppression, even at 24 hours after surgery.

The Role of CXCR3 in Neurological Diseases

BACKGROUND

Neurological diseases have become an obvious challenge due to insufficient therapeutic intervention. Therefore, novel drugs for various neurological disorders are in desperate need. Recently, compelling evidence has demonstrated that chemokine receptor CXCR3, which is a G protein-coupled receptor in the CXC chemokine receptor family, may play a pivotal role in the development of neurological diseases. The aim of this review is to provide evidence for the potential of CXCR3 as a therapeutic target for neurological diseases.

METHODS

English journal articles that focused on the invovlement of CXCR3 in neurological diseases were searched via PubMed up to May 2017. Moreover, reference lists from identified articles were included for overviews.

RESULTS

The expression level of CXCR3 in T cells was significantly elevated in several neurological diseases, including multiple sclerosis (MS), glioma, Alzheimer's disease (AD), chronic pain, human T-lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and bipolar disorder. CXCR3 antagonists showed therapeutic effects in these neurological diseases.

CONCLUSION

These studies provided hard evidence that CXCR3 plays a vital role in the pathogenesis of MS, glioma, AD, chronic pain, HAM/TSP and bipolar disorder. CXCR3 is a crucial molecule in neuroinflammatory and neurodegenerative diseases. It regulates the activation of infiltrating cells and resident immune cells. However, the exact functions of CXCR3 in neurological diseases are inconclusive. Thus, it is important to understand the topic of chemokines and the scope of their activity in neurological diseases.

The Roles of Chemokine CXCL13 in the Development of Bone Cancer Pain and the Regulation of Morphine Analgesia in Rats

Chemokines are important regulators of immune, inflammatory, and neuronal responses in peripheral and central pain pathway. The aim of this study was to investigate whether chemokine (C-X-C motif) ligand 13 (CXCL13) and its receptor (C-X-C chemokine receptor type 5, CXCR5) involve in the development of bone cancer pain (BCP) and the regulation of morphine analgesia in rats. The change of pain behaviors in BCP rats were measured by testing paw withdrawal threshold (PWT). The levels of CXCL13, CXCR5 and signal pathway proteins (p-p38, p-ERK and p-AKT etc.) in the spinal cord were measured via western blots. The expression of CXCL13 and CXCR5 in spinal cord was increased in BCP rats. The BCP rats showed decrease of PWTs, which was relieved by CXCR5i. Intrathecally injection of murine recombinant CXCL13 (mrCXCL13) decreased the PWTs of BCP rats and opposed morphine-induced analgesia in BCP rats. In BCP rats, the signal pathway proteins (p38, ERK and AKT) in the spinal cord were activated. CXCL13 and morphine had contrary effect on the phosphorylation of these proteins. MrCXCL13 directly increased the levels of p-p38, p-ERK and p-AKT in BCP rats. However, morphine decreased the levels of these proteins in BCP rats. While blocking the activation of p-p38, p-ERK and p-AKT, morphine analgesia was enhanced. These results suggest CXCL13 participated in bone cancer pain and opposed morphine analgesia via p38, ERK and AKT pathways. It may be a target to enhance pain management in cancer pain patients.

Targeting Cytokines for Morphine Tolerance: A Narrative Review

BACKGROUND

Despite its various side effects, morphine has been widely used in clinics for decades due to its powerful analgesic effect. Morphine tolerance is one of the major side effects, hindering its long-term usage for pain therapy. Currently, the thorough cellular and molecular mechanisms underlying morphine tolerance remain largely uncertain.

METHODS

We searched the PubMed database with Medical subject headings (MeSH) including 'morphine tolerance', 'cytokines', 'interleukin 1', 'interleukin 1 beta', 'interleukin 6', 'tumor necrosis factor alpha', 'interleukin 10', 'chemokines'. Manual searching was carried out by reviewing the reference lists of relevant studies obtained from the primary search. The searches covered the period from inception to November 1, 2017.

RESULTS

The expression levels of certain chemokines and pro-inflammatory cytokines were significantly increased in animal models of morphine tolerance. Cytokines and cytokine receptor antagonist showed potent effect of alleviating the development of morphine tolerance.

CONCLUSION

Cytokines play a fundamental role in the development of morphine tolerance. Therapeutics targeting cytokines may become alternative strategies for the management of morphine tolerance.

Targeting inflammatory components in neuropathic pain: The analgesic effect of thymulin related peptide

Neuropathic pain is considered to be pathological in nature and has been shown to involve, at least partially, dysregulated inflammatory processes. It is a severe chronic disease that can develop following lesions to the central nervous system or to peripheral nerves. The peripheral nerve damage can be caused by either diseases such as diabetes, or by trauma. A common underlying mechanism of neuropathic pain is the presence of inflammation at the site of the damaged or affected nerve(s). This inflammatory response, especially when unresolved, initiates and maintains a cascade of events resulting in the activation of innate immune cells at the site of tissue injury. The release of inflammatory mediators such as cytokines, neurotrophic factors, and chemokines initiates local actions and can result in a more generalized immune response. The resultant neuroinflammatory environment can cause activation of glial cells, which can release, in an uncontrolled manner, more of these mediators and exasperate the situation, thus having a prominent role in nociception. The neuropathic pain pathophysiology is complex and includes peripheral and central neuronal alterations as well as neuro-immune interactions, which become more prominent during inflammatory reactions. This report focuses on how targeting inflammatory mediators may result in novel therapeutic approaches to neuropathic pain management.

Pharmacological blockade of CXCR3 by (±)-NBI-74330 reduces neuropathic pain and enhances opioid effectiveness - Evidence from in vivo and in vitro studies

It has been suggested that CXCR3 is important for nociception. Our experiments were conducted to evaluate involvement of CXCR3 and its ligands (CXCL4, CXCL9, CXCL10, CXCL11/CCL21) in neuropathic pain. Our studies give new evidence that intrathecal administration of each CXCR3 ligand induces pain-like behaviour in naive mice that occurs shortly after injection due to its location of neurons, which is confirmed by immunofluorescent staining. Moreover, intrathecal administrations of CXCL9, CXCL10, CCL21 neutralizing antibodies diminished pain-related behaviour. RT-PCR/Western blot analysis unprecedentedly showed spinal elevated levels of CXCR3 after chronic constriction injury of the sciatic nerve in rats in parallel with different time-course changes of its endogenous ligands. Initially, on day 2 we observed spinal increased levels of CXCL10 and CXCL11 indicating that these chemokines have important roles in triggering neuropathy. Then, on day 7, we observed increased levels of CXCL4, CXCL9, CXCL10. Interestingly, changes in CXCL9 level persisted until day 28, suggesting that these chemokines are responsible for long-term, persistent neuropathy. Additionally, in DRG the CXCL4, CXCL9 were elevated. The results obtained from primary glial cultures, suggests that all CXCR3 ligands can be produced in microglia, but also, except for CXCL4, in astrocytes. We provide the first evidence that in neuropathy chronic intrathecal administration of CXCR3 antagonist, (±)-NBI-74330, attenuates hypersensitivity with concomitant occurrence of microglial and some of CXCR3 ligands activation observed in the spinal cord and/or DRG level. This paper underlies the significance of CXCR3 in neuropathic pain and shows therapeutic potential of its blockade for enhancement of morphine analgesia as the major novelty of this work.

Role of Plant Derived Alkaloids and Their Mechanism in Neurodegenerative Disorders

Neurodegenerative diseases are conventionally demarcated as disorders with selective loss of neurons. Conventional as well as newer molecules have been tested but they offer just symptomatic advantages along with abundant side effects. The discovery of more compelling molecules that can halt the pathology of these diseases will be considered as a miracle of present time. Several synthetic compounds are available but they may cause several other health issues. Therefore, natural molecules from the plants and other sources are being discovered to replace available medicines. In conventional medicational therapies, several plants have been reported to bestow remedial effects. Phytochemicals from medicinal plants can provide a better and safer alternative to synthetic molecules. Many phytochemicals have been identified that cure the human body from a number of diseases. The present article reviews the potential efficacy of plant-derived alkaloids, which possess potential therapeutic effects against several NDDs including Alzheimer's disease (AD), Huntington disease (HD), Parkinson's disease (PD), Epilepsy, Schizophrenia, and stroke. Alkaloids include isoquinoline, indole, pyrroloindole, oxindole, piperidine, pyridine, aporphine, vinca, β-carboline, methylxanthene, lycopodium, and erythrine byproducts. Alkaloids constitute positive roles in ameliorating pathophysiology of these illnesses by functioning as muscarinic and adenosine receptors agonists, anti-oxidant, anti-amyloid and MAO inhibitors, acetylcholinestrase and butyrylcholinesterase inhibitor, inhibitor of α-synuclein aggregation, dopaminergic and nicotine agonist, and NMDA antagonist.

Endoplasmic Reticulum Stress in Spinal Cord Contributes to the Development of Morphine Tolerance

Morphine tolerance remains an intractable problem, which hinders its prolonged use in clinical practice. Endoplasmic reticulum (ER) stress has been proved to play a fundamental role in the pathogenesis of Alzheimer's disease, diabetes, atherosclerosis, cancer, etc. In this study, we provide the first direct evidence that ER stress may be a significant driver of morphine tolerance. Binding immunoglobulin protein (BiP), the ER stress marker, was significantly upregulated in neurons in spinal dorsal horn in rats being treated with morphine for 7 days. Additionally, chronic morphine treatment resulted in the activation of three arms of unfolded protein response (UPR): inositol-requiring enzyme 1/X-box binding protein 1 (IRE1/XBP1), protein kinase RNA-like ER kinase/eukaryotic initiation factor 2 subunit alpha (PERK/eIF2α), and activating transcription factor 6 (ATF6). More importantly, inhibiting either one of the three cascades could attenuate the development of morphine tolerance. Taken together, our results suggest that ER stress in spinal cord might contribute to the development of morphine tolerance. These findings implicate a potential clinical strategy for preventing morphine tolerance and may contribute to expanding the morphine usage in clinic.

The importance of chemokines in neuropathic pain development and opioid analgesic potency

The treatment of neuropathic pain resulting from nervous system malfunction remains a challenging problem for doctors and scientists. The lower effectiveness of conventionally used analgesics in neuropathic pain is associated with complex and not fully understood mechanisms of its development. Undoubtedly, interactions between immune and nervous system are crucial for maintenance of painful neuropathy. Nerve injury induces glial cell activation and thus enhances the production of numerous pronociceptive factors by these cells, including interleukins and chemokines. Increased release of those factors reduces the analgesic efficacy of opioids, which is significantly lower in neuropathic pain than in other painful conditions. This review discusses the role of chemokines from all four subfamilies as essential mediators of neuron-glia interactions occurring under neuropathic pain conditions. Based on available data, we analyse the influence of chemokines on opioid properties. Finally, we identify new direct and indirect pharmacological targets whose modulation may result in effective therapy of neuropathic pain, possibly in combination with opioids.

Cellular and Molecular Mechanisms of Calcium/Calmodulin-Dependent Protein Kinase II in Chronic Pain

Chronic pain, often defined as any pain lasting more than 3 months, is poorly managed because of its multifaceted and complex mechanisms. Calcium/calmodulin-dependent protein kinase II (CaMKII) is a multifunctional serine/threonine kinase that plays a fundamental role in synaptic plasticity, learning, and memory. Recent emerging evidence demonstrates increased expression and activity of CaMKII in the spinal cord and dorsal root ganglia of various chronic pain models. Moreover, our previous studies also find that inhibiting CaMKII could attenuate inflammatory pain and neuropathic pain. In this review, we provide evidence for the involvement of CaMKII in the initiation and development of chronic pain, including neuropathic pain, bone cancer pain, and inflammatory pain. Novel CaMKII inhibitors with potent inhibitory effect and high specificity may be alternative therapeutic strategies for the management of chronic pain in the future.

Potential role of CXCL10/CXCR3 signaling in the development of morphine tolerance in periaqueductal gray

Tolerance to morphine antinociception hinders its long-term use in clinical practice. Interaction between neuron and microglia has been proved to play critical role in the mechanism of morphine tolerance, while CXCL10/CXCR3 signaling has been implicated in neuron-glia signaling and morphine analgesia. This study aims to investigate whether CXCL10/CXCR3 signaling in periaqueductal gray (PAG) contributes to the development of morphine tolerance by modulating neuron-microglia interaction. The results showed that the expressions of CXCR3 and CXCL10 were gradually increased in parallel with repeated morphine administration and activation of microglia. CXCR3 was co-localized with neuronal marker NeuN, while CXCL10 was derived from microglia. Microglia inhibitor minocycline significantly attenuated the expression of CXCL10, besides, both minocycline and CXCR3 inhibitor alleviated the development of morphine tolerance. Taken together, our study provided the evidence that CXCL10/CXCR3 signaling in PAG is involved in the development of morphine analgesic tolerance via neuron-microglia interaction.

Spinal CX3CL1/CX3CR1 May Not Directly Participate in the Development of Morphine Tolerance in Rats

CX3CL1 (fractalkine), the sole member of chemokine CX3C family, is implicated in inflammatory and neuropathic pain via activating its receptor CX3CR1 on neural cells in spinal cord. However, it has not been fully elucidated whether CX3CL1 or CX3CR1 contributes to the development of morphine tolerance. In this study, we found that chronic morphine exposure did not alter the expressions of CX3CL1 and CX3CR1 in spinal cord. And neither exogenous CX3CL1 nor CX3CR1 inhibitor could affect the development of morphine tolerance. The cellular localizations of spinal CX3CL1 and CX3CR1 changed from neuron and microglia, respectively, to all the neural cells during the development of morphine tolerance. A microarray profiling revealed that 15 members of chemokine family excluding CX3CL1 and CX3CR1 were up-regulated in morphine-treated rats. Our study provides evidence that spinal CX3CL1 and CX3CR1 may not be involved in the development of morphine tolerance directly.

Breaking barriers to novel analgesic drug development

Acute and chronic pain complaints, although common, are generally poorly served by existing therapies. This unmet clinical need reflects a failure to develop novel classes of analgesics with superior efficacy, diminished adverse effects and a lower abuse liability than those currently available. Reasons for this include the heterogeneity of clinical pain conditions, the complexity and diversity of underlying pathophysiological mechanisms, and the unreliability of some preclinical pain models. However, recent advances in our understanding of the neurobiology of pain are beginning to offer opportunities for developing novel therapeutic strategies and revisiting existing targets, including modulating ion channels, enzymes and G-protein-coupled receptors.

The RS504393 Influences the Level of Nociceptive Factors and Enhances Opioid Analgesic Potency in Neuropathic Rats

Increasing evidence has indicated that activated glial cells releasing nociceptive factors, such as interleukins and chemokines, are of key importance for neuropathic pain. Significant changes in the production of nociceptive factors are associated with the low effectiveness of opioids in neuropathic pain. Recently, it has been suggested that CCL2/CCR2 signaling is important for nociception. Here, we studied the time course changes in the mRNA/protein level of CD40/Iba-1, CCL2 and CCR2 in the spinal cord/dorsal root ganglia (DRG) in rats following chronic constriction injury (CCI) of the sciatic nerve. Moreover, we examined the influence of intrathecal preemptive and repeated (daily for 7 days) administration of RS504393, CCR2 antagonist, on pain-related behavior and the associated biochemical changes of some nociceptive factors as well as its influence on opioid effectiveness. We observed simultaneous upregulation of Iba-1, CCL2, CCR2 in the spinal cord on 7th day after CCI. Additionally, we demonstrated that repeated administration of RS504393 not only attenuated tactile/thermal hypersensitivity but also enhanced the analgesic properties of morphine and buprenorphine under neuropathy. Our results proof that repeated administration of RS504393 reduced the mRNA and/or protein levels of pronociceptive factors, such as IL-1beta, IL-18, IL-6 and inducible nitric oxide synthase (iNOS), and some of their receptors in the spinal cord and/or DRG. Furthermore, RS504393 elevated the spinal protein level of antinociceptive IL-1alpha and IL-18 binding protein. Our data provide new evidence that CCR2 is a promising target for diminishing neuropathic pain and enhancing the opioid analgesic effects.

The Role of Spinal GABAB Receptors in Cancer-Induced Bone Pain in Rats

Cancer-induced bone pain (CIBP) remains a major challenge in advanced cancer patients because of our lack of understanding of its mechanisms. Previous studies have shown the vital role of γ-aminobutyric acid B receptors (GABABRs) in regulating nociception and various neuropathic pain models have shown diminished activity of GABABRs. However, the role of spinal GABABRs in CIBP remains largely unknown. In this study, we investigated the specific cellular mechanisms of GABABRs in the development and maintenance of CIBP in rats. Our behavioral results show that acute as well as chronic intrathecal treatment with baclofen, a GABABR agonist, significantly attenuated CIBP-induced mechanical allodynia and ambulatory pain. The expression levels of GABABRs were significantly decreased in a time-dependent manner and colocalized mostly with neurons and a minority with astrocytes and microglia. Chronic treatment with baclofen restored the expression of GABABRs and markedly inhibited the activation of cyclic adenosine monophosphate (cAMP)-dependent protein kinase and the cAMP-response element-binding protein signaling pathway.

PERSPECTIVE

Our findings provide, to our knowledge, the first evidence that downregulation of GABABRs contribute to the development and maintenance of CIBP and restored diminished GABABRs attenuate CIBP-induced pain behaviors at least partially by inhibiting the protein kinase/cAMP-response element-binding protein signaling pathway. Therefore, spinal GABABR may become a potential therapeutic target for the management of CIBP.

MHC-I promotes apoptosis of GABAergic interneurons in the spinal dorsal horn and contributes to cancer induced bone pain

Cancer induced bone pain (CIBP) remains one of the most intractable clinical problems due to poor understanding of its underlying mechanisms. Recent studies demonstrate the decline of inhibitory interneurons, especially GABAergic interneurons in the spinal cord, can evoke generation of chronic pain. It has also been reported that neuronal MHC-I expression renders neurons vulnerable to cytotoxic CD8⁺ T cells and finally lead to neurons apoptosis in a variety neurological disorders. However, whether MHC-I could induce the apoptosis of GABAergic interneurons in spinal cord and contribute to the development of CIBP remains unknown. In this study, we investigated roles of MHC-I and underlying mechanisms in CIBP on a rat model. Our results showed that increased MHC-I expression on GABAergic interneurons could deplete GABAergic interneurons by inducing their apoptosis in the spinal dorsal horn of tumor-bearing rats. Pretreatment of MHC-I RNAi-lentivirus could prevent the apoptosis of GABAergic interneurons and therefore alleviated mechanical allodynia induced by tumor cells intratibial injection. Additionally, we also found that CD8⁺ T cells were colocalized with MHC-I and GABAergic neurons and presented a significant and persistent increase in the spinal cord of tumor-bearing rats. Taken together, these findings indicated that MHC-I could evoke CIBP by promoting apoptosis of GABAergic interneurons in the dorsal horn, and this apoptosis was closely related to local CD8⁺ T cells.

The Walker 256 Breast Cancer Cell- Induced Bone Pain Model in Rats

The majority of patients with terminal breast cancer show signs of bone metastasis, the most common cause of pain in cancer. Clinically available drug treatment options for the relief of cancer-associated bone pain are limited due to either inadequate pain relief and/or dose-limiting side-effects. One of the major hurdles in understanding the mechanism by which breast cancer causes pain after metastasis to the bones is the lack of suitable preclinical models. Until the late twentieth century, all animal models of cancer induced bone pain involved systemic injection of cancer cells into animals, which caused severe deterioration of animal health due to widespread metastasis. In this mini-review we have discussed details of a recently developed and highly efficient preclinical model of breast cancer induced bone pain: Walker 256 cancer cell- induced bone pain in rats. The model involves direct localized injection of cancer cells into a single tibia in rats, which avoids widespread metastasis of cancer cells and hence animals maintain good health throughout the experimental period. This model closely mimics the human pathophysiology of breast cancer induced bone pain and has great potential to aid in the process of drug discovery for treating this intractable pain condition.

Targeting glia for bone cancer pain

INTRODUCTION

Bone cancer pain (BCP) remains to be a clinical challenge with limited pharmaceutical interventions. Therefore, novel therapeutic targets for the management of BCP are in desperate need. Recently, a growing body of evidence has suggested that glial cells may play a pivotal role in the pathogenesis of BCP. Areas covered: This review summarizes the recent progress in the understanding of glia in BCP and reveals the potential therapeutic targets in glia for BCP treatment. Expert opinion: Pharmacological interventions inhibiting the activation of glial cells, suppressing glia-derived proinflammatory cytokines, cell surface receptors, and the intracellular signaling pathways may be beneficial for the pain management of advanced cancer patients. However, these pharmacological interventions should not disrupt the normal function of glia cells since they play a vital supportive and protective role in the central nervous system.

Gene expression in term placentas is regulated more by spinal or epidural anesthesia than by late-onset preeclampsia or gestational diabetes mellitus

Pre-eclampsia (PE) and gestational diabetes mellitus (GDM) are common complications of pregnancy, but the mechanisms underlying these disorders remain unclear. The aim was to identify the extent of altered gene expression in term placentas from pregnant women with late-onset PE and GDM compared to controls. RNAseq identified few significantly differentially regulated genes in placental biopsies between PE, GDM, or uncomplicated pregnancy (n = 10 each group). Five genes were altered in placentas from PE including 4 non-coding genes and Angiopoietin 2 (ANGPT2). No genes were significantly regulated by GDM. In contrast, many genes were significantly regulated by fetal, maternal and delivery-specific variables, particularly spinal and epidural anesthesia. We selected ANGPT2 and Chemokine (C-X-C motif) ligand 14 (CXCL14) to test with qPCR in a larger set of placentas (n = 475) and found no differences between the groups. However, regression analysis revealed a stronger association between placental ANGPT2 and CXCL14 mRNA expression and fetal, maternal and delivery-specific variables than diagnostic group. To conclude, the gene expression in term placentas are highly affected by fetal, maternal and delivery specific variables. Few regulated genes were found in late-onset PE and GDM placentas, which may suggest that these conditions could be more affected by maternal factors.

Interleukin-6: an emerging regulator of pathological pain

Interleukin-6 is an inflammatory cytokine with wide-ranging biological effects. It has been widely demonstrated that neuroinflammation plays a critical role in the development of pathological pain. Recently, various pathological pain models have shown elevated expression levels of interleukin-6 and its receptor in the spinal cord and dorsal root ganglia. Additionally, the administration of interleukin-6 could cause mechanical allodynia and thermal hyperalgesia, and an intrathecal injection of anti-interleukin-6 neutralizing antibody alleviated these pain-related behaviors. These studies indicated a pivotal role of interleukin-6 in pathological pain. In this review, we summarize the recent progress in understanding the roles and mechanisms of interleukin-6 in mediating pathological pain associated with bone cancer, peripheral nerve injury, spinal cord injury, chemotherapy-induced peripheral neuropathy, complete Freund’s adjuvant injection, and carrageenan injection. Understanding and regulating interleukin-6 could be an interesting lead to novel therapeutic strategies for pathological pain.

Minocycline attenuates bone cancer pain in rats by inhibiting NF-κB in spinal astrocytes

AIM

To investigate the mechanisms underlying the anti-nociceptive effect of minocycline on bone cancer pain (BCP) in rats.

METHODS

A rat model of BCP was established by inoculating Walker 256 mammary carcinoma cells into tibial medullary canal. Two weeks later, the rats were injected with minocycline (50, 100 μg, intrathecally; or 40, 80 mg/kg, ip) twice daily for 3 consecutive days. Mechanical paw withdrawal threshold (PWT) was used to assess pain behavior. After the rats were euthanized, spinal cords were harvested for immunoblotting analyses. The effects of minocycline on NF-κB activation were also examined in primary rat astrocytes stimulated with IL-1β in vitro.

RESULTS

BCP rats had marked bone destruction, and showed mechanical tactile allodynia on d 7 and d 14 after the operation. Intrathecal injection of minocycline (100 μg) or intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced mechanical tactile allodynia. Furthermore, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of GFAP (astrocyte marker) and PSD95 in spinal cord. Moreover, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of NF-κB, p-IKKα and IκBα in spinal cord. In IL-1β-stimulated primary rat astrocytes, pretreatment with minocycline (75, 100 μmol/L) significantly inhibited the translocation of NF-κB to nucleus.

CONCLUSION

Minocycline effectively alleviates BCP by inhibiting the NF-κB signaling pathway in spinal astrocytes.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Identification of lncRNA expression profile in the spinal cord of mice following spinal nerve ligation-induced neuropathic pain

Background

Neuropathic pain that caused by lesion or dysfunction of the nervous system is associated with gene expression changes in the sensory pathway. Long noncoding RNAs (lncRNAs) have been reported to be able to regulate gene expression. Identifying lncRNA expression patterns in the spinal cord under normal and neuropathic pain conditions is essential for understanding the genetic mechanisms behind the pathogenesis of neuropathic pain.

Results

Spinal nerve ligation (SNL) induced rapid and persistent pain hypersensitivity, characterized by mechanical allodynia and heat hyperalgesia. Meanwhile, astrocytes and microglia were dramatically activated in the ipsilateral spinal cord dorsal horn at 10 days after SNL. Further lncRNA microarray and mRNA microarray analysis showed that the expression profiles of lncRNA and mRNA between SNL and sham-operated mice were greatly changed at 10 days. The 511 differentially expressed (>2 fold) lncRNAs (366 up-regulated, 145 down-regulated) and 493 mRNAs (363 up-regulated, 122 down-regulated) were finally identified. The expression patterns of several lncRNAs and mRNAs were further confirmed by qPCR. Functional analysis of differentially expressed (DE) mRNAs showed that the most significant enriched biological processes of up-regulated genes in SNL include immune response, defense response, and inflammation response, which are important pathogenic mechanisms underlying neuropathic pain. 35 DE lncRNAs have neighboring or overlapping DE mRNAs in genome, which is related to Toll-like receptor signaling, cytokine–cytokine receptor interaction, and peroxisome proliferator-activated receptor signaling pathway.

Conclusion

Our findings uncovered the expression pattern of lncRNAs and mRNAs in the mice spinal cord under neuropathic pain condition. These lncRNAs and mRNAs may represent new therapeutic targets for the treatment of neuropathic pain.

Opioid and chemokine receptor crosstalk: a promising target for pain therapy?

Chemokines and opioids are important regulators of immune, inflammatory and neuronal responses in peripheral and central pain pathways. Recent studies have provided insights into the functional interactions between chemokine receptors and opioid receptors, and their role in pain modulation. In this Progress article, we discuss how crosstalk between these two systems might provide a molecular and cellular framework for the development of novel analgesic therapies for the management of acute and/or chronic pain.

Genomewide analysis of rat periaqueductal gray-dorsal horn reveals time-, region- and frequency-specific mRNA expression changes in response to electroacupuncture stimulation

Electroacupuncture (EA) has been widely applied for illness prevention, treatment or rehabilitation in the clinic, especially for pain management. However, the molecular events that induce these changes remain largely uncharacterized. The periaqueductal gray (PAG) and the spinal dorsal horn (DH) have been verified as two critical regions in the response to EA stimulation in EA analgesia. In this study, a genetic screen was conducted to delineate the gene expression profile in the PAG-DH regions of rats to explore the molecular events of the analgesic effect induced by low-frequency (2-Hz) and high-frequency (100-Hz) EAs. Microarray analysis at two different time points after EA stimulation revealed time-, region- and frequency-specific gene expression changes. These expression differences suggested that modulation of neural-immune interaction in the central nervous system played an important role during EA analgesia. Furthermore, low-frequency EA could regulate gene expression to a greater degree than high-frequency EA. Altogether, the present study offers, for the first time, a characterized transcriptional response pattern in the PAG-DH regions followed by EA stimulation and, thus, provides a solid experimental framework for future in-depth analysis of the mechanisms underlying EA-induced effects.