From the neurobiology of extinction to improved clinical treatments

Sex difference affects fear extinction but not lithium efficacy in rats following fear-conditioning with respect to the hippocampal level of BDNF

In rodents, exposure to electrical shock and creating a strong fear memory using fear-conditioning model can induce PTSD-like behavior. In this study, we induced a fear-conditioning model in rats and investigated freezing (PTSD-like) behavior, 21 days after three shocks exposure (0.6 mA, 3 s, 30 seconds interval) in both male and female rats. Lithium was injected intraperitoneally (100 mg/kg) in three protocols: (1) 1 h after fear-conditioning (2) 1 h, 24 h, and 48 h after fear-conditioning (3), 1 h, 24 h, 48 h, 72 h, and 96 h after fear-conditioning. Extinction training (20 sounds without shocks, 75 dB, 3 s, 30 seconds interval) was performed in three protocols: (1) 1 h after fear-conditioning (one session), (2) 1 h, 24 h, and 48 h after fear-conditioning (three sessions), (3), 1 h, 24 h, 48 h, 72 h, and 96 h after fear-conditioning (five sessions). Forced swim test (FST) and hot plate were used to assess behavior. Results showed that lithium in all protocols had no effect on freezing behavior, FST, and pain subthreshold in all rats. Extinction training decreased freezing behavior, with more efficacy in females. In males, only 5-session training was effective, while in females all protocols were effective. Extinction training also altered pain perception and the results of FST, depending on the sessions and was different in males and females. Brain-derived neurotrophic factor (BDNF) mRNA level was increased in females following 3 and 5 sessions, and in males following 5 sessions extinction training. In conclusion, we suggested that there is a sex difference for the effect of extinction training on freezing behavior and BDNF mRNA level in a rat model of fear-conditioning.

Within-patient association between emotion regulation and outcome in prolonged exposure for posttraumatic stress disorder

OBJECTIVE

Difficulties with emotion regulation (ER) are a risk factor for the development and maintenance of posttraumatic stress disorder (PTSD). Less is known about temporal relations between ER and PTSD symptom change during treatment, including whether ER may represent a more potent change ingredient for some patients relative to others. This study examined the association between within-patient changes in ER and next-session PTSD symptom change and whether this association was more pronounced for patients with poorer baseline ER, more severe depression, or higher borderline personality disorder symptoms.

METHOD

Data derived from a randomized controlled trial (NCT01600456) in which 149 adults with PTSD received up to 10 sessions of prolonged exposure (PE) or PE + sertraline. Patients rated difficulties with ER and PTSD symptoms repeatedly during treatment. Moderators were assessed at baseline.

RESULTS

Cross-lagged, dynamic structural equation models revealed that ER improvements were associated with next-session reductions in PTSD (standardized effect = 0.13). PTSD symptom reduction was also associated with next-session ER improvement (standardized effect = 0.34). Moderator analyses revealed that the within-person ER-PTSD symptoms association was stronger for patients with higher baseline depression (standardized effect = 0.39).

CONCLUSIONS

Reductions in PTSD symptoms may facilitate ER improvements during PE and PE augmented with sertraline rather than improvements in ER producing changes in PTSD symptoms. For patients with higher severity co-occurring depression, ER may represent a more active change ingredient. PE therapists could therefore consider placing particular emphasis on improving ER capabilities when working with this subgroup of patients. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Modulation of synapse-related gene expression in the cerebellum and prefrontal cortex of rats subjected to the contextual fear conditioning paradigm

The contextual fear conditioning (CFC) paradigm is the most productive approach for understanding the neurobiology of learning and memory as it allows to follow the evolution of memory traces of a conditioned stimulus and a specific context. The formation of long-term memory involves alterations in synaptic efficacy and neural transmission. It is known that the prefrontal cortex (PFC) exerts top-down control over subcortical structures to regulate behavioural responses. Moreover, cerebellar structures are involved in storing conditioned responses. The purpose of this research was to determine if the response to conditioning and stressful challenge is associated with alterations in synapse-related genes mRNA levels in the PFC, cerebellar vermis (V), and hemispheres (H) of young adult male rats. Four groups of Wistar rats were examined: naïve, CFC, shock only (SO), and exploration (EXPL). The behavioural response was evaluated by measuring the total freezing duration. Real-Time PCR was employed to quantify mRNA levels of some genes involved in synaptic plasticity. The results obtained from this study showed alterations in gene expression in different synapse-related genes after exposure to stressful stimuli and positioning to new environment. In conclusion, conditioning behavioural stimuli change the expression profile of molecules involved in neural transmission.

Counterconditioning reduces contextual renewal in a novel context but not in the acquisition context

As extinction is a context-dependent form of learning, conditioned responses tend to return when the conditioned stimulus (CS) is encountered outside the extinction context, known as contextual renewal. Counterconditioning is a technique that may lead to a more persistent reduction of the conditioned response. However, the effects of aversive-to-appetitive counterconditioning on contextual renewal in rodent studies are mixed. Further, research in humans is sparse, particularly direct statistical comparisons between counterconditioning and standard extinction techniques within the same study. Using a causal associative learning framework (the allergist task) implemented online, we compared the effectiveness of counterconditioning to standard extinction in preventing the renewal of judgements on the allergic properties of different food items (CSs). In a between-subjects design, 328 participants first learned that particular food items (CSs) lead to an allergic reaction in a specific restaurant (context A). Next, one CS was extinguished (no allergic reaction) while another CS was counterconditioned (positive outcome) in restaurant B. Causal judgements of the allergic properties of food items occurred in either the response acquisition context (ABA group, N = 112), the response reduction context where extinction and counterconditioning had occurred (ABB group, N = 107), or a novel context (ABC group, N = 109). Results showed that counterconditioning, compared to extinction, diminished the renewal of causal judgements to the CS in a novel context (ABC group). Still, casual judgements returned for both counter-conditioned and extinguished CSs in the response acquisition context (ABA group). Counterconditioning and extinction were similarly effective at preventing recovery of causal judgements in the response reduction context (ABB group); however, only in context B did participants choose the counter-conditioned CS as less likely to cause an allergic reaction in comparison to the extinguished CS. These findings indicate scenarios in which counterconditioning is more effective than standard extinction at diminishing the return of threat associations, with implications for improving the generalization of safety learning.

Expanding the canon: An inclusive neurobiology of thalamic and subthalamic fear circuits

Appropriate expression of fear in the face of threats in the environment is essential for survival. The sustained expression of fear in the absence of threat signals is a central pathological feature of trauma- and anxiety-related disorders. Our understanding of the neural circuitry that controls fear inhibition coalesces around the amygdala, hippocampus, and prefrontal cortex. By discussing thalamic and sub-thalamic influences on fear-related learning and expression in this review, we suggest a more inclusive neurobiological framework that expands our canonical view of fear. First, we visit how fear-related learning and expression is influenced by the aforementioned canonical brain regions. Next, we review emerging data that shed light on new roles for thalamic and subthalamic nuclei in fear-related learning and expression. Then, we highlight how these neuroanatomical hubs can modulate fear via integration of sensory and salient stimuli, gating information flow and calibrating behavioral responses, as well as maintaining and updating memory representations. Finally, we propose that the presence of this thalamic and sub-thalamic neuroanatomy in parallel with the tripartite prefrontal cortex-amygdala-hippocampus circuit allows for dynamic modulation of information based on interoceptive and exteroceptive signals. This article is part of the Special Issue on "Fear, Anxiety and PTSD".

The effectiveness of extinction training in male rats: Temporal considerations and brain mechanisms

The extinction of conditioned fear is frequently used in laboratories as a model for human exposure therapy and is crucial for studies of posttraumatic stress disorder (PTSD). However, the efficacy of specific protocols can vary greatly, and the underlying brain mechanisms are not sufficiently clarified. To address this issue, variable starting time (one or twenty-eight days after fear conditioning) and extinction protocols were used, and the efficacy and durability of fear extinction were also studied. Changes in the behavior, stress hormone levels and neuronal activation patterns of stressed rats were analyzed. Conditioned fear was rapidly and efficiently extinguished by all the protocols investigated. However, when these extinction protocols were initiated one day after fear training, conditioned fear relapsed spontaneously four weeks later. In contrast, when extinction trials were started 28 days after conditioning, no relapse occurred. Hormone measurements taken by the end of extinction trials indicated that adrenocorticotropin, but not corticosterone responses reflected behavioral extinction without any sign of relapse. The last extinction training increased the activation of the medial prefrontal cortex and decreased the activation of the central and medial amygdala when extinction began one day after fear conditioning. By contrast, the activation of the basolateral amygdala and the entire hippocampus decreased by the last training session when extinction started 28 days after fear conditioning. Our findings show that extinction training can extinguish remote fear memories more effectively than recent ones, and that the brain mechanisms underlying remote and recent fear memory extinction differ. Laboratory models should also focus on a later time point to increase their translational value.

Angiotensin II Regulates the Neural Expression of Subjective Fear in Humans: A Precision Pharmaco-Neuroimaging Approach

BACKGROUND

Rodent models and pharmacological neuroimaging studies in humans have been used to test novel pharmacological agents to reduce fear. However, these strategies are limited with respect to determining process-specific effects on the actual subjective experience of fear, which represents the key symptom that motivates patients to seek treatment. In this study, we used a novel precision pharmacological functional magnetic resonance imaging approach based on process-specific neuroaffective signatures to determine effects of the selective angiotensin II type 1 receptor (AT1R) antagonist losartan on the subjective experience of fear.

METHODS

In a double-blind, placebo-controlled, randomized pharmacological functional magnetic resonance imaging design, healthy participants (N = 87) were administered 50 mg losartan or placebo before they underwent an oddball paradigm that included neutral, novel, and fear oddballs. Effects of losartan on brain activity and connectivity as well as on process-specific multivariate neural signatures were examined.

RESULTS

AT1R blockade selectively reduced neurofunctional reactivity to fear-inducing visual oddballs in terms of attenuating dorsolateral prefrontal activity and amygdala-ventral anterior cingulate communication. Neurofunctional decoding further demonstrated fear-specific effects in that AT1R blockade reduced the neural expression of subjective fear but not of threat or nonspecific negative affect and did not influence reactivity to novel oddballs.

CONCLUSIONS

These results show a specific role of the AT1R in regulating the subjective fear experience and demonstrate the feasibility of a precision pharmacological functional magnetic resonance imaging approach to the affective characterization of novel receptor targets for fear in humans.

Hippocampal cholinergic receptors and the mTOR participation in fear-motivated inhibitory avoidance extinction memory

Evidence has demonstrated the hippocampal cholinergic system and the mammalian target of rapamycin (mTOR) participation during the memory formation of aversive events. This study assessed the role of these systems in the hippocampus for the extinction memory process by submitting male Wistar rats to fear-motivated step-down inhibitory avoidance (IA). The post-extinction session administration of the nicotinic and muscarinic cholinergic receptor antagonists, mecamylamine and scopolamine, respectively, both at doses of 2 µg/µl/side, and rapamycin, an mTOR inhibitor (0.02 µg/µl/side), into the CA1 region of the dorsal hippocampus, impaired the IA extinction memory. Furthermore, the nicotinic and muscarinic cholinergic receptor agonists, nicotine and muscarine, respectively, had a dose-dependent effect on the IA extinction memory when administered intra-CA1, immediately after the extinction session. Nicotine (0.6 µg/µl/side) and muscarine (0.02 µg/µl/side), respectively, had no effect, while the higher doses (6 and 2 µg/µl/side, respectively) impaired the IA extinction memory. Interestingly, the co-administration of muscarine at the lower dose blocked the impairment that was induced by rapamycin. This effect was not observed when nicotine at the lower dose was co-administered. These results have demonstrated the participation of the cholinergic receptors and mTOR in the hippocampus for IA extinction, and that the cholinergic agonists had a dose-dependent effect on the IA extinction memory. This study provides insights related to the behavioural aspects and the neurobiological properties underlying the early stage of fear-motivated IA extinction memory consolidation and suggests that there is hippocampal muscarinic receptor participation independent of mTOR in this memory process.

Blockade of D-serine signaling and adult hippocampal neurogenesis attenuates remote contextual fear memory following multiple memory retrievals in male mice

The retrieval of fear memories induces two opposing processes, reconsolidation, and extinction. The memory reconsolidation is an active process that involves gene expression and updates an existing memory. It is hypothesized that blockade of reconsolidation by manipulating the neurobiological factors, which are mechanistically involved in the process, could weaken or disrupt the original fear memory. The N-methyl-D-aspartate (NMDA) receptor and hippocampal neurogenesis play crucial roles in hippocampus-dependent memory processes, including reconsolidation. Using contextual fear conditioning paradigm with multiple retrievals, we attempted to weaken the original contextual fear memory by repeatedly disrupting retrieval-induced reconsolidation via downregulation of NMDA receptor signaling and inhibition of neurogenesis. In the first experiment, prior to fear conditioning, NMDA receptor signaling was downregulated by the genetic reduction of its co-agonist, D-serine, and the neurogenesis was dampened by focal X-ray irradiation on the hippocampus. We found that simultaneous D-serine reduction and neurogenesis dampening resulted in a progressive decrease in freezing following each retrieval, leading to an attenuation of remote contextual fear memory on day 28. In the second experiment using the same behavioral protocols, after conditioning, pharmacological approaches were conducted to simultaneously block D-serine signaling and neurogenesis, resulting in a similar suppressive effect on the remote fear memory. The present findings provide insights for understanding the role of D-serine-mediated NMDA receptor signaling and neurogenesis in memory retrieval and the maintenance of remote fear memory, and improving the efficacy of exposure-based therapy for the treatment of post-traumatic stress disorder (PTSD).

Putting the "mental" back in "mental disorders": a perspective from research on fear and anxiety

Mental health problems often involve clusters of symptoms that include subjective (conscious) experiences as well as behavioral and/or physiological responses. Because the bodily responses are readily measured objectively, these have come to be emphasized when developing treatments and assessing their effectiveness. On the other hand, the subjective experience of the patient reported during a clinical interview is often viewed as a weak correlate of psychopathology. To the extent that subjective symptoms are related to the underlying problem, it is often assumed that they will be taken care of if the more objective behavioral and physiological symptoms are properly treated. Decades of research on anxiety disorders, however, show that behavioral and physiological symptoms do not correlate as strongly with subjective experiences as is typically assumed. Further, the treatments developed using more objective symptoms as a marker of psychopathology have mostly been disappointing in effectiveness. Given that "mental" disorders are named for, and defined by, their subjective mental qualities, it is perhaps not surprising, in retrospect, that treatments that have sidelined mental qualities have not been especially effective. These negative attitudes about subjective experience took root in psychiatry and allied fields decades ago when there were few avenues for scientifically studying subjective experience. Today, however, cognitive neuroscience research on consciousness is thriving, and offers a viable and novel scientific approach that could help achieve a deeper understanding of mental disorders and their treatment.

Augmentation of Psychotherapy with Neurobiological Methods: Current State and Future Directions

BACKGROUND

Psychotherapy and pharmacotherapy are first-line treatments for mental disorders. Despite recent improvements, only approximately 50% of the patients reach sustained remission, indicating a need for novel developments. The main concept put forward in this systematic review and hypothesis article is the targeted co-administration of defined neurobiological interventions and specific psychotherapeutic techniques.

METHODS

We conducted a systematic literature search for randomized controlled trials comparing the efficacy of augmented psychotherapy to psychotherapy alone.

RESULTS

Thirty-five trials fulfilled the inclusion criteria. The majority (29 trials) used augmentation strategies such as D-cycloserine, yohimbine, or sleep to enhance the effects of exposure therapy for anxiety disorders. Fewer studies investigated noninvasive brain stimulation with the aim of improving cognitive control, psychedelic compounds with the aim of enhancing existentially oriented psychotherapy, and oxytocin to improve social communication during psychotherapy. Results demonstrate small augmentation effects for the enhancement of exposure therapy - however, some of the studies found negative results. Other methods are less thoroughly researched, and results are mixed.

CONCLUSIONS

This approach provides an open matrix for further research and has the potential to systematically guide future studies.

An epigenetic mechanism for over-consolidation of fear memories

Excessive fear is a hallmark of anxiety disorders, a major cause of disease burden worldwide. Substantial evidence supports a role of prefrontal cortex-amygdala circuits in the regulation of fear and anxiety, but the molecular mechanisms that regulate their activity remain poorly understood. Here, we show that downregulation of the histone methyltransferase PRDM2 in the dorsomedial prefrontal cortex enhances fear expression by modulating fear memory consolidation. We further show that Prdm2 knock-down (KD) in neurons that project from the dorsomedial prefrontal cortex to the basolateral amygdala (dmPFC-BLA) promotes increased fear expression. Prdm2 KD in the dmPFC-BLA circuit also resulted in increased expression of genes involved in synaptogenesis, suggesting that Prdm2 KD modulates consolidation of conditioned fear by modifying synaptic strength at dmPFC-BLA projection targets. Consistent with an enhanced synaptic efficacy, we found that dmPFC Prdm2 KD increased glutamatergic release probability in the BLA and increased the activity of BLA neurons in response to fear-associated cues. Together, our findings provide a new molecular mechanism for excessive fear responses, wherein PRDM2 modulates the dmPFC -BLA circuit through specific transcriptomic changes.

Environmental certainty influences the neural systems regulating responses to threat and stress

Flexible calibration of threat responding in accordance with the environment is an adaptive process that allows an animal to avoid harm while also maintaining engagement of other goal-directed actions. This calibration process, referred to as threat response regulation, requires an animal to calculate the probability that a given encounter will result in a threat so they can respond accordingly. Here we review the neural correlates of two highly studied forms of threat response suppression: extinction and safety conditioning. We focus on how relative levels of certainty or uncertainty in the surrounding environment alter the acquisition and application of these processes. We also discuss evidence indicating altered threat response regulation following stress exposure, including enhanced fear conditioning, and disrupted extinction and safety conditioning. To conclude, we discuss research using an animal model of coping that examines the impact of stressor controllability on threat responding, highlighting the potential for previous experiences with control, or other forms of coping, to protect against the effects of future adversity.

Efficacy Evaluation of Neurofeedback-Based Anxiety Relief

Anxiety disorder is a mental illness that involves extreme fear or worry, which can alter the balance of chemicals in the brain. This change and evaluation of anxiety state are accompanied by a comprehensive treatment procedure. It is well-known that the treatment of anxiety is chiefly based on psychotherapy and drug therapy, and there is no objective standard evaluation. In this paper, the proposed method focuses on examining neural changes to explore the effect of mindfulness regulation in accordance with neurofeedback in patients with anxiety. We designed a closed neurofeedback experiment that includes three stages to adjust the psychological state of the subjects. A total of 34 subjects, 17 with anxiety disorder and 17 healthy, participated in this experiment. Through the three stages of the experiment, electroencephalography (EEG) resting state signal and mindfulness-based EEG signal were recorded. Power spectral density was selected as the evaluation index through the regulation of neurofeedback mindfulness, and repeated analysis of variance (ANOVA) method was used for statistical analysis. The findings of this study reveal that the proposed method has a positive effect on both types of subjects. After mindfulness adjustment, the power map exhibited an upward trend. The increase in the average power of gamma wave indicates the relief of anxiety. The enhancement of the wave power represents an improvement in the subjects’ mindfulness ability. At the same time, the results of ANOVA showed that P < 0.05, i.e., the difference was significant. From the aspect of neurophysiological signals, we objectively evaluated the ability of our experiment to relieve anxiety. The neurofeedback mindfulness regulation can effect on the brain activity pattern of anxiety disorder patients.

Norepinephrine as a spatial memory reset signal

Contextual information is represented in the hippocampus (HPC) partially through the recruitment of distinct neuronal ensembles. It is believed that reactivation of these ensembles underlies memory retrieval processes. Recently, we showed that norepinephrine input from phasic locus coeruleus activation induces hippocampal plasticity resulting in the recruitment of new neurons and disengagement from previously established representations. We hypothesize that norepinephrine may provide a neuromodulatory mnemonic switch signaling the HPC to move from a state of retrieval to encoding in the presence of novelty, and therefore, plays a role in memory updating. Here, we tested whether bilateral dorsal dentate gyrus (dDG) infusions of the β-adrenergic receptor (BAR) agonist isoproterenol (ISO), administered prior to encoding or retrieval, would impair spatial working and reference memory by reverting, the system to encoding (thereby recruiting new neurons) potentially interfering with the retrieval of the previously established spatial ensemble. We also investigated whether dDG infusions of ISO could promote cognitive flexibility by switching the system to encoding when it is adaptive (ie, when new information is presented, eg, reversal learning). We found that intra-dDG infusions of ISO given prior to retrieval caused deficits in working and reference memory which was blocked by pretreatment with the BAR-antagonist, propranolol (PRO). In contrast, ISO administered prior to reversal learning led to improved performance. These data support our hypothesis that norepinephrine serves as a novelty signal to update HPC contextual representations via BAR activation-facilitated recruitment of new neurons. This can be both maladaptive and adaptive depending on the situation.

Plasticity of GluN1 at Ventral Hippocampal Synapses in the Infralimbic Cortex

Although the infralimbic cortex (IL) is not thought to play a role in fear acquisition, recent experiments found evidence that synaptic plasticity is occurring at ventral hippocampal (vHPC) synapses in IL during auditory fear acquisition as measured by changes in the N-methyl-D-aspartate (NMDA) receptor-mediated currents in male rats. These electrophysiological data suggest that fear conditioning changes the expression of NMDA receptors on vHPC-to-IL synapses. To further evaluate the plasticity of NMDA receptors at this specific synapse, we injected AAV particles expressing channelrhodopsin-EYFP into the vHPC of male and female rats to label vHPC projections with EYFP. To test for NMDA receptor changes in vHPC-to-IL synapses after fear learning, we used fluorescence-activated cell sorting (FACS) to quantify synaptosomes isolated from IL tissue punches that were positive for EYFP and the obligatory GluN1 subunit. More EYFP+/GluN1+ synaptosomes with greater average expression of GluN1 were isolated from male rats exposed to auditory fear conditioning (AFC) than those exposed to context and tones only or to contextual fear conditioning (CFC), suggesting that AFC increased NMDA receptor expression in males. In a second experiment, we found that pairing the tones and shocks was required to induce the molecular changes and that fear extinction did not reverse the changes. In contrast, females showed similar levels of EYFP+/GluN1+ synaptosomes in all behavioral groups. These findings suggest that AFC induces synaptic plasticity of NMDA receptors in the vHPC-to-IL projection in males, while female rats rely on different synaptic mechanisms.

Elevated activity in the dorsal dentate gyrus reduces expression of fear memory after fear extinction training

BACKGROUND

Effectively reducing the expression of certain aversive memories (fear or trauma memories) with extinction training is generally viewed to be therapeutically important. A deeper understanding of the biological basis for a more effective extinction process is also of high scientific importance.

METHODS

Our study involved intraventricular injection or local injection into the dorsal dentate gyrus of anti-neuregulin 1 antibodies (anti-NRG1) before fear extinction training, followed by testing the expression of fear memory 24 hours afterward or 9 days later. We used local injection of chemogenetic or optogenetic viruses into the dorsal dentate gyrus to manipulate the activity of the dorsal dentate gyrus and test the expression of fear memory. We also examined the effect of deep brain stimulation in the dorsal dentate gyrus on the expression of fear memory.

RESULTS

Mice that received intraventricular injection with anti-NRG1 antibodies exhibited lower expression of fear memory and increased density of activated excitatory neurons in the dorsal dentate gyrus. Injection of anti-NRG1 antibodies directly into the dorsal dentate gyrus also led to lower expression of fear memory and more activated neurons in the dorsal dentate gyrus. Inhibiting the activity of dorsal dentate gyrus excitatory neurons using an inhibitory designer receptor exclusively activated by designer drugs (DREADD) eliminated the effects of the anti-NRG1 antibodies. Enhancing the activity of the dorsal dentate gyrus with an excitatory DREADD or optogenetic stimulation resulted in lower expression of fear memory in mice that did not receive infusion of anti-NRG1 antibodies. Deep brain stimulation in the dorsal dentate gyrus effectively suppressed expression of fear memory, both during and after fear extinction training.

LIMITATIONS

The mechanism for the contribution of the dorsal dentate gyrus to the expression of fear memory needs further exploration.

CONCLUSION

Activation of the dorsal dentate gyrus may play an important role in modulating the expression of fear memory; its potential use in fear memory extinction is worthy of further exploration.

RNA editing of the 5-HT2C receptor in the central nucleus of the amygdala is involved in resilience behavior

Post-traumatic-stress-disorder (PTSD) is a stress-related condition that may develop after exposure to a severe trauma-event. One of the core brain areas that is considered to be a key regulatory region of PTSD is the amygdala. Specifically, the central amygdala (CeA) is involved in emotion processing and associative fear learning memory, two main circuits involved in PTSD. Long term dysregulation of trauma-related emotional processing may be caused by neuroadaptations that affect gene expression. The adenosine-(A) to-inosine (I) RNA editing machinery is a post-transcriptional process that converts a genomic encoded A to I and is critical for normal brain function and development. Such editing has the potential to increase the transcriptome diversity, and disruption of this process has been linked to various central nervous system disorders. Here, we employed a unique animal model to examine the possibility that the RNA editing machinery is involved in PTSD. Detection of RNA editing specifically in the CeA revealed changes in the editing pattern of the 5-HT2C serotonin receptor (5-HT2CR) transcript accompanied by dynamic changes in the expression levels of the ADAR family enzymes (ADAR and ADARb1). Deamination by ADAR and ADARb1 enzymes induces conformational changes in the 5-HT2CR that decrease the G-protein-coupling activity, agonist affinity, and thus serotonin signaling. Significantly, a single intra-CeA administration of a 5-HT2CR pharmacological antagonist produced a robust alleviation of PTSD-like behaviors (that was maintained for three weeks) as well as single systemic treatment. This work may suggest the way to a new avenue in the understanding of PTSD regulation.

Genome-wide translational profiling of amygdala Crh-expressing neurons reveals role for CREB in fear extinction learning

Fear and extinction learning are adaptive processes caused by molecular changes in specific neural circuits. Neurons expressing the corticotropin-releasing hormone gene (Crh) in central amygdala (CeA) are implicated in threat regulation, yet little is known of cell type-specific gene pathways mediating adaptive learning. We translationally profiled the transcriptome of CeA Crh-expressing cells (Crh neurons) after fear conditioning or extinction in mice using translating ribosome affinity purification (TRAP) and RNAseq. Differential gene expression and co-expression network analyses identified diverse networks activated or inhibited by fear vs extinction. Upstream regulator analysis demonstrated that extinction associates with reduced CREB expression, and viral vector-induced increased CREB expression in Crh neurons increased fear expression and inhibited extinction. These findings suggest that CREB, within CeA Crh neurons, may function as a molecular switch that regulates expression of fear and its extinction. Cell-type specific translational analyses may suggest targets useful for understanding and treating stress-related psychiatric illness.

Effects of ∆9-tetrahydrocannabinol on aversive memories and anxiety: a review from human studies

BACKGROUND

Posttraumatic stress disorder (PTSD) may stem from the formation of aberrant and enduring aversive memories. Some PTSD patients have recreationally used Cannabis, probably aiming at relieving their symptomatology. However, it is still largely unknown whether and how Cannabis or its psychotomimetic compound Δ⁹-tetrahydrocannabinol (THC) attenuates the aversive/traumatic memory outcomes. Here, we seek to review and discuss the effects of THC on aversive memory extinction and anxiety in healthy humans and PTSD patients.

METHODS

Medline, PubMed, Cochrane Library, and Central Register for Controlled Trials databases were searched to identify peer-reviewed published studies and randomized controlled trials in humans published in English between 1974 and July 2020, including those using only THC and THC combined with cannabidiol (CBD). The effect size of the experimental intervention under investigation was calculated.

RESULTS

At low doses, THC can enhance the extinction rate and reduce anxiety responses. Both effects involve the activation of cannabinoid type-1 receptors in discrete components of the corticolimbic circuitry, which could couterbalance the low "endocannabinoid tonus" reported in PTSD patients. The advantage of associating CBD with THC to attenuate anxiety while minimizing the potential psychotic or anxiogenic effect produced by high doses of THC has been reported. The effects of THC either alone or combined with CBD on aversive memory reconsolidation, however, are still unknown.

CONCLUSIONS

Current evidence from healthy humans and PTSD patients supports the THC value to suppress anxiety and aversive memory expression without producing significant adverse effects if used in low doses or when associated with CBD. Future studies are guaranteed to address open questions related to their dose ratios, administration routes, pharmacokinetic interactions, sex-dependent differences, and prolonged efficacy.

Odor modulates the temporal dynamics of fear memory consolidation

Systems consolidation (SC) theory proposes that recent, contextually rich memories are stored in the hippocampus (HPC). As these memories become remote, they are believed to rely more heavily on cortical structures within the prefrontal cortex (PFC), where they lose much of their contextual detail and become schematized. Odor is a particularly evocative cue for intense remote memory recall and despite these memories being remote, they are highly contextual. In instances such as posttraumatic stress disorder (PTSD), intense remote memory recall can occur years after trauma, which seemingly contradicts SC. We hypothesized that odor may shift the organization of salient or fearful memories such that when paired with an odor at the time of encoding, they are delayed in the de-contextualization process that occurs across time, and retrieval may still rely on the HPC, where memories are imbued with contextually rich information, even at remote time points. We investigated this by tagging odor- and non-odor-associated fear memories in male c57BL/6 mice and assessed recall and c-Fos expression in the dorsal CA1 (dCA1) and prelimbic cortex (PL) 1 or 21 d later. In support of SC, our data showed that recent memories were more dCA1-dependent whereas remote memories were more PL-dependent. However, we also found that odor influenced this temporal dynamic, biasing the memory system from the PL to the dCA1 when odor cues were present. Behaviorally, inhibiting the dCA1 with activity-dependent DREADDs had no effect on recall at 1 d and unexpectedly caused an increase in freezing at 21 d. Together, these findings demonstrate that odor can shift the organization of fear memories at the systems level.

The fluctuations of metabotropic glutamate receptor subtype 5 (mGluR5) in the amygdala in fear conditioning model of male Wistar rats following sleep deprivation, reverse circadian and napping

Sleep is involved in metabolic system, mental health and cognitive functions. Evidence shows that sleep deprivation (SD) negatively affects mental health and impairs cognitive functions, including learning and memory. Furthermore, the metabotropic glutamate receptor subtype 5 (mGluR5) is a metabolic biomarker, which is affected by various conditions, including stress, sleep deprivation, and cognitive and psychiatric disorders. In this research, we investigated the effect of SD and reverse circadian (RC), and two models of napping (continuous and non-continuous) combined with SD or RC on fear-conditioning memory, anxiety-like behavior and mGluR5 fluctuations in the amygdala. 64 male Wistar rats were used in this study. The water box apparatus was used to induce SD/RC for 48 h, and fear-conditioning memory apparatus was used to assess fear memory. The results showed, fear-conditioning memory was impaired following SD and RC, especially in contextual stage. However, anxiety-like behavior was increased. Furthermore, mGluR5 was increased in the left amygdala more than the right amygdala. Additionally, continuous napping significantly improved fear-conditioning memory, especially freezing behavior. In conclusion, following SD and RC, fear-conditioning memory in contextual stage is more vulnerable than in auditory stage. Furthermore, increase in anxiety-like behavior is related to increase in the activity of left amygdala and mGluR5 receptors.

Human Extinction Learning Is Accelerated by an Angiotensin Antagonist via Ventromedial Prefrontal Cortex and Its Connections With Basolateral Amygdala

BACKGROUND

Deficient extinction learning and threat adaptation in the ventromedial prefrontal cortex (vmPFC)-amygdala circuitry strongly impede the efficacy of exposure-based interventions in anxiety disorders. Recent animal models suggest a regulatory role of the renin-angiotensin system in both these processes. Against this background, the present randomized placebo-controlled pharmacologic functional magnetic resonance imaging experiment aimed at determining the extinction enhancing potential of the angiotensin II type 1 receptor antagonist losartan (LT) in humans.

METHODS

Seventy healthy male subjects underwent Pavlovian threat conditioning and received single-dose LT (50 mg) or placebo administration before extinction. Psychophysiological threat reactivity (skin conductance response) and neural activity during extinction served as primary outcomes. Psychophysiological interaction, voxelwise mediation, and novel multivariate pattern classification analyses were used to determine the underlying neural mechanisms.

RESULTS

LT significantly accelerated the decline of the psychophysiological threat response during within-session extinction learning. On the neural level, the acceleration was accompanied and critically mediated by threat-specific enhancement of vmPFC activation. Furthermore, LT enhanced vmPFC-basolateral amygdala coupling and attenuated the neural threat expression, particularly in the vmPFC, during early extinction.

CONCLUSIONS

Overall the results indicate that LT facilitates within-session threat memory extinction by augmenting threat-specific encoding in the vmPFC and its regulatory control over the amygdala. The findings document a pivotal role of angiotensin regulation of extinction learning in humans and suggest that adjunct LT administration has the potential to facilitate the efficacy of exposure-based interventions in anxiety disorders.

Making translation work: Harmonizing cross-species methodology in the behavioural neuroscience of Pavlovian fear conditioning

Translational neuroscience bridges insights from specific mechanisms in rodents to complex functions in humans and is key to advance our general understanding of central nervous function. A prime example of translational research is the study of cross-species mechanisms that underlie responding to learned threats, by employing Pavlovian fear conditioning protocols in rodents and humans. Hitherto, evidence for (and critique of) these cross-species comparisons in fear conditioning research was based on theoretical viewpoints. Here, we provide a perspective to substantiate these theoretical concepts with empirical considerations of cross-species methodology. This meta-research perspective is expected to foster cross-species comparability and reproducibility to ultimately facilitate successful transfer of results from basic science into clinical applications.

Development of the Parent-Rated Anxiety Scale for Youth With Autism Spectrum Disorder

OBJECTIVE

Anxiety is common in youth with autism spectrum disorder (ASD). There is no accepted outcome measure for anxiety in this population.

METHOD

Following a series of focus groups with parents of youth with ASD, we generated 72 items (scored 0-3). Parents of 990 youth with ASD (aged 5-17 years; 80.8% male) completed an online survey. Factor analysis and item response theory analyses reduced the content to a single factor with 25 items. Youth with at least mild anxiety (n = 116; aged 5-17 years; 79.3% male) participated in a comprehensive clinical assessment to evaluate the validity and reliability of the 25-item Parent-Rated Anxiety Scale for ASD (PRAS-ASD).

RESULTS

In the online sample, the mean PRAS-ASD score was 29.04 ± 14.9 (range, 0-75). The coefficient α was 0.93. The item response theory results indicated excellent reliability across a wide range of scores with low standard errors. In the clinical sample (n = 116), the PRAS-ASD mean was 31.0 ± 15.6 (range, 1-65). Pearson correlations with parent ratings of ASD symptom severity, repetitive behavior, and disruptive behavior ranged 0.33 to 0.66, supporting divergent validity of the PRAS-ASD. Pearson correlation with a parent-rated measure of anxiety used in the general pediatric population of 0.83 supported convergent validity. A total of 40 participants (32 boys, 8 girls; mean age, 11.9 ± 3.4 years) returned at time 2 (mean, 12.2 days) and time 3 (mean, 24.2 days). Intraclass correlation showed test-retest reliabilities of 0.88 and 0.86 at time 2 and time 3, respectively.

CONCLUSION

The 25-item PRAS-ASD is a reliable and valid scale for measuring anxiety in youth with ASD.

[Anxiety in the elderly]

Anxiety occurs in about one third of people over 65 years of age. However, its identification in this age has significant difficulties. The clinical manifestations, pathogenetic mechanisms, approaches to the diagnosis and treatment of various types of anxiety are described in the article. Particular attention is paid to the comorbidity of anxiety disorders in elderly patients. A comprehensive approach to the treatment of elderly patients with anxiety includes psychotherapeutic and pharmacotherapeutic approaches. Special attention should be paid to the efficacy and safety of the drugs, which is especially important in this category of patients.

The hypothalamic-pituitary-adrenal axis in PTSD: Pathophysiology and treatment interventions

Questions of how altered functioning of the hypothalamic pituitary adrenal (HPA) axis contribute to the development and maintenance of posttraumatic stress disorder (PTSD) have been the focus of extensive animal and human research. As a rule, results have been inconsistent across studies, likely due to a variety of confounding variables that have received inadequate attention. Important confounding factors include the effects of early life stress, biological sex, and the glucocorticoid used for interventions. In this manuscript we review: 1) the literature on identified abnormalities of HPA axis function in PTSD, both in terms of basal functioning and as part of challenge paradigms; 2) the role of HPA axis function pre- and immediately post-trauma as a risk factor for PTSD development; 3) the impact of HPA axis genes' allelic variants and epigenetic modifications on PTSD risk; 4) the contributions of HPA axis components to fear learning and extinction; and 5) therapeutic manipulations of the HPA axis to both prevent and treat PTSD, including the role of glucocorticoids as part of medication enhanced psychotherapy.

Theranostic pharmacology in PTSD: Neurobiology and timing

Recent reviews and treatment guidelines regard trauma-focused cognitive-behavior therapies as the treatments of choice for chronic post-traumatic stress disorder (PTSD). However, many patients do not engage in this treatment when it is available, drop out before completion, or do not respond. Medications remain widely used, alone and in conjunction with psychotherapy, although the limitations of traditional monoamine-based pharmacotherapy are increasingly recognized. This article will review recent developments in psychopharmacology for PTSD, with a focus on current clinical data that apply putative neurobiologic mechanisms to medication use-i.e., a theranostic approach. A theranostic approach however, also requires consideration of timing, pre, peri or post trauma in conjunction with underlying dynamic processes affecting synaptic plasticity, the HPA axis, hippocampal activation, PFC-amygdala circuitry and fear memory.

Effects of a histone deacetylase 3 inhibitor on extinction and reinstatement of cocaine self-administration in rats

RATIONALE

A challenge in treating substance use disorder is that successful treatment often does not persist, resulting in relapse and continued drug seeking. One approach to persistently weaken drug-seeking behaviors is to pair exposure to drug-associated cues or behaviors with delivery of a compound that may strengthen the inhibition of the association between drug cues and behavior.

OBJECTIVES

We evaluated whether a selective histone deacetylase 3 (HDAC3) inhibitor could promote extinction and weaken contextual control of operant drug seeking after intravenous cocaine self-administration.

METHODS

Male Long-Evans rats received a systemic injection of the HDAC3 inhibitor RGFP966 either before or immediately after the first extinction session. Persistence of extinction was tested over subsequent extinction sessions, as well as tests of reinstatement that included cue-induced reinstatement, contextual renewal, and cocaine-primed reinstatement. Additional extinction sessions occurred between each reinstatement test. We also evaluated effects of RGFP966 on performance and motivation during stable fixed ratio operant responding for cocaine and during a progressive ratio of reinforcement.

RESULTS

RGFP966 administered before the first extinction session led to significantly less responding during subsequent extinction and reinstatement tests compared to vehicle-injected rats. Follow-up studies found that these effects were not likely due to a performance deficit or a change in motivation to self-administer cocaine, as injections of RGFP966 had no effect on stable responding during a fixed or progressive ratio schedule. In addition, RGFP966 administered just after the first extinction session had no effect during early extinction and reinstatement tests, but weakened long-term responding during later extinction sessions.

CONCLUSIONS

These results suggest that a systemic injection of a selective HDAC3 inhibitor can enhance extinction and suppress reinstatement after cocaine self-administration. The finding that behavioral and pharmacological manipulations can be combined to decrease drug seeking provides further potential for treatment by epigenetic modulation.

Methylenedioxymethamphetamine (MDMA) in Psychiatry: Pros, Cons, and Suggestions

BACKGROUND

For a number of mental health disorders, including posttraumatic stress disorders (PTSD), there are not many available treatment options. Recently, there has been renewed interest in the potential of methylenedioxymethamphetamine (MDMA) to restore function for patients with these disorders. The primary hypothesis is that MDMA, via prosocial effects, increases the ability of patients to address the underlying psychopathology of the disorder. However, the use of MDMA poses potential problems of neurotoxicity, in addition to its own potential for misuse.

METHODS

In this article, the proposed potential of MDMA as an adjunct to psychotherapy for PTSD is evaluated. The rationale for the use of MDMA and the positive results of studies that have administered MDMA in the treatment of PTSD are provided (pros). A description of potential adverse effects of treatment is also presented (cons). An overview of MDMA pharmacology and pharmacokinetics and a description of potential adverse effects of treatments are also presented. Methylenedioxymethamphetamine-produced oxytocin release and decreased expression of fear conditioning as well as one of the MDMA enantiomers (the n R- entaniomer) are suggested as potential mechanisms for the beneficial effects of MDMA in PTSD (suggestions).

RESULTS

There is some evidence that MDMA facilitates recovery of PTSD. However, the significant adverse effects of MDMA raise concern for its adoption as a pharmacotherapy. Alternative potential treatments with less adverse effects and that are based on the ubiquitous pharmacology of MDMA are presented.

CONCLUSIONS

We suggest that additional research investigating the basis for the putative beneficial effects of MDMA might reveal an effective treatment with fewer adverse effects. Suggestions of alternative treatments based on the behavioral pharmacology and toxicology of MDMA and its enantiomers are presented.

Locus Coeruleus Phasic, But Not Tonic, Activation Initiates Global Remapping in a Familiar Environment

Locus coeruleus (LC) neurons, the source of hippocampal norepinephrine (NE), are activated by novelty and changes in environmental contingencies. Based on the role of monoamines in reconfiguring invertebrate networks, and data from mammalian systems, a network reset hypothesis for the effects of LC activation has been proposed. We used the cellular compartmental analysis of temporal FISH technique based on the cellular distribution of immediate early genes to examine the effect of LC activation and inactivation, on regional hippocampal maps in male rats, when LC activity was manipulated just before placement in a second familiar (A/A) and/or novel environment (A/B). We found that bilateral phasic, but not tonic, activation of LC reset hippocampal maps in the A/A condition, whereas silencing the LC with clonidine before placement in the A/B condition blocked map reset and a familiar map emerged in the dentate gyrus, proximal and distal CA1, and CA3c. However, CA3a and CA3b encoded the novel environment. These results support a role for phasic LC responses in generating novel hippocampal sequences during memory encoding and, potentially, memory updating. The silencing experiments suggest that novel environments may not be recognized as different by dentate gyrus and CA1 without LC input. The functional distinction between phasic and tonic LC activity argues that these parameters are critical for determining network changes. These data are consistent with the hippocampus activating internal network representations to encode novel experiential episodes and suggest LC input is critical for this role.SIGNIFICANCE STATEMENT Burst activation of the broadly projecting novelty signaling system of the locus coeruleus initiates new network representations throughout the hippocampus despite unchanged external environments. Tonic activation does not alter network representations in the same condition. This suggests differences in the temporal parameters of neuromodulator network activation are critical for neuromodulator function. Silencing this novelty signaling system prevented the appearance of new network representations in a novel environment. Instead, familiar representations were expressed in a subset of hippocampal areas, with another subset encoding the novel environment. This "being in two places at once" argues for independent functional regions within the hippocampus. These experiments strengthen the view that internal states are major determinants of the brain's construction of environmental representations.

Extinction of Fear Memory Attenuates Conditioned Cardiovascular Fear Reactivity

Post-traumatic stress disorder (PTSD) is characterized by a heightened emotional and physiological state and an impaired ability to suppress or extinguish traumatic fear memories. Exaggerated physiological responses may contribute to increased cardiovascular disease (CVD) risk in this population, but whether treatment for PTSD can offset CVD risk remains unknown. To further evaluate physiological correlates of fear learning, we used a novel pre-clinical conditioned cardiovascular testing paradigm and examined the effects of Pavlovian fear conditioning and extinction training on mean arterial pressure (MAP) and heart rate (HR) responses. We hypothesized that a fear conditioned cardiovascular response could be detected in a novel context and attenuated by extinction training. In a novel context, fear conditioned mice exhibited marginal increases in MAP (∼3 mmHg) and decreases in HR (∼20 bpm) during CS presentation. In a home cage context, the CS elicited significant increases in both HR (100 bpm) and MAP (20 mmHg). Following extinction training, the MAP response was suppressed while CS-dependent HR responses were variable. These pre-clinical data suggest that extinction learning attenuates the acute MAP responses to conditioned stimuli over time, and that MAP and HR responses may extinguish at different rates. These results suggest that in mouse models of fear learning, conditioned cardiovascular responses are modified by extinction training. Understanding these processes in pre-clinical disease models and in humans with PTSD may be important for identifying interventions that facilitate fear extinction and attenuate hyper-physiological responses, potentially leading to improvements in the efficacy of exposure therapy and PTSD–CVD comorbidity outcomes.

Exposure-based therapy changes amygdala and hippocampus resting-state functional connectivity in patients with posttraumatic stress disorder

BACKGROUND

Recent research suggests that posttraumatic stress disorder (PTSD) is associated with altered amygdala and hippocampal resting-state functional connectivity (rsFC). However, less research has examined whether Prolonged Exposure (PE), a first line exposure-based treatment for PTSD, has the potential to alter resting state neural networks.

METHODS

A total of 24 patients with PTSD and 26 matched trauma-exposed healthy controls (TEHCs) underwent resting-state functional magnetic resonance imaging (fMRI) at baseline. PTSD patients were scanned a second time after completing 10-session PE in which patients narrated a detailed trauma account (imaginal exposure) and confronted trauma reminders (in vivo exposure) to extinguish trauma-related fear responses. TEHC were scanned again following a 10-week waiting period. Seed regions of interest (ROIs) included centromedial amygdala (CMA), basolateral amygdala (BLA), and the hippocampus.

RESULTS

Post- versus pretreatment comparisons indicated increased rsFC of the BLA and CMA with the orbitofrontal cortex (OFC), and hippocampus-medial prefrontal cortex (mPFC) among patients with PTSD, but not among TEHC participants.

CONCLUSIONS

Enhanced amygdala and hippocampus rsFC with prefrontal cortical regions following PE could underlie improved capacity for inhibition and re-evaluation of threat, and heightened memory encoding and retrieval ability, respectively. These findings encourage further investigation of this circuitry as a therapeutic target in PTSD.

Schisandra chinensis Fructus and Its Active Ingredients as Promising Resources for the Treatment of Neurological Diseases

Neurological diseases (NDs) are a leading cause of death worldwide and tend to mainly affect people under the age of 50. High rates of premature death and disability caused by NDs undoubtedly constrain societal development. However, effective therapeutic drugs and methods are very limited. Schisandra chinensis Fructus (SCF) is the dry ripe fruit of Schisandra chinensis (Turcz.) Baill, which has been used in traditional Chinese medicine for thousands of years. Recent research has indicated that SCF and its active ingredients show a protective role in NDs, including cerebrovascular diseases, neurodegenerative diseases, or depression. The key neuroprotective mechanisms of SCF and its active ingredients have been demonstrated to include antioxidation, suppression of apoptosis, anti-inflammation, regulation of neurotransmitters, and modulation of brain-derived neurotrophic factor (BDNF) related pathways. This paper summarizes studies of the role of SCF and its active ingredients in protecting against NDs, and highlights them as promising resources for future treatment. Furthermore, novel insights on the future challenges of SCF and its active ingredients are offered.

The Role of Serine Racemase in the Pathophysiology of Brain Disorders

The N-methyl-d-aspartate receptor (NMDAR) is unique in requiring two agonists to bind simultaneously to open its cation channel: the neurotransmitter, glutamate, and the coagonists, glycine, or d-serine. The Snyder laboratory was the first to clone serine racemase (SR), the enzyme that synthesizes d-serine, and to localize it immunocytochemically. Our laboratory has focused on the role of d-serine in brain disorders. Silencing the expression of SR, a risk gene for schizophrenia (SCZ), in mice (SR-/-), results in a phenotype that closely resembles SCZ including: cortical atrophy, reduced dendritic spine density and complexity, downregulation of parvalbumin-positive cortical GABAergic neurons, and cognitive impairments. This pathology can be reversed by treatment of SR-/- mice with d-serine in adulthood. SR-/- mice also exhibit abnormal response toward abusable substances, such as stimulants. They show reduced behavioral sensitization to d-amphetamine, but fail to extinguish it. Place preference to cocaine is altered, and the hedonic response to it is profoundly impaired as assessed by intracranial self-stimulation. d-cycloserine, a partial agonist at the NMDAR glycine modulatory site, shows therapeutic benefit for treating pathologic anxiety in combination with behavioral therapies. Studies in vitro with cortical culture and in vivo with middle cerebral artery occlusion show that silencing SR provides substantial protection against ischemic neuronal death. Finally, the switch of SR expression from neurons to reactive astrocytes after closed head trauma accounts for the reduced in vivo neuroplasticity, electroencephalogram abnormalities, and cognitive impairments.

Heart rate variability of chronic posttraumatic stress disorder in the Korean veterans

Patients with post-traumatic stress disorder (PTSD) have lower heart rate variability (HRV) than the general population, but findings in this area have been inconsistent. This study was conducted to investigate the characteristics of HRV in patients with PTSD and to evaluate associations between PTSD symptoms and HRV indices. Sixty-eight patients with PTSD and 73 controls without PTSD were evaluated. HRV was measured in all subjects after they completed self-reported questionnaires. Patients with PTSD had significantly more depressed moods, anxiety, and poorer sleep quality than individuals in the non-PTSD group. Standard deviations of NN intervals (SDNN), the square root of the mean squared differences of successive NN intervals (RMSSD), and log high-frequency (LNHF) were significantly lower in the PTSD group than in the non-PTSD group. Comparisons of HRV indices among four sub-groups according to presence/absence of PTSD and experiences of combat-related or other trauma indicated that individuals in the PTSD group who had experienced combat-related trauma had the lowest HRV indices. These indices included SDNN, RMSSD, and LNHF. Further, SDNN, RMSSD, and HF power were significantly associated with symptoms of hyperarousal. HRV measures might be useful physiological parameters in assessing and monitoring sympathovagal function in patients with PTSD.

Posttraumatic Stress Disorder: an integrated overview and neurobiological rationale for pharmacology

Thirty years of research on the biology of posttraumatic stress disorder now provides a foundation for hypotheses related to the mechanisms underlying the pharmacotherapy of this disorder. Only two medications, sertraline and paroxetine, are approved by the U.S. Food and Drug Administration for the treatment of PTSD. While these medications are somewhat effective, other treatment mechanisms must be explored to address the unmet need for effective treatment. This article provides a concise summary of advances in our understanding of the neurobiology of PTSD that suggest novel approaches to pharmacotherapy.

Extinction after fear memory reactivation fails to eliminate renewal in rats

Retrieving fear memories just prior to extinction has been reported to effectively erase fear memories and prevent fear relapse. The current study examined whether the type of retrieval procedure influences the ability of extinction to impair fear renewal, a form of relapse in which responding to a conditional stimulus (CS) returns outside of the extinction context. Rats first underwent Pavlovian fear conditioning with an auditory CS and footshock unconditional stimulus (US); freezing behavior served as the index of conditioned fear. Twenty-four hours later, the rats underwent a retrieval-extinction procedure. Specifically, 1h prior to extinction (45 CS-alone trials; 44 for rats receiving a CS reminder), fear memory was retrieved by either a single exposure to the CS alone, the US alone, a CS paired with the US, or exposure to the conditioning context itself. Over the next few days, conditional freezing to the extinguished CS was tested in the extinction and conditioning context in that order (i.e., an ABBA design). In the extinction context, rats that received a CS+US trial before extinction exhibited higher levels of conditional freezing than animals in all other groups, which did not differ from one another. In the renewal context, all groups showed renewal, and none of the reactivation procedures reduced renewal relative to a control group that did not receive a reactivation procedure prior to extinction. These data suggest retrieval-extinction procedures may have limited efficacy in preventing fear renewal.

Less fear, more diversity

Fear is an instinctual response that’s adaptive and critical for survival when it is short-lived but can lead to anxiety disorders when chronic. Studying how the brain controls our fears helps us understand the mechanisms required to recover from traumatic experiences and what goes wrong when we don’t. Research in rodents has identified neural circuits and molecular mechanisms regulating fear expression. Rodent work has been amenable to translation to humans and has led to improvements in clinical therapies for anxiety disorders. The societal benefit of this type of research is magnified when performed in minority-serving institutions, offering high-caliber training opportunities to increase ethnic diversity in science.

Dynamic expression of FKBP5 in the medial prefrontal cortex regulates resiliency to conditioned fear

The factors influencing resiliency to the development of post-traumatic stress disorder (PTSD) remain to be elucidated. Clinical studies associate PTSD with polymorphisms of the FK506 binding protein 5 (FKBP5). However, it is unclear whether changes in FKBP5 expression alone could produce resiliency or susceptibility to PTSD-like symptoms. In this study, we used rats as an animal model to examine whether FKBP5 in the infralimbic (IL) or prelimbic (PL) medial prefrontal cortex regulates fear conditioning or extinction. First, we examined FKBP5 expression in IL and PL during fear conditioning or extinction. In contrast to the stable expression of FKBP5 seen in PL, FKBP5 expression in IL increased after fear conditioning and remained elevated even after extinction suggesting that IL FKBP5 levels may modulate fear conditioning or extinction. Consistent with this possibility, reducing basal FKBP5 expression via local infusion of FKBP5–shRNA into IL reduced fear conditioning. Furthermore, reducing IL FKBP5, after consolidation of the fear memory, enhanced extinction memory indicating that IL FKBP5 opposed formation of the extinction memory. Our findings demonstrate that lowering FKBP5 expression in IL is sufficient to both reduce fear acquisition and enhance extinction, and suggest that lower expression of FKBP5 in the ventral medial prefrontal cortex could contribute to resiliency to PTSD.

Genetic approaches for the study of PTSD: Advances and challenges

Post-traumatic stress disorder (PTSD) is a highly debilitating stress and anxiety-related disorder that occurs in response to specific trauma or abuse. Genetic risk factors may account for up to 30-40% of the heritability of PTSD. Understanding the gene pathways that are associated with PTSD, and how those genes interact with the fear and stress circuitry to mediate risk and resilience for PTSD will enable the development of targeted therapies to prevent the occurrence of or decrease the severity of this complex multi-gene disorder. This review will summarize recent research on genetic approaches to understanding PTSD risk and resilience in human populations, including candidate genes and their epigenetic modifications, genome-wide association studies and neural imaging genetics approaches. Despite challenges faced within this field of study such as inconsistent results and replications, genetic approaches still offer exciting opportunities for the identification and development of novel therapeutic targets and therapies in the future.

Trauma cognitions are related to symptoms up to 10 years after cognitive behavioral treatment for posttraumatic stress disorder

OBJECTIVES

This study examined (a) relationships between trauma-related cognitions and posttraumatic stress disorder (PTSD) symptoms from pretreatment through a long-term period after cognitive-behavioral therapy (CBT) for PTSD and (b) whether these relationships were impacted by treatment type.

METHOD

Participants were 171 women randomized into treatment for PTSD after rape. Measures of self-reported trauma-related cognitions and interviewer-assessed PTSD symptoms (i.e., Posttraumatic Maladaptive Beliefs Scale, Trauma-Related Guilt Inventory, and Clinician-Administered PTSD Scale) were obtained at pretreatment, posttreatment, and 3-month, 9-month, and 5-10 year follow-ups. Multilevel regression analyses were used to examine relationships between trauma-related cognitions and PTSD symptoms throughout the study period and whether these relationships differed as a function of treatment type (i.e., Cognitive Processing Therapy or Prolonged Exposure).

RESULTS

Initial multilevel regression analyses that examined mean within-participant associations suggested that beliefs regarding Reliability and Trustworthiness of Others, Self-Worth and Judgment, Threat of Harm, and Guilt were related to PTSD symptoms throughout follow-up. Growth curve modeling suggested that patterns of belief change throughout follow-up were similar to those previously observed in PTSD symptoms over the same time period. Finally, multilevel mediation analyses that incorporated time further suggested that change in beliefs was related to change in symptoms throughout follow-up. With 1 minor exception, relationships between beliefs and symptoms were not moderated by treatment type.

CONCLUSIONS

These data suggest that trauma-related cognitions are a potential mechanism for long-term maintenance of treatment gains after CBT for PTSD. Moreover, these cognitions may be a common, rather than specific, treatment maintenance mechanism. (PsycINFO Database Record

Reconsolidation and extinction: Using epigenetic signatures to challenge conventional wisdom

Epigenetic mechanisms have the potential to give rise to lasting changes in cell function that ultimately can affect behavior persistently. This concept is especially interesting with respect to fear reconsolidation and fear memory extinction. These two behavioral approaches are used in the laboratory to investigate how fear memory can be attenuated, which becomes important when searching for therapeutic intervention to treat anxiety disorders and post-traumatic stress disorder. Here we review the role of several key epigenetic mechanisms in reconsolidation and extinction of learned fear and their potential to persistently alter behavioral responses to conditioned cues. We also briefly discuss how epigenetic mechanisms may establish persistent behaviors that challenge our definitions of extinction and reconsolidation.

Environmental enrichment facilitates cocaine-cue extinction, deters reacquisition of cocaine self-administration and alters AMPAR GluA1 expression and phosphorylation

This study investigated the combination of environmental enrichment (EE) with cocaine-cue extinction training on reacquisition of cocaine self-administration. Rats were trained under a second-order schedule for which responses were maintained by cocaine injections and cocaine-paired stimuli. During three weekly extinction sessions, saline was substituted for cocaine but cocaine-paired stimuli were presented. Rats received 4-h periods of EE at strategic time points during extinction training, or received NoEE. Additional control rats received EE or NoEE without extinction training. One week later, reacquisition of cocaine self-administration was evaluated for 15 sessions, and then GluA1 expression, a cellular substrate for learning and memory, was measured in selected brain regions. EE provided both 24 h before and immediately after extinction training facilitated extinction learning and deterred reacquisition of cocaine self-administration for up to 13 sessions. Each intervention by itself (EE alone or extinction alone) was ineffective, as was EE scheduled at individual time points (EE 4 h or 24 h before, or EE immediately or 6 h after, each extinction training session). Under these conditions, rats rapidly reacquired baseline rates of cocaine self-administration. Cocaine self-administration alone decreased total GluA1 and/or pSer845GluA1 expression in basolateral amygdala and nucleus accumbens. Extinction training, with or without EE, opposed these changes and also increased total GluA1 in ventromedial prefrontal cortex and dorsal hippocampus. EE alone increased pSer845GluA1 and EE combined with extinction training decreased pSer845GluA1 in ventromedial prefrontal cortex. EE might be a useful adjunct to extinction therapy by enabling neuroplasticity that deters relapse to cocaine self-administration.

Translational Approaches Targeting Reconsolidation

Maladaptive learned responses and memories contribute to psychiatric disorders that constitute a significant socio-economic burden. Primary treatment methods teach patients to inhibit maladaptive responses, but do not get rid of the memory itself, which explains why many patients experience a return of symptoms even after initially successful treatment. This highlights the need to discover more persistent and robust techniques to diminish maladaptive learned behaviours. One potentially promising approach is to alter the original memory, as opposed to inhibiting it, by targeting memory reconsolidation. Recent research shows that reactivating an old memory results in a period of memory flexibility and requires restorage, or reconsolidation, for the memory to persist. This reconsolidation period allows a window for modification of a specific old memory. Renewal of memory flexibility following reactivation holds great clinical potential as it enables targeting reconsolidation and changing of specific learned responses and memories that contribute to maladaptive mental states and behaviours. Here, we will review translational research on non-human animals, healthy human subjects, and clinical populations aimed at altering memories by targeting reconsolidation using biological treatments (electrical stimulation, noradrenergic antagonists) or behavioural interference (reactivation-extinction paradigm). Both approaches have been used successfully to modify aversive and appetitive memories, yet effectiveness in treating clinical populations has been limited. We will discuss that memory flexibility depends on the type of memory tested and the brain regions that underlie specific types of memory. Further, when and how we can most effectively reactivate a memory and induce flexibility is largely unclear. Finally, the development of drugs that can target reconsolidation and are safe for use in humans would optimize cross-species translations. Increasing the understanding of the mechanism and limitations of memory flexibility upon reactivation should help optimize efficacy of treatments for psychiatric patients.

Novel pharmacological treatment strategies for posttraumatic stress disorder

INTRODUCTION

A wide range of medications have been studied for posttraumatic stress disorder (PTSD) and a number are registered for this indication. Nevertheless, current pharmacotherapies are only partially effective in some patients, and are minimally effective in others. Thus novel treatment avenues need to be explored. Areas covered: In considering novel pharmacological agents for the treatment of PTSD, this paper takes a translational approach. We outline how advances in our understanding of the underlying neurobiology of PTSD may inform the identification of potential new treatment targets, including glutamatergic, noradrenergic and opioid pathways. Expert commentary: Continued investigation of the neural substrates and signalling pathways involved in responses to trauma may inform the development of novel treatment targets for future drug development for PTSD. However, the translation of preclinical findings to clinical practice is likely to be complex and gradual.

Serotonin regulates brain-derived neurotrophic factor expression in select brain regions during acute psychological stress

Previous studies suggest that serotonin (5-HT) might interact with brain-derived neurotrophic factor (BDNF) during the stress response. However, the relationship between 5-HT and BDNF expression under purely psychological stress is unclear. In this study, one hour before psychological stress exposure, the 5-HT1A receptor agonist 8-OH-DPAT or antagonist MDL73005, or the 5-HT2A receptor agonist DOI or antagonist ketanserin were administered to rats exposed to psychological stress. Immunohistochemistry and in situ hybridization revealed that after psychological stress, with the exception of the ventral tegmental area, BDNF protein and mRNA expression levels were higher in the 5-HT1A and the 5-HT2A receptor agonist groups compared with the solvent control no-stress or psychological stress group in the CA1 and CA3 of the hippocampus, prefrontal cortex, central amygdaloid nucleus, dorsomedial hypothalamic nucleus, dentate gyrus, shell of the nucleus accumbens and the midbrain periaqueductal gray. There was no significant difference between the two agonist groups. In contrast, after stress exposure, BDNF protein and mRNA expression levels were lower in the 5-HT1A and 5-HT2A receptor antagonist groups than in the solvent control non-stress group, with the exception of the ventral tegmental area. Our findings suggest that 5-HT regulates BDNF expression in a rat model of acute psychological stress.