1 4850 145 OPIOIDS AND OPIOID RECEPTORS; UNDERSTANDING PHARMACOLOGICAL MECHANISMS AS A KEY TO THERAPEUTIC ADVANCES AND MITIGATION OF THE MISUSE CRISIS. OPIOIDS ARE A MAINSTAY IN ACUTE PAIN MANAGEMENT AND PRODUCE THEIR EFFECTS AND SIDE EFFECTS (E.G., TOLERANCE, OPIOID-USE DISORDER AND IMMUNE SUPPRESSION) BY INTERACTION WITH OPIOID RECEPTORS. I WILL DISCUSS OPIOID PHARMACOLOGY IN SOME CONTROVERSIAL AREAS OF ENQUIRY OF ANAESTHETIC RELEVANCE. THE MAIN OPIOID TARGET IS THE MICRO (MU,MOP) RECEPTOR BUT OTHER MEMBERS OF THE OPIOID RECEPTOR FAMILY, DELTA (DELTA; DOP) AND KAPPA (KAPPA; KOP) OPIOID RECEPTORS ALSO PRODUCE ANALGESIC ACTIONS. THESE ARE NALOXONE-SENSITIVE. THERE IS IMPORTANT CLINICAL DEVELOPMENT RELATING TO THE NOCICEPTIN/ORPHANIN FQ (NOP) RECEPTOR, AN OPIOID RECEPTOR THAT IS NOT NALOXONE-SENSITIVE. BETTER UNDERSTANDING OF THE DRIVERS FOR OPIOID EFFECTS AND SIDE EFFECTS MAY FACILITATE SEPARATION OF SIDE EFFECTS AND PRODUCTION OF SAFER DRUGS. OPIOIDS BIND TO THE RECEPTOR ORTHOSTERIC SITE TO PRODUCE THEIR EFFECTS AND CAN ENGAGE MONOMER OR HOMO-, HETERODIMER RECEPTORS. SOME LIGANDS CAN DRIVE ONE INTRACELLULAR PATHWAY OVER ANOTHER. THIS IS THE BASIS OF BIASED AGONISM (OR FUNCTIONAL SELECTIVITY). OPIOID ACTIONS AT THE ORTHOSTERIC SITE CAN BE MODULATED ALLOSTERICALLY AND POSITIVE ALLOSTERIC MODULATORS THAT ENHANCE OPIOID ACTION ARE IN DEVELOPMENT. AS WELL AS TARGETING LIGAND-RECEPTOR INTERACTION AND TRANSDUCTION, MODULATING RECEPTOR EXPRESSION AND HENCE FUNCTION IS ALSO TRACTABLE. THERE IS EVIDENCE FOR EPIGENETIC ASSOCIATIONS WITH DIFFERENT TYPES OF PAIN AND ALSO SUBSTANCE MISUSE. AS LONG AS THE OPIOID NARRATIVE IS DEFINED BY THE 'OPIOID CRISIS' THE DRIVE TO REMOVE THEM COULD GATHER PACE. THIS WILL DENY USE WHERE THEY ARE EFFECTIVE, AND ACCESS TO MORPHINE FOR PAIN RELIEF IN LOW INCOME COUNTRIES. 2023 2 1706 28 DYNORPHIN/KOP AND NOCICEPTIN/NOP GENE EXPRESSION AND EPIGENETIC CHANGES BY COCAINE IN RAT STRIATUM AND NUCLEUS ACCUMBENS. COCAINE INDUCES NEUROCHEMICAL CHANGES OF ENDOGENOUS PRODYNORPHIN-KAPPA OPIOID RECEPTOR (PDYN-KOP) AND PRONOCICEPTIN/ORPHANINFQ-NOCICEPTIN RECEPTOR (PN/OFQ-NOP) SYSTEMS. BOTH SYSTEMS PLAY AN IMPORTANT ROLE IN REWARDING MECHANISMS AND ADDICTIVE STIMULUS PROCESSING BY MODULATING DRUG-INDUCED DOPAMINERGIC ACTIVATION IN THE MESOCORTICO-LIMBIC BRAIN AREAS. THEY ARE ALSO INVOLVED IN REGULATING STRESS MECHANISMS RELATED TO ADDICTION. THE AIM OF THIS STUDY WAS TO INVESTIGATE POSSIBLE CHANGES OF GENE EXPRESSION OF THE DYNORPHINERGIC AND NOCICEPTINERGIC SYSTEM COMPONENTS IN THE NUCLEUS ACCUMBENS (NA) AND IN MEDIAL AND LATERAL CAUDATE PUTAMEN (MCPU AND LCPU, RESPECTIVELY) OF RATS, FOLLOWING CHRONIC SUBCUTANEOUS INFUSION OF COCAINE. IN ADDITION, THE EPIGENETIC HISTONE MODIFICATIONS H3K4ME3 AND H3K27ME3 (AN ACTIVATING AND A REPRESSIVE MARKER, RESPECTIVELY) AT THE PROMOTER LEVEL OF THE PDYN, KOP, PN/OFQ AND NOP GENES WERE INVESTIGATED. RESULTS SHOWED THAT COCAINE INDUCED PDYN GENE EXPRESSION UP-REGULATION IN THE NA AND LCPU, AND ITS DOWN-REGULATION IN THE MCPU, WHEREAS KOP MRNA LEVELS WERE UNCHANGED. MOREOVER, COCAINE EXPOSURE DECREASED PN/OFQ GENE EXPRESSION IN THE NA AND LCPU, WHILE NOP MRNA LEVELS APPEARED SIGNIFICANTLY INCREASED IN THE NA AND DECREASED IN THE LCPU. SPECIFIC CHANGES OF THE H3K4ME3 AND H3K27ME3 LEVELS WERE FOUND AT PDYN, PN/OFQ, AND NOP GENE PROMOTER, CONSISTENT WITH THE OBSERVED GENE EXPRESSION ALTERATIONS. THE PRESENT FINDINGS CONTRIBUTE TO BETTER DEFINE THE ROLE OF ENDOGENOUS PDYN-KOP AND PN/OFQ-NOP SYSTEMS IN NEUROPLASTICITY MECHANISMS FOLLOWING CHRONIC COCAINE TREATMENT. THE EPIGENETIC HISTONE MODIFICATIONS UNDERLYING THE GENE EXPRESSION CHANGES LIKELY MEDIATE THE EFFECTS OF COCAINE ON TRANSCRIPTIONAL REGULATION OF SPECIFIC GENE PROMOTERS THAT RESULT IN LONG-LASTING DRUG-INDUCED PLASTICITY. 2014 3 2363 37 EPIGENETIC REGULATION OF SPINAL CORD GENE EXPRESSION CONTRIBUTES TO ENHANCED POSTOPERATIVE PAIN AND ANALGESIC TOLERANCE SUBSEQUENT TO CONTINUOUS OPIOID EXPOSURE. BACKGROUND: OPIOIDS HAVE BECOME THE MAINSTAY FOR TREATMENT OF MODERATE TO SEVERE PAIN AND ARE COMMONLY USED TO TREAT SURGICAL PAIN. WHILE OPIOID ADMINISTRATION HAS BEEN SHOWN TO CAUSE OPIOID-INDUCED HYPERALGESIA AND TOLERANCE, INTERACTIONS BETWEEN OPIOID ADMINISTRATION AND SURGERY WITH RESPECT TO THESE PROBLEMATIC ADAPTATIONS HAVE SCARCELY BEEN ADDRESSED. ACCUMULATING EVIDENCE SUGGESTS OPIOIDS AND NOCICEPTIVE SIGNALING MAY CONVERGE ON EPIGENETIC MECHANISMS IN SPINAL CORD TO ENHANCE OR PROLONG NEUROPLASTIC CHANGES. EPIGENETIC REGULATION OF BDNF (BRAIN-DERIVED NEUROTROPHIC FACTOR) AND PDYN (PRODYNORPHIN) GENES MAY BE INVOLVED. RESULTS: FOUR DAYS OF ASCENDING DOSES OF MORPHINE TREATMENT CAUSED OPIOID-INDUCED HYPERALGESIA AND REDUCED OPIOID ANALGESIC EFFICACY IN MICE. BOTH OPIOID-INDUCED HYPERALGESIA AND THE REDUCED OPIOID ANALGESIC EFFICACY WERE ENHANCED IN MICE THAT RECEIVED HINDPAW INCISIONS. THE EXPRESSION OF BDNF AND PDYN (QPCR) WAS INCREASED AFTER MORPHINE TREATMENT AND INCISION. CHROMATIN IMMUNOPRECIPITATION ASSAYS DEMONSTRATED THAT THE PDYN AND BDNF PROMOTERS WERE MORE STRONGLY ASSOCIATED WITH ACETYLATED H3K9 AFTER MORPHINE PLUS INCISION THAN IN THE MORPHINE OR INCISION ALONE GROUPS. SELECTIVE TROPOMYOSIN-RELATED KINASE B (ANA-12) AND KAPPA-OPIOID RECEPTOR (NOR-BINALTORPHIMINE) ANTAGONISTS WERE ADMINISTERED INTRATHECALLY, BOTH REDUCED HYPERALGESIA ONE OR THREE DAYS AFTER SURGERY. ADMINISTRATION OF ANA-12 OR NOR-BINALTORPHIMINE ATTENUATED THE DECREASED MORPHINE ANALGESIC EFFICACY ON DAY 1, BUT ONLY NOR-BINALTORPHIMINE WAS EFFECTIVE ON DAY 3 AFTER INCISION IN OPIOID-EXPOSED GROUP. COADMINISTRATION OF HISTONE ACETYLTRANSFERASE INHIBITOR ANACARDIC ACID DAILY WITH MORPHINE BLOCKED THE DEVELOPMENT OF OPIOID-INDUCED HYPERALGESIA AND ATTENUATED INCISION-ENHANCED HYPERALGESIA IN MORPHINE-TREATED MICE. ANACARDIC ACID HAD SIMILAR EFFECTS ON ANALGESIC TOLERANCE, SHOWING THE INVOLVEMENT OF HISTONE ACETYLATION IN THE INTERACTIONS DETECTED. CONCLUSIONS: SPINAL EPIGENETIC CHANGES INVOLVING BDNF AND PDYN MAY CONTRIBUTE TO THE ENHANCED POSTOPERATIVE NOCICEPTIVE SENSITIZATION AND ANALGESIC TOLERANCE OBSERVED AFTER CONTINUOUS OPIOID EXPOSURE. TREATMENTS BLOCKING THE EPIGENETICALLY MEDIATED UP-REGULATION OF THESE GENES OR ADMINISTRATION OF TRKB OR KAPPA-OPIOID RECEPTOR ANTAGONISTS MAY IMPROVE THE CLINICAL UTILITY OF OPIOIDS, PARTICULARLY AFTER SURGERY. 2016 4 3315 26 HIPPOCAMPAL MU OPIOID RECEPTORS ARE MODULATED FOLLOWING COCAINE SELF-ADMINISTRATION IN RAT. COCAINE ADDICTION IS A COMPLEX PATHOLOGY INDUCED BY LONG-TERM BRAIN CHANGES. UNDERSTANDING THE NEUROCHEMICAL CHANGES UNDERLYING THE REINFORCING EFFECTS OF THIS DRUG OF ABUSE IS CRITICAL FOR REDUCING THE SOCIETAL BURDEN OF DRUG ADDICTION. THE MU OPIOID RECEPTOR PLAYS A MAJOR ROLE IN DRUG REWARD. THIS RECEPTOR IS MODULATED BY CHRONIC COCAINE TREATMENT IN SPECIFIC BRAIN STRUCTURES, BUT FEW STUDIES INVESTIGATED NEUROCHEMICAL ADAPTATIONS INDUCED BY VOLUNTARY COCAINE INTAKE. IN THIS STUDY, WE INVESTIGATED WHETHER INTRAVENOUS COCAINE-SELF ADMINISTRATION (0.33 MG/KG/INJECTION, FIXED-RATIO 1 [FR1], 10 DAYS) IN RATS INDUCES TRANSCRIPTIONAL AND FUNCTIONAL CHANGES OF THE MU OPIOID RECEPTOR IN REWARD-RELATED BRAIN REGIONS. EPIGENETIC PROCESSES WITH HISTONE MODIFICATIONS WERE EXAMINED FOR TWO ACTIVATING MARKS, H3K4ME3, AND H3K27AC. WE FOUND AN INCREASE OF MU OPIOID RECEPTOR GENE EXPRESSION ALONG WITH A POTENTIATION OF ITS FUNCTIONALITY IN HIPPOCAMPUS OF COCAINE SELF-ADMINISTERING ANIMALS COMPARED TO SALINE CONTROLS. CHROMATIN IMMUNOPRECIPITATION FOLLOWED BY QPCR REVEALED NO MODIFICATIONS OF THE HISTONE MARK H3K4ME3 AND H3K27AC LEVELS AT MU OPIOID RECEPTOR PROMOTER. OUR STUDY HIGHLIGHTS THE HIPPOCAMPUS AS AN IMPORTANT TARGET TO FURTHER INVESTIGATE NEUROADAPTIVE PROCESSES LEADING TO COCAINE ADDICTION. 2021 5 1220 22 CRISPR/CAS9-BASED MUTAGENESIS OF HISTONE H3.1 IN SPINAL DYNORPHINERGIC NEURONS ATTENUATES THERMAL SENSITIVITY IN MICE. BURN INJURY IS A TRAUMA RESULTING IN TISSUE DEGRADATION AND SEVERE PAIN, WHICH IS PROCESSED FIRST BY NEURONAL CIRCUITS IN THE SPINAL DORSAL HORN. WE HAVE RECENTLY SHOWN THAT IN MICE, EXCITATORY DYNORPHINERGIC (PDYN) NEURONS PLAY A PIVOTAL ROLE IN THE RESPONSE TO BURN-INJURY-ASSOCIATED TISSUE DAMAGE VIA HISTONE H3.1 PHOSPHORYLATION-DEPENDENT SIGNALING. AS PDYN NEURONS WERE MOSTLY ASSOCIATED WITH MECHANICAL ALLODYNIA, THEIR INVOLVEMENT IN THERMONOCICEPTION HAD TO BE FURTHER ELUCIDATED. USING A CUSTOM-MADE AAV9_MUTH3.1 VIRUS COMBINED WITH THE CRISPR/CAS9 SYSTEM, HERE WE PROVIDE EVIDENCE THAT BLOCKING HISTONE H3.1 PHOSPHORYLATION AT POSITION SERINE 10 (S10) IN SPINAL PDYN NEURONS SIGNIFICANTLY INCREASES THE THERMAL NOCICEPTIVE THRESHOLD IN MICE. IN CONTRAST, NEITHER MECHANOSENSATION NOR ACUTE CHEMONOCICEPTION WAS AFFECTED BY THE TRANSGENIC MANIPULATION OF HISTONE H3.1. THESE RESULTS SUGGEST THAT BLOCKING RAPID EPIGENETIC TAGGING OF S10H3 IN SPINAL PDYN NEURONS ALTERS ACUTE THERMOSENSATION AND THUS EXPLAINS THE INVOLVEMENT OF PDYN CELLS IN THE IMMEDIATE RESPONSE TO BURN-INJURY-ASSOCIATED TISSUE DAMAGE. 2022 6 4511 34 MU OPIOID RECEPTOR-TRIGGERED NOTCH-1 ACTIVATION CONTRIBUTES TO MORPHINE TOLERANCE: ROLE OF NEURON-GLIA COMMUNICATION. THE DEVELOPMENT OF ANALGESIC TOLERANCE TO OPIOIDS IS AN IMPORTANT LIMITATION IN THE MANAGEMENT OF CHRONIC PAIN. SPINAL CORD GLIAL CELL ACTIVATION APPEARS TO PLAY A PIVOTAL ROLE IN THE DEVELOPMENT AND MAINTENANCE OF OPIOID TOLERANCE, INDICATING THE PRESENCE OF AN OPIOID-INDUCED NEURONAL-GLIAL INTERACTION; HOWEVER, HOW OPIOIDS DRIVE THIS CROSS-TALK IS STILL ELUSIVE. IN SEARCH OF TREATMENTS TO ATTENUATE MORPHINE ANALGESIC TOLERANCE, OUR RESEARCH FOCUSED ON THE ROLE OF NOTCH SIGNALING PATHWAY, ONE OF THE MOST IMPORTANT MECHANISMS OF CELL-TO-CELL INTERACTIONS, IN THE SPINAL DORSAL HORN AFTER MORPHINE REPEATED EXPOSURE AND WHETHER NOTCH INHIBITION ATTENUATES MORPHINE ANALGESIC TOLERANCE. DOUBLE IMMUNOFLUORESCENCE EXPERIMENTS ON SPINAL SECTIONS FROM MORPHINE-TOLERANT MICE SHOWED A NEURONAL LOCALIZATION OF NOTCH-1 RECEPTOR WHEREAS THE NOTCH LIGAND JAGGED WAS LOCALIZED ON NEIGHBORING ASTROCYTES. MORPHINE-INDUCED MU OPIOID RECEPTOR (MOR) STIMULATION TRIGGERED NOTCH-1 SIGNALING ACTIVATION AND THIS EVENT WAS MEDIATED BY ASTROCYTE JNK ACTIVATION. NOTCH-1 ACTIVATION SELECTIVELY REDUCED THE EXPRESSION OF HISTONE DEACETYLASE (HDAC)-1, RESULTING IN AN OVERPHOSPHORYLATION OF PKC AND ERK, KINASES INVOLVED IN MOR PHOSPHORYLATION AND INTERNALIZATION AFTER REPEATED MORPHINE EXPOSURE. NOTCH-1 SIGNALING INHIBITION, THROUGH INTRATHECAL ADMINISTRATION OF THE GAMMA-SECRETASE INHIBITOR, DAPT, COUNTERACTED PKC AND ERK OVERPHOSPHORYLATION, MOR INTERNALIZATION, AND ANALGESIC TOLERANCE. CONVERSELY, THE HDAC-1 INHIBITOR, LG325, FURTHER AGGRAVATED MOR INTERNALIZATION, PKC OVERPHOSPHORYLATION, AND ANALGESIC TOLERANCE.OUR FINDINGS IMPLICATE THE MOR-TRIGGERED NOTCH-1 SIGNALING IN PROMOTING MOR INTERNALIZATION AND MORPHINE ANALGESIC TOLERANCE BY EPIGENETIC REGULATION MECHANISMS. THESE DATA SUGGEST THAT NOTCH-1 INHIBITORS COULD REPRESENT AN INNOVATIVE THERAPEUTIC PERSPECTIVE FOR THE MANAGEMENT OF OPIOID TOLERANCE IN CHRONIC PAIN THERAPY. 2020 7 2364 36 EPIGENETIC REGULATION OF SPINAL CORD GENE EXPRESSION CONTROLS OPIOID-INDUCED HYPERALGESIA. BACKGROUND: THE LONG TERM USE OF OPIOIDS FOR THE TREATMENT OF PAIN LEADS TO A GROUP OF MALADAPTATIONS WHICH INCLUDES OPIOID-INDUCED HYPERALGESIA (OIH). OIH TYPICALLY RESOLVES WITHIN FEW DAYS AFTER CESSATION OF MORPHINE TREATMENT IN MICE BUT IS PROLONGED FOR WEEKS IF HISTONE DEACETYLASE (HDAC) ACTIVITY IS INHIBITED DURING OPIOID TREATMENT. THE PRESENT WORK SEEKS TO IDENTIFY GENE TARGETS SUPPORTING THE EPIGENETIC EFFECTS RESPONSIBLE FOR OIH PROLONGATION. RESULTS: MICE WERE TREATED WITH MORPHINE ACCORDING TO AN ASCENDING DOSE PROTOCOL. SOME MICE ALSO RECEIVED THE SELECTIVE HDAC INHIBITOR SUBEROYLANILIDE HYDROXAMIC ACID (SAHA) ADDITIONALLY. CHRONIC MORPHINE TREATMENT WITH SIMULTANEOUS HDAC INHIBITION ENHANCED OIH, AND SEVERAL SPINAL CORD GENES WERE UP-REGULATED. THE EXPRESSION OF BDNF (BRAIN-DERIVED NEUROTROPHIC FACTOR) AND PDYN (PRODYNORPHIN) WERE MOST CLOSELY RELATED TO THE OBSERVED BEHAVIORAL CHANGES. CHIP (CHROMATIN IMMUOPRECIPATION) ASSAYS DEMONSTRATED THAT PROMOTER REGIONS OF PDYN AND BDNF WERE STRONGLY ASSOCIATED WITH ACEH3K9 (ACETYLATED HISTONE H3 LYSINE9) AFTER MORPHINE AND SAHA TREATMENT. FURTHERMORE, MORPHINE TREATMENT CAUSED AN INCREASE IN SPINAL BDNF AND DYNORPHIN LEVELS, AND THESE LEVELS WERE FURTHER INCREASED IN SAHA TREATED MICE. THE SELECTIVE TRKB (TROPOMYOSIN-RECEPTOR-KINASE) ANTAGONIST ANA-12 REDUCED OIH WHEN GIVEN ONE OR SEVEN DAYS AFTER CESSATION OF MORPHINE. TREATMENT WITH THE SELECTIVE KAPPA OPIOID RECEPTOR ANTAGONIST NOR-BNI ALSO REDUCED ESTABLISHED OIH. THE CO-ADMINISTRATION OF EITHER RECEPTOR ANTAGONIST AGENT DAILY WITH MORPHINE RESULTED IN ATTENUATION OF HYPERALGESIA PRESENT ONE DAY AFTER CESSATION OF TREATMENT. ADDITIONALLY, REPEATED MORPHINE EXPOSURE INDUCED A RISE IN BDNF EXPRESSION THAT WAS ASSOCIATED WITH AN INCREASED NUMBER OF BDNF+ CELLS IN THE SPINAL CORD DORSAL HORN, SHOWING STRONG CO-LOCALIZATION WITH ACEH3K9 IN NEURONAL CELLS. LASTLY, SPINAL APPLICATION OF LOW DOSE BDNF OR DYNORPHIN A AFTER RESOLUTION OF OIH PRODUCED MECHANICAL HYPERSENSITIVITY, WITH NO EFFECT IN CONTROLS. CONCLUSIONS: THE PRESENT STUDY IDENTIFIED TWO GENES WHOSE EXPRESSION IS REGULATED BY EPIGENETIC MECHANISMS DURING MORPHINE EXPOSURE. TREATMENTS AIMED AT PREVENTING THE ACETYLATION OF HISTONES OR BLOCKING BDNF AND DYNORPHIN SIGNALING MAY REDUCE OIH AND IMPROVE LONG-TERM PAIN USING OPIOIDS. 2014 8 4163 30 MECP2 REPRESSION OF G9A IN REGULATION OF PAIN AND MORPHINE REWARD. OPIOIDS ARE COMMONLY USED FOR PAIN RELIEF, BUT THEIR STRONG REWARDING EFFECTS DRIVE OPIOID MISUSE AND ABUSE. HOW PAIN AFFECTS THE LIABILITY OF OPIOID ABUSE IS UNKNOWN AT PRESENT. IN THIS STUDY, WE IDENTIFIED AN EPIGENETIC REGULATING CASCADE ACTIVATED BY BOTH PAIN AND THE OPIOID MORPHINE. BOTH PERSISTENT PAIN AND REPEATED MORPHINE UPREGULATED THE TRANSCRIPTIONAL REGULATOR MECP2 IN MOUSE CENTRAL NUCLEUS OF THE AMYGDALA (CEA). CHROMATIN IMMUNOPRECIPITATION ANALYSIS REVEALED THAT MECP2 BOUND TO AND REPRESSED THE TRANSCRIPTIONAL REPRESSOR HISTONE DIMETHYLTRANSFERASE G9A, REDUCING G9A-CATALYZED REPRESSIVE MARK H3K9ME2 IN CEA. REPRESSION OF G9A ACTIVITY INCREASED EXPRESSION OF BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF). BEHAVIORALLY, PERSISTENT INFLAMMATORY PAIN INCREASED THE SENSITIVITY TO ACQUIRING MORPHINE-INDUCED, REWARD-RELATED BEHAVIOR OF CONDITIONED PLACE PREFERENCE IN MICE. LOCAL VIRAL VECTOR-MEDIATED MECP2 OVEREXPRESSION, CRE-INDUCED G9A KNOCKDOWN, AND CEA APPLICATION OF BDNF MIMICKED, WHEREAS MECP2 KNOCKDOWN INHIBITED, THE PAIN EFFECT. THESE RESULTS SUGGEST THAT MECP2 DIRECTLY REPRESSES G9A AS A SHARED MECHANISM IN CENTRAL AMYGDALA FOR REGULATION OF EMOTIONAL RESPONSES TO PAIN AND OPIOID REWARD, AND FOR THEIR BEHAVIORAL INTERACTION. 2014 9 4498 27 MORPHINE REGULATES ARGONAUTE 2 AND TH EXPRESSION AND ACTIVITY BUT NOT MIR-133B IN MIDBRAIN DOPAMINERGIC NEURONS. EPIGENETIC CHANGES SUCH AS MICRORNAS (MIRS)/AGO2-INDUCED GENE SILENCING REPRESENT COMPLEX MOLECULAR SIGNATURE THAT REGULATE CELLULAR PLASTICITY. RECENT STUDIES SHOWED INVOLVEMENT OF MIRS AND AGO2 IN DRUG ADDICTION. IN THIS STUDY, WE SHOW THAT CHANGES IN GENE EXPRESSION INDUCED BY MORPHINE AND MORPHINE WITHDRAWAL OCCUR WITH CONCOMITANT EPIGENETIC MODIFICATIONS IN THE MESOLIMBIC DOPAMINERGIC (DA) PATHWAY [VENTRAL TEGMENTAL AREA (VTA)/NUCLEUS ACCUMBENS (NAC) SHELL], WHICH IS CRITICALLY INVOLVED IN DRUG-INDUCED DEPENDENCE. WE FOUND THAT ACUTE OR CHRONIC MORPHINE ADMINISTRATION AS WELL AS MORPHINE WITHDRAWAL DID NOT MODIFY MIR-133B MESSENGER RNA (MRNA) EXPRESSION IN THE VTA, WHEREAS AGO2 PROTEIN LEVELS WERE DECREASED AND INCREASED IN MORPHINE-DEPENDENT RATS AND AFTER MORPHINE WITHDRAWAL, RESPECTIVELY. THESE CHANGES WERE PARALLELED WITH ENHANCED AND DECREASED NAC TYROSINE HYDROXYLASE (TH) PROTEIN (AN EARLY DA MARKER) IN MORPHINE-DEPENDENT RATS AND AFTER WITHDRAWAL, RESPECTIVELY. WE ALSO OBSERVED CHANGES IN TH MRNA EXPRESSION IN THE VTA THAT COULD BE RELATED TO AGO2-INDUCED TRANSLATIONAL REPRESSION OF TH MRNA DURING MORPHINE WITHDRAWAL. HOWEVER, THE VTA NUMBER OF TH-POSITIVE NEURONS SUFFERED NO ALTERATIONS AFTER THE DIFFERENT TREATMENT. ACUTE MORPHINE ADMINISTRATION PRODUCED A MARKED INCREASE IN TH ACTIVITY AND DA TURNOVER IN THE NAC (SHELL). IN CONTRAST, PRECIPITATED MORPHINE WITHDRAWAL DECREASED TH ACTIVATION AND DID NOT CHANGE DA TURNOVER. THESE FINDINGS PROVIDE NEW INFORMATION INTO THE POSSIBLE CORRELATION BETWEEN AGO2/MIRS COMPLEX REGULATION AND DA NEURONS PLASTICITY DURING OPIATE ADDICTION. 2015 10 5021 27 PERSISTENT PAIN MAINTAINS MORPHINE-SEEKING BEHAVIOR AFTER MORPHINE WITHDRAWAL THROUGH REDUCED MECP2 REPRESSION OF GLUA1 IN RAT CENTRAL AMYGDALA. AS LONG-TERM OPIOIDS ARE INCREASINGLY USED FOR CONTROL OF CHRONIC PAIN, HOW PAIN AFFECTS THE REWARDING EFFECT OF OPIOIDS AND HENCE RISK OF PRESCRIPTION OPIOID MISUSE AND ABUSE REMAINS A HEALTHCARE CONCERN AND A CHALLENGING ISSUE IN CURRENT PAIN MANAGEMENT. IN THIS STUDY, USING A RAT MODEL OF MORPHINE SELF-ADMINISTRATION, WE INVESTIGATED THE MOLECULAR MECHANISMS UNDERLYING THE IMPACT OF PAIN ON OPERANT BEHAVIOR OF MORPHINE INTAKE AND MORPHINE SEEKING BEFORE AND AFTER MORPHINE WITHDRAWAL. WE FOUND THAT RATS WITH PERSISTENT PAIN CONSUMED A SIMILAR AMOUNT OF DAILY MORPHINE TO THAT IN CONTROL RATS WITHOUT PAIN, BUT MAINTAINED THEIR LEVEL-PRESSING BEHAVIOR OF MORPHINE SEEKING AFTER ABSTINENCE OF MORPHINE AT 0.2 MG/KG, WHEREAS THIS BEHAVIOR WAS GRADUALLY DIMINISHED IN CONTROL RATS. IN THE CENTRAL NUCLEUS OF AMYGDALA (CEA), A LIMBIC STRUCTURE CRITICALLY INVOLVED IN THE AFFECTIVE DIMENSION OF PAIN, PROTEINS OF GLUA1 SUBUNITS OF GLUTAMATE AMPA RECEPTORS WERE UPREGULATED DURING MORPHINE WITHDRAWAL, AND VIRAL KNOCKDOWN OF CEA GLUA1 ELIMINATED THE MORPHINE-SEEKING BEHAVIOR IN WITHDRAWN RATS OF THE PAIN GROUP. CHROMATIN IMMUNOPRECIPITATION ANALYSIS REVEALED THAT THE METHYL CPG-BINDING PROTEIN 2 (MECP2) WAS ENRICHED IN THE PROMOTER REGION OF GRIA1 ENCODING GLUA1 AND THIS ENRICHMENT WAS SIGNIFICANTLY ATTENUATED IN WITHDRAWN RATS OF THE PAIN GROUP. FURTHERMORE, VIRAL OVEREXPRESSION OF CEA MECP2 REPRESSED THE GLUA1 LEVEL AND ELIMINATED THE MAINTENANCE OF MORPHINE-SEEKING BEHAVIOR AFTER MORPHINE WITHDRAWAL. THESE RESULTS SUGGEST DIRECT MECP2 REPRESSION OF GLUA1 FUNCTION AS A LIKELY MECHANISM FOR MORPHINE-SEEKING BEHAVIOR MAINTAINED BY LONG-LASTING AFFECTIVE PAIN AFTER MORPHINE WITHDRAWAL. 2015 11 4160 34 MECP2 EPIGENETIC SILENCING OF OPRM1 GENE IN PRIMARY SENSORY NEURONS UNDER NEUROPATHIC PAIN CONDITIONS. OPIOIDS ARE THE LAST OPTION FOR THE PHARMACOLOGICAL TREATMENT OF NEUROPATHIC PAIN, BUT THEIR ANTINOCICEPTIVE EFFECTS ARE LIMITED. DECREASED MU OPIOID RECEPTOR (MOR) EXPRESSION IN THE PERIPHERAL NERVOUS SYSTEM MAY CONTRIBUTE TO THIS. HERE, WE SHOWED THAT NERVE INJURY INDUCED HYPERMETHYLATION OF THE OPRM1 GENE PROMOTER AND AN INCREASED EXPRESSION OF METHYL-CPG BINDING PROTEIN 2 (MECP2) IN INJURED DORSAL ROOT GANGLION (DRG). THE DOWNREGULATION OF MOR IN THE DRG IS CLOSELY RELATED TO THE AUGMENTATION OF MECP2, AN EPIGENETIC REPRESSOR, WHICH COULD RECRUIT HDAC1 AND BIND TO THE METHYLATED REGIONS OF THE OPRM1 GENE PROMOTER. MECP2 KNOCKDOWN RESTORED THE EXPRESSION OF MOR IN INJURED DRG AND ENHANCED THE ANALGESIC EFFECT OF MORPHINE, WHILE THE MIMICKING OF THIS INCREASE VIA THE INTRATHECAL INFUSION OF VIRAL VECTOR-MEDIATED MECP2 WAS SUFFICIENT TO REDUCE MOR IN THE DRG. MOREOVER, HDAC1 INHIBITION WITH SUBEROYLANILIDE HYDROXAMIC ACID, AN HDAC INHIBITOR, ALSO PREVENTED MOR REDUCTION IN THE DRG OF NEUROPATHIC PAIN MICE, CONTRIBUTING TO THE AUGMENTATION OF MORPHINE ANALGESIA EFFECTS. MECHANISTICALLY, UPREGULATED MECP2 PROMOTES THE BINDING OF A HIGH LEVEL OF HDCA1 TO HYPERMETHYLATED REGIONS OF THE OPRM1 GENE PROMOTER, REDUCES THE ACETYLATION OF HISTONE H3 (ACH3) LEVELS OF THE OPRM1 GENE PROMOTER, AND ATTENUATES OPRM1 TRANSCRIPTION IN INJURED DRG. THUS, UPREGULATED MECP2 AND HDAC1 IN OPRM1 GENE PROMOTER SITES, NEGATIVELY REGULATES MOR EXPRESSION IN INJURED DRG, MITIGATING THE ANALGESIC EFFECT OF THE OPIOIDS. TARGETING MECP2/HDAC1 MAY THUS PROVIDE A NEW SOLUTION FOR IMPROVING THE THERAPEUTIC EFFECT OF OPIOIDS IN A CLINICAL SETTING. 2021 12 4615 30 NERVE INJURY DIMINISHES OPIOID ANALGESIA THROUGH LYSINE METHYLTRANSFERASE-MEDIATED TRANSCRIPTIONAL REPRESSION OF MU-OPIOID RECEPTORS IN PRIMARY SENSORY NEURONS. THE MU-OPIOID RECEPTOR (MOR, ENCODED BY OPRM1) AGONISTS ARE THE MAINSTAY ANALGESICS FOR TREATING MODERATE TO SEVERE PAIN. NERVE INJURY CAUSES DOWN-REGULATION OF MORS IN THE DORSAL ROOT GANGLION (DRG) AND DIMINISHES THE OPIOID EFFECT ON NEUROPATHIC PAIN. HOWEVER, THE EPIGENETIC MECHANISMS UNDERLYING THE DIMINISHED MOR EXPRESSION CAUSED BY NERVE INJURY ARE NOT CLEAR. G9A (ENCODED BY EHMT2), A HISTONE 3 AT LYSINE 9 METHYLTRANSFERASE, IS A KEY CHROMATIN REGULATOR RESPONSIBLE FOR GENE SILENCING. IN THIS STUDY, WE DETERMINED THE ROLE OF G9A IN DIMINISHED MOR EXPRESSION AND OPIOID ANALGESIC EFFECTS IN ANIMAL MODELS OF NEUROPATHIC PAIN. WE FOUND THAT NERVE INJURY IN RATS INDUCED A LONG-LASTING REDUCTION IN THE EXPRESSION LEVEL OF MORS IN THE DRG BUT NOT IN THE SPINAL CORD. NERVE INJURY CONSISTENTLY INCREASED THE ENRICHMENT OF THE G9A PRODUCT HISTONE 3 AT LYSINE 9 DIMETHYLATION IN THE PROMOTER OF OPRM1 IN THE DRG. G9A INHIBITION OR SIRNA KNOCKDOWN FULLY REVERSED MOR EXPRESSION IN THE INJURED DRG AND POTENTIATED THE MORPHINE EFFECT ON PAIN HYPERSENSITIVITY INDUCED BY NERVE INJURY. IN MICE LACKING EHMT2 IN DRG NEURONS, NERVE INJURY FAILED TO REDUCE THE EXPRESSION LEVEL OF MORS AND THE MORPHINE EFFECT. IN ADDITION, G9A INHIBITION OR EHMT2 KNOCKOUT IN DRG NEURONS NORMALIZED NERVE INJURY-INDUCED REDUCTION IN THE INHIBITORY EFFECT OF THE OPIOID ON SYNAPTIC GLUTAMATE RELEASE FROM PRIMARY AFFERENT NERVES. OUR FINDINGS INDICATE THAT G9A CONTRIBUTES CRITICALLY TO TRANSCRIPTIONAL REPRESSION OF MORS IN PRIMARY SENSORY NEURONS IN NEUROPATHIC PAIN. G9A INHIBITORS MAY BE USED TO ENHANCE THE OPIOID ANALGESIC EFFECT IN THE TREATMENT OF CHRONIC NEUROPATHIC PAIN. 2016 13 6612 25 ULTRA-LOW-DOSE NALOXONE ENHANCES THE ANTINOCICEPTIVE EFFECT OF MORPHINE IN PTX-TREATED RATS: REGULATION ON GLOBAL HISTONE METHYLATION. OBJECTIVE: EPIGENETIC REPROGRAMMING MAY HAVE A POSSIBLE ROLE IN NEUROPATHIC PAIN DEVELOPMENT; THE PRESENT STUDY EXAMINED THE GLOBAL PATTERNS OF LYSINE HISTONE MODIFICATION. IN THIS SERIAL STUDY WE ANALYZED THE LEVELS OF HISTONE 3 LYSINE 4 MONOMETHYLATION, HISTONE 3 LYSINE 4 DIMETHYLATION, AND HISTONE 3 LYSINE 9 TRIMETHYLATION IN PERTUSSIS TOXIN (PTX)-INDUCED THERMAL HYPERALGESIC RAT SPINAL CORDS. METHODS: MALE WISTAR RATS IMPLANTED WITH AN INTRATHECAL CATHETER RECEIVED A SINGLE INTRATHECAL PTX (1 MUG IN 5 MUL SALINE) INJECTION. FOUR DAYS LATER, THEY WERE RANDOMLY ASSIGNED TO RECEIVE EITHER A SINGLE INJECTION OF SALINE, OR ULTRA-LOW-DOSE NALOXONE (15 NG IN 5 MUL SALINE), FOLLOWED BY MORPHINE (10 MUG IN 5 MUL SALINE) INJECTION 30 MINUTES LATER. RESULTS: THE RESULTS SHOWED THAT PTX INJECTION INDUCED THERMAL HYPERALGESIA AND SIGNIFICANT INCREASE OF GLOBAL HISTONE METHYLATION IN THE SPINAL CORDS. INTRATHECAL MORPHINE ALONE DID NOT AFFECT THE THERMAL HYPERALGESIA AND GLOBAL HISTONE METHYLATION. IN CONTRAST, INTRATHECAL ADMINISTRATION OF ULTRA-LOW-DOSE NALOXONE PLUS MORPHINE SIGNIFICANTLY ATTENUATED THE PTX-INDUCED THERMAL HYPERALGESIA AND DOWN-REGULATED THE GLOBAL HISTONE METHYLATION. CONCLUSION: THE RESULTS SUGGEST THAT ULTRA-LOW-DOSE NALOXONE MIGHT BE CLINICAL VALUABLE FOR NEUROPATHIC PAIN MANAGEMENT VIA REGULATING GLOBAL HISTONE MODIFICATION. 2012 14 2883 32 G9A INHIBITS CREB-TRIGGERED EXPRESSION OF MU OPIOID RECEPTOR IN PRIMARY SENSORY NEURONS FOLLOWING PERIPHERAL NERVE INJURY. NEUROPATHIC PAIN, A DISTRESSING AND DEBILITATING DISORDER, IS STILL POORLY MANAGED IN CLINIC. OPIOIDS, LIKE MORPHINE, REMAIN THE MAINSTAY OF PRESCRIBED MEDICATIONS IN THE TREATMENT OF THIS DISORDER, BUT THEIR ANALGESIC EFFECTS ARE HIGHLY UNSATISFACTORY IN PART DUE TO NERVE INJURY-INDUCED REDUCTION OF OPIOID RECEPTORS IN THE FIRST-ORDER SENSORY NEURONS OF DORSAL ROOT GANGLIA. G9A IS A REPRESSOR OF GENE EXPRESSION. WE FOUND THAT NERVE INJURY-INDUCED INCREASES IN G9A AND ITS CATALYZED REPRESSIVE MARKER H3K9M2 ARE RESPONSIBLE FOR EPIGENETIC SILENCING OF OPRM1, OPRK1, AND OPRD1 GENES IN THE INJURED DORSAL ROOT GANGLIA. BLOCKING THESE INCREASES RESCUED DORSAL ROOT GANGLIA OPRM1, OPRK1, AND OPRD1 GENE EXPRESSION AND MORPHINE OR LOPERAMIDE ANALGESIA AND PREVENTED THE DEVELOPMENT OF MORPHINE OR LOPERAMIDE-INDUCED ANALGESIC TOLERANCE UNDER NEUROPATHIC PAIN CONDITIONS. CONVERSELY, MIMICKING THESE INCREASES REDUCED THE EXPRESSION OF THREE OPIOID RECEPTORS AND PROMOTED THE MU OPIOID RECEPTOR-GATED RELEASE OF PRIMARY AFFERENT NEUROTRANSMITTERS. MECHANISTICALLY, NERVE INJURY-INDUCED INCREASES IN THE BINDING ACTIVITY OF G9A AND H3K9ME2 TO THE OPRM1 GENE WERE ASSOCIATED WITH THE REDUCED BINDING OF CYCLIC AMP RESPONSE ELEMENT BINDING PROTEIN TO THE OPRM1 GENE. THESE FINDINGS SUGGEST THAT G9A PARTICIPATES IN THE NERVE INJURY-INDUCED REDUCTION OF THE OPRM1 GENE LIKELY THROUGH G9A-TRIGGERED BLOCKAGE IN THE ACCESS OF CYCLIC AMP RESPONSE ELEMENT BINDING PROTEIN TO THIS GENE. 2016 15 742 24 CANNABINOID CB2 RECEPTORS ARE UPREGULATED VIA BIVALENT HISTONE MODIFICATIONS AND CONTROL PRIMARY AFFERENT INPUT TO THE SPINAL CORD IN NEUROPATHIC PAIN. TYPE-2 CANNABINOID RECEPTORS (CB2, ENCODED BY THE CNR2 GENE) ARE MAINLY EXPRESSED IN IMMUNE CELLS, AND CB2 AGONISTS NORMALLY HAVE NO ANALGESIC EFFECT. HOWEVER, NERVE INJURY UPREGULATES CB2 IN THE DORSAL ROOT GANGLION (DRG), FOLLOWING WHICH CB2 STIMULATION REDUCES NEUROPATHIC PAIN. IT IS UNCLEAR HOW NERVE INJURY INCREASES CB2 EXPRESSION OR HOW CB2 ACTIVITY IS TRANSFORMED IN NEUROPATHIC PAIN. IN THIS STUDY, IMMUNOBLOTTING SHOWED THAT SPINAL NERVE LIGATION (SNL) INDUCED A DELAYED AND SUSTAINED INCREASE IN CB2 EXPRESSION IN THE DRG AND DORSAL SPINAL CORD SYNAPTOSOMES. RNASCOPE IN SITU HYBRIDIZATION ALSO SHOWED THAT SNL SUBSTANTIALLY INCREASED CB2 MRNA LEVELS, MOSTLY IN MEDIUM AND LARGE DRG NEURONS. FURTHERMORE, WE FOUND THAT THE SPECIFIC CB2 AGONIST JWH-133 SIGNIFICANTLY INHIBITS THE AMPLITUDE OF DORSAL ROOT-EVOKED GLUTAMATERGIC EXCITATORY POSTSYNAPTIC CURRENTS IN SPINAL DORSAL HORN NEURONS IN SNL RATS, BUT NOT IN SHAM CONTROL RATS; INTRATHECAL INJECTION OF JWH-133 REVERSED PAIN HYPERSENSITIVITY IN SNL RATS, BUT HAD NO EFFECT IN SHAM CONTROL RATS. IN ADDITION, CHROMATIN IMMUNOPRECIPITATION-QPCR ANALYSIS SHOWED THAT SNL INCREASED ENRICHMENT OF TWO ACTIVATING HISTONE MARKS (H3K4ME3 AND H3K9AC) AND DIMINISHED OCCUPANCY OF TWO REPRESSIVE HISTONE MARKS (H3K9ME2 AND H3K27ME3) AT THE CNR2 PROMOTER IN THE DRG. IN CONTRAST, SNL HAD NO EFFECT ON DNA METHYLATION LEVELS AROUND THE CNR2 PROMOTER. OUR FINDINGS SUGGEST THAT PERIPHERAL NERVE INJURY PROMOTES CB2 EXPRESSION IN PRIMARY SENSORY NEURONS VIA EPIGENETIC BIVALENT HISTONE MODIFICATIONS AND THAT CB2 ACTIVATION REDUCES NEUROPATHIC PAIN BY ATTENUATING NOCICEPTIVE TRANSMISSION FROM PRIMARY AFFERENT NERVES TO THE SPINAL CORD. 2022 16 2003 22 EPIGENETIC AND TRANSCRIPTIONAL CONTROL OF THE OPIOID PRODYNORPHINE GENE: IN-DEPTH ANALYSIS IN THE HUMAN BRAIN. NEUROPEPTIDES SERVE AS NEUROHORMONES AND LOCAL PARACRINE REGULATORS THAT CONTROL NEURAL NETWORKS REGULATING BEHAVIOR, ENDOCRINE SYSTEM AND SENSORIMOTOR FUNCTIONS. THEIR EXPRESSION IS CHARACTERIZED BY EXCEPTIONALLY RESTRICTED PROFILES. CIRCUIT-SPECIFIC AND ADAPTIVE EXPRESSION OF NEUROPEPTIDE GENES MAY BE DEFINED BY TRANSCRIPTIONAL AND EPIGENETIC MECHANISMS CONTROLLED BY CELL TYPE AND SUBTYPE SEQUENCE-SPECIFIC TRANSCRIPTION FACTORS, INSULATORS AND SILENCERS. THE OPIOID PEPTIDE DYNORPHINS PLAY A CRITICAL ROLE IN NEUROLOGICAL AND PSYCHIATRIC DISORDERS, PAIN PROCESSING AND STRESS, WHILE THEIR MUTATIONS CAUSE PROFOUND NEURODEGENERATION IN THE HUMAN BRAIN. IN THIS REVIEW, WE FOCUS ON THE PRODYNORPHIN GENE AS A MODEL FOR THE IN-DEPTH EPIGENETIC AND TRANSCRIPTIONAL ANALYSIS OF EXPRESSION OF THE NEUROPEPTIDE GENES. PRODYNORPHIN STUDIES MAY PROVIDE A FRAMEWORK FOR ANALYSIS OF MECHANISMS RELEVANT FOR REGULATION OF NEUROPEPTIDE GENES IN NORMAL AND PATHOLOGICAL HUMAN BRAIN. 2021 17 6536 31 TRANSCRIPTIONAL REGULATION OF TYPE-2 METABOTROPIC GLUTAMATE RECEPTORS: AN EPIGENETIC PATH TO NOVEL TREATMENTS FOR CHRONIC PAIN. ACTIVATION OF METABOTROPIC GLUTAMATE 2 (MGLU2) RECEPTORS INHIBITS PAIN TRANSMISSION AT THE SYNAPSES BETWEEN PRIMARY AFFERENT FIBERS AND NEURONS IN THE DORSAL HORN OF THE SPINAL CORD. IN ADDITION, MGLU2 RECEPTORS ARE FOUND IN PERIPHERAL NOCICEPTORS, AND IN PAIN-REGULATORY CENTERS OF THE BRAIN STEM AND FOREBRAIN. MGLU2 RECEPTOR AGONISTS PRODUCE ANALGESIA IN MODELS OF INFLAMMATORY AND NEUROPATHIC PAIN, BUT THEIR USE IS LIMITED BY THE DEVELOPMENT OF TOLERANCE. A NEW THERAPEUTIC STRATEGY COULD BE BASED ON THE TRANSCRIPTIONAL REGULATION OF MGLU2 RECEPTORS VIA THE ACETYLATION-PROMOTED ACTIVATION OF THE P65/RELA TRANSCRIPTION FACTOR. "EPIGENETIC" DRUGS THAT INCREASE MGLU2 RECEPTOR EXPRESSION, INCLUDING L-ACETYLCARNITINE AND INHIBITORS OF HISTONE DEACETYLASES, HAVE A DIFFERENT ANALGESIC PROFILE WITH NO TOLERANCE TO THE THERAPEUTIC EFFECT AFTER REPEATED DOSING. 2010 18 2353 28 EPIGENETIC REGULATION OF OPIOID-INDUCED HYPERALGESIA, DEPENDENCE, AND TOLERANCE IN MICE. REPEATED ADMINISTRATION OF OPIOIDS SUCH AS MORPHINE INDUCES PERSISTENT BEHAVIORAL CHANGES INCLUDING OPIOID-INDUCED HYPERALGESIA (OIH), TOLERANCE, AND PHYSICAL DEPENDENCE. IN THE CURRENT WORK WE EXPLORED HOW THE BALANCE OF HISTONE ACETYLTRANSFERASE (HAT) VERSUS HISTONE DEACETYLASE (HDAC) MIGHT REGULATE THESE MORPHINE-INDUCED CHANGES. NOCICEPTIVE THRESHOLDS, ANALGESIA, AND PHYSICAL DEPENDENCE WERE ASSESSED DURING AND FOR A PERIOD OF SEVERAL WEEKS AFTER MORPHINE EXPOSURE. TO PROBE THE ROLES OF HISTONE ACETYLATION, THE HAT INHIBITOR CURCUMIN OR A SELECTIVE HDAC INHIBITOR SUBEROYLANILIDE HYDROXAMIC ACID (SAHA) WAS ADMINISTERED DAILY TO GROUPS OF ANIMALS. HISTONE ACETYLATION IN SPINAL CORD WAS ASSESSED BY WESTERN BLOT AND IMMUNOHISTOCHEMISTRY. CONCURRENT ADMINISTRATION OF CURCUMIN WITH MORPHINE FOR 4 DAYS SIGNIFICANTLY REDUCED DEVELOPMENT OF OPIOID-INDUCED MECHANICAL ALLODYNIA, THERMAL HYPERALGESIA, TOLERANCE, AND PHYSICAL DEPENDENCE. CONVERSELY, THE HDAC INHIBITOR SAHA ENHANCED THESE RESPONSES. INTERESTINGLY, SAHA TREATMENT AFTER THE TERMINATION OF OPIOID ADMINISTRATION SUSTAINED THESE BEHAVIORAL CHANGES FOR AT LEAST 4 WEEKS. HISTONE H3 ACETYLATION IN THE DORSAL HORN OF THE SPINAL CORD WAS INCREASED AFTER CHRONIC MORPHINE TREATMENT, BUT H4 ACETYLATION WAS UNCHANGED. MOREOVER, WE OBSERVED A DECREASE IN HDAC ACTIVITY IN THE SPINAL CORDS OF MORPHINE-TREATED MICE WHILE OVERALL HAT ACTIVITY WAS UNCHANGED, SUGGESTING A SHIFT TOWARD A STATE OF ENHANCED HISTONE ACETYLATION. PERSPECTIVE: THE CURRENT STUDY INDICATES THAT EPIGENETIC MECHANISMS PLAY A CRUCIAL ROLE IN OPIOID-INDUCED LONG-LASTING NEUROPLASTICITY. THESE RESULTS PROVIDE NEW SIGHT INTO UNDERSTANDING THE MECHANISMS OF OPIOID-INDUCED NEUROPLASTICITY AND SUGGEST NEW STRATEGIES TO LIMIT OPIOID ABUSE POTENTIAL AND INCREASE THE VALUE OF THESE DRUGS AS ANALGESICS. 2013 19 69 25 A MEDIAL PREFRONTAL CORTEX-NUCLEUS ACUMENS CORTICOTROPIN-RELEASING FACTOR CIRCUITRY FOR NEUROPATHIC PAIN-INCREASED SUSCEPTIBILITY TO OPIOID REWARD. RECENT STUDIES HAVE SHOWN THAT PERSISTENT PAIN FACILITATES THE RESPONSE TO MORPHINE REWARD. HOWEVER, THE CIRCUIT MECHANISM UNDERLYING THIS PROCESS REMAINS AMBIGUOUS. IN THIS STUDY, USING CHRONIC CONSTRICTION INJURY (CCI) OF THE SCIATIC NERVE IN MICE, WE FOUND THAT PERSISTENT NEUROPATHIC PAIN REDUCED THE MINIMUM NUMBER OF MORPHINE CONDITIONING SESSIONS REQUIRED TO INDUCE CONDITIONED PLACE PREFERENCE (CPP) BEHAVIOR. THIS DOSE OF MORPHINE HAD NO EFFECT ON THE PAIN THRESHOLD. IN THE MEDIAL PREFRONTAL CORTEX (MPFC), WHICH IS INVOLVED IN BOTH PAIN AND EMOTION PROCESSING, CORTICOTROPIN-RELEASING FACTOR (CRF) EXPRESSING NEURONAL ACTIVITY WAS INCREASED IN CCI MICE. CHEMOGENETIC INHIBITION OF MPFC CRF NEURONS REVERSED CCI-INDUCED MORPHINE CPP FACILITATION. FURTHERMORE, THE NUCLEUS ACUMENS (NAC) RECEIVED MPFC CRF FUNCTIONAL PROJECTIONS THAT EXERTED EXCITATORY EFFECTS ON NAC NEURONS. OPTOGENETIC INHIBITION OF MPCF NEURONAL TERMINALS OR LOCAL INFUSION OF THE CRF RECEPTOR 1 (CRFR1) ANTAGONIST IN THE NAC RESTORED THE EFFECTS OF NEUROPATHIC PAIN ON MORPHINE-INDUCED CPP BEHAVIOR, BUT NOT IN NORMAL MICE. ON A MOLECULAR LEVEL, IN CCI MICE, CRFR1 PROTEIN EXPRESSION WAS INCREASED IN THE NAC BY A HISTONE DIMETHYLTRANSFERASE G9A-MEDIATED EPIGENETIC MECHANISM. LOCAL G9A KNOCKDOWN INCREASED THE EXPRESSION OF CRFR1 AND MIMICKED CCI-INDUCED HYPERSENSITIVITY TO ACQUIRING MORPHINE CPP. TAKEN TOGETHER, THESE FINDINGS DEMONSTRATE A PREVIOUSLY UNKNOWN AND SPECIFIC MPFC CRF ENGAGEMENT OF NAC NEURONAL CIRCUITS, THE SENSITIZATION OF WHICH FACILITATES BEHAVIORAL RESPONSES TO MORPHINE REWARD IN NEUROPATHIC PAIN STATES VIA CRFR1S. 2018 20 4618 34 NERVE INJURY-INDUCED EPIGENETIC SILENCING OF OPIOID RECEPTORS CONTROLLED BY DNMT3A IN PRIMARY AFFERENT NEURONS. OPIOIDS ARE THE GOLD STANDARD FOR PHARMACOLOGICAL TREATMENT OF NEUROPATHIC PAIN, BUT THEIR ANALGESIC EFFECTS ARE UNSATISFACTORY IN PART DUE TO NERVE INJURY-INDUCED DOWNREGULATION OF OPIOID RECEPTORS IN DORSAL ROOT GANGLIA (DRG) NEURONS. HOW NERVE INJURY DRIVES SUCH DOWNREGULATION REMAINS ELUSIVE. DNA METHYLTRANSFERASE (DNMT)-TRIGGERED DNA METHYLATION REPRESSES GENE EXPRESSION. WE SHOW HERE THAT BLOCKING THE NERVE INJURY-INDUCED INCREASE IN DRG DNMT3A (A DE NOVO DNMT) RESCUED THE EXPRESSION OF OPRM1 AND OPRK1 MRNAS AND THEIR RESPECTIVE ENCODING MU-OPIOID RECEPTOR (MOR) AND KAPPA-OPIOID RECEPTOR (KOR) PROTEINS IN THE INJURED DRG. BLOCKING THIS INCREASE ALSO PREVENTED THE NERVE INJURY-INDUCED INCREASE IN DNA METHYLATION IN THE PROMOTER AND 5'-UNTRANSLATED REGION OF THE OPRM1 GENE IN THE INJURED DRG, RESTORED MORPHINE OR LOPERAMIDE (A PERIPHERAL ACTING MOR PREFERRING AGONIST) ANALGESIC EFFECTS, AND ATTENUATED THE DEVELOPMENT OF THEIR ANALGESIC TOLERANCE UNDER NEUROPATHIC PAIN CONDITIONS. MIMICKING THIS INCREASE REDUCED THE EXPRESSION OF OPRM1 AND OPRK1 MRNAS AND THEIR CODING MOR AND KOR IN DRG AND AUGMENTED MOR-GATED NEUROTRANSMITTER RELEASE FROM THE PRIMARY AFFERENTS. MECHANISTICALLY, DNMT3A REGULATION OF OPRM1 GENE EXPRESSION REQUIRED THE METHYL-CPG-BINDING PROTEIN 1, MBD1, AS MBD1 KNOCKOUT RESULTED IN THE DECREASED BINDING OF DNMT3A TO THE OPRM1 GENE PROMOTER AND BLOCKED THE DNMT3A-TRIGGERED REPRESSION OF OPRM1 GENE EXPRESSION IN DRG NEURONS. THESE DATA SUGGEST THAT DNMT3A IS REQUIRED FOR NERVE INJURY-INDUCED AND MBD1-MEDIATED EPIGENETIC SILENCING OF THE MOR AND KOR IN THE INJURED DRG. DNMT3A INHIBITION MAY SERVE AS A PROMISING ADJUVANT THERAPY FOR OPIOID USE IN NEUROPATHIC PAIN MANAGEMENT. 2017