1 1179 115 CONVERGENCE AND DIVERGENCE IN THE ETIOLOGY OF MYELIN IMPAIRMENT IN PSYCHIATRIC DISORDERS AND DRUG ADDICTION. IMPAIRMENT OF OLIGODENDROGLIA (OL)-DEPENDENT MYELINATION IN THE CENTRAL NERVOUS SYSTEM (CNS) IS A REMARKABLE PARALLEL RECENTLY IDENTIFIED IN MAJOR PSYCHIATRIC DISORDERS AND CHRONIC DRUG ABUSE. NEUROIMAGING AND NEUROPATHOLOGICAL STUDIES REVEALED MYELIN DEFECTS AND MICROARRAY-PROFILING ANALYSIS DEMONSTRATED ABERRANT EXPRESSION OF MYELIN-RELATED GENES IN SCHIZOPHRENIA (SZ), BIPOLAR DISORDER (BD), MAJOR DEPRESSIVE DISORDER (MDD) AND COCAINE ADDICTION. HOWEVER, THE ETIOLOGY UNDERLYING MYELIN IMPAIRMENT IN THESE CLINICALLY DISTINCT SUBJECTS REMAINS ELUSIVE. THIS ARTICLE REVIEWS MYELIN IMPAIRMENT IN LINE WITH DOPAMINERGIC DYSFUNCTION, A PRIME NEUROPATHOPHYSIOLOGICAL TRAIT SHARED IN PSYCHIATRIC DISORDERS AND DRUG ABUSE, AS WELL AS THE GENETIC AND EPIGENETIC ALTERATIONS ASSOCIATED WITH THESE DISEASES. THE CURRENT FINDINGS SUPPORT THE HYPOTHESIS THAT ABERRANT DOPAMINE (DA) ACTION ON OLS IS A COMMON PATHOLOGIC MECHANISM FOR MYELIN IMPAIRMENT IN THE AFOREMENTIONED MENTAL MORBIDITIES, WHEREAS INHERITED GENETIC VARIATIONS THAT SPECIFICALLY AFFECT OL DEVELOPMENT AND MYELINOGENESIS MAY FURTHER INCREASE MYELIN VULNERABILITY IN PSYCHIATRIC DISORDERS. IMPORTANTLY, OL DEFECT IS NOT ONLY A PATHOLOGICAL CONSEQUENCE BUT ALSO A CAUSATIVE FACTOR FOR DOPAMINERGIC DYSFUNCTION. HENCE, MYELIN IMPAIRMENT IS A KEY FACTOR IN THE PATHOGENIC LOOP OF PSYCHIATRIC DISEASES AND DRUG ADDICTION. 2008 2 4758 36 NOVEL TREATMENT STRATEGIES TARGETING MYELIN AND OLIGODENDROCYTE DYSFUNCTION IN SCHIZOPHRENIA. OLIGODENDROCYTES ARE THE GLIAL CELLS RESPONSIBLE FOR THE FORMATION OF THE MYELIN SHEATH AROUND AXONS. DURING NEURODEVELOPMENT, OLIGODENDROCYTES UNDERGO MATURATION AND DIFFERENTIATION, AND LATER REMYELINATION IN ADULTHOOD. ABNORMALITIES IN THESE PROCESSES HAVE BEEN ASSOCIATED WITH BEHAVIORAL AND COGNITIVE DYSFUNCTIONS AND THE DEVELOPMENT OF VARIOUS MENTAL ILLNESSES LIKE SCHIZOPHRENIA. SEVERAL STUDIES HAVE IMPLICATED OLIGODENDROCYTE DYSFUNCTION AND MYELIN ABNORMALITIES IN THE DISORDER, TOGETHER WITH ALTERED EXPRESSION OF MYELIN-RELATED GENES SUCH AS OLIG2, CNP, AND NRG1. HOWEVER, THE MOLECULAR MECHANISMS SUBJACENT OF THESE ALTERATIONS REMAIN ELUSIVE. SCHIZOPHRENIA IS A SEVERE, CHRONIC PSYCHIATRIC DISORDER AFFECTING MORE THAN 23 MILLION INDIVIDUALS WORLDWIDE AND ITS SYMPTOMS USUALLY APPEAR AT THE BEGINNING OF ADULTHOOD. CURRENTLY, THE MAJOR THERAPEUTIC STRATEGY FOR SCHIZOPHRENIA RELIES ON THE USE OF ANTIPSYCHOTICS. DESPITE THEIR WIDESPREAD USE, THE EFFECTS OF ANTIPSYCHOTICS ON GLIAL CELLS, ESPECIALLY OLIGODENDROCYTES, REMAIN UNCLEAR. THUS, IN THIS REVIEW WE HIGHLIGHT THE CURRENT KNOWLEDGE REGARDING OLIGODENDROCYTE DYSFUNCTION IN SCHIZOPHRENIA, COMPILING DATA FROM (EPI)GENETIC STUDIES AND UP-TO-DATE MODELS TO INVESTIGATE THE ROLE OF OLIGODENDROCYTES IN THE DISORDER. IN ADDITION, WE EXAMINED POTENTIAL TARGETS CURRENTLY INVESTIGATED FOR THE IMPROVEMENT OF SCHIZOPHRENIA SYMPTOMS. RESEARCH IN THIS AREA HAS BEEN INVESTIGATING POTENTIAL BENEFICIAL COMPOUNDS, INCLUDING THE D-AMINO ACIDS D-ASPARTATE AND D-SERINE, THAT ACT AS NMDA RECEPTOR AGONISTS, MODULATING THE GLUTAMATERGIC SIGNALING; THE ANTIOXIDANT N-ACETYLCYSTEINE, A PRECURSOR IN THE SYNTHESIS OF GLUTATHIONE, PROTECTING AGAINST THE REDOX IMBALANCE; AS WELL AS LITHIUM, AN INHIBITOR OF GLYCOGEN SYNTHASE KINASE 3BETA (GSK3BETA) SIGNALING, CONTRIBUTING TO OLIGODENDROCYTE SURVIVAL AND FUNCTIONING. IN CONCLUSION, THERE IS STRONG EVIDENCE LINKING OLIGODENDROCYTE DYSFUNCTION TO THE DEVELOPMENT OF SCHIZOPHRENIA. HENCE, A BETTER UNDERSTANDING OF OLIGODENDROCYTE DIFFERENTIATION, AS WELL AS THE EFFECTS OF ANTIPSYCHOTIC MEDICATION IN THESE CELLS, COULD HAVE POTENTIAL IMPLICATIONS FOR UNDERSTANDING THE DEVELOPMENT OF SCHIZOPHRENIA AND FINDING NEW TARGETS FOR DRUG DEVELOPMENT. 2020 3 2011 35 EPIGENETIC BASIS OF MENTAL ILLNESS. PSYCHIATRIC DISORDERS ARE COMPLEX MULTIFACTORIAL ILLNESSES INVOLVING CHRONIC ALTERATIONS IN NEURAL CIRCUIT STRUCTURE AND FUNCTION AS WELL AS LIKELY ABNORMALITIES IN GLIAL CELLS. WHILE GENETIC FACTORS ARE IMPORTANT IN THE ETIOLOGY OF MOST MENTAL DISORDERS, THE RELATIVELY HIGH RATES OF DISCORDANCE AMONG IDENTICAL TWINS, PARTICULARLY FOR DEPRESSION AND OTHER STRESS-RELATED SYNDROMES, CLEARLY INDICATE THE IMPORTANCE OF ADDITIONAL MECHANISMS. ENVIRONMENTAL FACTORS SUCH AS STRESS ARE KNOWN TO PLAY A ROLE IN THE ONSET OF THESE ILLNESSES. EXPOSURE TO SUCH ENVIRONMENTAL INSULTS INDUCES STABLE CHANGES IN GENE EXPRESSION, NEURAL CIRCUIT FUNCTION, AND ULTIMATELY BEHAVIOR, AND THESE MALADAPTATIONS APPEAR DISTINCT BETWEEN DEVELOPMENTAL VERSUS ADULT EXPOSURES. INCREASING EVIDENCE INDICATES THAT THESE SUSTAINED ABNORMALITIES ARE MAINTAINED BY EPIGENETIC MODIFICATIONS IN SPECIFIC BRAIN REGIONS. INDEED, TRANSCRIPTIONAL DYSREGULATION AND THE ABERRANT EPIGENETIC REGULATION THAT UNDERLIES THIS DYSREGULATION IS A UNIFYING THEME IN PSYCHIATRIC DISORDERS. HERE, WE PROVIDE A PROGRESS REPORT OF EPIGENETIC STUDIES OF THE THREE MAJOR PSYCHIATRIC SYNDROMES, DEPRESSION, SCHIZOPHRENIA, AND BIPOLAR DISORDER. WE REVIEW THE LITERATURE DERIVED FROM ANIMAL MODELS OF THESE DISORDERS AS WELL AS FROM STUDIES OF POSTMORTEM BRAIN TISSUE FROM HUMAN PATIENTS. WHILE EPIGENETIC STUDIES OF MENTAL ILLNESS REMAIN AT EARLY STAGES, UNDERSTANDING HOW ENVIRONMENTAL FACTORS RECRUIT THE EPIGENETIC MACHINERY WITHIN SPECIFIC BRAIN REGIONS TO CAUSE LASTING CHANGES IN DISEASE SUSCEPTIBILITY AND PATHOPHYSIOLOGY IS REVEALING NEW INSIGHT INTO THE ETIOLOGY AND TREATMENT OF THESE CONDITIONS. 2016 4 534 32 ASTROGLIA IN THE VULNERABILITY TO AND MAINTENANCE OF STRESS-MEDIATED NEUROPATHOLOGY AND DEPRESSION. SIGNIFICANT STRESS EXPOSURE AND PSYCHIATRIC DEPRESSION ARE ASSOCIATED WITH MORPHOLOGICAL, BIOCHEMICAL, AND PHYSIOLOGICAL DISTURBANCES OF ASTROCYTES IN SPECIFIC BRAIN REGIONS RELEVANT TO THE PATHOPHYSIOLOGY OF THOSE DISORDERS, SUGGESTING THAT ASTROCYTES ARE INVOLVED IN THE MECHANISMS UNDERLYING THE VULNERABILITY TO OR MAINTENANCE OF STRESS-RELATED NEUROPATHOLOGY AND DEPRESSION. TO UNDERSTAND THOSE MECHANISMS A VARIETY OF STUDIES HAVE PROBED THE EFFECT OF VARIOUS MODALITIES OF STRESS EXPOSURE ON THE METABOLISM, GENE EXPRESSION AND PLASTICITY OF ASTROCYTES. THESE STUDIES HAVE UNCOVERED THE PARTICIPATION OF VARIOUS CELLULAR PATHWAYS, SUCH AS THOSE FOR INTRACELLULAR CALCIUM REGULATION, NEUROIMMUNE RESPONSES, EXTRACELLULAR IONIC REGULATION, GAP JUNCTIONS-BASED CELLULAR COMMUNICATION, AND REGULATION OF NEUROTRANSMITTER AND GLIOTRANSMITTER RELEASE AND UPTAKE. MORE RECENTLY EPIGENETIC MODIFICATIONS RESULTING FROM EXPOSURE TO CHRONIC FORMS OF STRESS OR TO EARLY LIFE ADVERSITY HAVE BEEN SUGGESTED TO AFFECT NOT ONLY NEURONAL MECHANISMS BUT ALSO GENE EXPRESSION AND PHYSIOLOGY OF ASTROCYTES AND OTHER GLIAL CELLS. HOWEVER, MUCH REMAINS TO BE LEARNED TO UNDERSTAND THE SPECIFIC ROLE OF THOSE AND OTHER MODIFICATIONS IN THE ASTROGLIAL CONTRIBUTION TO THE VULNERABILITY TO AND MAINTENANCE OF STRESS-RELATED DISORDERS AND DEPRESSION, AND FOR LEVERAGING THAT KNOWLEDGE TO ACHIEVE MORE EFFECTIVE PSYCHIATRIC THERAPIES. 2022 5 6324 27 THE ROLE OF ALPHA-SYNUCLEIN IN THE PATHOPHYSIOLOGY OF ALCOHOLISM. ALCOHOLISM HAS COMPLEX ETIOLOGY AND THERE IS EVIDENCE FOR BOTH GENETIC AND ENVIRONMENTAL FACTORS IN ITS PATHOPHYSIOLOGY. CHRONIC, LONG-TERM ALCOHOL ABUSE AND ALCOHOL DEPENDENCE ARE ASSOCIATED WITH NEURONAL LOSS WITH THE PREFRONTAL CORTEX BEING PARTICULARLY SUSCEPTIBLE TO NEUROTOXIC DAMAGE. THIS BRAIN REGION IS INVOLVED IN THE DEVELOPMENT AND PERSISTENCE OF ALCOHOL ADDICTION AND NEUROTOXIC DAMAGE IS LIKELY TO EXACERBATE THE REINFORCING EFFECTS OF ALCOHOL AND MAY HINDER TREATMENT. UNDERSTANDING THE MECHANISM OF ALCOHOL'S NEUROTOXIC EFFECTS ON THE BRAIN AND THE GENETIC RISK FACTORS ASSOCIATED WITH ALCOHOL ABUSE ARE THE FOCUS OF CURRENT RESEARCH. BECAUSE OF ITS WELL-ESTABLISHED ROLE IN NEURODEGENERATIVE AND NEUROPSYCHOLOGICAL DISORDERS, AND ITS EMERGING ROLE IN THE PATHOPHYSIOLOGY OF ADDICTION, HERE WE REVIEW THE GENETIC AND EPIGENETIC FACTORS INVOLVED IN REGULATING ALPHA-SYNUCLEIN EXPRESSION AND ITS POTENTIAL ROLE IN THE PATHOPHYSIOLOGY OF CHRONIC ALCOHOL ABUSE. ELUCIDATION OF THE MECHANISMS OF ALPHA-SYNUCLEIN REGULATION MAY PROVE BENEFICIAL IN UNDERSTANDING THE ROLE OF THIS KEY SYNAPTIC PROTEIN IN DISEASE AND ITS POTENTIAL FOR THERAPEUTIC MODULATION IN THE TREATMENT OF SUBSTANCE USE DISORDERS AS WELL AS OTHER NEURODEGENERATIVE DISEASES. 2013 6 4424 34 MOLECULAR AND NEUROLOGIC RESPONSES TO CHRONIC ALCOHOL USE. THIS CHAPTER PROVIDES AN OVERVIEW OF CURRENT KNOWLEDGE ON THE MOLECULAR AND CLINICAL ASPECTS OF CHRONIC ALCOHOL EFFECTS ON THE CENTRAL NERVOUS SYSTEM. THIS DRUG IS ALMOST UBIQUITOUS, WIDELY ENJOYED SOCIALLY, BUT PRODUCES A DIVERSE SPECTRUM OF NEUROLOGIC DISEASE WHEN ABUSED. ACUTELY, ALCOHOL INTERACTS PREDOMINANTLY WITH GAMMA-AMINOBUTYRIC ACID-A (GABA-A) AND N-METHYL-D-ASPARTATE (NMDA) RECEPTORS, BUT TRIGGERS DIVERSE SIGNALING EVENTS WITHIN WELL-DEFINED NEURAL PATHWAYS. THESE EVENTS RESULT IN ADAPTIVE CHANGES IN GENE EXPRESSION THAT ULTIMATELY PRODUCE TWO MAJOR STATES: ADDICTION AND TOXICITY. EPIGENETIC MODIFICATIONS OF CHROMATIN COULD LEAD TO LONG-LIVED OR EVEN TRANSGENERATIONAL CHANGES IN GENE EXPRESSION, THUS PRODUCING ASPECTS OF THE HERITABILITY OF ALCOHOL USE DISORDERS (AUD) AND LONG-TERM BEHAVIORS SUCH AS RECIDIVISM. THE DIVERSE CLINICAL SYNDROMES PRODUCED BY CHRONIC ALCOHOL ACTIONS IN THE CENTRAL NERVOUS SYSTEM REFLECT THE MOLECULAR PATHOLOGY AND PREDOMINANTLY INVOLVE ASPECTS OF TOLERANCE/WITHDRAWAL, SELECTIVE VULNERABILITY (MANIFEST AS CENTRAL PONTINE MYELINOLYSIS, MARCHIAFAVA-BIGNAMI DISEASE), AND ADDITIONAL ENVIRONMENTAL FACTORS (E.G., THIAMINE DEFICIENCY IN WERNICKE-KORSAKOFF'S SYNDROME). ADDITIONALLY, DELETERIOUS ASPECTS OF CHRONIC ALCOHOL ON SIGNALING, SYNAPTIC TRANSMISSION, AND CELL TOXICITY LEAD TO PRIMARY ALCOHOLIC DEMENTIA. GENETICALLY DETERMINED ASPECTS OF MYELIN STRUCTURE AND ALCOHOL ACTIONS ON MYELIN GENE EXPRESSION MAY BE A PROMINENT MOLECULAR MECHANISM RESULTING IN A PREDISPOSITION TO, OR CAUSATION OF, AUD AND MULTIPLE OTHER NEUROLOGIC COMPLICATIONS OF CHRONIC ALCOHOL. THE DRAMATIC PROGRESS MADE IN UNDERSTANDING MOLECULAR ACTIONS OF ALCOHOL HOLDS GREAT PROMISE FOR OUR EVENTUAL TREATMENT OR PREVENTION OF AUD AND NEUROLOGIC COMPLICATIONS RESULTING FROM CHRONIC ALCOHOL ABUSE. 2014 7 2598 24 EPIGENETICS OF THE DEPRESSED BRAIN: ROLE OF HISTONE ACETYLATION AND METHYLATION. MAJOR DEPRESSIVE DISORDER IS A CHRONIC, REMITTING SYNDROME INVOLVING WIDELY DISTRIBUTED CIRCUITS IN THE BRAIN. STABLE ALTERATIONS IN GENE EXPRESSION THAT CONTRIBUTE TO STRUCTURAL AND FUNCTIONAL CHANGES IN MULTIPLE BRAIN REGIONS ARE IMPLICATED IN THE HETEROGENEITY AND PATHOGENESIS OF THE ILLNESS. EPIGENETIC EVENTS THAT ALTER CHROMATIN STRUCTURE TO REGULATE PROGRAMS OF GENE EXPRESSION HAVE BEEN ASSOCIATED WITH DEPRESSION-RELATED BEHAVIOR, ANTIDEPRESSANT ACTION, AND RESISTANCE TO DEPRESSION OR 'RESILIENCE' IN ANIMAL MODELS, WITH INCREASING EVIDENCE FOR SIMILAR MECHANISMS OCCURRING IN POSTMORTEM BRAINS OF DEPRESSED HUMANS. IN THIS REVIEW, WE DISCUSS RECENT ADVANCES IN OUR UNDERSTANDING OF EPIGENETIC CONTRIBUTIONS TO DEPRESSION, IN PARTICULAR THE ROLE OF HISTONE ACETYLATION AND METHYLATION, WHICH ARE REVEALING NOVEL MECHANISTIC INSIGHT INTO THE SYNDROME THAT MAY AID IN THE DEVELOPMENT OF NOVEL TARGETS FOR DEPRESSION TREATMENT. 2013 8 2092 20 EPIGENETIC EFFECT OF CHRONIC STRESS ON DOPAMINE SIGNALING AND DEPRESSION. BECAUSE OF THE COMPLEX CAUSAL FACTORS LEADING TO DEPRESSION, EPIGENETICS IS OF CONSIDERABLE INTEREST FOR THE UNDERSTANDING EFFECT OF STRESS IN DEPRESSION. DOPAMINE IS A KEY NEUROTRANSMITTER IMPORTANT IN MANY PHYSIOLOGICAL FUNCTIONS, INCLUDING MOTOR CONTROL, MOOD, AND THE REWARD PATHWAY. THESE FACTORS LEAD MANY DRUGS TO TARGET DOPAMINE RECEPTORS IN TREATING DEPRESSIVE DISORDERS. IN THIS REVIEW, WE TRY TO PORTRAY HOW CHRONIC STRESS AS AN EPIGENETIC FACTOR CHANGES THE GENE REGULATION PATTERN BY INTERRUPTING DOPAMINE SIGNALING MECHANISM. 2013 9 6174 39 THE HIPPOCAMPUS, NEUROTROPHIC FACTORS AND DEPRESSION: POSSIBLE IMPLICATIONS FOR THE PHARMACOTHERAPY OF DEPRESSION. DEPRESSION IS A PREVALENT, HIGHLY DEBILITATING MENTAL DISORDER AFFECTING UP TO 15% OF THE POPULATION AT LEAST ONCE IN THEIR LIFETIME, WITH HUGE COSTS FOR SOCIETY. NEUROBIOLOGICAL MECHANISMS OF DEPRESSION ARE STILL NOT WELL KNOWN, ALTHOUGH THERE IS CONSENSUS ABOUT INTERPLAY BETWEEN GENETIC AND ENVIRONMENTAL FACTORS. ANTIDEPRESSANT MEDICATIONS ARE FREQUENTLY USED IN DEPRESSION, BUT AT LEAST 50% OF PATIENTS ARE POOR RESPONDERS, EVEN TO MORE RECENTLY DISCOVERED MEDICATIONS. FURTHERMORE, CLINICAL RESPONSE ONLY OCCURS FOLLOWING WEEKS TO MONTHS OF TREATMENT AND ONLY CHRONIC TREATMENT IS EFFECTIVE, SUGGESTING THAT ACTIONS BEYOND THE RAPIDLY OCCURRING EFFECT OF ENHANCING MONOAMINERGIC SYSTEMS, SUCH AS ADAPTATION OF THESE SYSTEMS, ARE RESPONSIBLE FOR THE EFFECTS OF ANTIDEPRESSANTS. RECENT STUDIES INDICATE THAT AN IMPAIRMENT OF SYNAPTIC PLASTICITY (NEUROGENESIS, AXON BRANCHING, DENDRITOGENESIS AND SYNAPTOGENESIS) IN SPECIFIC AREAS OF THE CNS, PARTICULARLY THE HIPPOCAMPUS, MAY BE A CORE FACTOR IN THE PATHOPHYSIOLOGY OF DEPRESSION. THE ABNORMAL NEURAL PLASTICITY MAY BE RELATED TO ALTERATIONS IN THE LEVELS OF NEUROTROPHIC FACTORS, NAMELY BRAIN-DERIVED NEUROTROPHIC FACTOR (BDNF), WHICH PLAY A CENTRAL ROLE IN PLASTICITY. AS BDNF IS REPRESSED BY STRESS, EPIGENETIC REGULATION OF THE BDNF GENE MAY PLAY AN IMPORTANT ROLE IN DEPRESSION. THE HIPPOCAMPUS IS SMALLER IN DEPRESSED PATIENTS, ALTHOUGH IT IS UNCLEAR WHETHER SMALLER SIZE IS A CONSEQUENCE OF DEPRESSION OR A PRE-EXISTING, VULNERABILITY MARKER FOR DEPRESSION. ENVIRONMENTAL STRESSORS TRIGGERING ACTIVATION OF THE HYPOTHALAMIC-PITUITARY-ADRENAL AXIS CAUSE THE BRAIN TO BE EXPOSED TO CORTICOSTEROIDS, AFFECTING NEUROBEHAVIOURAL FUNCTIONS WITH A STRONG DOWNREGULATION OF HIPPOCAMPAL NEUROGENESIS, AND ARE A MAJOR RISK FACTOR FOR DEPRESSION. ANTIDEPRESSANT TREATMENT INCREASES BDNF LEVELS, STIMULATES NEUROGENESIS AND REVERSES THE INHIBITORY EFFECTS OF STRESS, BUT THIS EFFECT IS EVIDENT ONLY AFTER 3-4 WEEKS OF ADMINISTRATION, THE TIME COURSE FOR MATURATION OF NEW NEURONS. THE ABLATION OF HIPPOCAMPAL NEUROGENESIS BLOCKS THE BEHAVIOURAL EFFECTS OF ANTIDEPRESSANTS IN ANIMAL MODELS. THE ABOVE FINDINGS SUGGEST NEW POSSIBLE TARGETS FOR THE PHARMACOTHERAPY OF DEPRESSION SUCH AS NEUROTROPHIC FACTORS, THEIR RECEPTORS AND RELATED INTRACELLULAR SIGNALLING CASCADES; AGENTS COUNTERACTING THE EFFECTS OF STRESS ON HIPPOCAMPAL NEUROGENESIS (INCLUDING ANTAGONISTS OF CORTICOSTEROIDS, INFLAMMATORY CYTOKINES AND THEIR RECEPTORS); AND AGENTS FACILITATING THE ACTIVATION OF GENE EXPRESSION AND INCREASING THE TRANSCRIPTION OF NEUROTROPHINS IN THE BRAIN. 2011 10 3708 19 INFLUENCE OF PHARMACOLOGICAL AND EPIGENETIC FACTORS TO SUPPRESS NEUROTROPHIC FACTORS AND ENHANCE NEURAL PLASTICITY IN STRESS AND MOOD DISORDERS. STRESS-INDUCED MAJOR DEPRESSION AND MOOD DISORDERS ARE CHARACTERIZED BY BEHAVIOURAL ABNORMALITIES AND PSYCHIATRIC ILLNESS, LEADING TO DISABILITY AND IMMATURE MORTALITY WORLDWIDE. NEUROBIOLOGICAL MECHANISMS OF STRESS AND MOOD DISORDERS ARE DISCUSSED CONSIDERING RECENT FINDINGS, AND CHALLENGES TO ENHANCE PHARMACOLOGICAL EFFECTS OF ANTIDEPRESSANT, AND MOOD STABILIZERS. PHARMACOLOGICAL ENHANCEMENT OF KETAMINE AND SCOPOLAMINE REGULATES DEPRESSION AT THE MOLECULAR LEVEL, INCREASING SYNAPTIC PLASTICITY IN PREFRONTAL REGIONS. BLOOD-DERIVED NEUROTROPHIC FACTORS FACILITATE MOOD-DEFICIT SYMPTOMS. EPIGENETIC FACTORS MAINTAIN STRESS-RESILIENCE IN HIPPOCAMPAL REGION. REGULATION OF NEUROTROPHIC FACTORS BLOCKADES STRESS, AND ENHANCES NEURONAL SURVIVAL THOUGH IT PARALYZES LIMBIC REGIONS. MOLECULAR AGENTS AND NEUROTROPHIC FACTORS ALSO CONTROL BEHAVIORAL AND SYNAPTIC PLASTICITY IN ADDICTION AND STRESS DISORDERS. FUTURE RESEARCH ON NEURONAL DYNAMICS AND CELLULAR ACTIONS CAN BE DIRECTED TO OBTAIN THE ETIOLOGY OF SYNAPTIC DYSREGULATION IN MOOD DISORDER AND STRESS. FOR THE FIRST TIME, THE CURRENT REVIEW CONTRIBUTES TO THE LITERATURE OF SYNAPTIC PLASTICITY REPRESENTING THE ROLE OF EPIGENETIC MECHANISMS AND GLUCOCORTICOID RECEPTORS TO PREDICT DEPRESSION AND ANXIETY IN CLINICAL CONDITIONS. 2019 11 4633 27 NEUROIMMUNE ACTIVATION DRIVES MULTIPLE BRAIN STATES. NEUROIMMUNE SIGNALING IS INCREASINGLY IDENTIFIED AS A CRITICAL COMPONENT OF NEURONAL PROCESSES UNDERLYING MEMORY, EMOTION AND COGNITION. THE INTERACTIONS OF MICROGLIA AND ASTROCYTES WITH NEURONS AND SYNAPSES, AND THE INDIVIDUAL CYTOKINES AND IMMUNE SIGNALING MOLECULES THAT MEDIATE THESE INTERACTIONS ARE A CURRENT FOCUS OF MUCH RESEARCH. HERE, WE DISCUSS NEUROIMMUNE ACTIVATION AS A MECHANISM TRIGGERING DIFFERENT STATES THAT MODULATE COGNITIVE AND AFFECTIVE PROCESSES TO ALLOW FOR APPROPRIATE BEHAVIOR DURING AND AFTER ILLNESS OR INJURY. WE PROPOSE THAT THESE STATES LIE ON A CONTINUUM FROM A NAIVE HOMEOSTATIC BASELINE STATE IN THE ABSENCE OF STIMULATION, TO ACUTE NEUROIMMUNE ACTIVITY AND CHRONIC ACTIVATION. IMPORTANTLY, CONSEQUENCES OF ILLNESS OR INJURY INCLUDING COGNITIVE DEFICITS AND MOOD IMPAIRMENTS CAN PERSIST LONG AFTER RESOLUTION OF IMMUNE SIGNALING. THIS SUGGESTS THAT NEUROIMMUNE ACTIVATION ALSO RESULTS IN AN ENDURING SHIFT IN THE HOMEOSTATIC BASELINE STATE WITH LONG LASTING CONSEQUENCES FOR NEURAL FUNCTION AND BEHAVIOR. SUCH DIFFERENT STATES CAN BE IDENTIFIED IN A MULTIDIMENSIONAL WAY, USING PATTERNS OF CYTOKINE AND GLIAL ACTIVATION, BEHAVIORAL AND COGNITIVE CHANGES, AND EPIGENETIC SIGNATURES. IDENTIFYING DISTINCT NEUROIMMUNE STATES AND THEIR CONSEQUENCES FOR NEURAL FUNCTION WILL PROVIDE A FRAMEWORK FOR PREDICTING VULNERABILITY TO DISORDERS OF MEMORY, COGNITION AND EMOTION BOTH DURING AND LONG AFTER RECOVERY FROM ILLNESS. 2018 12 4328 27 MICRORNAS, STEM CELLS IN BIPOLAR DISORDER, AND LITHIUM THERAPEUTIC APPROACH. BIPOLAR DISORDER (BD) IS A SEVERE, CHRONIC, AND DISABLING NEUROPSYCHIATRIC DISORDER CHARACTERIZED BY RECURRENT MOOD DISTURBANCES (MANIA/HYPOMANIA AND DEPRESSION, WITH OR WITHOUT MIXED FEATURES) AND A CONSTELLATION OF COGNITIVE, PSYCHOMOTOR, AUTONOMIC, AND ENDOCRINE ABNORMALITIES. THE ETIOLOGY OF BD IS MULTIFACTORIAL, INCLUDING BOTH BIOLOGICAL AND EPIGENETIC FACTORS. RECENTLY, MICRORNAS (MIRNAS), A CLASS OF EPIGENETIC REGULATORS OF GENE EXPRESSION PLAYING A CENTRAL ROLE IN BRAIN DEVELOPMENT AND PLASTICITY, HAVE BEEN RELATED TO SEVERAL NEUROPSYCHIATRIC DISORDERS, INCLUDING BD. MOREOVER, AN ALTERATION IN THE NUMBER/DISTRIBUTION AND DIFFERENTIATION POTENTIAL OF NEURAL STEM CELLS HAS ALSO BEEN DESCRIBED, SIGNIFICANTLY AFFECTING BRAIN HOMEOSTASIS AND NEUROPLASTICITY. THIS REVIEW AIMED TO EVALUATE THE MOST RELIABLE SCIENTIFIC EVIDENCE ON MIRNAS AS BIOMARKERS FOR THE DIAGNOSIS OF BD AND ASSESS THEIR IMPLICATIONS IN RESPONSE TO MOOD STABILIZERS, SUCH AS LITHIUM. NEURAL STEM CELL DISTRIBUTION, REGULATION, AND DYSFUNCTION IN THE ETIOLOGY OF BD ARE ALSO DISSECTED. 2022 13 4642 35 NEURONAL PLASTICITY: A LINK BETWEEN STRESS AND MOOD DISORDERS. ALTHOUGH STRESS REPRESENTS THE MAJOR ENVIRONMENTAL ELEMENT OF SUSCEPTIBILITY FOR MOOD DISORDERS, THE RELATIONSHIP BETWEEN STRESS AND DISEASE REMAINS TO BE FULLY ESTABLISHED. IN THE PRESENT ARTICLE WE REVIEW THE EVIDENCE IN SUPPORT FOR A ROLE OF NEURONAL PLASTICITY, AND IN PARTICULAR OF NEUROTROPHIC FACTORS. EVEN THOUGH DECREASED LEVELS OF NOREPINEPHRINE AND SEROTONIN MAY UNDERLIE DEPRESSIVE SYMPTOMS, COMPELLING EVIDENCE NOW SUGGESTS THAT MOOD DISORDERS ARE CHARACTERIZED BY REDUCED NEURONAL PLASTICITY, WHICH CAN BE BROUGHT ABOUT BY EXPOSURE TO STRESS AT DIFFERENT STAGES OF LIFE. INDEED THE EXPRESSION OF NEUROTROPHIC MOLECULES, SUCH AS THE NEUROTROPHIN BDNF, IS REDUCED IN DEPRESSED SUBJECTS AS WELL AS IN EXPERIMENTAL ANIMALS EXPOSED TO ADVERSE EXPERIENCE AT EARLY STAGES OF LIFE OR AT ADULTHOOD. THESE CHANGES SHOW AN ANATOMICAL SPECIFICITY AND MIGHT BE SUSTAINED BY EPIGENETIC MECHANISMS. PHARMACOLOGICAL INTERVENTION MAY NORMALIZE SUCH DEFECTS AND IMPROVE NEURONAL FUNCTION THROUGH THE MODULATION OF THE SAME FACTORS THAT ARE DEFECTIVE IN DEPRESSION. SEVERAL STUDIES HAVE DEMONSTRATED THAT CHRONIC, BUT NOT ACUTE, ANTIDEPRESSANT TREATMENT INCREASES THE EXPRESSION OF BDNF AND MAY ENHANCE ITS LOCALIZATION AT SYNAPTIC LEVEL. ANTIDEPRESSANT TREATMENT CAN NORMALIZE DEFICITS IN NEUROTROPHIN EXPRESSION PRODUCED BY CHRONIC STRESS PARADIGMS, BUT MAY ALSO ALTER THE MODULATION OF BDNF UNDER ACUTE STRESSFUL CONDITIONS. IN SUMMARY, THERE IS GOOD AGREEMENT IN CONSIDERING NEURONAL PLASTICITY, AND THE EXPRESSION OF KEY PROTEINS SUCH AS THE NEUROTROPHIN BDNF, AS A CENTRAL PLAYER FOR THE EFFECTS OF STRESS ON BRAIN FUNCTION AND ITS IMPLICATION FOR PSYCHOPATHOLOGY. ACCORDINGLY, EFFECTIVE TREATMENTS SHOULD NOT LIMIT THEIR EFFECTS TO THE CONTROL OF NEUROTRANSMITTER AND HORMONAL DYSFUNCTIONS, BUT SHOULD BE ABLE TO NORMALIZE DEFECTIVE MECHANISMS THAT SUSTAIN THE IMPAIRMENT OF NEURONAL PLASTICITY. 2009 14 2415 30 EPIGENETIC SIGNALING IN PSYCHIATRIC DISORDERS: STRESS AND DEPRESSION. PSYCHIATRIC DISORDERS ARE COMPLEX MULTIFACTORIAL DISORDERS INVOLVING CHRONIC ALTERATIONS IN NEURAL CIRCUIT STRUCTURE AND FUNCTION. WHILE GENETIC FACTORS PLAY A ROLE IN THE ETIOLOGY OF DISORDERS SUCH AS DEPRESSION, ADDICTION, AND SCHIZOPHRENIA, RELATIVELY HIGH RATES OF DISCORDANCE AMONG IDENTICAL TWINS CLEARLY POINT TO THE IMPORTANCE OF ADDITIONAL FACTORS. ENVIRONMENTAL FACTORS, SUCH AS STRESS, PLAY A MAJOR ROLE IN THE PSYCHIATRIC DISORDERS BY INDUCING STABLE CHANGES IN GENE EXPRESSION, NEURAL CIRCUIT FUNCTION, AND ULTIMATELY BEHAVIOR. INSULTS AT THE DEVELOPMENTAL STAGE AND IN ADULTHOOD APPEAR TO INDUCE DISTINCT MALADAPTATIONS. INCREASING EVIDENCE INDICATES THAT THESE SUSTAINED ABNORMALITIES ARE MAINTAINED BY EPIGENETIC MODIFICATIONS IN SPECIFIC BRAIN REGIONS. INDEED, TRANSCRIPTIONAL DYSREGULATION AND ASSOCIATED ABERRANT EPIGENETIC REGULATION IS A UNIFYING THEME IN PSYCHIATRIC DISORDERS. ASPECTS OF DEPRESSION CAN BE MODELED IN ANIMALS BY INDUCING DISEASE-LIKE STATES THROUGH ENVIRONMENTAL MANIPULATIONS, AND THESE STUDIES CAN PROVIDE A MORE GENERAL UNDERSTANDING OF EPIGENETIC MECHANISMS IN PSYCHIATRIC DISORDERS. UNDERSTANDING HOW ENVIRONMENTAL FACTORS RECRUIT THE EPIGENETIC MACHINERY IN ANIMAL MODELS IS PROVIDING NEW INSIGHTS INTO DISEASE MECHANISMS IN HUMANS. 2014 15 1796 29 EFFECT OF GERM-FREE STATUS ON TRANSCRIPTIONAL PROFILES IN THE NUCLEUS ACCUMBENS AND TRANSCRIPTOMIC RESPONSE TO CHRONIC MORPHINE. OPIOID USE DISORDER IS A PUBLIC HEALTH CRISIS THAT CAUSES TREMENDOUS SUFFERING FOR PATIENTS AS WELL AS SUBSTANTIAL SOCIAL AND ECONOMIC COSTS FOR SOCIETY. THERE ARE CURRENTLY AVAILABLE TREATMENTS FOR PATIENTS WITH OPIOID USE DISORDER, BUT THEY REMAIN INTOLERABLE OR INEFFECTIVE FOR MANY. THUS THE NEED TO DEVELOP NEW AVENUES FOR THERAPEUTICS DEVELOPMENT IN THIS SPACE IS GREAT. SUBSTANTIAL WORK IN MODELS OF SUBSTANCE USE DISORDERS, INCLUDING OPIOID USE DISORDER, DEMONSTRATES THAT PROLONGED EXPOSURE TO DRUGS OF ABUSE LEADS TO MARKED TRANSCRIPTIONAL AND EPIGENETIC DYSREGULATION IN LIMBIC SUBSTRUCTURES. IT IS WIDELY BELIEVED THAT THESE CHANGES IN GENE REGULATION IN RESPONSE TO DRUGS ARE A KEY DRIVING FACTOR IN THE PERPETUATION OF DRUG TAKING AND SEEKING BEHAVIORS. THUS, DEVELOPMENT OF INTERVENTIONS THAT COULD SHAPE TRANSCRIPTIONAL REGULATION IN RESPONSE TO DRUGS OF ABUSE WOULD BE OF HIGH VALUE. OVER THE PAST DECADE THERE HAS BEEN A SURGE IN RESEARCH DEMONSTRATING THAT THE RESIDENT BACTERIA OF THE GASTROINTESTINAL TRACT, COLLECTIVELY THE GUT MICROBIOME, CAN HAVE TREMENDOUS INFLUENCE ON NEUROBIOLOGICAL AND BEHAVIORAL PLASTICITY. PREVIOUS WORK FROM OUR GROUP AND OTHERS HAS DEMONSTRATED THAT ALTERATIONS IN THE GUT MICROBIOME CAN ALTER BEHAVIORAL RESPONSES TO OPIOIDS IN MULTIPLE PARADIGMS. ADDITIONALLY, WE HAVE PREVIOUSLY REPORTED THAT DEPLETION OF THE GUT MICROBIOME WITH ANTIBIOTICS MARKEDLY SHIFTS THE TRANSCRIPTOME OF THE NUCLEUS ACCUMBENS FOLLOWING PROLONGED MORPHINE EXPOSURE. IN THIS MANUSCRIPT WE PRESENT A COMPREHENSIVE ANALYSIS OF THE EFFECTS OF THE GUT MICROBIOME ON TRANSCRIPTIONAL REGULATION OF THE NUCLEUS ACCUMBENS FOLLOWING MORPHINE BY UTILIZING GERM-FREE, ANTIBIOTIC TREATED, AND CONTROL MICE. THIS ALLOWS FOR DETAILED UNDERSTANDING OF THE ROLE OF THE MICROBIOME IN REGULATING BASELINE TRANSCRIPTOMIC CONTROL, AS WELL AS RESPONSE TO MORPHINE. WE FIND THAT GERM-FREE STATUS LEADS TO A MARKED GENE DYSREGULATION IN A MANNER DISTINCT TO ADULT MICE TREATED WITH ANTIBIOTICS, AND THAT ALTERED GENE PATHWAYS ARE HIGHLY RELATED TO CELLULAR METABOLIC PROCESSES. THESE DATA PROVIDE ADDITIONAL INSIGHT INTO THE ROLE OF THE GUT MICROBIOME IN MODULATING BRAIN FUNCTION AND LAY A FOUNDATION FOR FURTHER STUDY IN THIS AREA. 2023 16 2414 28 EPIGENETIC SIGNALING IN PSYCHIATRIC DISORDERS. PSYCHIATRIC DISORDERS ARE COMPLEX MULTIFACTORIAL ILLNESSES INVOLVING CHRONIC ALTERATIONS IN NEURAL CIRCUIT STRUCTURE AND FUNCTION. WHILE GENETIC FACTORS ARE IMPORTANT IN THE ETIOLOGY OF DISORDERS SUCH AS DEPRESSION AND ADDICTION, RELATIVELY HIGH RATES OF DISCORDANCE AMONG IDENTICAL TWINS CLEARLY INDICATE THE IMPORTANCE OF ADDITIONAL MECHANISMS. ENVIRONMENTAL FACTORS SUCH AS STRESS OR PRIOR DRUG EXPOSURE ARE KNOWN TO PLAY A ROLE IN THE ONSET OF THESE ILLNESSES. SUCH EXPOSURE TO ENVIRONMENTAL INSULTS INDUCES STABLE CHANGES IN GENE EXPRESSION, NEURAL CIRCUIT FUNCTION, AND ULTIMATELY BEHAVIOR, AND THESE MALADAPTATIONS APPEAR DISTINCT BETWEEN DEVELOPMENTAL AND ADULT EXPOSURES. INCREASING EVIDENCE INDICATES THAT THESE SUSTAINED ABNORMALITIES ARE MAINTAINED BY EPIGENETIC MODIFICATIONS IN SPECIFIC BRAIN REGIONS. INDEED, TRANSCRIPTIONAL DYSREGULATION AND ASSOCIATED ABERRANT EPIGENETIC REGULATION IS A UNIFYING THEME IN PSYCHIATRIC DISORDERS. ASPECTS OF DEPRESSION AND ADDICTION CAN BE MODELED IN ANIMALS BY INDUCING DISEASE-LIKE STATES THROUGH ENVIRONMENTAL MANIPULATIONS (E.G., CHRONIC STRESS, DRUG ADMINISTRATION). UNDERSTANDING HOW ENVIRONMENTAL FACTORS RECRUIT THE EPIGENETIC MACHINERY IN ANIMAL MODELS REVEALS NEW INSIGHT INTO DISEASE MECHANISMS IN HUMANS. 2014 17 1722 24 DYSREGULATION OF BRAIN DOPAMINE SYSTEMS IN MAJOR DEPRESSIVE DISORDER. MAJOR DEPRESSIVE DISORDER (MDD OR DEPRESSION) IS A DEBILITATING NEUROPSYCHIATRIC SYNDROME WITH GENETIC, EPIGENETIC, AND ENVIRONMENTAL CONTRIBUTIONS. DEPRESSION IS ONE OF THE LARGEST CONTRIBUTORS TO CHRONIC DISEASE BURDEN; IT AFFECTS MORE THAN ONE IN SIX INDIVIDUALS IN THE UNITED STATES. A WIDE ARRAY OF CELLULAR AND MOLECULAR MODIFICATIONS DISTRIBUTED ACROSS A VARIETY OF NEURONAL PROCESSES AND CIRCUITS UNDERLIE THE PATHOPHYSIOLOGY OF DEPRESSION-NO ESTABLISHED MECHANISM CAN EXPLAIN ALL ASPECTS OF THE DISEASE. MDD SUFFERS FROM A VAST TREATMENT GAP WORLDWIDE, AND LARGE NUMBERS OF INDIVIDUALS WHO REQUIRE TREATMENT DO NOT RECEIVE ADEQUATE CARE. THIS MINI-REVIEW FOCUSES ON DYSREGULATION OF BRAIN DOPAMINE (DA) SYSTEMS IN THE PATHOPHYSIOLOGY OF MDD AND DESCRIBING NEW CELLULAR TARGETS FOR POTENTIAL MEDICATION DEVELOPMENT FOCUSED ON DA-MODULATED MICRO-CIRCUITS. WE ALSO EXPLORE HOW NEURODEVELOPMENTAL FACTORS MAY MODIFY RISK FOR LATER EMERGENCE OF MDD, POSSIBLY THROUGH DOPAMINERGIC SUBSTRATES IN THE BRAIN. 2021 18 252 30 ADVANCEMENTS IN THE UNDERLYING PATHOGENESIS OF SCHIZOPHRENIA: IMPLICATIONS OF DNA METHYLATION IN GLIAL CELLS. SCHIZOPHRENIA (SZ) IS A CHRONIC AND SEVERE MENTAL ILLNESS FOR WHICH CURRENTLY THERE IS NO CURE. AT PRESENT, THE EXACT MOLECULAR MECHANISM INVOLVED IN THE UNDERLYING PATHOGENESIS OF SZ IS UNKNOWN. THE DISEASE IS THOUGHT TO BE CAUSED BY A COMBINATION OF GENETIC, BIOLOGICAL, PSYCHOLOGICAL, AND ENVIRONMENTAL FACTORS. RECENT STUDIES HAVE SHOWN THAT EPIGENETIC REGULATION IS INVOLVED IN SZ PATHOLOGY. SPECIFICALLY, DNA METHYLATION, ONE OF THE EARLIEST FOUND EPIGENETIC MODIFICATIONS, HAS BEEN EXTENSIVELY LINKED TO MODULATION OF NEURONAL FUNCTION, LEADING TO PSYCHIATRIC DISORDERS SUCH AS SZ. HOWEVER, INCREASING EVIDENCE INDICATES THAT GLIAL CELLS, ESPECIALLY DYSFUNCTIONAL OLIGODENDROCYTES UNDERGO DNA METHYLATION CHANGES THAT CONTRIBUTE TO THE PATHOGENESIS OF SZ. THIS REVIEW PRIMARILY FOCUSES ON DNA METHYLATION INVOLVED IN GLIAL DYSFUNCTIONS IN SZ. CLARIFYING THIS MECHANISM MAY LEAD TO THE DEVELOPMENT OF NEW THERAPEUTIC INTERVENTIONAL STRATEGIES FOR THE TREATMENT OF SZ AND OTHER ILLNESSES BY CORRECTING ABNORMAL METHYLATION IN GLIAL CELLS. 2015 19 2963 26 GENETIC AND EPIGENETIC MECHANISMS LINKING PAIN AND PSYCHIATRIC DISORDERS. THE NEUROPHYSIOLOGICAL LINK BETWEEN NEUROPATHIC PAIN AND DEPRESSION REMAINS UNKNOWN DESPITE EVIDENT HIGH COMORBIDITY OF THESE TWO DISORDERS. HOWEVER, THERE IS CONVINCING EVIDENCE THAT GENOTYPE PLAYS A ROLE IN BOTH PAIN AND DEPRESSION. USING VARIOUS TYPES OF GENETIC ANALYSIS - POPULATION GENETICS, CYTOGENETICS AND MOLECULAR TECHNOLOGIES - SPECIFIC GENES HAVE BEEN IMPLICATED IN MEDIATING ALMOST ALL ASPECTS OF NOCICEPTION AND MOOD DISORDERS. THE CURRENT REVIEW ATTEMPTS TO IDENTIFY SPECIFIC GENES AND EPIGENETIC MECHANISMS COMMON TO BOTH DISORDERS. IT IS CONCLUDED THAT EXTERNAL AND INTERNAL FACTORS (INFLAMMATION, STRESS, GENDER, ETC.) THAT CONTRIBUTE TO THE PATHOLOGIES MAY DO SO THROUGH EPIGENETIC MECHANISMS THAT MAY AFFECT EXPRESSION OF THESE PARTICULAR GENES. THE POSSIBLE INVOLVEMENT OF EPIGENETIC REGULATION IN PAIN AND PSYCHIATRIC DISORDERS SUGGESTS THAT TREATMENTS TARGETING EPIGENETIC MECHANISMS THAT MEDIATE ADVERSE LIFE EVENTS SHOULD BE CONSIDERED. 2015 20 1252 24 CURRENT PERSPECTIVES ON THE NEUROBIOLOGY OF DRUG ADDICTION: A FOCUS ON GENETICS AND FACTORS REGULATING GENE EXPRESSION. DRUG ADDICTION IS A CHRONIC, RELAPSING DISORDER DEFINED BY CYCLIC PATTERNS OF COMPULSIVE DRUG SEEKING AND TAKING INTERSPERSED WITH EPISODES OF ABSTINENCE. WHILE GENETIC VARIABILITY MAY INCREASE THE RISK OF ADDICTIVE BEHAVIOURS IN AN INDIVIDUAL, EXPOSURE TO A DRUG RESULTS IN NEUROADAPTATIONS IN INTERCONNECTED BRAIN CIRCUITS WHICH, IN SUSCEPTIBLE INDIVIDUALS, ARE BELIEVED TO UNDERLIE THE TRANSITION TO, AND MAINTENANCE OF, AN ADDICTED STATE. THESE ADAPTATIONS CAN OCCUR AT THE CELLULAR, MOLECULAR, OR (EPI)GENETIC LEVEL AND ARE ASSOCIATED WITH SYNAPTIC PLASTICITY AND ALTERED GENE EXPRESSION, THE LATTER BEING MEDIATED VIA BOTH FACTORS AFFECTING TRANSLATION (EPIGENETICS) AND TRANSCRIPTION (NON CODING MICRORNAS) OF THE DNA OR RNA ITSELF. NEW ADVANCES USING TECHNIQUES SUCH AS OPTOGENETICS HAVE THE POTENTIAL TO INCREASE OUR UNDERSTANDING OF THE MICROCIRCUITRY MEDIATING ADDICTIVE BEHAVIOURS. HOWEVER, THE PROCESSES LEADING TO ADDICTION ARE COMPLEX AND MULTIFACTORIAL AND THUS WE FACE A MAJOR CONTEMPORARY CHALLENGE TO ELUCIDATE THE FACTORS IMPLICATED IN THE DEVELOPMENT AND MAINTENANCE OF AN ADDICTED STATE. 2012