High density electroencephalographic (EEG) measures were used to assess the effects of acute delta 9-tetrahyrdrocannabidol (THC) administration on extinction of conditioned fear responses. Fear conditioning was initiated using a differential classical conditioning paradigm that paired an aversive unconditioned stimulus (shock) with a signaling stimulus (CS+), whereas another stimulus served as a safety signal (CS-). Evoked potentials, induced event-related spectral perturbations (ERSP), and associated intertrial coherence (ITC) measures were used to quantify the acquisition and extinction of conditioned fear responses. Participants (N = 10 males) exhibited conditioning to the CS+ across fear acquisition training, as reflected by greater late positive (posterior sites) and late negative (anterior sites) potential amplitude to the CS+ relative to the CS-. Acute administration of THC facilitated extinction of the conditioned response to the CS+ relative to placebo, as reflected by greater LPP and LNP amplitude to the CS+ relative to the CS- in the placebo, but not THC condition. ERSP analyses suggest the lack of difference between CS+ and CS- ERP amplitude may be partially explained by a shifting of attention from external stimuli to internal processing in the THC condition. However, relative to placebo, THC administration also increased the amplitude of some measures of the conditioned response (LNP) to the CS-, suggesting a generalization of fear or lack of discrimination in this condition.

abstract: Post-Traumatic Stress Disorder (PTSD) is characterized by intrusive memories from a traumatic event. Current therapies rarely lead to complete remission. PTSD can be modeled in rodents using chronic stress (creating vulnerable phenotype) combined with fear conditioning (modeling a traumatic experience), resulting in attenuated extinction learning and impaired recall of extinction. Studies typically investigate cognition soon after chronic stress ends; however, as days and weeks pass (“rest” period) some cognitive functions may improve compared to soon after stress. Whether a rest period between chronic stress and fear conditioning/extinction would lead to improvements is unclear. In Chapter 2, male rats were chronically stressed by restraint (6hr/d/21d), a reliable method to produce cognitive changes, or assigned to a non-stressed control group (CON). After chronic stress ended, fear conditioning occurred within a day (STR-IMM), or after three (STR-R3) or six weeks (STR-R6). During the first three extinction trials, differences emerged in fear to the non-shock context: STR-R3/R6 showed significantly less fear to the context than did STR-IMM or CON. Differences were unlikely attributable to generalization or to second-order conditioning. Therefore, a rest period following chronic stress may lead to improved fear extinction and discrimination between the conditioned stimulus and environment. In Chapter 3, the infralimbic cortex (IL) was investigated due to the IL’s importance in fear extinction. Rats were infused with chemogenetics to target IL glutamatergic neurons and then assigned to CON, STR-IMM or STR-R3. During the rest period of STR-R3 and the restraint for STR-IMM, the IL was inhibited using CNO (1mg/kg BW, i.p., daily), which ended before behavioral testing. STR-R3 with IL inhibition failed to demonstrate a tone-shock association as spontaneous recovery was not observed. CON with IL inhibition behaved somewhat like STR-IMM; freezing to the extinction context was enhanced. Consequently, inhibiting IL function during the rest period following chronic stress was particularly disruptive for learning in STR-R3, impaired freezing to a safe context for CON, and had no effect in STR-IMM. These studies show that time since the end of chronic stress (recently ended or with a delay) can interact with IL functioning to modify fear learning and response. / Dissertation/Thesis / Doctoral Dissertation Psychology 2020

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Posttraumatic stress disorder (PTSD) is a severe, chronic and debilitating psychiatric disorder that can present after the experience of a life-threatening traumatic event. D-cycloserine (DCS), a partial N-methyl-D-aspartate (NMDA) receptor agonist, has been found to augment cognitive behavioural therapy by facilitating fear extinction; however, the precise mechanisms whereby DCS ameliorates fear triggered by a traumatic context remains to be fully elucidated. This study aimed to (i) identify the molecular mechanisms of intrahippocampally administered DCS in facilitating fear extinction in a rat model of PTSD by investigating gene expression profiles in the left dorsal hippocampus (LDH) of male Sprague Dawley rats and (ii) determine whether microRNA (miRNA) expression and DNA methylation mediated these gene expression changes. An adapted version of the PTSD animal model described by Siegmund and Wotjak (2007) was utilised. The total number of 120 rats were grouped into four experimental groups (of 30 rats per group) based on fear conditioning and the intrahippocampal administration of either DCS or saline: (1) fear conditioned + intrahippocampal saline administration (FS), (2) fear conditioned + intrahippocampal DCS administration (FD), (3) control + intrahippocampal saline administration (CS) and (4) control + intrahippocampal DCS administration (CD). Behavioural tests (the light/dark [L/D] avoidance test, forced swim test and open field test) were conducted to assess anxiety and PTSD-like behaviours. The L/D avoidance test was the most sensitive behavioural test of anxiety and was subsequently used to differentiate maladapted (animals that displayed anxiety-like behaviour) and well-adapted (animals that did not display anxiety-like behaviour) subgroups. In order to identify genes that were differentially expressed between FS maladapted (FSM) (n = 6) vs. FD well-adapted (FDW) (n = 6) groups, RNA sequencing was performed on the Illumina HiSeq 2000 which generated more than 60 million reads per sample. This was followed by subsequent bioinformatics analyses (using the software programs TopHat, Bowtie, Cuffdiff and Bio-Ontological Relationship Graph (BORG) database (that identifies genes that may be biologically relevant) to identify biologically relevant differentially expressed genes between the treatment groups. Epigenetic mechanisms mediating observed differences in gene expression were investigated by conducting DNA methylation and miRNAseq analyses in the FDW and FSM experimental groups. DNA methylation was investigated using real-time quantitative PCR (qPCR) amplification followed by high resolution melt analysis on the Rotor-GeneTM 6000. Differences in miRNA expression levels between the FDW and FSM groups were investigated by sequencing the miRNA fraction on the MiSeq platform. The bioinformatics pipeline used to analyse the RNAseq data identified 93 genes that were significantly downregulated in the FDW group compared to the FSM group. Forty-two of these genes were predicted to be biologically relevant (based on BORG analysis). Integrative network analyses revealed subsets of differentially expressed genes common across biological functions, pathways and disorders. The co-administration of DCS and behavioural fear extinction downregulated immune system genes and genes that transcribe proinflammatory and oxidative stress molecules. These molecules mediate neuroinflammation and subsequently cause neuronal damage. DCS also regulated genes involved in learning and memory processes. Additionally, a subset of the genes, which have been found to be associated with disorders that commonly co-occur with PTSD (such as cardiovascular disease, metabolic disease, Alzheimer‘s and Parkinson‘s disease), was downregulated by the co-administration of DCS and behavioural fear extinction. In order to determine whether real-time qPCR analysis would be sensitive enough to detect differential expression in those genes found to be differentially expressed in RNAseq analysis, the expression of nine genes was analysed using SYBR Green qPCR technology. In the LDH, six of the nine genes were found to be differentially expressed between FDW and FSM groups and one gene, matrix metallopeptidase 9 (MMP9), was observed to be differentially expressed between these two groups in the blood. Three of the nine genes for which differential expression levels were investigated using SYBR Green real-time qPCR, contained CpG islands and were used for CpG island DNA methylation analysis. Results indicated that CpG island DNA methylation did not mediate differential gene expression of TRH, NPY or MT2A. Bioinformatics analysis of miRNAseq data identified 23 miRNAs that were differentially expressed between the FDW and FSM groups. Several of these miRNAs have previously been found to be involved in brain development and behavioural measures of anxiety. Furthermore, functional luciferase analysis indicated that the upregulation of rno-mi31a-5p could have facilitated the downregulation of interleukin 1 receptor antagonist gene (IL1RN) as detected in RNAseq. RNAseq and miRNAseq analyses in this PTSD animal model identified differentially expressed genes and miRNAs that serve to broaden our understanding of the mechanism whereby DCS facilitates fear extinction. To this end, immune system genes and genes transcribing proinflammatory and oxidative stress molecules were among the genes that were found to be differentially expressed between the FDW and FSM groups. Based on the results obtained, it can be hypothesised that DCS attenuates neuroinflammation and subsequent neuronal damage, and also regulates genes involved in learning and memory processes. Concomitantly, these gene expression alterations mediate optimal neuronal functioning, plasticity, learning and memory (such as fear extinction memory) which contribute to the fear extinction process. Furthermore, biologically relevant differentially expressed genes that were associated with DCS facilitation of fear extinction and with other chronic medical conditions, such as cardiovascular disease and metabolic diseases, might help to explain the co-occurrence of these disorders with PTSD. In conclusion, Identifying the molecular underpinnings of DCS-mediated fear extinction brings us closer to understanding the process of fear extinction and could, in future work be used to explore novel therapeutic targets to effectively treat PTSD and related disorders. / AFRIKAANSE OPSOMMING: Posttraumatiese stressindroom is 'n ernstige, kroniese aftakelende psigiatriese toestand wat kan ontwikkel na 'n lewensgevaarlike traumatiese gebeurtenis. Daar is bevind dat die gesamentlike toediening van D-sikloserien (DCS), 'n N-metiel-D-aspartaat (NMDA) reseptor agonis, en kognitiewe gedragsterapie effektief is in die bemiddeling van vrees uitwissing; maar die presiese meganisme waar deur DCS die vrees wat deur 'n traumatiese konteks ontlok word verminder, is egter onduidelik. Hierdie studie het beoog om (i) die molekulêre meganismes te identifiseer waardeur intra-hippokampaal toegediende DCS vrees uitwissing fasiliteer, in 'n rot model van posttraumatiese stressindroom, deur geen uitdrukkingsprofiele in the linker dorsale hippokampus (LDH) van manlike Sprague Dawley rotte te ondersoek en (ii) om te bepaal of mikroRNA (miRNA) uitdrukking en DNA metilering die veranderinge in geen uitdrukking bemiddel het. 'n Gewysigde weergawe van die posttraumatiese stressindroom diere model, beskryf deur Siegmund en Wotjak (2007), was gebruik tydens die studie. Rotte was in vier groepe verdeel, vrees kondisionering + soutwater (FS), vrees kondisionering + DCS (FD), kontrole + soutwater (CS) en kontrole + DCS (CD). Gedragstoetse was uitgevoer om angstige, vreesvolle en posttraumatiese stressindroom-tipe gedrag te evalueer. Gedurende die lig/donker (L/D) vermydingstoets het die FS groep aansienlik meer tyd in die donker kompartement deurgebring ('n indikasie van vreesvolle gedrag) in vergelyking met die CS en die FD groepe wat meer tyd in die verligte kompartement deurgebring het ('n indikasie van vreeslose gedrag). Die L/D toets was die mees sensitiewe gedragstoets vir angstige en vreesvolle gedrag en was gevolglik gebruik om die diere te sub-groepeer in wanaangepaste (diere wat angstige en vreesvolle gedrag vertoon het) en goedaangepaste (diere wat nie angstige en vreesvolle gedrag vertoon het nie) subgroepe. Nuwe generasie RNA volgordebepaling (RNAseq) van die LDH RNA en daaropvolgende bioinformatiese analise was uitgevoer om gene te identifiseer wat differensieel uitgedruk is tussen die twee behandelingsgroepe van belang in die betrokke studie, naamlik FS wanaangepaste (FSM) teenoor FD goedaangepaste (FDW) groepe. Epigenetiese analises was uitgevoer om te bepaal of differensieel uitgedrukte miRNAs of CpG-eiland DNA metilasie die differensiële geenuitdrukking bemiddel het. Bioinformatiese analises van die RNAseq data het 93 gene geïdentifiseer waarvan die geen uitdrukking beduidend onderdruk was in die FDW groep in vergelyking met die FSM groep; 42 van hierdie gene was voorspel om biologies relevant te wees. Geïntegreerde netwerk analise het onthul dat sekere van die differensieel uitgedrukte gene gemeenskaplik was tussen verskeie biologiese funksies, padweë en versteurings. DCS het die uitdrukking van immuun-sisteem gene en pro-inflammatoriese en oksidatiewe stres gene verlaag. Hierdie molekules medieer neuro-inflammasie wat gevolglik tot neurale skade lei. DCS het ook gene gereguleer wat betrokke is by leer en geheue prosesse. DCS het onder meer ook die geenuitdrukking verlaag van 'n sub-groep van gene wat voorheen geassosier is met komorbiede versteurings van PTSD. SYBR Green real-time qPCR (werklike tyd kwantitatiewe polimerase ketting reaksie) analise was ondersoek om te bepaal of hierdie metode sensitief genoeg sou wees om die verlaagde geen-uitdrukking van verskeie van die biologies relevante differensieel uitgedrukte gene te identifiseer, in dieselfde LDH komplementêre DNA (cDNA) monsters as wat in die RNAseq gebruik is, asook in die bloed cDNA monsters. SYBR Green real-time qPCR was in staat om ses, van die nege, differensieel uitgedrukte gene in die LDH cDNA monsters en een geen, matriks metallopeptidase 9 (MMP9), in die bloed cDNA monsters op te tel. Drie van die gene waarvoor SYBR Green real-time qPCR gebruik is om differensiële geenuitdrukking te toets, het CpG eilande bevat en was gevolglik gebruik in CpG eiland DNA metilering analises. Resultate het getoon dat CpG eiland DNA metilering nie die differensiële geenuitdrukking van TRH, NPY of MT2A gedryf het nie. Bioinformatiese analises van die miRNAseq data het 23 miRNAs geïdentifiseer wat differensieël uitgedruk was tussen die FDW en FSM groepe. Verskeie van hierdie miRNAs is reeds voorheen beskryf om betrokke te wees in brein ontwikkeling en angs gedrags metings. Funksionele luciferase analises het verder aangedui dat die verhoogde uitdrukking van rno-mi31a-5p moontlik die verlaagde geen uitdrukking van IL1RN, soos waargeneem in die RNAseq data, kon bewerkstellig het. RNAseq en miRNAseq analises in hierdie posttraumatiese stressindroom dieremodel het differensieël uitgedrukte gene en miRNAs geïdentifiseer wat dien om die verstaanswyse te verbreed van hoe DCS die vrees uitwissings proses fasiliteer. Die meganismes waardeur DCS vrees uitwissings bewerkstellig het sluit die verlaging van immuun-sisteem geen-uitdrukking in, sowel as verlaagde uitdrukking van gene wat pro-inflammatoriese en oksidatiewe stress gene transkribeer. DCS het daardeur neuro-inflammasie en gevolglike neurale skade voorkom. DCS het daarmee saam ook gene gereguleer wat betrokke is by leer en geheue prosesse. Hierdie gesamentlike veranderings in geen uitdrukking het gelei tot die uiteindelike bewerkstelling van optimale neurale funksionering, plastisiteit, leer en geheue prosesse wat uiteindelik bygedra het tot vrees uitwissing. Biologies relevante differensieël uitgedrukte gene wat ook geassosieer was met ander kondisies, soos middel verwante versteurings en metaboliese versteurings, kan help om die komorbiditeit met posttraumatiese stressindroom te verklaar. Identifisering van die molekulêre grondslae van DCS bemiddelde vrees uitwissing verbreed ons begrip en verstaan van vrees uitwissing en kan moontlik, in toekomstige navorsing gebruik word om nuwe innoverende terapeutiese teikens te verken om sodoende posttraumatiese stressindroom meer effektief te kan behandel.

As consequências de eventos estressantes sobre a saúde humana, principalmente relacionada à condição psiquiátrica, tem ganhado notoriedade nos últimos anos em decorrência do crescente número de comorbidades associadas ao estresse registradas nas grandes cidades. Transtornos emocionais relacionados a sintomas de ansiedade são comuns dentre os relatados na clínica psiquiátrica e ganham importância em trabalhos científicos devotados ao estresse, que lançam mão de abordagens diversas para compreender os mecanismos neurobiológicos subjacentes à a persistência de sintomas ansiosos decorrentes de um evento estressante. Trabalhos prévios mostraram que tanto o estresse agudo de contenção quanto a administração sistêmica de corticosterona (CORT, hormônio glicocorticoide murino) promovem, 10 dias depois, comportamento do tipo ansioso e remodelamento dendrítico no complexo basolateral da amígdala (BLA) em ratos. Além disso, alguns trabalhos recentes mostraram que a exposição ao enriquecimento ambiental (EA) reverteu o efeito ansiogênico e sobre a modulação dendrítica do BLA induzidos por estresse repetido. Em trabalho recente, nós verificamos que o EA preveniu o efeito ansiogênico imediato do estresse agudo de contenção. Esse efeito protetor do EA pareceu estar relacionado a seu efeito preventivo no aumento da atividade neuronal e do receptor de glicocorticoide (GR) no BLA. No presente trabalho, nós verificamos que o EA preveniu tanto o surgimento do comportamento do tipo ansioso quanto o déficit de extinção da memória de medo induzidos por estresse agudo de contenção verificados 10 dias depois. Porém, não está claro se esses efeitos estão relacionados com alterações na árvore dendrítica do BLA e/ou com a atividade de GR no mesmo núcleo. Dessa forma, um dos objetivos centrais do trabalho foi determinar se o efeito preventivo do EA na persistência das alterações comportamentais, e nas alterações morfológicos no BLA, induzidas por estresse agudo, são atribuidas às ações de CORT. Nós observamos que o efeito preventivo do EA na ansiedade e no déficit de extinção, verificados 10 dias após o estresse, não estão relacionados à prevenção no aumento da densidade de espinhos dendríticos do BLA. Além disso, ainibição da síntese de CORT por metirapona preveniu a emergência do comportamento do tipo ansioso 10 dias após o estresse, indicando que a sinalização desse hormônio é crucial para os efeitos comportamentais tardios relacionados ao estresse agudo. Finalmente, lançando mão do uso da tecnologia do DNA recombinante, nós verificamos que a inibição da atividade genômicoa de GR no BLA preveniu o comportamento do tipo ansioso manifestado 10 dias após o estresse. / The consequences of stressful events on human health, especially related to psychiatric disorders, have gained attention in recent years due the increasing number of comorbidities associated to stress in large cities. Anxiety-related disorders are common among the psychiatric patients and are widely present in studies devoted to stress, which use different approaches to investigate the neurobiological mechanisms underlying the persistence of anxiety symptoms caused by a stressful event. Either acute restraint stress or systemic injection of corticosterone (CORT, a rodent glucocorticoid) in rats leads to enhanced anxiety-like behavior and dendritic branch remodeling in the basolateral amygdala complex (BLA) 10 days later. Also, some studies showed that exposure to environmental enrichment (EE) reverted the long- lasting anxiety-like behavior and the repeated stress-induced BLA dendritic hypertrophy in rats. In a recent study, we found that EE prevented anxiety-related behavior in adult rats observed immediately after acute restraint stress. This protective role of EE appears to be due to the prevention of the stress-induced increase in neuronal activity and in glucocorticoid receptor (GR) nuclear activity in the BLA. In this study, we showed that EE prevented the restraint stress-induced long-lasting anxiety and contextual fear extinction impairment in adult rats. However, it is not yet clear if this protective role of EE is related to changes in the dendritic branch and/or in the GR signaling in the BLA. The present study sought to determine whether the preventive effect of EE on persistent stress-related changes in behavior as well as in the BLA morphology and activity are attributed to CORT signaling. We found that the EE- induced protection on anxiety-like behavior and fear extinction impairment 10 days after acute restraint stress was not related to prevention of the increase in spine density in BLA. Moreover, systemic injection of GC synthesis inhibitor (metyrapone) prevented the anxiety-like behavior 10 days after stress, showing that GC signaling during stress is crucial to late stress-related behavior. Finally, by antagonizing the genomic signaling of the endogenous GR in the BLA, through the use of recombinant DNA technology, we prevented the emergence of anxiety-related behavior 10 days after acute stress.

No description available.

The ventral tegmental area (VTA) and its dopaminergic (DA) mesocorticolimbic projections are thought to be essential in the brain’s reward neurocircuitry. In humans and animal experimental subjects, mild electrical VTA stimulation increases dopamine levels and can induce euphoria. Paradoxically, aversive stimuli activate VTA neurons and forebrain DA activity, and excessive electrical stimulation of the VTA exaggerates fearfulness. Research suggests that experimental manipulation of either the amygdala or the VTA has similar effects on the acquisition and expression of Pavlovian conditioned fear. Recently it was demonstrated that electrical stimulation of the amygdala produced fear extinction deficits in rats. Fear extinction involves the progressive dissipation of conditioned fear responses by repeated non-reinforced exposure to a conditioned stimulus (CS). Maladaptive states of fear in fear-related anxiety disorders, such as post-traumatic stress disorders (PTSD) or specific phobias are thought to reflect fear extinction learning deficits. The primary purpose of the present study was to examine the effects of intra-VTA stimulation on fear extinction learning. Using fear-potentiated startle as a behavioural index of conditioned fear, it was found that 120 VTA stimulations paired or unpaired with non-reinforced CS presentations impaired the extinction of conditioned fear. This effect was not apparent in rats that received electrical stimulation of the substantia nigra (SN), suggesting that not all midbrain regions respond similarly. Electrical stimulation parameters did not have aversive affects because rats failed to show fear conditioning when electrical VTA stimulation was used as the unconditioned stimulus. Also, VTA stimulation did not alter conditioned fear expression in non-extinguished animals. Based on the results it is suggested that VTA activation disinhibited conditioned fear responding. Therefore, VTA neuronal excitation by aversive stimuli may play a role in fear-related anxiety disorders thought to reflect extinction learning deficits.

The ventral tegmental area (VTA) and its dopaminergic (DA) mesocorticolimbic projections are thought to be essential in the brain’s reward neurocircuitry. In humans and animal experimental subjects, mild electrical VTA stimulation increases dopamine levels and can induce euphoria. Paradoxically, aversive stimuli activate VTA neurons and forebrain DA activity, and excessive electrical stimulation of the VTA exaggerates fearfulness. Research suggests that experimental manipulation of either the amygdala or the VTA has similar effects on the acquisition and expression of Pavlovian conditioned fear. Recently it was demonstrated that electrical stimulation of the amygdala produced fear extinction deficits in rats. Fear extinction involves the progressive dissipation of conditioned fear responses by repeated non-reinforced exposure to a conditioned stimulus (CS). Maladaptive states of fear in fear-related anxiety disorders, such as post-traumatic stress disorders (PTSD) or specific phobias are thought to reflect fear extinction learning deficits. The primary purpose of the present study was to examine the effects of intra-VTA stimulation on fear extinction learning. Using fear-potentiated startle as a behavioural index of conditioned fear, it was found that 120 VTA stimulations paired or unpaired with non-reinforced CS presentations impaired the extinction of conditioned fear. This effect was not apparent in rats that received electrical stimulation of the substantia nigra (SN), suggesting that not all midbrain regions respond similarly. Electrical stimulation parameters did not have aversive affects because rats failed to show fear conditioning when electrical VTA stimulation was used as the unconditioned stimulus. Also, VTA stimulation did not alter conditioned fear expression in non-extinguished animals. Based on the results it is suggested that VTA activation disinhibited conditioned fear responding. Therefore, VTA neuronal excitation by aversive stimuli may play a role in fear-related anxiety disorders thought to reflect extinction learning deficits.

The present study used auditory fear conditioning to assess the impact of repeated binge-like episodes of alcohol exposure during adolescence on conditioned fear in adulthood. Male and female Long-Evans rats were subjected to adolescent intermittent ethanol (AIE) exposure by vapor inhalation between post-natal day 28 and 44. After aging into adulthood, rats then underwent fear conditioning by exposure to a series of tone-shock pairings. This was followed by cued-tone extinction training, and then testing of fear recovery. In male rats, AIE exposure enhanced conditioned freezing but did not alter the time-course of extinction of cued-tone freezing. During subsequent assessment of fear recovery, AIE exposed rats exhibited less freezing during contextual fear renewal, but greater freezing during extinction recall and spontaneous recovery. Compared to males, female rats exhibited significantly lower levels of freezing during fear conditioning, more rapid extinction of freezing behavior, and significantly lower levels of freezing during the tests of fear recovery. Unlike males that were all classified as high conditioners; female rats could be parsed into either a high or low conditioning group. However, irrespective of their level of conditioned freezing, both the high and low conditioning groups of female rats exhibited rapid extinction of conditioned freezing behavior and comparatively low levels of freezing in tests of fear recovery. Regardless of group classification, AIE had no effect on freezing behavior in female rats during acquisition, extinction, or fear recovery. Lastly, exposure of male rats to the mGlu5 positive allosteric modulator CDPPB prevented AIE-induced alterations in freezing. Taken together, these observations demonstrate sex-specific changes in conditioned fear behaviors that are reversible by pharmacological interventions that target mGlu5 receptor activation.

Fear memories are necessary to initiate anticipatory fear responses when we are confronted with cues that predict an impending threat. However, when a cue no longer predicts threat, an extinction memory is formed that actively inhibits the expression of the fear memory. Failure to acquire, consolidate, or recall extinction memories causes fear memory expression (i.e., fear responding) in the absence of threat, which is a hallmark characteristic of most anxiety-related disorders and post-traumatic stress disorder (PTSD). Of further importance, these disorders occur approximately twice as often in women than men, which is thought to partially rely on sex hormone mediated differences in fear extinction. Moreover, deficits in extinction memory processing can also hinder the success of extinction-based exposure therapy, which is commonly used to treat these disorders. Thus, a better understanding of the factors determining the quality of extinction memories is of utmost importance. The present thesis focuses on three of these factors including the female sex hormone 17β-estradiol (E2), fear extinction timing, and the noradrenergic arousal system. To examine the role of E2 (Manuscript 1; low E2 levels or high E2 levels) and fear extinction timing (Manuscript 2; either immediately or delayed after the initial fear memory formation), we used a special differential fear conditioning procedure that allowed us to separately assess fear memories and extinction memories via peripheral arousal responses (measured via skin conductance responses [SCR]) and, most importantly, via central neurophysiological indicators (measured via electroencephalography [EEG]). Concerning EEG parameters, we were especially interested in neural oscillations (especially in the theta and gamma range). To further advance the understanding of the neurophysiological foundations of both memory systems, we also aimed at disentangling oscillatory and non-oscillatory brain activity (Manuscript 2). Moreover, the crucial role of the noradrenergic arousal system for the quality of extinction memories is highlighted in a review of relevant rodent and human studies (Manuscript 3). By using the described multi-methodological approach, we were able to demonstrate for the first time that peripheral arousal as well as fear-related theta oscillations are sensitive to E2. This was indicated by less fear responding (attenuated peripheral arousal and attenuated theta oscillations) during the recall of fear and extinction memories under high peripheral E2 levels (Manuscript 1). Concerning the role of fear extinction timing, we demonstrate that delayed extinction is advantageous over immediate extinction in reducing peripheral arousal during the recall of the extinction memory (Manuscript 2). Additionally, by disentangling oscillatory and non-oscillatory brain activity, we demonstrate for the first time that oscillatory and non-oscillatory brain activity is sensitive to fear expression. Moreover, by reviewing different rodent and human studies, we highlight the important role of noradrenergic arousal for the recall of extinction memories and, importantly, provide a detailed mechanistic framework of how extinction deficits might be caused after immediate extinction (Manuscript 3). In sum, the present thesis underscores the important role of E2, fear extinction timing, and the noradrenergic system for the recall quality of fear memories and extinction memories in humans.

HINTERGRUND: Gefühle zu kontrollieren ist wichtig für ein erfolgreiches Agieren im täglichen Leben. Eine der häufigsten psychischen Störungen sind Angststörungen, bei denen fehlende Kontrolle der Emotionen vorliegt. Drei unterschiedliche Studientypen haben sich mit der Regulation negativer Emotionen auseinandergesetzt. Mittels Furchtextinktion, Placebobehandlung und willentlicher Emotionsregulation ist es möglich negative Emotionen zu reduzieren. ZIEL: Das Ziel war es, die Ergebnisse publizierter hirnbildgebender Studien zu vergleichen um ein mögliches übergreifendes Regulationszentrum über negative Emotionen zu identifizieren. MATERIAL UND METHODEN: Mit Hilfe der activation likelihood estimation (ALE) wurde eine koordinatenbasierte Metaanalyse der Ergebnisse bildgebender Studien gesunder Probanden der Jahre 2000 bis 2010 durchgeführt um Gehirnaktivierungen und- deaktivierungen bei Reduktion negativer Emotionen zu identifzieren. ERGEBNISSE: Es zeigten sich Gehirnaktivierungen im ventromedialen präfrontralem Kortex (VMPFC) in allen drei domänspezifischen ALE-Metaanalysen, begleitet von einer Amygdaladeaktivierung. In den Placebo- und Emotionsregulationsstudien wurden zudem Gehirnaktivierungen im anterioren Gyrus cinguli und der anterioren Inselrinde beobachtet. FAZIT: Der VMPFC scheint als Regulationszentrum über negative Emotionen eine entscheidende Rolle während der Emotionskontrolle einzunehmen und die Amygdala als Teil des limbischen Systems zu deaktivieren. Zudem scheinen zusätzliche Gehirnregionen bei anspruchsvolleren Formen der Emotionsregulation eine Rolle zu spielen.