1 1538 132 DNA METHYLATION IN ANIMAL MODELS OF PSYCHOSIS. SCHIZOPHRENIA (SZ) IS A DEBILITATING DISEASE THAT IMPACTS 1% OF THE POPULATION WORLDWIDE. ASSOCIATION STUDIES HAVE SHOWN THAT INHERITED GENETIC MUTATIONS ACCOUNT FOR A PORTION OF DISEASE RISK. HOWEVER, ENVIRONMENTAL FACTORS PLAY AN IMPORTANT ROLE IN THE PATHOPHYSIOLOGY OF THE DISEASE BY ALTERING CELLULAR EPIGENETIC MARKS AT THE LEVEL OF CHROMATIN. POSTMORTEM BRAIN STUDIES OF SZ SUBJECTS SUGGEST THAT THE DYNAMIC EQUILIBRIUM BETWEEN DNA METHYLATION AND DEMETHYLATION NETWORK COMPONENTS IS DISRUPTED AT THE LEVEL OF INDIVIDUAL SZ TARGET GENES. HEREIN, WE REVIEW THE ROLE OF DNA METHYLATION AND DEMETHYLATION IN THE CONTEXT OF WHAT IS CURRENTLY KNOWN REGARDING SZ. FURTHERMORE, WE DESCRIBE THE DEFICITS THAT ACCOMPANY TWO MOUSE MODELS OF SZ. THE CHRONIC METHIONINE MOUSE MODEL OF SZ IS PREDICATED ON THE ADMINISTRATION OF METHIONINE TO SZ PATIENTS AND CONTROLS IN THE CONTEXT OF CLINICAL STUDIES THAT WERE CARRIED OUT DURING THE 1960S AND 1970S. THE PRENATAL RESTRAINT STRESS MODEL OF SZ IS BASED ON A PROLONGED STRESS PARADIGM ADMINISTERED TO PREGNANT DAMS DURING GESTATION DAYS 7-21. THE ADULT OFFSPRING OF THESE DAMS SHOW VARIOUS BEHAVIORAL AND BIOCHEMICAL DEFICITS IN ADULTHOOD. BOTH MODELS ARE EPIGENETIC IN ORIGIN AND MIMIC THE POSITIVE AND NEGATIVE SYMPTOMS, AS WELL AS THE COGNITIVE ENDOPHENOTYPES COMMONLY OBSERVED IN SZ PATIENTS. WE ALSO DISCUSS THE UTILITY OF TYPICAL AND ATYPICAL ANTIPSYCHOTIC DRUGS IN ALLEVIATING THESE SYMPTOMS IN EACH MODEL. 2018 2 4390 45 MODELING THE MOLECULAR EPIGENETIC PROFILE OF PSYCHOSIS IN PRENATALLY STRESSED MICE. BASED ON POSTMORTEM BRAIN STUDIES, OUR OVERARCHING EPIGENETIC HYPOTHESIS IS THAT CHRONIC SCHIZOPHRENIA (SZ) IS A PSYCHOPATHOLOGICAL CONDITION INVOLVING DYSREGULATION OF THE DYNAMIC EQUILIBRIUM AMONG DNA METHYLATION/DEMETHYLATION NETWORK COMPONENTS AND THE EXPRESSION OF SZ TARGET GENES, INCLUDING GABAERGIC AND GLUTAMATERGIC GENES. SZ HAS A NATURAL COURSE, STARTING WITH A PRODROMAL PHASE, A FIRST EPISODE THAT OCCURS IN ADOLESCENTS OR IN YOUNG ADULTS, AND LATER DETERIORATION OVER THE ADULT YEARS. HENCE, THE EPIGENETIC STATUS AT EACH NEURODEVELOPMENTAL STAGE OF THE DISEASE CANNOT BE STUDIED JUST IN POSTMORTEM BRAIN OF CHRONIC SZ PATIENTS, BUT REQUIRES THE USE OF NEURODEVELOPMENTAL ANIMAL MODELS. WE HAVE DIRECTED THE FOCUS OF OUR RESEARCH TOWARD STUDYING THE EPIGENETIC SIGNATURE OF THE SZ BRAIN IN THE OFFSPRING OF DAMS STRESSED DURING PREGNANCY (PRS MICE). ADULT PRS MICE HAVE BEHAVIORAL DEFICITS REMINISCENT OF BEHAVIORS OBSERVED IN PSYCHOTIC PATIENTS. THE ADULT PRS BRAIN, LIKE THAT OF POSTMORTEM CHRONIC SZ PATIENTS, IS CHARACTERIZED BY A SIGNIFICANT INCREASE IN DNA METHYLTRANSFERASE 1, TET METHYLCYTOSINE DIOXYGENASE 1 (TET1), 5-METHYLCYTOSINE, AND 5-HYDROXYMETHYLCYTOSINE AT SZ CANDIDATE GENE PROMOTERS AND A REDUCTION IN THE EXPRESSION OF GLUTAMATERGIC AND GABAERGIC GENES. IN PRS MICE, MEASUREMENTS OF EPIGENETIC BIOMARKERS FOR SZ CAN BE ASSESSED AT DIFFERENT STAGES OF DEVELOPMENT WITH THE GOAL OF FURTHER ELUCIDATING THE PATHOPHYSIOLOGY OF THIS DISEASE AND PREDICTING TREATMENT RESPONSES AT SPECIFIC STAGES OF THE ILLNESS, WITH PARTICULAR ATTENTION TO EARLY DETECTION AND POSSIBLY EARLY INTERVENTION. 2014 3 252 29 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 4 4370 30 MIRNAS AND THEIR ROLE IN THE CORRELATION BETWEEN SCHIZOPHRENIA AND CANCER (REVIEW). SCHIZOPHRENIA (SZ) AND CANCER (CA) HAVE A BROAD SPECTRUM OF CLINICAL PHENOTYPES AND A COMPLEX BIOLOGICAL BACKGROUND, IMPLICATING A LARGE NUMBER OF GENETIC AND EPIGENETIC FACTORS. SZ IS A CHRONIC NEURODEVELOPMENTAL DISORDER SIGNIFIED BY AN INCREASE IN THE EXPRESSION OF APOPTOTIC MOLECULAR SIGNALS, WHEREAS CA IS CONVERSELY CHARACTERIZED BY AN INCREASE IN APPROPRIATE MOLECULAR SIGNALING THAT STIMULATES UNCONTROLLED CELL PROLIFERATION. THE RATHER LOW RISK OF DEVELOPING CA IN PATIENTS SUFFERING FROM SZ IS A HYPOTHESIS THAT IS STILL UNDER DEBATE. RECENT EVIDENCE HAS INDICATED THAT MICRORNAS (MIRNAS OR MIRS), A LARGE GROUP OF SMALL NON?CODING OLIGONOUCLEOTIDES, MAY PLAY A SIGNIFICANT ROLE IN THE DEVELOPMENT OF CA AND MAJOR PSYCHIATRIC DISORDERS, SUCH AS SZ, BIPOLAR DISORDER, AUTISM SPECTRUM DISORDERS, SUICIDALITY AND DEPRESSION, THROUGH THEIR INTERFERENCE WITH THE EXPRESSION OF MULTIPLE GENES. FOR INSTANCE, THE POSSIBLE ROLE OF LET?7, MIR?98 AND MIR?183 AS BIOMARKERS FOR CA AND SZ WAS INVESTIGATED IN OUR PREVIOUS RESEARCH STUDIES. THEREFORE, FURTHER INVESTIGATIONS ON THE EXPRESSION PROFILES OF THESE REGULATORY, SMALL RNA MOLECULES AND THE MOLECULAR PATHWAYS THROUGH WHICH THEY EXERT THEIR CONTROL MAY PROVIDE A PLAUSIBLE EXPLANATION AS TO WHETHER THERE IS A CORRELATION BETWEEN PSYCHIATRIC DISORDERS AND LOW RISK OF DEVELOPING CA. 2016 5 1810 29 EFFECTS OF ANTIPSYCHOTICS ON THE BDNF IN SCHIZOPHRENIA. BRAIN-DERIVED NEUROTROPIC FACTOR (BDNF) IS INVOLVED IN THE DEVELOPMENT OF THE BRAIN, AND LIKELY INFLUENCES THE NEUROPLASTICITY IN SCHIZOPHRENIA. BDNF IS ALSO BELIEVED TO INTERACT WITH OTHER NEUROTRANSMITTER SYSTEMS IMPLICATED IN SCHIZOPHRENIA, SUCH AS DOPAMINE, GLUTAMATE, SEROTONIN AND GABA. THEREFORE, BDNF IS A CANDIDATE GENE FOR SCHIZOPHRENIA. IN PAST DECADES, THE BLOOD (SERUM OR PLASMA) BDNF PROTEIN LEVELS AND BDNF GENE ALLELES AND GENOTYPES TO THE CLINICAL FEATURES OF SCHIZOPHRENIA, SUCH AS AGE OF ONSET, CLINICAL SUBTYPES, SYMPTOM SEVERITY, AND DRUG RESPONSE, HAVE BEEN EVALUATED AMONG DIFFERENT POPULATIONS. HOWEVER, THE RESULTS ARE STILL INCONSISTENT. FURTHER, DIFFERENT DRUGS HAVE BEEN REPORTED TO HAVE DIFFERENT EFFECTS ON BDNF PROTEIN LEVELS. A CROSS-SECTIONAL SURVEY REVEALED THAT SERUM BDNF LEVELS IN CHRONIC SCHIZOPHRENIC PATIENTS TREATED WITH CLOZAPINE EXCEEDED THOSE OF PATIENTS TREATED WITH RISPERIDONE OR WITH TYPICAL ANTIPSYCHOTICS. IN RECENT TIMES, BDNF EPIGENETIC STUDIES HAVE ALSO BEEN CONDUCTED IN CLINICAL STUDIES OF SCHIZOPHRENIA TO ADDRESS THE QUESTION OF WHY PATIENTS WITH THE SAME GENE GENOTYPE AND ALLELES HAVE DIFFERENT CLINICAL PRESENTATIONS. IN ADDITION, THE EFFECTS OF DIFFERENT ANTIPSYCHOTIC DRUGS ON GENE METHYLATION AND PROTEIN ACETYLATION HAVE ALSO BEEN REPORTED. IN CONCLUSION, MORE DATA ARE NEEDED REGARDING BDNF IN THE BRAIN AND IN PERIPHERAL BLOOD, INCLUDING PROTEIN LEVELS, SINGLE NUCLEOTIDE POLYMORPHISMS, EPIGENETIC REGULATION, AND CLINICAL DATA IN ORDER TO UNDERSTAND THE ROLE OF BDNF IN SCHIZOPHRENIA. 2013 6 4206 44 METABOTROPIC GLUTAMATE 2/3 RECEPTORS AND EPIGENETIC MODIFICATIONS IN PSYCHOTIC DISORDERS: A REVIEW. SCHIZOPHRENIA AND BIPOLAR DISORDER ARE CHRONIC PSYCHIATRIC DISORDERS, BOTH CONSIDERED AS "MAJOR PSYCHOSIS"; THEY ARE THOUGHT TO SHARE SOME PATHOGENETIC FACTORS INVOLVING A DYSFUNCTIONAL GENE X ENVIRONMENT INTERACTION. ALTERATIONS IN THE GLUTAMATERGIC TRANSMISSION HAVE BEEN SUGGESTED TO BE INVOLVED IN THE PATHOGENESIS OF PSYCHOSIS. OUR GROUP DEVELOPED AN EPIGENETIC MODEL OF SCHIZOPHRENIA ORIGINATED BY PRENATAL RESTRAINT STRESS (PRS) PARADIGM IN MICE. PRS MICE DEVELOPED SOME BEHAVIORAL ALTERATIONS OBSERVED IN SCHIZOPHRENIC PATIENTS AND CLASSIC ANIMAL MODELS OF SCHIZOPHRENIA, I.E. DEFICITS IN SOCIAL INTERACTION, LOCOMOTOR ACTIVITY AND PREPULSE INHIBITION. THEY ALSO SHOWED SPECIFIC CHANGES IN PROMOTER DNA METHYLATION ACTIVITY OF GENES RELATED TO SCHIZOPHRENIA SUCH AS REELIN, BDNF AND GAD67, AND ALTERED EXPRESSION AND FUNCTION OF MGLU2/3 RECEPTORS IN THE FRONTAL CORTEX. INTERESTINGLY, BEHAVIORAL AND MOLECULAR ALTERATIONS WERE REVERSED BY TREATMENT WITH MGLU2/3 AGONISTS. BASED ON THESE FINDINGS, WE SPECULATE THAT PHARMACOLOGICAL MODULATION OF THESE RECEPTORS COULD HAVE A GREAT IMPACT ON EARLY PHASE TREATMENT OF PSYCHOSIS TOGETHER WITH THE POSSIBILITY TO MODULATE SPECIFIC EPIGENETIC KEY PROTEIN INVOLVED IN THE DEVELOPMENT OF PSYCHOSIS. IN THIS REVIEW, WE WILL DISCUSS IN MORE DETAILS THE SPECIFIC FEATURES OF THE PRS MICE AS A SUITABLE EPIGENETIC MODEL FOR MAJOR PSYCHOSIS. WE WILL THEN FOCUS ON KEY PROTEINS OF CHROMATIN REMODELING MACHINERY AS POTENTIAL TARGET FOR NEW PHARMACOLOGICAL TREATMENT THROUGH THE ACTIVATION OF METABOTROPIC GLUTAMATE RECEPTORS. 2016 7 5645 29 SEX DEPENDENT ALTERATION OF EPIGENETIC MARKS AFTER CHRONIC MORPHINE TREATMENT IN MICE ORGANS. EPIGENETIC MARKS MAY BE ALSO AFFECTED BY SEVERAL FACTORS, SUCH AS AGE, LIFESTYLE, EARLY LIFE EXPERIENCES AND EXPOSURE TO CHEMICALS OR DRUGS, SUCH AS OPIOIDS. PREVIOUS STUDIES HAVE FOCUSED ON HOW MORPHINE EPIGENETICALLY REGULATES DIFFERENT REGIONS OF THE BRAIN THAT ARE IMPLICATED IN TOLERANCE, DEPENDENCE AND OTHER PSYCHIATRIC DISORDERS MORE RELATED TO THE PHYSIO-PATHOLOGICAL EFFECTS OF OPIOIDS. NEVERTHELESS, A SIGNIFICANT KNOWLEDGE GAP REMAINS REGARDING THE EFFECT OF CHRONIC TREATMENT ON OTHER ORGANS AND BIOLOGICAL SYSTEMS. THEREFORE, THE AIM OF THIS WORK IS TO INCREASE OUR KNOWLEDGE ABOUT THE IMPACT OF CHRONIC MORPHINE EXPOSURE ON DNA METHYLATION AND HISTONE MODIFICATION LEVELS IN EACH OF THE ORGANS OF MALE AND FEMALE MODEL MICE IN VIVO. OUR RESULTS REVEAL, FOR THE FIRST TIME, THAT CHRONIC MORPHINE TREATMENT INDUCED CHANGES IN DNA METHYLATION/HYDROXYMETHYLATION AND HISTONE MODIFICATION IN-VIVO AT THE SYSTEMIC LEVEL, REVEALING A POTENTIAL PHYSIOLOGICAL EFFECT ON THE REGULATION OF GENE EXPRESSION. NOTABLY, MORPHINE-INDUCED EPIGENETIC MODIFICATION OCCURS IN A SEX-DEPENDENT MANNER, REVEALING THE EXISTENCE OF DIFFERENT UNDERLYING MECHANISMS OF EPIGENETIC MODIFICATION IN MALE AND FEMALE MICE. 2021 8 6184 42 THE IMPACT OF ENVIRONMENTAL FACTORS IN SEVERE PSYCHIATRIC DISORDERS. DURING THE LAST DECADES, SCHIZOPHRENIA HAS BEEN REGARDED AS A DEVELOPMENTAL DISORDER. THE NEURODEVELOPMENTAL HYPOTHESIS PROPOSES SCHIZOPHRENIA TO BE RELATED TO GENETIC AND ENVIRONMENTAL FACTORS LEADING TO ABNORMAL BRAIN DEVELOPMENT DURING THE PRE- OR POSTNATAL PERIOD. FIRST DISEASE SYMPTOMS APPEAR IN EARLY ADULTHOOD DURING THE SYNAPTIC PRUNING AND MYELINATION PROCESS. META-ANALYSES OF STRUCTURAL MRI STUDIES REVEALING HIPPOCAMPAL VOLUME DEFICITS IN FIRST-EPISODE PATIENTS AND IN THE LONGITUDINAL DISEASE COURSE CONFIRM THIS HYPOTHESIS. APART FROM THE INFLUENCE OF RISK GENES IN SEVERE PSYCHIATRIC DISORDERS, ENVIRONMENTAL FACTORS MAY ALSO IMPACT BRAIN DEVELOPMENT DURING THE PERINATAL PERIOD. SEVERAL ENVIRONMENTAL FACTORS SUCH AS ANTENATAL MATERNAL VIRUS INFECTIONS, OBSTETRIC COMPLICATIONS ENTAILING HYPOXIA AS COMMON FACTOR OR STRESS DURING NEURODEVELOPMENT HAVE BEEN IDENTIFIED TO PLAY A ROLE IN SCHIZOPHRENIA AND BIPOLAR DISORDER, POSSIBLY CONTRIBUTING TO SMALLER HIPPOCAMPAL VOLUMES. IN MAJOR DEPRESSION, PSYCHOSOCIAL STRESS DURING THE PERINATAL PERIOD OR IN ADULTHOOD IS AN IMPORTANT TRIGGER. IN ANIMAL STUDIES, CHRONIC STRESS OR REPEATED ADMINISTRATION OF GLUCOCORTICOIDS HAVE BEEN SHOWN TO INDUCE DEGENERATION OF GLUCOCORTICOID-SENSITIVE HIPPOCAMPAL NEURONS AND MAY CONTRIBUTE TO THE PATHOPHYSIOLOGY OF AFFECTIVE DISORDERS. EPIGENETIC MECHANISMS ALTERING THE CHROMATIN STRUCTURE SUCH AS HISTONE ACETYLATION AND DNA METHYLATION MAY MEDIATE EFFECTS OF ENVIRONMENTAL FACTORS TO TRANSCRIPTIONAL REGULATION OF SPECIFIC GENES AND BE A PROMINENT FACTOR IN GENE-ENVIRONMENTAL INTERACTION. IN ANIMAL MODELS, GENE-ENVIRONMENTAL INTERACTION SHOULD BE INVESTIGATED MORE INTENSELY TO UNRAVEL PATHOPHYSIOLOGICAL MECHANISMS. THESE FINDINGS MAY LEAD TO NEW THERAPEUTIC STRATEGIES INFLUENCING EPIGENETIC TARGETS IN SEVERE PSYCHIATRIC DISORDERS. 2014 9 4642 37 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 10 2011 39 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 11 4276 31 MICROGLIA FROM OFFSPRING OF DAMS WITH ALLERGIC ASTHMA EXHIBIT EPIGENOMIC ALTERATIONS IN GENES DYSREGULATED IN AUTISM. DYSREGULATION IN IMMUNE RESPONSES DURING PREGNANCY INCREASES THE RISK OF A HAVING A CHILD WITH AN AUTISM SPECTRUM DISORDER (ASD). ASTHMA IS ONE OF THE MOST COMMON CHRONIC DISEASES AMONG PREGNANT WOMEN, AND SYMPTOMS OFTEN WORSEN DURING PREGNANCY. WE RECENTLY DEVELOPED A MOUSE MODEL OF MATERNAL ALLERGIC ASTHMA (MAA) THAT INDUCES CHANGES IN SOCIABILITY, REPETITIVE, AND PERSEVERATIVE BEHAVIORS IN THE OFFSPRING. SINCE EPIGENETIC CHANGES HELP A STATIC GENOME ADAPT TO THE MATERNAL ENVIRONMENT, ACTIVATION OF THE IMMUNE SYSTEM MAY EPIGENETICALLY ALTER FETAL MICROGLIA, THE BRAIN'S RESIDENT IMMUNE CELLS. WE THEREFORE TESTED THE HYPOTHESIS THAT EPIGENOMIC ALTERATIONS TO MICROGLIA MAY BE INVOLVED IN BEHAVIORAL ABNORMALITIES OBSERVED IN MAA OFFSPRING. WE USED THE GENOME-WIDE APPROACHES OF WHOLE GENOME BISULFITE SEQUENCING TO EXAMINE DNA METHYLATION AND RNA SEQUENCING TO EXAMINE GENE EXPRESSION IN MICROGLIA FROM JUVENILE MAA OFFSPRING. DIFFERENTIALLY METHYLATED REGIONS WERE ENRICHED FOR IMMUNE SIGNALING PATHWAYS AND IMPORTANT MICROGLIAL DEVELOPMENTAL TRANSCRIPTION FACTOR BINDING MOTIFS. DIFFERENTIAL EXPRESSION ANALYSIS IDENTIFIED GENES INVOLVED IN CONTROLLING MICROGLIAL SENSITIVITY TO THE ENVIRONMENT AND SHAPING NEURONAL CONNECTIONS IN THE DEVELOPING BRAIN. DIFFERENTIALLY EXPRESSED GENES SIGNIFICANTLY OVERLAPPED GENES WITH ALTERED EXPRESSION IN HUMAN ASD CORTEX, SUPPORTING A ROLE FOR MICROGLIA IN THE PATHOGENESIS OF ASD. 2018 12 4093 33 MATERNAL SEPARATION FOLLOWED BY CHRONIC MILD STRESS IN ADULTHOOD IS ASSOCIATED WITH CONCERTED EPIGENETIC REGULATION OF AP-1 COMPLEX GENES. DEPRESSION IS ONE OF THE MOST PREVALENT MENTAL DISEASES WORLDWIDE. PATIENTS WITH PSYCHIATRIC DISEASES OFTEN HAVE A HISTORY OF CHILDHOOD NEGLECT, INDICATING THAT EARLY-LIFE EXPERIENCES PREDISPOSE TO PSYCHIATRIC DISEASES IN ADULTHOOD. TWO STRONG MODELS WERE USED IN THE PRESENT STUDY: THE MATERNAL SEPARATION/EARLY DEPRIVATION MODEL (MS) AND THE CHRONIC MILD STRESS MODEL (CMS). IN BOTH MODELS, WE FOUND CHANGES IN THE EXPRESSION OF A NUMBER OF GENES SUCH AS CREB AND NPY. STRIKINGLY, THERE WAS A CLEAR REGULATION OF EXPRESSION OF FOUR GENES INVOLVED IN THE AP-1 COMPLEX: C-FOS, C-JUN, FOSB, AND JUN-B. INTERESTINGLY, DIFFERENT EXPRESSION LEVELS WERE OBSERVED DEPENDING ON THE MODEL, WHEREAS THE COMBINATION OF THE MODELS RESULTED IN A NORMAL LEVEL OF GENE EXPRESSION. THE EFFECTS OF MS AND CMS ON GENE EXPRESSION WERE ASSOCIATED WITH DISTINCT HISTONE METHYLATION/ACETYLATION PATTERNS OF ALL FOUR GENES. THE EPIGENETIC CHANGES, LIKE GENE EXPRESSION, WERE ALSO DEPENDENT ON THE SPECIFIC STRESSOR OR THEIR COMBINATION. THE OBTAINED RESULTS SUGGEST THAT SINGLE LIFE EVENTS LEAVE A MARK ON GENE EXPRESSION AND THE EPIGENETIC SIGNATURE OF GENE PROMOTERS, BUT A COMBINATION OF DIFFERENT STRESSORS AT DIFFERENT LIFE STAGES CAN FURTHER CHANGE GENE EXPRESSION THROUGH EPIGENETIC FACTORS, POSSIBLY CAUSING THE LONG-LASTING ADVERSE EFFECTS OF STRESS. 2021 13 6174 42 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 14 2598 25 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 15 2472 35 EPIGENETIC TRANSMISSION OF THE IMPACT OF EARLY STRESS ACROSS GENERATIONS. BACKGROUND: TRAUMATIC EXPERIENCES IN EARLY LIFE ARE RISK FACTORS FOR THE DEVELOPMENT OF BEHAVIORAL AND EMOTIONAL DISORDERS. SUCH DISORDERS CAN PERSIST THROUGH ADULTHOOD AND HAVE OFTEN BEEN REPORTED TO BE TRANSMITTED ACROSS GENERATIONS. METHODS: TO INVESTIGATE THE TRANSGENERATIONAL EFFECT OF EARLY STRESS, MICE WERE EXPOSED TO CHRONIC AND UNPREDICTABLE MATERNAL SEPARATION FROM POSTNATAL DAY 1 TO 14. RESULTS: WE SHOW THAT CHRONIC AND UNPREDICTABLE MATERNAL SEPARATION INDUCES DEPRESSIVE-LIKE BEHAVIORS AND ALTERS THE BEHAVIORAL RESPONSE TO AVERSIVE ENVIRONMENTS IN THE SEPARATED ANIMALS WHEN ADULT. MOST OF THE BEHAVIORAL ALTERATIONS ARE FURTHER EXPRESSED BY THE OFFSPRING OF MALES SUBJECTED TO MATERNAL SEPARATION, DESPITE THE FACT THAT THESE MALES ARE REARED NORMALLY. CHRONIC AND UNPREDICTABLE MATERNAL SEPARATION ALSO ALTERS THE PROFILE OF DNA METHYLATION IN THE PROMOTER OF SEVERAL CANDIDATE GENES IN THE GERMLINE OF THE SEPARATED MALES. COMPARABLE CHANGES IN DNA METHYLATION ARE ALSO PRESENT IN THE BRAIN OF THE OFFSPRING AND ARE ASSOCIATED WITH ALTERED GENE EXPRESSION. CONCLUSIONS: THESE FINDINGS HIGHLIGHT THE NEGATIVE IMPACT OF EARLY STRESS ON BEHAVIORAL RESPONSES ACROSS GENERATIONS AND ON THE REGULATION OF DNA METHYLATION IN THE GERMLINE. 2010 16 5649 26 SEX DIFFERENCES IN PSYCHOSTIMULANT ABUSE: IMPLICATIONS FOR ESTROGEN RECEPTORS AND HISTONE DEACETYLASES. SUBSTANCE ABUSE IS A CHRONIC PATHOLOGICAL DISORDER THAT NEGATIVELY AFFECTS MANY HEALTH AND NEUROLOGICAL PROCESSES. A GROWING BODY OF LITERATURE HAS REVEALED GENDER DIFFERENCES IN SUBSTANCE USE. COMPARED TO MEN, WOMEN DISPLAY DISTINCT DRUG-USE PHENOTYPES ACCOMPANIED BY RECOVERY AND REHABILITATION DISPARITIES. THESE OBSERVATIONS HAVE LED TO THE NOTION THAT SEX-DEPENDENT SUSCEPTIBILITIES EXIST ALONG THE PROGRESSION TO ADDICTION. WITHIN THIS SCOPE, NEUROADAPTATIONS FOLLOWING PSYCHOSTIMULANT EXPOSURE ARE THOUGHT TO BE DISTINCT FOR EACH SEX. THIS REVIEW SUMMARIZES CLINICAL FINDINGS AND ANIMAL RESEARCH REPORTING SEX DIFFERENCES IN THE SUBJECTIVE AND BEHAVIORAL RESPONSES TO COCAINE, METHAMPHETAMINE, AND NICOTINE. THIS DISCUSSION IS FOLLOWED BY AN EXAMINATION OF EPIGENETIC AND MOLECULAR ALTERATIONS IMPLICATED IN THE ADDICTION PROCESS. SPECIAL CONSIDERATION IS GIVEN TO HISTONE DEACETYLASES AND ESTROGEN RECEPTOR-MEDIATED GENE EXPRESSION. 2022 17 110 30 A ROLE FOR ACTIVITY-DEPENDENT EPIGENETICS IN THE DEVELOPMENT AND TREATMENT OF MAJOR DEPRESSIVE DISORDER. CHRONIC STRESSORS, DURING DEVELOPMENTAL SENSITIVE PERIODS AND BEYOND, CONTRIBUTE TO THE RISK OF DEVELOPING PSYCHIATRIC CONDITIONS, INCLUDING MAJOR DEPRESSIVE DISORDER (MDD). EPIGENETIC MECHANISMS INCLUDING DNA METHYLATION AND HISTONE MODIFICATIONS, AT KEY STRESS RESPONSE AND NEUROTROPHIN GENES, ARE INCREASINGLY IMPLICATED IN MEDIATING THIS RISK. ALTHOUGH THE EXACT MECHANISMS THROUGH WHICH STRESSFUL ENVIRONMENTAL STIMULI ALTER THE EPIGENOME ARE STILL UNCLEAR, RESEARCH FROM THE LEARNING AND MEMORY FIELDS INDICATES THAT EPIGENOMIC MARKS CAN BE ALTERED, AT LEAST IN PART, THROUGH CALCIUM-DEPENDENT SIGNALING CASCADES IN DIRECT RESPONSE TO NEURONAL ACTIVITY. IN THIS REVIEW, WE HIGHLIGHT KEY FINDINGS FROM THE STRESS, MDD, AND LEARNING AND MEMORY FIELDS TO PROPOSE A MODEL WHERE STRESS REGULATES DOWNSTREAM CELLULAR FUNCTIONING THROUGH ACTIVITY-DEPENDENT EPIGENETIC CHANGES. FURTHERMORE, WE SUGGEST THAT BOTH TYPICAL AND NOVEL ANTIDEPRESSANT TREATMENTS MAY EXERT POSITIVE INFLUENCE THROUGH SIMILAR, ACTIVITY-DEPENDENT PATHWAYS. 2018 18 5164 33 PRECLINICAL AND CLINICAL EVIDENCE OF DNA METHYLATION CHANGES IN RESPONSE TO TRAUMA AND CHRONIC STRESS. EXPOSURE TO CHRONIC STRESS, EITHER REPEATED SEVERE ACUTE OR MODERATE SUSTAINED STRESS, IS ONE OF THE STRONGEST RISK FACTORS FOR THE DEVELOPMENT OF PSYCHOPATHOLOGIES SUCH AS POST-TRAUMATIC STRESS DISORDER AND DEPRESSION. CHRONIC STRESS IS LINKED WITH SEVERAL LASTING BIOLOGICAL CONSEQUENCES, PARTICULARLY TO THE STRESS ENDOCRINE SYSTEM BUT ALSO AFFECTING INTERMEDIATE PHENOTYPES SUCH AS BRAIN STRUCTURE AND FUNCTION, IMMUNE FUNCTION, AND BEHAVIOR. ALTHOUGH GENETIC PREDISPOSITION CONFERS A PROPORTION OF THE RISK, THE MOST RELEVANT MOLECULAR MECHANISMS DETERMINING THOSE SUSCEPTIBLE AND RESILIENT TO THE EFFECTS OF STRESS AND TRAUMA MAY BE EPIGENETIC. EPIGENETICS REFERS TO THE MECHANISMS THAT REGULATE GENOMIC INFORMATION BY DYNAMICALLY CHANGING THE PATTERNS OF TRANSCRIPTION AND TRANSLATION OF GENES. MOUNTING EVIDENCE FROM PRECLINICAL RODENT AND CLINICAL POPULATION STUDIES STRONGLY SUPPORT THAT EPIGENETIC MODIFICATIONS CAN OCCUR IN RESPONSE TO TRAUMATIC AND CHRONIC STRESS. HERE, WE DISCUSS THIS LITERATURE EXAMINING STRESS-INDUCED EPIGENETIC CHANGES IN PRECLINICAL MODELS AND CLINICAL COHORTS OF STRESS AND TRAUMA OCCURRING EARLY IN LIFE OR IN ADULTHOOD. WE HIGHLIGHT THAT A COMPLEX RELATIONSHIP BETWEEN THE TIMING OF ENVIRONMENTAL STRESSORS AND GENETIC PREDISPOSITIONS LIKELY MEDIATE THE RESPONSE TO CHRONIC STRESS OVER TIME, AND THAT A BETTER UNDERSTANDING OF EPIGENETIC CHANGES IS NEEDED BY FURTHER INVESTIGATIONS IN LONGITUDINAL AND POSTMORTEM BRAIN CLINICAL COHORTS. 2017 19 4277 38 MICROGLIA SEQUELAE: BRAIN SIGNATURE OF INNATE IMMUNITY IN SCHIZOPHRENIA. SCHIZOPHRENIA IS A PSYCHIATRIC DISORDER WITH SIGNIFICANT IMPACT ON INDIVIDUALS AND SOCIETY. THE CURRENT PHARMACOLOGIC TREATMENT, WHICH PRINCIPALLY ALLEVIATES PSYCHOSIS, IS FOCUSED ON NEUROTRANSMITTERS MODULATION, RELYING ON DRUGS WITH SEVERE SIDE EFFECTS AND INEFFECTIVENESS IN A SIGNIFICANT PERCENTAGE OF CASES. THEREFORE, AND DUE TO DIFFICULTIES INHERENT TO DIAGNOSIS AND TREATMENT, IT IS VITAL TO REASSESS ALTERNATIVE CELLULAR AND MOLECULAR DRUG TARGETS. DISTINCT RISK FACTORS - GENETIC, DEVELOPMENTAL, EPIGENETIC, AND ENVIRONMENTAL - HAVE BEEN ASSOCIATED WITH DISEASE ONSET AND PROGRESSION, GIVING RISE TO THE PROPOSAL OF DIFFERENT PATHOPHYSIOLOGICAL MECHANISMS AND PUTATIVE PHARMACOLOGICAL TARGETS. IMMUNITY IS INVOLVED AND, PARTICULARLY MICROGLIA - INNATE IMMUNE CELLS OF THE CENTRAL NERVOUS SYSTEM, CRITICALLY INVOLVED IN BRAIN DEVELOPMENT - HAVE CAPTURED ATTENTION AS CELLULAR PLAYERS. MICROGLIA UNDERGO MARKED MORPHOLOGIC AND FUNCTIONAL ALTERATIONS IN THE HUMAN DISEASE, AS WELL AS IN ANIMAL MODELS OF SCHIZOPHRENIA, AS REPORTED IN SEVERAL ORIGINAL PAPERS. WE CLUSTER THE MAIN FINDINGS OF CLINICAL STUDIES BY GROUPS OF PATIENTS: (1) AT ULTRA-HIGH RISK OF PSYCHOSIS, (2) WITH A FIRST EPISODE OF PSYCHOSIS OR RECENT-ONSET SCHIZOPHRENIA, AND (3) WITH CHRONIC SCHIZOPHRENIA; IN TRANSLATIONAL STUDIES, WE HIGHLIGHT THE TIME WINDOW OF APPEARANCE OF PARTICULAR MICROGLIA ALTERATIONS IN THE MOST WELL STUDIED ANIMAL MODEL IN THE FIELD (MATERNAL IMMUNE ACTIVATION). THE ORGANIZATION OF CLINICAL AND TRANSLATIONAL FINDINGS BASED ON SCHIZOPHRENIA-ASSOCIATED MICROGLIA CHANGES IN DIFFERENT PHASES OF THE DISEASE COURSE MAY HELP DEFINING A TEMPORAL PATTERN OF MICROGLIA CHANGES AND MAY DRIVE THE DESIGN OF NOVEL THERAPEUTIC STRATEGIES. 2022 20 1981 32 EPIGENETIC ALTERATIONS IN DNA AND HISTONE MODIFICATIONS CAUSED BY DEPRESSION AND ANTIDEPRESSANT DRUGS: LESSONS FROM THE RODENT MODELS. EPIGENETIC MODIFICATIONS REGULATE CHROMATIN FOLDING AND FUNCTION. EPIGENETIC MECHANISMS REGULATE TRANSCRIPTION MEDIATING EFFECTS OF VARIOUS STIMULI ON GENE EXPRESSION. THESE MECHANISMS ARE INVOLVED IN TRANSCRIPTIONAL CONTROL IN VARIOUS PHYSIOLOGICAL AND PATHOLOGICAL CONDITIONS INCLUDING NEUROPSYCHIATRIC DISORDERS AND BEHAVIORAL ABNORMALITIES SUCH AS DEPRESSION. IN RODENTS, EXPOSURE TO CHRONIC SOCIAL STRESS WAS SHOWN TO INDUCE BEHAVIORAL IMPAIRMENTS AND MEMORY/LEARNING DEFICITS THAT RESEMBLE DEPRESSIVE-LIKE PHENOTYPE IN HUMANS. THE RODENT MODELS OF CHRONIC STRESS WERE WIDELY USED TO STUDY MOLECULAR MECHANISMS OF DEPRESSION. IN THESE MODELS, EARLY EXPOSURE TO CHRONIC STRESS SUCH AS PRENATAL OR POSTNATAL STRESS INDUCES LONG-TERM HYPERACTIVE STRESS RESPONSES, BEHAVIORAL ABNORMALITIES, AND FUNCTIONAL IMPAIRMENTS IN BRAIN FUNCTION THAT PERSIST IN ADULTHOOD. FURTHERMORE, THESE ALTERATIONS CAN BE TRANSMITTED TO OFFSPRING OF CHRONICALLY STRESSED ANIMALS ACROSS SEVERAL GENERATIONS. MOLECULAR STUDIES IN ANIMAL MODELS SHOWED THAT CHRONIC STRESS INDUCES STABLE EPIGENETIC CHANGES IN SPECIFIC BRAIN REGIONS, PRIMARILY IN THE LIMBIC SYSTEM. THESE CHANGES LEAD TO LONG-LASTING ABNORMALITIES IN BEHAVIOR THAT PERSIST IN ADULTHOOD AND CAN BE TRANSMITTED TO OFFSPRING. TREATMENT WITH EPIGENETICALLY ACTIVE ANTIDEPRESSANTS DISRUPTS THE ABNORMAL STRESS-INDUCED EPIGENETIC PROGRAMMING AND PROVIDES EPIGENETIC PATTERNS THAT RESEMBLE EPIGENETIC BACKGROUND OF STRESS RESILIENT INDIVIDUALS. 2017