Stress-induced epigenetic regulation of κ-opioid receptor gene involves transcription factor c-Myc

Multiomic Network Analysis Identifies Dysregulated Neurobiological Pathways in Opioid Addiction

BACKGROUND

Opioid addiction is a worldwide public health crisis. In the United States, for example, opioids cause more drug overdose deaths than any other substance. However, opioid addiction treatments have limited efficacy, meaning that additional treatments are needed.

METHODS

To help address this problem, we used network-based machine learning techniques to integrate results from genome-wide association studies of opioid use disorder and problematic prescription opioid misuse with transcriptomic, proteomic, and epigenetic data from the dorsolateral prefrontal cortex of people who died of opioid overdose and control individuals.

RESULTS

We identified 211 highly interrelated genes identified by genome-wide association studies or dysregulation in the dorsolateral prefrontal cortex of people who died of opioid overdose that implicated the Akt, BDNF (brain-derived neurotrophic factor), and ERK (extracellular signal-regulated kinase) pathways, identifying 414 drugs targeting 48 of these opioid addiction-associated genes. Some of the identified drugs are approved to treat other substance use disorders or depression.

CONCLUSIONS

Our synthesis of multiomics using a systems biology approach revealed key gene targets that could contribute to drug repurposing, genetics-informed addiction treatment, and future discovery.

Voluntary Exercise Ameliorates Chronic Ethanol Withdrawal-Induced Adaptations of Opioid Receptor Expression in the Nucleus Accumbens, Dopamine Release, and Ethanol Consumption

Exercise has increasingly been recognized as an adjunctive therapy for alcohol-use disorder (AUD), yet our understanding of its underlying neurological mechanisms remains limited. This knowledge gap impedes the development of evidence-based exercise guidelines for AUD treatment. Chronic ethanol (EtOH) exposure has been shown to upregulate and sensitize kappa opioid receptors (KORs) in the nucleus accumbens (NAc), which is innervated by dopamine (DA) neurons in the midbrain ventral tegmental area (VTA), which may contribute to AUD-related behaviors. In this study, we investigated the impact of voluntary exercise in EtOH-dependent mice on EtOH consumption, KOR and delta opioid receptor (DOR) expression in the NAc and VTA, and functional effects on EtOH-induced alterations in DA release in the NAc. Our findings reveal that voluntary exercise reduces EtOH consumption, reduces KOR and enhances DOR expression in the NAc, and modifies EtOH-induced adaptations in DA release, suggesting a competitive interaction between exercise-induced and EtOH-induced alterations in KOR expression. We also found changes to DOR expression in the NAc and VTA with voluntary exercise but no significant changes to DA release. These findings elucidate the complex interplay of AUD-related neurobiological processes, highlighting the potential for exercise as a therapeutic intervention for AUD.

Opioid modulation of prefrontal cortex cells and circuits

Several neurochemical systems converge in the prefrontal cortex (PFC) to regulate cognitive and motivated behaviors. A rich network of endogenous opioid peptides and receptors spans multiple PFC cell types and circuits, and this extensive opioid system has emerged as a key substrate underlying reward, motivation, affective behaviors, and adaptations to stress. Here, we review the current evidence for dysregulated cortical opioid signaling in the pathogenesis of psychiatric disorders. We begin by providing an introduction to the basic anatomy and function of the cortical opioid system, followed by a discussion of endogenous and exogenous opioid modulation of PFC function at the behavioral, cellular, and synaptic level. Finally, we highlight the therapeutic potential of endogenous opioid targets in the treatment of psychiatric disorders, synthesizing clinical reports of altered opioid peptide and receptor expression and activity in human patients and summarizing new developments in opioid-based medications. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Microbiome Depletion Increases Fentanyl Self-Administration and Alters the Striatal Proteome Through Short-Chain Fatty Acids

Opioid use disorder (OUD) is a public health crisis currently being exacerbated by increased rates of use and overdose of synthetic opioids, primarily fentanyl. Therefore, the identification of novel biomarkers and treatment strategies to reduce problematic fentanyl use and relapse to fentanyl taking is critical. In recent years, there has been a growing body of work demonstrating that the gut microbiome can serve as a potent modulator of the behavioral and transcriptional responses to both stimulants and opioids. Here, we advance this work to define how manipulations of the microbiome drive fentanyl intake and fentanyl-seeking in a translationally relevant drug self-administration model. Depletion of the microbiome of male rats with broad spectrum antibiotics leads to increased drug administration on increased fixed ratio, progressive ratio, and drug seeking after abstinence. Utilizing 16S  sequencing of microbiome contents from these animals, specific populations of bacteria from the gut microbiome correlate closely with levels of drug taking. Additionally, global proteomic analysis of the nucleus accumbens following microbiome manipulation and fentanyl administration to define how microbiome status alters the functional proteomic landscape in this key limbic substructure. These data demonstrate that an altered microbiome leads to marked changes in the synaptic proteome in response to repeated fentanyl treatment. Finally, behavioral effects of microbiome depletion are reversible by upplementation of the microbiome derived short-chain fatty acid metabolites. Taken together, these findings establish clear relevance for gut-brain signaling in models of OUD and lay foundations for further translational work in this space.

Electro-conductive chitosan/graphene bio-nanocomposite scaffold for tissue engineering of the central nervous system

Degenerative central nervous system (CNS) disorders and traumatic brain injuries are common nowadays. These may induce the loss of neuronal cells and delicate connections essential for optimal CNS function. The CNS tissue has restricted regeneration ability, hindering the development of effective therapies. Developing cell and tissue instructive materials may bring up new treatment possibilities. In this study, chitosan-graphene nano platelets (GNPs) composite films were developed to regenerate brain cells. This study evaluates the effects of GNP concentration (0.5, 1 and 2 wt%) and their alignment on mechanical, electrical, surface, protein adsorption and biological properties of the regenerative scaffolds. Incorporating and aligning GNPs into chitosan matrix improved all the physical and biological properties. On reinforced scaffolds, HT22 cell morphology mimics pyramidal brain cells, which are responsible for the brain's highly branched neural network. Additionally, the reinforced scaffolds supported Mesenchymal Stem like Cells growth and were biocompatible in vivo. The alignment of GNPs in the chitosan matrix offered the appropriate physicochemical and biological properties to promote adhesion, proliferation and shape morphogenesis of hippocampal HT22 neuronal cells. Overall, this study delineates the enormous potential offered by the GNP-reinforced scaffolds for regeneration of central nervous system, especially the brain.

Oxycodone withdrawal induces HDAC1/HDAC2-dependent transcriptional maladaptations in the reward pathway in a mouse model of peripheral nerve injury

The development of physical dependence and addiction disorders due to misuse of opioid analgesics is a major concern with pain therapeutics. We developed a mouse model of oxycodone exposure and subsequent withdrawal in the presence or absence of chronic neuropathic pain. Oxycodone withdrawal alone triggered robust gene expression adaptations in the nucleus accumbens, medial prefrontal cortex and ventral tegmental area, with numerous genes and pathways selectively affected by oxycodone withdrawal in mice with peripheral nerve injury. Pathway analysis predicted that histone deacetylase (HDAC) 1 is a top upstream regulator in opioid withdrawal in nucleus accumbens and medial prefrontal cortex. The novel HDAC1/HDAC2 inhibitor, Regenacy Brain Class I HDAC Inhibitor (RBC1HI), attenuated behavioral manifestations of oxycodone withdrawal, especially in mice with neuropathic pain. These findings suggest that inhibition of HDAC1/HDAC2 may provide an avenue for patients with chronic pain who are dependent on opioids to transition to non-opioid analgesics.

Contribution of the opioid system to depression and to the therapeutic effects of classical antidepressants and ketamine

Major depressive disorder (MDD) afflicts approximately 5 % of the world population, and about 30-50 % of patients who receive classical antidepressant medications do not achieve complete remission (treatment resistant depressive patients). Emerging evidence suggests that targeting opioid receptors mu (MOP), kappa (KOP), delta (DOP), and the nociceptin/orphanin FQ receptor (NOP) may yield effective therapeutics for stress-related psychiatric disorders. As depression and pain exhibit significant overlap in their clinical manifestations and molecular mechanisms involved, it is not a surprise that opioids, historically used to alleviate pain, emerged as promising and effective therapeutic options in the treatment of depression. The opioid signaling is dysregulated in depression and numerous preclinical studies and clinical trials strongly suggest that opioid modulation can serve as either an adjuvant or even an alternative to classical monoaminergic antidepressants. Importantly, some classical antidepressants require the opioid receptor modulation to exert their antidepressant effects. Finally, ketamine, a well-known anesthetic whose extremely efficient antidepressant effects were recently discovered, was shown to mediate its antidepressant effects via the endogenous opioid system. Thus, although opioid system modulation is a promising therapeutical venue in the treatment of depression further research is warranted to fully understand the benefits and weaknesses of such approach.

Molecular and Epigenetic Aspects of Opioid Receptors in Drug Addiction and Pain Management in Sport

Opioids are substances derived from opium (natural opioids). In its raw state, opium is a gummy latex extracted from Papaver somniferum. The use of opioids and their negative health consequences among people who use drugs have been studied. Today, opioids are still the most commonly used and effective analgesic treatments for severe pain, but their use and abuse causes detrimental side effects for health, including addiction, thus impacting the user's quality of life and causing overdose. The mesocorticolimbic dopaminergic circuitry represents the brain circuit mediating both natural rewards and the rewarding aspects of nearly all drugs of abuse, including opioids. Hence, understanding how opioids affect the function of dopaminergic circuitry may be useful for better knowledge of the process and to develop effective therapeutic strategies in addiction. The aim of this review was to summarize the main features of opioids and opioid receptors and focus on the molecular and upcoming epigenetic mechanisms leading to opioid addiction. Since synthetic opioids can be effective for pain management, their ability to induce addiction in athletes, with the risk of incurring doping, is also discussed.

Convergent actions of stress and stimulants via epigenetic regulation of neural circuitry

The dorsal striatum integrates prior and current information to guide appropriate decision-making. Chronic stress and stimulant exposure interferes with decision-making, and can confer similar cognitive and behavioral inflexibilities. This review examines the literature on acute and chronic regulation of the epigenome by stress and stimulants. Recent evidence suggests that exposures to stress and stimulants share similarities in the manners in which they regulate the dorsal striatum epigenome through DNA methylation, transposable element activity, and histone post-translational modifications. These findings suggest that chronic stress and stimulant exposure leads to the accumulation of epigenetic modifications that impair immediate and future neuron function and activity. Such epigenetic mechanisms represent potential therapeutic targets for ameliorating convergent symptoms of stress and addiction.

Maternal deprivation effect on morphine-induced CPP is related to changes in Opioid receptors in selected rat brain regions (hippocampus, prefrontal cortex, and nucleus accumbens)

Early-life environmental conditions affect offspring's development. Maternal deprivation (MD) can induce persistent changes that give rise to neuropsychiatric diseases including substance abuse disorders. However, long-lasting mechanisms that determine vulnerability to drug addiction remain unknown. We hypothesized that MD could induce changes in Opioid system, HPA (hypothalamic-pituitary-adrenal) axis, and BDNF (brain-derived neurotrophic factor), so may be involved in the drug abuse in later life. Male offspring of Wistar rats (n=8 per group) were subjected to 3h of daily MD during postnatal days 1-14. In adulthood, morphine-induced CPP (conditioned place preference) was investigated using two doses of morphine (3 and 5mg/kg). Serum corticosterone level was measured by ELISA method. The expression level of genes in selected brain regions (hippocampus, prefrontal cortex, and nucleus accumbens) was determined by qPCR (quantitative PCR). A greater morphine-induced CPP was observed in MD rats with 3 and 5mg/kg morphine compared to controls. MD group had a higher corticosterone level. A significant decrease was observed in the expression of BDNF gene (in all of the selected brain regions) and GR (glucocorticoid receptor) gene (in the hippocampus and nucleus accumbens) in MD rats. Also, a significant increase in the expression of μ Opioid receptor (in all of the selected brain regions) and κ Opioid receptor (in the prefrontal cortex and nucleus accumbens) was observed in MD rats. Our results suggest that MD induces alterations in the HPA axis function, BDNF level, and Opioid receptors system that enhance vulnerability to morphine at adulthood.

Striatum Hyperactivity Triggers Relapse to Morphine and Methamphetamine (Polydrug) Dependence in Mice

Introduction:

κ-opioid receptor (KOPr) system has been linked to relapse to many substances, especially opioids. Positive responses were recently reported in morphine and methamphetamine (polydrug)-dependent mice treated with buprenorphine and naltrexone, a functional κ antagonist.

Objectives:

This study aimed to determine the specific brain region that is responsive to KOPr treatment following polydrug dependence.

Materials and Methods:

The polydrug-dependent mice model was developed using conditioned place preference (CPP) method. Following successful withdrawal phase, the mice were treated with 0.3 mg/kg buprenorphine and 1.0 mg/kg naltrexone. Four brain regions (hippocampus, prefrontal cortex, amygdala, and striatum) were investigated using immunohistochemistry technique. This is to quantify the changes in KOPr expression in each major brain region that was primarily involved in addiction neurocircuits of many substances. Unpaired Student’s t test was used to analyze all results, where P < 0.05 is considered significant.

Results:

The results showed that treatment with buprenorphine and naltrexone successfully attenuated relapse in 60% of mice (n = 14). A significant upregulation of KOPr was detected in striatum at the end of post-withdrawal phase (P < 0.01, n = 12). This treatment successfully suppressed KOPr in striatum (P < 0.001, n = 12), which supports the positive results seen in the CPP setting. No significant changes were observed in other brain regions studied.

Conclusion:

The hyperactivity of striatum suggests that the affected brain region following KOPr antagonist treatment is the region that primarily controls the drug rewarding activity, in which nucleus accumbens is located. This indicates that manipulation of KOPr system is one of the potential targets to treat morphine- or methamphetamine-dependence problem.

Turning the 'Tides on Neuropsychiatric Diseases: The Role of Peptides in the Prefrontal Cortex

Recent advancements in technology have enabled researchers to probe the brain with the greater region, cell, and receptor specificity. These developments have allowed for a more thorough understanding of how regulation of the neurophysiology within a region is essential for maintaining healthy brain function. Stress has been shown to alter the prefrontal cortex (PFC) functioning, and evidence links functional impairments in PFC brain activity with neuropsychiatric disorders. Moreover, a growing body of literature highlights the importance of neuropeptides in the PFC to modulate neural signaling and to influence behavior. The converging evidence outlined in this review indicates that neuropeptides in the PFC are specifically impacted by stress, and are found to be dysregulated in numerous stress-related neuropsychiatric disorders including substance use disorder, major depressive disorder (MDD), posttraumatic stress disorder, and schizophrenia. This review explores how neuropeptides in the PFC function to regulate the neural activity, and how genetic and environmental factors, such as stress, lead to dysregulation in neuropeptide systems, which may ultimately contribute to the pathology of neuropsychiatric diseases.

Buprenorphine prevents stress-induced blunting of nucleus accumbens dopamine response and approach behavior to food reward in mice

Alterations to the mesolimbic dopamine (DA) system are thought to underlie dysfunctional reward processing in stress-related psychiatric disorders. Using in vivio microdialysis in awake freely moving mice, we assessed the effects of stress on the motivational and neurochemical correlates underlying conditioned approach behavior for palatable food in the non-deprived mouse. Mice trained to approach and consume food in a familiar environment exhibited a 30% increase in nucleus accumbens shell (AcbSh) extracellular dopamine levels coincident with approach towards and consumption of the food reward. This effect was not observed in mice that were presented with the food in an unfamiliar environment or were exposed for the first time and were region specific. The addition of an acute environmental stressor (bright light and novel scent) during food exposure decreased DA release and delayed approach to the food. The disruptive impact of acute novelty stress on DA levels and approach behavior was reversed in animals pretreated with buprenorphine, an opioid drug with antidepressant-like and anxiolytic effects. Together, these data indicate that exposure to mild stress reduces incentive drive to approach palatable food via alterations in AcbSh dopamine responsiveness to food reward. Moreover, they implicate the brain opioid system as a potential pharmacological target for counteracting behavioral and neurochemical elements associated with stress.

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Dual regulation of lin28a by Myc is necessary during zebrafish retina regeneration

Cellular reprogramming leading to induction of Muller glia-derived progenitor cells (MGPCs) with stem cell characteristics is essential for zebrafish retina regeneration. Although several regeneration-specific genes are characterized, the significance of MGPC-associated Mycb induction remains unknown. Here, we show that early expression of Mycb induces expression of genes like ascl1a, a known activator of lin28a in MGPCs. Notably, mycb is simultaneously activated by Ascl1a and repressed by Insm1a in regenerating retina. Here, we unravel a dual role of Mycb in lin28a expression, both as an activator through Ascl1a in MGPCs and a repressor in combination with Hdac1 in neighboring cells. Myc inhibition reduces the number of MGPCs and abolishes normal regeneration. Myc in collaboration with Hdac1 inhibits her4.1, an effector of Delta-Notch signaling. Further, we also show the repressive role of Delta-Notch signaling on lin28a expression in post-injured retina. Our studies reveal mechanistic understanding of Myc pathway during zebrafish retina regeneration, which could pave way for therapeutic intervention during mammalian retina regeneration.

Epigenetic Regulation of the Kappa Opioid Receptor by Child Abuse

BACKGROUND

Experiences of abuse and neglect during childhood are major predictors of the emergence of depressive and suicidal behaviors throughout life. The underlying biological mechanisms, however, remain poorly understood. Here, we focused on the opioid system as a potential brain substrate mediating these effects.

METHODS

Postmortem samples from three brain structures regulating social bonds and emotions were analyzed. Groups were constituted of depressed individuals who died by suicide, with or without a history of severe child abuse, and of psychiatrically healthy control subjects. Expression of opioid peptides and receptors was measured using real-time polymerase chain reaction. DNA methylation, a major epigenetic mark, was investigated using targeted bisulfite sequencing and characterized at functional level using in vitro reporter assays. Finally, oxidative bisulfite sequencing was used to differentiate methylation and hydroxymethylation of DNA.

RESULTS

A history of child abuse specifically associated in the anterior insula with a downregulation of the kappa opioid receptor (Kappa), as well as decreased DNA methylation in the second intron of the Kappa gene. In vitro assays further showed that this intron functions as a genomic enhancer where glucocorticoid receptor binding regulates Kappa expression, unraveling a new mechanism mediating the well-established interactions between endogenous opioids and stress. Finally, results showed that child abuse is associated in the Kappa intron with a selective reduction in levels of DNA hydroxymethylation, likely mediating the observed downregulation of the receptor.

CONCLUSIONS

Altogether, our findings uncover new facets of Kappa physiology, whereby this receptor may be epigenetically regulated by stressful experiences, in particular as a function of early social life.

Chronic nicotine-induced changes in gene expression of delta and kappa-opioid receptors and their endogenous ligands in the mesocorticolimbic system of the rat

Delta and kappa opioid receptors (DOR and KOR, respectively) and their endogenous ligands, proenkephalin (PENK) and prodynorphin (PDYN)-derived opioid peptides are proposed as important mediators of nicotine reward. This study investigated the regulatory effect of chronic nicotine treatment on the gene expression of DOR, KOR, PENK and PDYN in the mesocorticolimbic system. Three groups of rats were injected subcutaneously with nicotine at doses of 0.2, 0.4, or 0.6 mg/kg/day for 6 days. Rats were decapitated 1 hr after the last dose on day six, as this timing coincides with increased dopamine release in the mesocorticolimbic system. mRNA levels in the ventral tegmental area (VTA), lateral hypothalamic area (LHA), amygdala (AMG), dorsal striatum (DST), nucleus accumbens, and medial prefrontal cortex were measured by quantitative real-time PCR. Our results showed that nicotine upregulated DOR mRNA in the VTA at all of the doses employed, in the AMG at the 0.4 and 0.6 mg/kg doses, and in the DST at the 0.4 mg/kg dose. Conversely, PDYN mRNA was reduced in the LHA with 0.6 mg/kg nicotine and in the AMG with 0.4 mg/kg nicotine. KOR mRNA was also decreased in the DST with 0.6 mg/kg nicotine. Nicotine did not regulate PENK mRNA in any brain region studied.

Isoproterenol increases histone deacetylase 6 expression and cell migration by inhibiting ERK signaling via PKA and Epac pathways in human lung cancer cells

Stress conditions are correlated with tumor growth, progression and metastasis. We hypothesized that stress signals might affect tumor progression via epigenetic control of gene expression and investigated the effects of stress signals on the expression levels of histone deacetylases (HDACs) and the underlying mechanisms of these effects in lung cancer cells. Treatment with isoproterenol (ISO), an analog of the stress signal epinephrine, increased the expression of HDAC6 protein and mRNA in H1299 lung cancer cells. ISO caused the deacetylation of α-tubulin and stimulated cell migration in an HDAC6-dependent manner. HDAC6 expression was increased by treatment with selective activators of cAMP-dependent protein kinase (PKA) or exchange protein activated by cAMP (Epac). ISO activated Rap1 via Epac, and constitutively active Rap1A increased the HDAC6 level; however, the knockdown of Rap1A decreased the 8-(4-cholorophenylthio)-2′-O-methyl-cAMP-induced increase in HDAC6 expression. Both PKA and Rap1A decreased c-Raf activation to inhibit extracellular signal-regulated kinase (ERK) signaling. Inhibition of ERK caused an increase in HDAC6 expression, and constitutively active MEK1 decreased the ISO-induced HDAC6 expression. We concluded that ISO increases HDAC6 expression via a PKA/Epac/ERK-dependent pathway that stimulates the migration of lung cancer cells. This study suggests that stress signals can stimulate the migration of cancer cells by inducing HDAC6 expression in lung cancer cells.

The role of the dynorphin/κ opioid receptor system in anxiety

Anxiety disorders are the most common and prevalent forms of psychiatric disease, although the biological basis of anxiety is not well understood. The dynorphin/κ opioid receptor system is widely distributed in the central nervous system and has been shown to play a critical role in modulating mood and emotional behaviors. In the present review, we summarize current literature relating to the role played by the dynorphin/κ opioid receptor system in anxiety and κ opioid receptor antagonists as potential therapeutic agents for the treatment of anxiety disorders.

Behavioral stress reduces RIP140 expression in astrocyte and increases brain lipid accumulation

Receptor-interacting protein 140 (RIP140) is highly expressed in the brain, and acts in neurons and microglia to affect emotional responses. The present study reveals an additional function of RIP140 in the brain, which is to regulate brain lipid homeostasis via its action in astrocytes. We found forced swim stress (FSS) significantly reduces the expression level of RIP140 and elevates cholesterol content in the brain. Mechanistically, FSS elevates endoplasmic reticulum stress, which suppresses RIP140 expression by increasing microRNA 33 (miR33) that targets RIP140 mRNA's 3'-untranslated region. Consequentially, cholesterol biosynthesis and export are dramatically increased in astrocyte, the major source of brain cholesterol. These results demonstrate that RIP140 plays an important role in maintaining brain cholesterol homeostasis through, partially, regulating cholesterol metabolism in, and mobilization from, astrocyte. Altering RIP140 levels can disrupt brain cholesterol homeostasis, which may contribute to behavioral stress-induced neurological disorders.

Epigenetic modification of DRG neuronal gene expression subsequent to nerve injury: etiological contribution to complex regional pain syndromes (Part II)

Cumulating evidence indicated that nerve injury-associated cellular and molecular changes play an essential role in contributing to the development of pathological pain, and more recent findings implicated the critical role of epigenetic mechanisms in pain-related sensitization in the DRG subsequent to nerve injury. In this part of the dyad review (Part II), we reviewed and paid special attention on the etiological contribution of DGR gene expression modulated by epigenetic mechanisms of CRPS. As essential effectors to different molecular activation, we first discussed the activation of various signaling pathways that subsequently from nerve injury, and in further illustrated the fundamental and functional underpinnings of nerve injury-induced pain, in which we argued for the potential epigenetic mechanisms in response to sensitizing stimuli or injury. Therefore, understanding the specific mediating factors that influence individual epigenetic differences contributing to pain sensitivity and responsiveness to analgesics possesses crucial clinical implications.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

β-arrestin protects neurons by mediating endogenous opioid arrest of inflammatory microglia

Microglial activation worsens neuronal loss and contributes to progressive neurological diseases like Parkinson's disease (PD). This inflammatory progression is countered by dynorphin (Dyn), the endogenous ligand of the kappa-opioid receptor (KOR). We show that microglial β-arrestin mediates the ability of Dyn/KOR to limit endotoxin-elicited production of pro-inflammatory effectors and cytokines, subsequently protecting neurons from inflammation-induced neurotoxicity. Agonist-activated KOR enhances the interaction of β-arrestin2 with transforming growth factor-beta-activated kinase 1 (TAK1)-binding protein 1 (TAB1), disrupting TAK1-TAB1 mediated pro-inflammatory gene expression. We reveal a new physiological role for β-arrestin in neuroprotection via receptor internalization-triggered blockade of signal effectors of microglial inflammatory neurotoxicity. This result offers novel drug targets in the convergent KOR/β-arrestin2 and inflammatory pathways for treating microglial inflammatory neuropathologies like PD.